Bar Types and Aggregation Methods for Algorithmic Trading

Every candlestick chart you've ever seen on Binance, TradingView, or any exchange UI is built the same way: aggregate trades within a fixed time window — 1 minute, 5 minutes, 1 hour — and produce an OHLCV bar. This is so ubiquitous that most traders never question it. But for algorithmic trading, the choice of bar type and aggregation method are two independent decisions — and most systems conflate them.

This article separates the two axes of candle construction: what kind of bar you build (17 types) and how you aggregate them into higher timeframes (3 methods). The combination gives 51 possible configurations, each with different properties for backtesting, live trading, and signal generation.

For an introduction to how raw trades become standard candles, see Trading Candles Demystified.

TL;DR

Candle construction has two independent axes: bar type and aggregation method
17 base bar types: time, tick, volume, dollar, Renko, range, volatility, Heikin-Ashi, Kagi, Line Break, P&F, tick imbalance (TIB), volume imbalance (VIB), run, CUSUM, entropy, delta
3 aggregation methods: calendar-aligned, rolling window, adaptive rolling
17 × 3 = 51 possible combinations, each with different properties
Most systems use only one combination: calendar-aligned time bars. The other 50 are untapped.
Practical recommendation: use multiple combinations in layers — rolling time bars for signals, calendar time bars for market structure, information-driven bars for microstructure

Two Axes of Candle Construction

The traditional view puts all bar types on a flat list: time bars, tick bars, volume bars, Renko, etc. This is misleading. There are actually two orthogonal choices:

Axis 1 — Base Bar Type (17 types): How do you decide when a new bar closes? After a fixed time interval? After N trades? After a price movement? When information content changes? This determines what "one bar" means.

Axis 2 — Aggregation Method (3 methods): How do you compose base bars into higher-timeframe candles? Align to calendar boundaries (00:00, 01:00, ...)? Use a rolling window of the last N bars? Adapt the window size to volatility?

These two axes are independent. You can have:

Calendar-aligned tick bars — aggregate tick bars that closed between 14:00 and 14:59 into a single hourly candle
Rolling volume bars — take the last 24 volume bars regardless of when they closed
Adaptive delta bars — use a volatility-driven window over delta bars

The standard "1-hour candle" is just one point in this 17×3 matrix: time bars + calendar alignment. Every other combination is an alternative worth considering.

1. Time Bars (Standard)

Uneven information density: rigid time boundaries treat 200-trade quiet hours the same as 50,000-trade announcement hours.

The default. A new bar forms after a fixed time interval: 1 minute, 5 minutes, 1 hour. Every exchange provides these natively.

Properties:

During the Asian session (00:00–08:00 UTC), a 1-hour candle might contain 200 trades. During a Binance listing announcement, the same window could contain 50,000 trades. Time bars treat both as equivalent. Detecting such activity spikes is critical for bot protection — see Anomaly Detection for Trading Bots.
All market participants see the same candle boundaries — a Schelling point. This makes time bars essential for analyzing crowd behavior.
Indicators computed on partial candles (after restart) produce garbage values.

from datetime import datetime

def time_until_valid_hourly_candle():
    """How long until the first complete hourly candle after restart."""
    now = datetime.utcnow()
    minutes_into_hour = now.minute
    seconds_into_minute = now.second

    wait_seconds = (60 - minutes_into_hour) * 60 - seconds_into_minute
    wait_seconds += 3600

    return wait_seconds

2–4. Activity-Based Bars

Activity-based bars Tick, volume, and dollar bars: three ways to let market participation — not the clock — determine bar boundaries.

Instead of sampling at fixed time intervals, sample after a fixed amount of market activity. This produces bars with roughly equal "information content" regardless of time of day.

2. Tick Bars

A new bar forms after every N trades (ticks). During high activity, bars form rapidly. During quiet periods, a single bar might span hours.

from collections import deque
from dataclasses import dataclass

@dataclass
class OHLCV:
    timestamp: int
    open: float
    high: float
    low: float
    close: float
    volume: float

class TickBarGenerator:
    """
    Generates a new bar every `threshold` trades.
    Each bar contains equal number of market "opinions".
    """

    def __init__(self, threshold: int = 1000):
        self.threshold = threshold
        self.trades: list[tuple[float, float]] = []  # (price, qty)
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        self.trades.append((price, qty))

        if len(self.trades) >= self.threshold:
            self._close_bar(timestamp)

    def _close_bar(self, timestamp: int):
        prices = [t[0] for t in self.trades]
        volumes = [t[1] for t in self.trades]

        bar = OHLCV(
            timestamp=timestamp,
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)
        self.trades = []
        return bar

Pros: Adapts to market activity naturally. Returns from tick bars tend to be closer to normally distributed than time-bar returns — a property that improves the performance of many statistical models.

Cons: Requires raw trade stream (not available from all data providers for historical data). Bar timing is unpredictable — you can't say "the next bar will close at X."

3. Volume Bars

A new bar forms after N contracts (or coins, in crypto) have traded. Similar to tick bars, but weighted by trade size — a single 100-BTC trade contributes 100x more than a 1-BTC trade.

class VolumeBarGenerator:
    """
    Generates a new bar every `threshold` units of volume.
    Normalizes for trade size: one large order ≠ one small order.
    """

    def __init__(self, threshold: float = 100.0):
        self.threshold = threshold
        self.accumulated_volume = 0.0
        self.trades: list[tuple[int, float, float]] = []  # (ts, price, qty)
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        self.trades.append((timestamp, price, qty))
        self.accumulated_volume += qty

        if self.accumulated_volume >= self.threshold:
            self._close_bar()

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)
        self.accumulated_volume = 0.0
        self.trades = []
        return bar

4. Dollar Bars

A new bar forms after a fixed notional value (in USD/USDT) has been exchanged. The most robust of the activity-based bars because it normalizes for both trade count and price level.

Consider: if ETH goes from $1,000 to$ 4,000, selling $10,000 worth of ETH requires 2.5 ETH at$ 4,000 but 10 ETH at $1,000. Volume bars would treat these differently; dollar bars treat them the same.

class DollarBarGenerator:
    """
    Generates a new bar every `threshold` dollars (USDT) of notional volume.
    Most robust normalization: independent of price level.

    Lopez de Prado (2018) recommends dollar bars as the default
    for most quantitative applications.
    """

    def __init__(self, threshold: float = 1_000_000.0):
        self.threshold = threshold
        self.accumulated_dollars = 0.0
        self.trades: list[tuple[int, float, float]] = []
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        self.trades.append((timestamp, price, qty))
        self.accumulated_dollars += price * qty

        if self.accumulated_dollars >= self.threshold:
            self._close_bar()

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)
        self.accumulated_dollars = 0.0
        self.trades = []
        return bar

Choosing the Threshold

The threshold for activity-based bars should produce roughly the same number of bars per day as the time bars you're replacing. For BTCUSDT on Binance:

Bar Type	Typical Threshold	~Bars/Day	Equivalent TF
Tick	1,000 trades	~1,400	~1m
Tick	50,000 trades	~28	~1h
Volume	100 BTC	~600	~2-3m
Volume	2,400 BTC	~25	~1h
Dollar	$1M	~1,400	~1m
Dollar	$50M	~28	~1h

These numbers are approximate and shift dramatically with market regime. During a rally or crash, activity-based bars will produce 5-10x more bars than usual — which is exactly the point.

5–7. Price-Based Bars

Price-based bars Renko bricks, range bars, and volatility bars: sampling only when price moves enough to matter.

Price-based bars ignore both time and activity. A new bar forms only when price moves by a specified amount. This naturally filters sideways noise and highlights trends.

5. Renko Bars

A new Renko "brick" forms when the closing price moves by at least N units from the previous brick's close. Bricks are always the same size, creating a clean visual representation of trend direction.

class RenkoBarGenerator:
    """
    Generates Renko bricks based on price movement.

    Key property: during sideways movement, no new bricks form.
    During strong trends, bricks form rapidly.
    """

    def __init__(self, brick_size: float = 10.0):
        self.brick_size = brick_size
        self.bricks: list[dict] = []
        self.last_close: float | None = None

    def on_price(self, timestamp: int, price: float, volume: float = 0.0):
        if self.last_close is None:
            self.last_close = price
            return []

        new_bricks = []
        diff = price - self.last_close
        num_bricks = int(abs(diff) / self.brick_size)

        if num_bricks == 0:
            return []

        direction = 1 if diff > 0 else -1

        for i in range(num_bricks):
            brick_open = self.last_close
            brick_close = self.last_close + direction * self.brick_size

            brick = {
                'timestamp': timestamp,
                'open': brick_open,
                'high': max(brick_open, brick_close),
                'low': min(brick_open, brick_close),
                'close': brick_close,
                'volume': volume / num_bricks if num_bricks > 0 else 0,
                'direction': direction,
            }
            new_bricks.append(brick)
            self.last_close = brick_close

        self.bricks.extend(new_bricks)
        return new_bricks

Dynamic Renko uses ATR (Average True Range) instead of a fixed brick size, adapting to volatility automatically.

6. Range Bars

Each bar has a fixed high-low range. When the range is exceeded, the bar closes and a new one begins. Unlike Renko, range bars include wicks and can show intra-bar volatility.

class RangeBarGenerator:
    """
    Generates bars with a fixed high-low range.

    Difference from Renko: range bars show the full OHLC within
    the range, not just brick direction. More information-rich.
    """

    def __init__(self, range_size: float = 20.0):
        self.range_size = range_size
        self.current_high: float | None = None
        self.current_low: float | None = None
        self.current_open: float | None = None
        self.current_volume: float = 0.0
        self.current_start_ts: int = 0
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        if self.current_open is None:
            self.current_open = price
            self.current_high = price
            self.current_low = price
            self.current_start_ts = timestamp

        self.current_high = max(self.current_high, price)
        self.current_low = min(self.current_low, price)
        self.current_volume += qty

        if self.current_high - self.current_low >= self.range_size:
            bar = OHLCV(
                timestamp=timestamp,
                open=self.current_open,
                high=self.current_high,
                low=self.current_low,
                close=price,
                volume=self.current_volume,
            )
            self.bars.append(bar)

            self.current_open = price
            self.current_high = price
            self.current_low = price
            self.current_volume = 0.0
            self.current_start_ts = timestamp

            return bar

        return None

Key difference between Renko and Range bars: Renko tracks only closing prices and shows direction; range bars track the full price range and show structure within the bar. Range bars are generally more useful for algorithmic trading because they preserve high-low information needed for stop-loss and take-profit simulation.

7. Volatility Bars

A new bar forms when the intra-bar volatility reaches a dynamic threshold — for example, a multiple of recent ATR. Unlike range bars (fixed threshold), volatility bars adapt to market conditions.

class VolatilityBarGenerator:
    """
    Generates bars when intra-bar volatility reaches a threshold.

    Similar to range bars, but the threshold adapts to market conditions
    using a rolling ATR measure. In calm markets, bars need less
    absolute movement to close; in volatile markets, more.
    """

    def __init__(
        self,
        atr_period: int = 14,
        atr_multiplier: float = 1.0,
        initial_threshold: float = 20.0,
    ):
        self.atr_period = atr_period
        self.atr_multiplier = atr_multiplier
        self.threshold = initial_threshold

        self.recent_ranges: list[float] = []
        self.current_open: float | None = None
        self.current_high: float | None = None
        self.current_low: float | None = None
        self.current_volume: float = 0.0
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        if self.current_open is None:
            self.current_open = price
            self.current_high = price
            self.current_low = price

        self.current_high = max(self.current_high, price)
        self.current_low = min(self.current_low, price)
        self.current_volume += qty

        intra_bar_range = self.current_high - self.current_low

        if intra_bar_range >= self.threshold:
            bar = OHLCV(
                timestamp=timestamp,
                open=self.current_open,
                high=self.current_high,
                low=self.current_low,
                close=price,
                volume=self.current_volume,
            )
            self.bars.append(bar)

            self.recent_ranges.append(intra_bar_range)
            if len(self.recent_ranges) > self.atr_period:
                self.recent_ranges = self.recent_ranges[-self.atr_period:]
            if len(self.recent_ranges) >= self.atr_period:
                avg_range = sum(self.recent_ranges) / len(self.recent_ranges)
                self.threshold = avg_range * self.atr_multiplier

            self.current_open = price
            self.current_high = price
            self.current_low = price
            self.current_volume = 0.0
            return bar

        return None

8. Heikin-Ashi (Smoothed Transformation)

Heikin-Ashi transformation Heikin-Ashi: averaging transforms noisy candles into smooth trend signals — but at the cost of exact price information.

Heikin-Ashi (Japanese for "average bar") is not a bar type — it's a transformation that can be applied on top of any base bar type. It smooths candles by averaging current and previous bar values:

HA Close = (Open + High + Low + Close) / 4
HA Open = (Previous HA Open + Previous HA Close) / 2
HA High = max(High, HA Open, HA Close)
HA Low = min(Low, HA Open, HA Close)

Trends appear as sequences of same-colored candles with no lower wicks (uptrend) or no upper wicks (downtrend).

class HeikinAshiTransformer:
    """
    Transforms standard OHLCV candles into Heikin-Ashi candles.

    Can be applied on top of ANY bar type: time bars, volume bars,
    rolling bars, etc. It's a transformation, not a sampling method.

    WARNING: HA prices are synthetic — they don't represent real
    traded prices. Never use HA close for order placement or
    PnL calculation. Use HA only for signal generation, then
    execute at real prices.
    """

    def __init__(self):
        self.prev_ha_open: float | None = None
        self.prev_ha_close: float | None = None

    def transform(self, candle: OHLCV) -> OHLCV:
        ha_close = (candle.open + candle.high + candle.low + candle.close) / 4

        if self.prev_ha_open is None:
            ha_open = (candle.open + candle.close) / 2
        else:
            ha_open = (self.prev_ha_open + self.prev_ha_close) / 2

        ha_high = max(candle.high, ha_open, ha_close)
        ha_low = min(candle.low, ha_open, ha_close)

        self.prev_ha_open = ha_open
        self.prev_ha_close = ha_close

        return OHLCV(
            timestamp=candle.timestamp,
            open=ha_open,
            high=ha_high,
            low=ha_low,
            close=ha_close,
            volume=candle.volume,
        )

    def transform_series(self, candles: list[OHLCV]) -> list[OHLCV]:
        """Transform an entire series. Resets state first."""
        self.prev_ha_open = None
        self.prev_ha_close = None
        return [self.transform(c) for c in candles]


def ha_trend_signal(ha_candles: list[OHLCV], lookback: int = 3) -> int:
    """
    Simple HA trend signal.

    Returns:
        +1: bullish (N consecutive green HA candles with no lower wick)
        -1: bearish (N consecutive red HA candles with no upper wick)
         0: no clear trend
    """
    if len(ha_candles) < lookback:
        return 0

    recent = ha_candles[-lookback:]

    all_bullish = all(
        c.close > c.open and abs(c.low - min(c.open, c.close)) < 1e-10
        for c in recent
    )

    all_bearish = all(
        c.close < c.open and abs(c.high - max(c.open, c.close)) < 1e-10
        for c in recent
    )

    if all_bullish:
        return 1
    elif all_bearish:
        return -1
    return 0

Critical caveat for backtesting: Heikin-Ashi prices are synthetic. If your backtest uses HA close as the entry price, results will be wrong. Always use HA for signal generation only and execute at real OHLC prices.

When HA is useful: Trend-following strategies that need clean "stay in" signals. Apply HA over any base bar type — time bars, volume bars, dollar bars — to filter false crossovers.

When HA is harmful: Any strategy that needs precise price levels — support/resistance, order book analysis, PIQ (Position In Queue). The averaging destroys exact price information.

9–11. Japanese Reversal Charts

Japanese charting methods Kagi, Line Break, and Point & Figure: time-free charting methods that focus purely on price structure.

These are traditional Japanese charting methods (alongside Renko) that discard time entirely and focus on price structure.

9. Kagi Charts

Kagi charts consist of vertical lines that change direction when price reverses by a specified amount. Lines change thickness when price breaks a previous high (thick = "yang" = demand) or previous low (thin = "yin" = supply).

class KagiChartGenerator:
    """
    Generates Kagi chart lines based on price reversals.

    Unlike Renko (fixed brick size), Kagi tracks the actual magnitude
    of each move and changes line thickness at breakout points.

    Useful for identifying support/resistance breaks and
    supply/demand shifts without time noise.
    """

    def __init__(self, reversal_amount: float = 10.0):
        self.reversal_amount = reversal_amount
        self.lines: list[dict] = []
        self.current_direction: int = 0  # 1=up, -1=down
        self.current_price: float | None = None
        self.extreme_price: float | None = None
        self.prev_high: float | None = None
        self.prev_low: float | None = None
        self.line_type: str = 'yang'  # 'yang' (thick) or 'yin' (thin)

    def on_price(self, timestamp: int, price: float):
        if self.current_price is None:
            self.current_price = price
            self.extreme_price = price
            return None

        if self.current_direction == 0:
            if price - self.current_price >= self.reversal_amount:
                self.current_direction = 1
                self.extreme_price = price
            elif self.current_price - price >= self.reversal_amount:
                self.current_direction = -1
                self.extreme_price = price
            return None

        if self.current_direction == 1:
            if price > self.extreme_price:
                self.extreme_price = price
                if self.prev_high is not None and price > self.prev_high:
                    self.line_type = 'yang'
            elif self.extreme_price - price >= self.reversal_amount:
                line = {
                    'timestamp': timestamp,
                    'start': self.current_price,
                    'end': self.extreme_price,
                    'direction': 'up',
                    'type': self.line_type,
                }
                self.lines.append(line)
                self.prev_high = self.extreme_price
                self.current_price = self.extreme_price
                self.extreme_price = price
                self.current_direction = -1
                if self.prev_low is not None and price < self.prev_low:
                    self.line_type = 'yin'
                return line
        else:
            if price < self.extreme_price:
                self.extreme_price = price
                if self.prev_low is not None and price < self.prev_low:
                    self.line_type = 'yin'
            elif price - self.extreme_price >= self.reversal_amount:
                line = {
                    'timestamp': timestamp,
                    'start': self.current_price,
                    'end': self.extreme_price,
                    'direction': 'down',
                    'type': self.line_type,
                }
                self.lines.append(line)
                self.prev_low = self.extreme_price
                self.current_price = self.extreme_price
                self.extreme_price = price
                self.current_direction = 1
                if self.prev_high is not None and price > self.prev_high:
                    self.line_type = 'yang'
                return line

        return None

10. Line Break Charts

Line break charts draw a new line (box) only when the closing price exceeds the high or low of the previous N lines (typically 3). No new line is drawn if the price stays within the range.

class LineBreakGenerator:
    """
    Generates Line Break bars (Three Line Break by default).

    A new bar is drawn only when the close exceeds the high or low
    of the last N bars. Filters out minor noise by requiring price
    to break through a multi-bar range.

    The 'N' parameter (line_count) controls sensitivity:
    - N=2: more sensitive, more bars, more noise
    - N=3: standard (Three Line Break)
    - N=4+: less sensitive, fewer bars, stronger signals
    """

    def __init__(self, line_count: int = 3):
        self.line_count = line_count
        self.lines: list[dict] = []

    def on_close(self, timestamp: int, close: float) -> dict | None:
        if not self.lines:
            self.lines.append({
                'timestamp': timestamp,
                'open': close,
                'close': close,
                'high': close,
                'low': close,
                'direction': 0,
            })
            return None

        lookback = self.lines[-self.line_count:] if len(self.lines) >= self.line_count else self.lines

        highest = max(l['high'] for l in lookback)
        lowest = min(l['low'] for l in lookback)
        last = self.lines[-1]

        new_line = None

        if close > highest:
            new_line = {
                'timestamp': timestamp,
                'open': last['close'],
                'close': close,
                'high': close,
                'low': last['close'],
                'direction': 1,
            }
        elif close < lowest:
            new_line = {
                'timestamp': timestamp,
                'open': last['close'],
                'close': close,
                'high': last['close'],
                'low': close,
                'direction': -1,
            }

        if new_line:
            self.lines.append(new_line)
            return new_line

        return None

11. Point & Figure Charts

Point & Figure (P&F) charts use columns of X's (rising prices) and O's (falling prices). Column switches require a reversal of typically 3 box sizes. One of the oldest methods of filtering noise and identifying support/resistance.

class PointAndFigureGenerator:
    """
    Generates Point & Figure chart data.

    X column: price rising by box_size increments.
    O column: price falling by box_size increments.
    Column switch: requires reversal_boxes * box_size movement
    in the opposite direction.

    Classic setting: box_size based on ATR, reversal_boxes = 3.
    """

    def __init__(self, box_size: float = 10.0, reversal_boxes: int = 3):
        self.box_size = box_size
        self.reversal_boxes = reversal_boxes
        self.reversal_amount = box_size * reversal_boxes

        self.columns: list[dict] = []
        self.current_direction: int = 0
        self.current_top: float | None = None
        self.current_bottom: float | None = None

    def on_price(self, timestamp: int, price: float):
        if self.current_top is None:
            box_price = self._round_to_box(price)
            self.current_top = box_price
            self.current_bottom = box_price
            self.current_direction = 1
            return None

        events = []

        if self.current_direction == 1:
            while price >= self.current_top + self.box_size:
                self.current_top += self.box_size
                events.append(('X', self.current_top, timestamp))

            if price <= self.current_top - self.reversal_amount:
                col = {
                    'type': 'X',
                    'top': self.current_top,
                    'bottom': self.current_bottom,
                    'boxes': int((self.current_top - self.current_bottom) / self.box_size) + 1,
                    'timestamp': timestamp,
                }
                self.columns.append(col)
                self.current_direction = -1
                self.current_top = self.current_top - self.box_size
                self.current_bottom = self._round_to_box(price)
                events.append(('new_column', 'O', timestamp))

        else:
            while price <= self.current_bottom - self.box_size:
                self.current_bottom -= self.box_size
                events.append(('O', self.current_bottom, timestamp))

            if price >= self.current_bottom + self.reversal_amount:
                col = {
                    'type': 'O',
                    'top': self.current_top,
                    'bottom': self.current_bottom,
                    'boxes': int((self.current_top - self.current_bottom) / self.box_size) + 1,
                    'timestamp': timestamp,
                }
                self.columns.append(col)
                self.current_direction = 1
                self.current_bottom = self.current_bottom + self.box_size
                self.current_top = self._round_to_box(price)
                events.append(('new_column', 'X', timestamp))

        return events if events else None

    def _round_to_box(self, price: float) -> float:
        return round(price / self.box_size) * self.box_size

Kagi, Line Break, and P&F in algorithmic trading: Primarily used for long-term trend detection and support/resistance identification. As a filter layer — "don't take long signals when the Kagi chart is in yin mode" — they add value by aligning trades with the macro structure.

12–14. Information-Driven Bars

Information-driven bars Imbalance bars, run bars, CUSUM filters, and entropy bars: sampling when the market tells us something has changed.

The most sophisticated approach, from Marcos Lopez de Prado's Advances in Financial Machine Learning (2018). The core insight: sample when new information arrives to the market, not at fixed intervals.

12. Tick Imbalance Bars (TIB)

If the market is in equilibrium, buyer-initiated and seller-initiated trades should roughly balance. When the imbalance exceeds our expectation, something has changed. Sample a bar at that moment.

Each trade is classified as buyer-initiated (+1) or seller-initiated (-1) using the tick rule. We track cumulative imbalance θ and sample when |θ| exceeds a dynamic threshold.

class TickImbalanceBarGenerator:
    """
    Generates bars when the cumulative tick imbalance exceeds
    expected levels — i.e., when "new information" arrives.

    Based on Lopez de Prado (2018), Chapter 2.
    """

    def __init__(
        self,
        expected_ticks_init: int = 1000,
        ewma_window: int = 100,
        min_ticks: int = 100,
        max_ticks: int = 50000,
    ):
        self.expected_ticks_init = expected_ticks_init
        self.ewma_window = ewma_window
        self.min_ticks = min_ticks
        self.max_ticks = max_ticks

        self.theta = 0.0
        self.prev_price: float | None = None
        self.prev_sign = 1
        self.trades: list[tuple[int, float, float]] = []

        self.bar_lengths: list[int] = []
        self.imbalances: list[float] = []
        self.expected_ticks = float(expected_ticks_init)
        self.expected_imbalance = 0.0

        self.bars: list[OHLCV] = []

    def _tick_sign(self, price: float) -> int:
        """Classify trade as buy (+1) or sell (-1) using tick rule."""
        if self.prev_price is None:
            self.prev_price = price
            return 1

        if price > self.prev_price:
            sign = 1
        elif price < self.prev_price:
            sign = -1
        else:
            sign = self.prev_sign

        self.prev_price = price
        self.prev_sign = sign
        return sign

    def on_trade(self, timestamp: int, price: float, qty: float):
        sign = self._tick_sign(price)
        self.theta += sign
        self.trades.append((timestamp, price, qty))

        threshold = self.expected_ticks * abs(self.expected_imbalance)
        if threshold == 0:
            threshold = self.expected_ticks_init * 0.5

        if abs(self.theta) >= threshold and len(self.trades) >= self.min_ticks:
            return self._close_bar()

        if len(self.trades) >= self.max_ticks:
            return self._close_bar()

        return None

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)

        self.bar_lengths.append(len(self.trades))
        self.imbalances.append(self.theta / len(self.trades))

        if len(self.bar_lengths) >= 2:
            alpha = 2.0 / (self.ewma_window + 1)
            self.expected_ticks = (
                alpha * self.bar_lengths[-1]
                + (1 - alpha) * self.expected_ticks
            )
            self.expected_ticks = max(
                self.min_ticks,
                min(self.max_ticks, self.expected_ticks)
            )
            self.expected_imbalance = (
                alpha * self.imbalances[-1]
                + (1 - alpha) * self.expected_imbalance
            )

        self.theta = 0.0
        self.trades = []
        return bar

13. Volume Imbalance Bars (VIB)

Extension of TIBs: instead of counting each trade as ±1, weight by signed volume. A 100-BTC buy contributes +100, a 1-BTC sell contributes -1. Captures large informed orders that might be split into many small trades.

class VolumeImbalanceBarGenerator:
    """
    Like TIBs, but uses signed volume instead of signed ticks.

    Captures the insight that a 100-BTC buy signal is 100x more
    informative than a 1-BTC buy signal.
    """

    def __init__(
        self,
        expected_ticks_init: int = 1000,
        ewma_window: int = 100,
    ):
        self.expected_ticks_init = expected_ticks_init
        self.ewma_window = ewma_window

        self.theta = 0.0
        self.prev_price: float | None = None
        self.prev_sign = 1
        self.trades: list[tuple[int, float, float]] = []

        self.bar_lengths: list[int] = []
        self.volume_imbalances: list[float] = []
        self.expected_ticks = float(expected_ticks_init)
        self.expected_vol_imbalance = 0.0

        self.bars: list[OHLCV] = []

    def _tick_sign(self, price: float) -> int:
        if self.prev_price is None:
            self.prev_price = price
            return 1
        if price > self.prev_price:
            sign = 1
        elif price < self.prev_price:
            sign = -1
        else:
            sign = self.prev_sign
        self.prev_price = price
        self.prev_sign = sign
        return sign

    def on_trade(self, timestamp: int, price: float, qty: float):
        sign = self._tick_sign(price)
        self.theta += sign * qty
        self.trades.append((timestamp, price, qty))

        threshold = self.expected_ticks * abs(self.expected_vol_imbalance)
        if threshold == 0:
            threshold = self.expected_ticks_init * 0.5

        if abs(self.theta) >= threshold and len(self.trades) >= 10:
            return self._close_bar()
        return None

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)

        self.bar_lengths.append(len(self.trades))
        self.volume_imbalances.append(self.theta / len(self.trades))

        alpha = 2.0 / (self.ewma_window + 1)
        if len(self.bar_lengths) >= 2:
            self.expected_ticks = (
                alpha * self.bar_lengths[-1] + (1 - alpha) * self.expected_ticks
            )
            self.expected_vol_imbalance = (
                alpha * self.volume_imbalances[-1]
                + (1 - alpha) * self.expected_vol_imbalance
            )

        self.theta = 0.0
        self.trades = []
        return bar

The Explosion Problem

A known issue with imbalance bars: the EWMA-based threshold can enter a positive feedback loop. The solution: clamp with min_ticks and max_ticks bounds.


self.expected_ticks = max(
    self.min_ticks,    # Floor: never less than 100 ticks
    min(
        self.max_ticks,  # Ceiling: never more than 50000 ticks
        new_expected_ticks
    )
)

14. Run Bars

Run bars track the length of the current directional run — the longest consecutive sequence of buys or sells. When a large informed trader splits an order into many small trades, the sequence becomes unusually long. Run bars detect this.

class TickRunBarGenerator:
    """
    Generates bars when the length of a directional run exceeds expectations.

    Based on Lopez de Prado (2018), Chapter 2.

    Difference from imbalance bars:
    - Imbalance bars track NET imbalance (buys minus sells)
    - Run bars track the MAXIMUM run length (consecutive buys OR sells)
    """

    def __init__(
        self,
        expected_ticks_init: int = 1000,
        ewma_window: int = 100,
        min_ticks: int = 100,
        max_ticks: int = 50000,
    ):
        self.expected_ticks_init = expected_ticks_init
        self.ewma_window = ewma_window
        self.min_ticks = min_ticks
        self.max_ticks = max_ticks

        self.prev_price: float | None = None
        self.prev_sign = 1
        self.trades: list[tuple[int, float, float]] = []

        self.buy_run = 0
        self.sell_run = 0
        self.max_buy_run = 0
        self.max_sell_run = 0

        self.bar_lengths: list[int] = []
        self.max_runs: list[float] = []
        self.expected_ticks = float(expected_ticks_init)
        self.expected_max_run = 0.0

        self.bars: list[OHLCV] = []

    def _tick_sign(self, price: float) -> int:
        if self.prev_price is None:
            self.prev_price = price
            return 1
        if price > self.prev_price:
            sign = 1
        elif price < self.prev_price:
            sign = -1
        else:
            sign = self.prev_sign
        self.prev_price = price
        self.prev_sign = sign
        return sign

    def on_trade(self, timestamp: int, price: float, qty: float):
        sign = self._tick_sign(price)
        self.trades.append((timestamp, price, qty))

        if sign == 1:
            self.buy_run += 1
            self.sell_run = 0
        else:
            self.sell_run += 1
            self.buy_run = 0

        self.max_buy_run = max(self.max_buy_run, self.buy_run)
        self.max_sell_run = max(self.max_sell_run, self.sell_run)

        theta = max(self.max_buy_run, self.max_sell_run)
        threshold = self.expected_ticks * self.expected_max_run if self.expected_max_run > 0 else self.expected_ticks_init * 0.3

        if theta >= threshold and len(self.trades) >= self.min_ticks:
            return self._close_bar()

        if len(self.trades) >= self.max_ticks:
            return self._close_bar()

        return None

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)

        max_run = max(self.max_buy_run, self.max_sell_run) / len(self.trades)
        self.bar_lengths.append(len(self.trades))
        self.max_runs.append(max_run)

        alpha = 2.0 / (self.ewma_window + 1)
        if len(self.bar_lengths) >= 2:
            self.expected_ticks = alpha * self.bar_lengths[-1] + (1 - alpha) * self.expected_ticks
            self.expected_ticks = max(self.min_ticks, min(self.max_ticks, self.expected_ticks))
            self.expected_max_run = alpha * self.max_runs[-1] + (1 - alpha) * self.expected_max_run

        self.trades = []
        self.buy_run = 0
        self.sell_run = 0
        self.max_buy_run = 0
        self.max_sell_run = 0

        return bar

Run bars can be extended to volume runs and dollar runs.

15. CUSUM Filter Bars

The CUSUM (Cumulative Sum) filter determines when to sample by tracking cumulative returns. Unlike imbalance bars (which work on raw trades), CUSUM can be applied to existing 1m OHLCV data — no tick data required.

class CUSUMFilterBarGenerator:
    """
    Symmetric CUSUM filter for event-based sampling.

    Based on Lopez de Prado (2018), Chapter 2.5.

    Key advantage over Bollinger Bands: CUSUM requires a FULL
    run of threshold magnitude before triggering. Bollinger Bands
    trigger repeatedly when price hovers near the band.

    Can be applied to 1m OHLCV data — no tick data required.
    """

    def __init__(self, threshold: float = 0.01):
        self.threshold = threshold
        self.s_pos = 0.0
        self.s_neg = 0.0
        self.prev_price: float | None = None
        self.buffer: list[OHLCV] = []
        self.bars: list[OHLCV] = []

    def on_candle_1m(self, candle: OHLCV) -> OHLCV | None:
        self.buffer.append(candle)

        if self.prev_price is None:
            self.prev_price = candle.close
            return None

        import math
        log_ret = math.log(candle.close / self.prev_price)
        self.prev_price = candle.close

        self.s_pos = max(0.0, self.s_pos + log_ret)
        self.s_neg = min(0.0, self.s_neg + log_ret)

        triggered = False

        if self.s_pos > self.threshold:
            self.s_pos = 0.0
            triggered = True

        if self.s_neg < -self.threshold:
            self.s_neg = 0.0
            triggered = True

        if triggered and len(self.buffer) >= 2:
            bars = self.buffer
            bar = OHLCV(
                timestamp=bars[-1].timestamp,
                open=bars[0].open,
                high=max(b.high for b in bars),
                low=min(b.low for b in bars),
                close=bars[-1].close,
                volume=sum(b.volume for b in bars),
            )
            self.bars.append(bar)
            self.buffer = []
            return bar

        return None

CUSUM + Triple Barrier Method: In Lopez de Prado's framework, CUSUM events are used as entry points for the Triple Barrier method — where each event triggers a trade with stop-loss, take-profit, and expiration barriers. For robust validation of such event-driven strategies, see Walk-Forward Optimization and Monte Carlo Bootstrap for Backtesting.

16. Entropy Bars

The most theoretically elegant approach: sample when the information content (Shannon entropy) of the intra-bar price series exceeds a threshold.

class EntropyBarGenerator:
    """
    Generates bars when the entropy of intra-bar returns exceeds
    a threshold.

    Based on Shannon's information theory: bars are sampled when
    "new information" arrives, measured as the entropy of the
    return distribution within the current bar.

    This is the most theoretically "pure" information-driven bar.
    """

    def __init__(
        self,
        entropy_threshold: float = 2.0,
        min_trades: int = 50,
        n_bins: int = 10,
    ):
        self.entropy_threshold = entropy_threshold
        self.min_trades = min_trades
        self.n_bins = n_bins
        self.trades: list[tuple[int, float, float]] = []
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        self.trades.append((timestamp, price, qty))

        if len(self.trades) < self.min_trades:
            return None

        entropy = self._compute_entropy()

        if entropy >= self.entropy_threshold:
            return self._close_bar()

        return None

    def _compute_entropy(self) -> float:
        import math

        prices = [t[1] for t in self.trades]
        if len(prices) < 2:
            return 0.0

        returns = [
            math.log(prices[i] / prices[i-1])
            for i in range(1, len(prices))
            if prices[i-1] > 0
        ]

        if not returns:
            return 0.0

        min_r = min(returns)
        max_r = max(returns)

        if max_r == min_r:
            return 0.0

        bin_width = (max_r - min_r) / self.n_bins
        bins = [0] * self.n_bins

        for r in returns:
            idx = min(int((r - min_r) / bin_width), self.n_bins - 1)
            bins[idx] += 1

        total = sum(bins)
        entropy = 0.0
        for count in bins:
            if count > 0:
                p = count / total
                entropy -= p * math.log2(p)

        return entropy

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)
        self.trades = []
        return bar

Practical note: Entropy bars are computationally expensive and primarily of research interest — but for ML-based strategies, they produce features with better statistical properties because each bar contains approximately equal "information."

17. Delta Bars (Order Flow)

Delta bars and order flow Cumulative delta: measuring the net force of aggressive buyers vs sellers in real time.

Delta bars sample based on cumulative delta — the running difference between buy volume and sell volume. Unlike imbalance bars (which use tick signs ±1), delta bars use actual volume-weighted order flow.

class DeltaBarGenerator:
    """
    Generates bars based on cumulative order flow delta.

    Delta = Buy Volume - Sell Volume (classified by aggressor side).

    Requires trade-level data with side classification
    (available from Binance aggTrades, Bybit trades, etc.)
    """

    def __init__(self, threshold: float = 500.0):
        self.threshold = threshold
        self.cumulative_delta = 0.0
        self.trades: list[tuple[int, float, float, int]] = []
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float, is_buyer_maker: bool):
        side = -1 if is_buyer_maker else 1
        signed_qty = side * qty

        self.cumulative_delta += signed_qty
        self.trades.append((timestamp, price, qty, side))

        if abs(self.cumulative_delta) >= self.threshold:
            return self._close_bar()

        return None

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        bar.delta = self.cumulative_delta  # type: ignore
        bar.buy_volume = sum(t[2] for t in self.trades if t[3] == 1)  # type: ignore
        bar.sell_volume = sum(t[2] for t in self.trades if t[3] == -1)  # type: ignore

        self.bars.append(bar)
        self.cumulative_delta = 0.0
        self.trades = []
        return bar

Delta divergence: One of the most powerful signals — price rising while cumulative delta is negative (sellers are aggressive but price still goes up, indicating limit buy absorption). Directly relevant to the behavioral fingerprinting approach described in the Digital Fingerprint: Trader Identification article. For market makers using the Avellaneda-Stoikov model, delta bars provide a real-time view of inventory risk and aggressor pressure.

Rolling window aggregation A circular buffer of base bars: new data enters, old data exits, and the aggregated candle is always valid.

Aggregation methods determine how base bars are composed into higher-timeframe (HTF) candles. They are independent of the bar type — you can apply any aggregation method to any base bar type.

Method A: Calendar-Aligned Aggregation

Aggregate all base bars that fall within a fixed calendar boundary. The "1-hour" candle covers all bars from 14:00:00 to 14:59:59.

Properties:

All market participants see the same boundaries — essential for market structure analysis, support/resistance, PIQ triggers
Cold start problem: partial candle after restart
Natural for time bars (this is what exchanges provide natively)
Also works for non-time bars: "all volume bars that closed between 14:00 and 15:00" = a calendar-aligned hourly candle from volume bars

Method B: Rolling Window Aggregation

Aggregate the last N closed base bars, recomputed on every new bar. A "1-hour" rolling candle = the last 60 closed 1-minute time bars, updated every minute.

The atomic unit is the closed base bar. This design choice gives:

No cold start. After N bars, the candle is valid. No partial-candle noise.
Backtest parity. If live trading uses the same atomic unit as the backtest engine, signals are identical.
Simple validation. One rule: if buffer not full: skip.

import numpy as np

class RollingCandleAggregator:
    """
    Produces rolling higher-timeframe candles from closed base bars.

    Works with ANY bar type: time bars, tick bars, volume bars,
    dollar bars, delta bars — anything that produces OHLCV output.

    Example: RollingCandleAggregator(window=60) with 1m time bars
    produces a "1h" candle updated every minute.

    Example: RollingCandleAggregator(window=24) with volume bars
    produces a candle spanning the last 24 volume bars.
    """

    def __init__(self, window: int):
        self.window = window
        self.buffer: deque[OHLCV] = deque(maxlen=window)

    def push(self, bar: OHLCV) -> OHLCV | None:
        """
        Add a closed base bar. Returns aggregated candle
        only when buffer is full (= candle is valid).
        """
        self.buffer.append(bar)

        if len(self.buffer) < self.window:
            return None

        return self._aggregate()

    def _aggregate(self) -> OHLCV:
        bars = list(self.buffer)
        return OHLCV(
            timestamp=bars[-1].timestamp,
            open=bars[0].open,
            high=max(b.high for b in bars),
            low=min(b.low for b in bars),
            close=bars[-1].close,
            volume=sum(b.volume for b in bars),
        )

    @property
    def is_valid(self) -> bool:
        return len(self.buffer) == self.window

Phase shift trade-off: Rolling candles close at :37 if you started at :37, not at :00 like everyone else's. This matters for strategies that depend on crowd-visible levels. The solution: use both — calendar for market structure, rolling for signals.

Method C: Adaptive Rolling Aggregation

Like rolling, but the window size adapts to current volatility. Calm markets → wider window (more smoothing). Volatile markets → narrower window (faster reaction).

class AdaptiveRollingAggregator:
    """
    Rolling window where the window size adapts to volatility.

    Works with any base bar type. Uses ATR of recent bars
    as the volatility measure.

    Low volatility → wider window (more smoothing, fewer signals)
    High volatility → narrower window (faster reaction)
    """

    def __init__(
        self,
        base_window: int = 60,
        min_window: int = 15,
        max_window: int = 240,
        atr_period: int = 14,
        atr_base: float | None = None,
    ):
        self.base_window = base_window
        self.min_window = min_window
        self.max_window = max_window
        self.atr_period = atr_period
        self.atr_base = atr_base

        self.all_candles: deque[OHLCV] = deque(maxlen=max_window)
        self.atr_values: deque[float] = deque(maxlen=atr_period * 2)
        self.current_window = base_window

    def push(self, bar: OHLCV) -> OHLCV | None:
        self.all_candles.append(bar)

        tr = bar.high - bar.low
        self.atr_values.append(tr)

        if len(self.atr_values) < self.atr_period:
            return None

        current_atr = sum(list(self.atr_values)[-self.atr_period:]) / self.atr_period

        if self.atr_base is None and len(self.atr_values) >= self.atr_period * 2:
            self.atr_base = sum(self.atr_values) / len(self.atr_values)

        if self.atr_base is None or self.atr_base == 0:
            return None

        vol_ratio = current_atr / self.atr_base
        self.current_window = int(self.base_window / vol_ratio)
        self.current_window = max(self.min_window, min(self.max_window, self.current_window))

        if len(self.all_candles) < self.current_window:
            return None

        bars = list(self.all_candles)[-self.current_window:]
        return OHLCV(
            timestamp=bars[-1].timestamp,
            open=bars[0].open,
            high=max(b.high for b in bars),
            low=min(b.low for b in bars),
            close=bars[-1].close,
            volume=sum(b.volume for b in bars),
        )

Every base bar type can be combined with every aggregation method. Some combinations are standard (calendar time bars = what exchanges give you), others are exotic but powerful.

Combination Examples

Base Bar Type	Calendar	Rolling	Adaptive
Time	Standard exchange candles	Always-valid HTF, no cold start	Vol-adaptive timeframe
Volume	"All volume bars this hour"	Last 24 volume bars	Wider window in calm markets
Dollar	Hourly dollar-bar aggregate	Last N dollar bars	Adaptive dollar windows
Tick Imbalance	Hourly imbalance aggregate	Last N imbalance events	Fast reaction in volatile regimes
Delta	Hourly net order flow	Rolling delta snapshot	Adaptive flow window
Renko	"Bricks this hour"	Last N bricks	Adaptive brick count

Hybrid Engine: Calendar + Rolling

In practice, you want both calendar and rolling aggregation simultaneously. The memory overhead is negligible — two deque buffers per timeframe per symbol.

class HybridCandleEngine:
    """
    Maintains both calendar-aligned and rolling candles
    for any base bar type.

    Calendar candles: for market structure, support/resistance, PIQ.
    Rolling candles: for indicators, signal generation, entries/exits.
    """

    def __init__(self):
        self.rolling = {
            '1h': RollingCandleAggregator(60),
            '4h': RollingCandleAggregator(240),
        }
        self.calendar: dict[str, list[OHLCV]] = {
            '1h': [],
            '4h': [],
        }
        self._calendar_buffer: dict[str, list[OHLCV]] = {
            '1h': [],
            '4h': [],
        }

    def on_bar(self, bar: OHLCV):
        """Process any base bar type — time, volume, tick, delta, etc."""
        rolling_results = {}
        for tf, agg in self.rolling.items():
            rolling_results[tf] = agg.push(bar)

        self._update_calendar(bar)

        return rolling_results

    def _update_calendar(self, bar: OHLCV):
        from datetime import datetime
        ts = datetime.utcfromtimestamp(bar.timestamp)

        for tf, minutes in [('1h', 60), ('4h', 240)]:
            self._calendar_buffer[tf].append(bar)

            total_minutes = ts.hour * 60 + ts.minute
            if (total_minutes + 1) % minutes == 0:
                bars = self._calendar_buffer[tf]
                if bars:
                    agg = OHLCV(
                        timestamp=bars[-1].timestamp,
                        open=bars[0].open,
                        high=max(b.high for b in bars),
                        low=min(b.low for b in bars),
                        close=bars[-1].close,
                        volume=sum(b.volume for b in bars),
                    )
                    self.calendar[tf].append(agg)
                    self._calendar_buffer[tf] = []

Time-Volume Hybrid: Calendar with Volume Splits

A special aggregation variant: calendar-aligned candles that force-close early when volume exceeds a threshold. Maintains time synchronization while adapting to activity spikes.

class TimeVolumeHybridGenerator:
    """
    Calendar-aligned candles that split when volume spikes.

    Rule: close the candle at the calendar boundary OR when
    accumulated volume exceeds vol_threshold, whichever comes first.

    Works with any base bar type — the volume trigger adds an
    extra split dimension on top of calendar alignment.
    """

    def __init__(
        self,
        interval_minutes: int = 60,
        vol_threshold: float = 5000.0,
    ):
        self.interval_minutes = interval_minutes
        self.vol_threshold = vol_threshold

        self.buffer: list[OHLCV] = []
        self.accumulated_volume = 0.0
        self.bars: list[OHLCV] = []

    def on_bar(self, bar: OHLCV) -> OHLCV | None:
        self.buffer.append(bar)
        self.accumulated_volume += bar.volume

        from datetime import datetime
        ts = datetime.utcfromtimestamp(bar.timestamp)
        total_minutes = ts.hour * 60 + ts.minute
        at_boundary = (total_minutes + 1) % self.interval_minutes == 0

        vol_spike = self.accumulated_volume >= self.vol_threshold

        if at_boundary or vol_spike:
            return self._close_bar(split_reason='volume' if vol_spike else 'time')

        return None

    def _close_bar(self, split_reason: str) -> OHLCV:
        bars = self.buffer
        bar = OHLCV(
            timestamp=bars[-1].timestamp,
            open=bars[0].open,
            high=max(b.high for b in bars),
            low=min(b.low for b in bars),
            close=bars[-1].close,
            volume=sum(b.volume for b in bars),
        )
        bar.split_reason = split_reason  # type: ignore
        bar.num_bars = len(bars)  # type: ignore

        self.bars.append(bar)
        self.buffer = []
        self.accumulated_volume = 0.0
        return bar

Practical Aggregation: Cascading Preload

Cascading aggregation Cascading preload: composing daily candles from hourly, and hourly from minute — bypassing API limits.

Exchanges limit how much historical data they serve. Binance gives ~1000 candles per REST request, OKX caps at 300. If you need a rolling 1D candle (1440 minutes), you can't always get enough 1m history. For real-time streaming of trades and order books via WebSocket, see CCXT Pro WebSocket Methods.

The solution: cascading aggregation — build higher timeframes from the highest resolution available at each depth, then stitch them together.

Rolling 1W candle:
├── 6 completed 1D candles ← fetch from REST /klines?interval=1d
├── 1 partial day:
│   ├── 23 completed 1h candles ← fetch from REST /klines?interval=1h
│   └── 1 partial hour:
│       └── N completed 1m candles ← fetch from REST /klines?interval=1m
└── Live: each new closed 1m candle updates the entire chain

This works because OHLCV aggregation is composable: the high of a 1D candle is the max of 24 1h highs, which is the max of 1440 1m highs.

Multi-Exchange Limits

Exchange	Max 1m Candles	Max 1h Candles	Notable Intervals
Binance	1,000	1,000	1m–1M, full range
Bybit	1,000	1,000	1–720, D/W/M
OKX	300	300	1m–1M (more restrictive)
Gate.io	1,000	1,000	10s–30d

Aggregation Consistency Check

The 1h candle from a REST API might not match what you'd compute from 60 1m candles. Always validate:

def validate_aggregation(
    candle_htf: OHLCV,
    candles_ltf: list[OHLCV],
    tolerance_pct: float = 0.001,
) -> dict[str, bool]:
    agg = OHLCV(
        timestamp=candles_ltf[-1].timestamp,
        open=candles_ltf[0].open,
        high=max(c.high for c in candles_ltf),
        low=min(c.low for c in candles_ltf),
        close=candles_ltf[-1].close,
        volume=sum(c.volume for c in candles_ltf),
    )

    def close_enough(a: float, b: float) -> bool:
        if a == 0 and b == 0:
            return True
        return abs(a - b) / max(abs(a), abs(b)) < tolerance_pct

    return {
        'open': close_enough(candle_htf.open, agg.open),
        'high': close_enough(candle_htf.high, agg.high),
        'low': close_enough(candle_htf.low, agg.low),
        'close': close_enough(candle_htf.close, agg.close),
        'volume': close_enough(candle_htf.volume, agg.volume),
    }

If validation fails consistently, always aggregate from 1m yourself — never trust the exchange's HTF candle for backtesting parity.

Comparison Matrix

Axis 1: Base Bar Types

#	Bar Type	Trigger	Tick Data Required	Best For
1	Time	Fixed interval	No	Market structure, crowd behavior
2	Tick	N trades	Yes	ML features, equal-opinion sampling
3	Volume	N units traded	Yes	Normalized activity analysis
4	Dollar	$N notional	Yes	Cross-asset comparison
5	Renko	Price ± N units	No	Trend following, noise filtering
6	Range	High-Low ≥ N	Yes	Breakout detection
7	Volatility	Adaptive range	Yes	Regime-adaptive analysis
8	Heikin-Ashi	Transformation	No	Trend confirmation (synthetic prices!)
9	Kagi	Price reversal	No	Supply/demand structure
10	Line Break	N-line breakout	No	Macro trend filter
11	Point & Figure	Box + reversal	No	Support/resistance mapping
12	TIB	Tick imbalance	Yes	Informed flow detection
13	VIB	Volume imbalance	Yes	Large order detection
14	Run	Run length	Yes	Order splitting detection
15	CUSUM	Cumulative return	No (1m closes)	Structural break events
16	Entropy	Shannon entropy	Yes	ML research, feature purity
17	Delta	Order flow delta	Yes (aggTrades)	Aggressor flow analysis

Axis 2: Aggregation Methods

Method	Alignment	Cold Start	Phase Shift	Best For
Calendar	Wall clock	Partial bar risk	None (crowd-aligned)	Market structure, PIQ, S/R
Rolling	N bars	None (after warmup)	Yes (shifted from :00)	Indicators, signals
Adaptive	Volatility-driven N	After ATR calibration	Yes	Vol-adaptive strategies

Practical Recommendations

Layered architecture Four-layer candle architecture: rolling signals, calendar structure, microstructure flow, and trend filters.

If your backtest engine runs on 1m OHLCV data:

Rolling time bars — simplest upgrade. Zero additional data. Eliminates cold start.
Hybrid (rolling + calendar) time bars — calendar for market structure, rolling for signals.
CUSUM filter — works on 1m closes, no tick data. "Something moved enough to be interesting."

If you have tick/trade data:

Dollar bars + rolling — recommended default from quant finance literature.
Volume imbalance bars + rolling — detects informed flow, samples more during significant events.
Delta bars + calendar — if you have aggressor-side classification, the most direct view of who is pushing the market.

As filters (apply Heikin-Ashi or Line Break on top of any base+aggregation combination):

Heikin-Ashi over rolling volume bars — clean trend signals on activity-normalized data.
Line Break / Kagi over daily calendar bars — macro trend filter.

For Marketmaker.cc specifically — a layered approach:

Layer 1 (signals): Rolling aggregation of time bars for indicators and entry/exit signals. No cold start, perfect backtest parity.
Layer 2 (market structure): Calendar-aligned time bars for support/resistance, hourly close analysis, and PIQ triggers.
Layer 3 (microstructure): Volume imbalance bars + delta bars from the raw trade stream for detecting informed flow, order splitting, and anticipating large moves. See also Digital Fingerprint: Trader Identification for behavioral pattern recognition on order flow data.
Layer 4 (trend filter): Heikin-Ashi transformation on rolling bars, or Line Break on 4h calendar closes, to keep signals aligned with macro direction.

Conclusion

Candle construction is not a single choice — it's two independent decisions:

What kind of bar? Time captures clock intervals. Activity (tick, volume, dollar) captures market participation. Price (Renko, range, volatility) captures movements. Information (imbalance, runs, CUSUM, entropy) captures arrivals of new information. Order flow (delta) captures aggressive pressure.
How to aggregate into higher timeframes? Calendar aligns with the crowd. Rolling eliminates cold start. Adaptive reacts to volatility.

The standard "1-hour candle from Binance" is just one cell in a 17×3 matrix. The other 50 combinations are available to anyone willing to implement them. For a production system, the answer is "pick the right combination for each layer of your decision engine."

The atomic unit — the closed base bar — remains the foundation. Everything else is aggregation.

For more on backtest accuracy with fine-grained data, see Adaptive Drill-Down: Backtest with Variable Granularity. For the impact of indicator precomputation on multi-timeframe strategies, see Aggregated Parquet Cache.

Useful Links

Citation

@article{soloviov2026bartypes,
  author = {Soloviov, Eugen},
  title = {Bar Types and Aggregation Methods for Algorithmic Trading},
  year = {2026},
  url = {https://marketmaker.cc/en/blog/post/beyond-time-bars-candle-construction},
  description = {Two-axis classification of candle construction: 17 base bar types × 3 aggregation methods = 51 combinations, with implementation code and practical recommendations for crypto algotrading.}
}

For an introduction to how raw trades become standard candles, see Trading Candles Demystified.

TL;DR

Candle construction has two independent axes: bar type and aggregation method
17 base bar types: time, tick, volume, dollar, Renko, range, volatility, Heikin-Ashi, Kagi, Line Break, P&F, tick imbalance (TIB), volume imbalance (VIB), run, CUSUM, entropy, delta
3 aggregation methods: calendar-aligned, rolling window, adaptive rolling
17 × 3 = 51 possible combinations, each with different properties
Most systems use only one combination: calendar-aligned time bars. The other 50 are untapped.
Practical recommendation: use multiple combinations in layers — rolling time bars for signals, calendar time bars for market structure, information-driven bars for microstructure

Two Axes of Candle Construction

The traditional view puts all bar types on a flat list: time bars, tick bars, volume bars, Renko, etc. This is misleading. There are actually two orthogonal choices:

These two axes are independent. You can have:

Calendar-aligned tick bars — aggregate tick bars that closed between 14:00 and 14:59 into a single hourly candle
Rolling volume bars — take the last 24 volume bars regardless of when they closed
Adaptive delta bars — use a volatility-driven window over delta bars

The standard "1-hour candle" is just one point in this 17×3 matrix: time bars + calendar alignment. Every other combination is an alternative worth considering.

1. Time Bars (Standard)

Uneven information density: rigid time boundaries treat 200-trade quiet hours the same as 50,000-trade announcement hours.

The default. A new bar forms after a fixed time interval: 1 minute, 5 minutes, 1 hour. Every exchange provides these natively.

Properties:

During the Asian session (00:00–08:00 UTC), a 1-hour candle might contain 200 trades. During a Binance listing announcement, the same window could contain 50,000 trades. Time bars treat both as equivalent. Detecting such activity spikes is critical for bot protection — see Anomaly Detection for Trading Bots.
All market participants see the same candle boundaries — a Schelling point. This makes time bars essential for analyzing crowd behavior.
Indicators computed on partial candles (after restart) produce garbage values.

from datetime import datetime

def time_until_valid_hourly_candle():
    """How long until the first complete hourly candle after restart."""
    now = datetime.utcnow()
    minutes_into_hour = now.minute
    seconds_into_minute = now.second

    wait_seconds = (60 - minutes_into_hour) * 60 - seconds_into_minute
    wait_seconds += 3600

    return wait_seconds

2–4. Activity-Based Bars

Activity-based bars Tick, volume, and dollar bars: three ways to let market participation — not the clock — determine bar boundaries.

Instead of sampling at fixed time intervals, sample after a fixed amount of market activity. This produces bars with roughly equal "information content" regardless of time of day.

2. Tick Bars

A new bar forms after every N trades (ticks). During high activity, bars form rapidly. During quiet periods, a single bar might span hours.

from collections import deque
from dataclasses import dataclass

@dataclass
class OHLCV:
    timestamp: int
    open: float
    high: float
    low: float
    close: float
    volume: float

class TickBarGenerator:
    """
    Generates a new bar every `threshold` trades.
    Each bar contains equal number of market "opinions".
    """

    def __init__(self, threshold: int = 1000):
        self.threshold = threshold
        self.trades: list[tuple[float, float]] = []  # (price, qty)
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        self.trades.append((price, qty))

        if len(self.trades) >= self.threshold:
            self._close_bar(timestamp)

    def _close_bar(self, timestamp: int):
        prices = [t[0] for t in self.trades]
        volumes = [t[1] for t in self.trades]

        bar = OHLCV(
            timestamp=timestamp,
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)
        self.trades = []
        return bar

Cons: Requires raw trade stream (not available from all data providers for historical data). Bar timing is unpredictable — you can't say "the next bar will close at X."

3. Volume Bars

A new bar forms after N contracts (or coins, in crypto) have traded. Similar to tick bars, but weighted by trade size — a single 100-BTC trade contributes 100x more than a 1-BTC trade.

class VolumeBarGenerator:
    """
    Generates a new bar every `threshold` units of volume.
    Normalizes for trade size: one large order ≠ one small order.
    """

    def __init__(self, threshold: float = 100.0):
        self.threshold = threshold
        self.accumulated_volume = 0.0
        self.trades: list[tuple[int, float, float]] = []  # (ts, price, qty)
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        self.trades.append((timestamp, price, qty))
        self.accumulated_volume += qty

        if self.accumulated_volume >= self.threshold:
            self._close_bar()

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)
        self.accumulated_volume = 0.0
        self.trades = []
        return bar

4. Dollar Bars

A new bar forms after a fixed notional value (in USD/USDT) has been exchanged. The most robust of the activity-based bars because it normalizes for both trade count and price level.

Consider: if ETH goes from $1,000 to$ 4,000, selling $10,000 worth of ETH requires 2.5 ETH at$ 4,000 but 10 ETH at $1,000. Volume bars would treat these differently; dollar bars treat them the same.

class DollarBarGenerator:
    """
    Generates a new bar every `threshold` dollars (USDT) of notional volume.
    Most robust normalization: independent of price level.

    Lopez de Prado (2018) recommends dollar bars as the default
    for most quantitative applications.
    """

    def __init__(self, threshold: float = 1_000_000.0):
        self.threshold = threshold
        self.accumulated_dollars = 0.0
        self.trades: list[tuple[int, float, float]] = []
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        self.trades.append((timestamp, price, qty))
        self.accumulated_dollars += price * qty

        if self.accumulated_dollars >= self.threshold:
            self._close_bar()

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)
        self.accumulated_dollars = 0.0
        self.trades = []
        return bar

Choosing the Threshold

The threshold for activity-based bars should produce roughly the same number of bars per day as the time bars you're replacing. For BTCUSDT on Binance:

Bar Type	Typical Threshold	~Bars/Day	Equivalent TF
Tick	1,000 trades	~1,400	~1m
Tick	50,000 trades	~28	~1h
Volume	100 BTC	~600	~2-3m
Volume	2,400 BTC	~25	~1h
Dollar	$1M	~1,400	~1m
Dollar	$50M	~28	~1h

These numbers are approximate and shift dramatically with market regime. During a rally or crash, activity-based bars will produce 5-10x more bars than usual — which is exactly the point.

5–7. Price-Based Bars

Price-based bars Renko bricks, range bars, and volatility bars: sampling only when price moves enough to matter.

Price-based bars ignore both time and activity. A new bar forms only when price moves by a specified amount. This naturally filters sideways noise and highlights trends.

5. Renko Bars

A new Renko "brick" forms when the closing price moves by at least N units from the previous brick's close. Bricks are always the same size, creating a clean visual representation of trend direction.

class RenkoBarGenerator:
    """
    Generates Renko bricks based on price movement.

    Key property: during sideways movement, no new bricks form.
    During strong trends, bricks form rapidly.
    """

    def __init__(self, brick_size: float = 10.0):
        self.brick_size = brick_size
        self.bricks: list[dict] = []
        self.last_close: float | None = None

    def on_price(self, timestamp: int, price: float, volume: float = 0.0):
        if self.last_close is None:
            self.last_close = price
            return []

        new_bricks = []
        diff = price - self.last_close
        num_bricks = int(abs(diff) / self.brick_size)

        if num_bricks == 0:
            return []

        direction = 1 if diff > 0 else -1

        for i in range(num_bricks):
            brick_open = self.last_close
            brick_close = self.last_close + direction * self.brick_size

            brick = {
                'timestamp': timestamp,
                'open': brick_open,
                'high': max(brick_open, brick_close),
                'low': min(brick_open, brick_close),
                'close': brick_close,
                'volume': volume / num_bricks if num_bricks > 0 else 0,
                'direction': direction,
            }
            new_bricks.append(brick)
            self.last_close = brick_close

        self.bricks.extend(new_bricks)
        return new_bricks

Dynamic Renko uses ATR (Average True Range) instead of a fixed brick size, adapting to volatility automatically.

6. Range Bars

Each bar has a fixed high-low range. When the range is exceeded, the bar closes and a new one begins. Unlike Renko, range bars include wicks and can show intra-bar volatility.

class RangeBarGenerator:
    """
    Generates bars with a fixed high-low range.

    Difference from Renko: range bars show the full OHLC within
    the range, not just brick direction. More information-rich.
    """

    def __init__(self, range_size: float = 20.0):
        self.range_size = range_size
        self.current_high: float | None = None
        self.current_low: float | None = None
        self.current_open: float | None = None
        self.current_volume: float = 0.0
        self.current_start_ts: int = 0
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        if self.current_open is None:
            self.current_open = price
            self.current_high = price
            self.current_low = price
            self.current_start_ts = timestamp

        self.current_high = max(self.current_high, price)
        self.current_low = min(self.current_low, price)
        self.current_volume += qty

        if self.current_high - self.current_low >= self.range_size:
            bar = OHLCV(
                timestamp=timestamp,
                open=self.current_open,
                high=self.current_high,
                low=self.current_low,
                close=price,
                volume=self.current_volume,
            )
            self.bars.append(bar)

            self.current_open = price
            self.current_high = price
            self.current_low = price
            self.current_volume = 0.0
            self.current_start_ts = timestamp

            return bar

        return None

7. Volatility Bars

A new bar forms when the intra-bar volatility reaches a dynamic threshold — for example, a multiple of recent ATR. Unlike range bars (fixed threshold), volatility bars adapt to market conditions.

class VolatilityBarGenerator:
    """
    Generates bars when intra-bar volatility reaches a threshold.

    Similar to range bars, but the threshold adapts to market conditions
    using a rolling ATR measure. In calm markets, bars need less
    absolute movement to close; in volatile markets, more.
    """

    def __init__(
        self,
        atr_period: int = 14,
        atr_multiplier: float = 1.0,
        initial_threshold: float = 20.0,
    ):
        self.atr_period = atr_period
        self.atr_multiplier = atr_multiplier
        self.threshold = initial_threshold

        self.recent_ranges: list[float] = []
        self.current_open: float | None = None
        self.current_high: float | None = None
        self.current_low: float | None = None
        self.current_volume: float = 0.0
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        if self.current_open is None:
            self.current_open = price
            self.current_high = price
            self.current_low = price

        self.current_high = max(self.current_high, price)
        self.current_low = min(self.current_low, price)
        self.current_volume += qty

        intra_bar_range = self.current_high - self.current_low

        if intra_bar_range >= self.threshold:
            bar = OHLCV(
                timestamp=timestamp,
                open=self.current_open,
                high=self.current_high,
                low=self.current_low,
                close=price,
                volume=self.current_volume,
            )
            self.bars.append(bar)

            self.recent_ranges.append(intra_bar_range)
            if len(self.recent_ranges) > self.atr_period:
                self.recent_ranges = self.recent_ranges[-self.atr_period:]
            if len(self.recent_ranges) >= self.atr_period:
                avg_range = sum(self.recent_ranges) / len(self.recent_ranges)
                self.threshold = avg_range * self.atr_multiplier

            self.current_open = price
            self.current_high = price
            self.current_low = price
            self.current_volume = 0.0
            return bar

        return None

8. Heikin-Ashi (Smoothed Transformation)

Heikin-Ashi transformation Heikin-Ashi: averaging transforms noisy candles into smooth trend signals — but at the cost of exact price information.

HA Close = (Open + High + Low + Close) / 4
HA Open = (Previous HA Open + Previous HA Close) / 2
HA High = max(High, HA Open, HA Close)
HA Low = min(Low, HA Open, HA Close)

Trends appear as sequences of same-colored candles with no lower wicks (uptrend) or no upper wicks (downtrend).

class HeikinAshiTransformer:
    """
    Transforms standard OHLCV candles into Heikin-Ashi candles.

    Can be applied on top of ANY bar type: time bars, volume bars,
    rolling bars, etc. It's a transformation, not a sampling method.

    WARNING: HA prices are synthetic — they don't represent real
    traded prices. Never use HA close for order placement or
    PnL calculation. Use HA only for signal generation, then
    execute at real prices.
    """

    def __init__(self):
        self.prev_ha_open: float | None = None
        self.prev_ha_close: float | None = None

    def transform(self, candle: OHLCV) -> OHLCV:
        ha_close = (candle.open + candle.high + candle.low + candle.close) / 4

        if self.prev_ha_open is None:
            ha_open = (candle.open + candle.close) / 2
        else:
            ha_open = (self.prev_ha_open + self.prev_ha_close) / 2

        ha_high = max(candle.high, ha_open, ha_close)
        ha_low = min(candle.low, ha_open, ha_close)

        self.prev_ha_open = ha_open
        self.prev_ha_close = ha_close

        return OHLCV(
            timestamp=candle.timestamp,
            open=ha_open,
            high=ha_high,
            low=ha_low,
            close=ha_close,
            volume=candle.volume,
        )

    def transform_series(self, candles: list[OHLCV]) -> list[OHLCV]:
        """Transform an entire series. Resets state first."""
        self.prev_ha_open = None
        self.prev_ha_close = None
        return [self.transform(c) for c in candles]


def ha_trend_signal(ha_candles: list[OHLCV], lookback: int = 3) -> int:
    """
    Simple HA trend signal.

    Returns:
        +1: bullish (N consecutive green HA candles with no lower wick)
        -1: bearish (N consecutive red HA candles with no upper wick)
         0: no clear trend
    """
    if len(ha_candles) < lookback:
        return 0

    recent = ha_candles[-lookback:]

    all_bullish = all(
        c.close > c.open and abs(c.low - min(c.open, c.close)) < 1e-10
        for c in recent
    )

    all_bearish = all(
        c.close < c.open and abs(c.high - max(c.open, c.close)) < 1e-10
        for c in recent
    )

    if all_bullish:
        return 1
    elif all_bearish:
        return -1
    return 0

When HA is useful: Trend-following strategies that need clean "stay in" signals. Apply HA over any base bar type — time bars, volume bars, dollar bars — to filter false crossovers.

When HA is harmful: Any strategy that needs precise price levels — support/resistance, order book analysis, PIQ (Position In Queue). The averaging destroys exact price information.

9–11. Japanese Reversal Charts

Japanese charting methods Kagi, Line Break, and Point & Figure: time-free charting methods that focus purely on price structure.

These are traditional Japanese charting methods (alongside Renko) that discard time entirely and focus on price structure.

9. Kagi Charts

class KagiChartGenerator:
    """
    Generates Kagi chart lines based on price reversals.

    Unlike Renko (fixed brick size), Kagi tracks the actual magnitude
    of each move and changes line thickness at breakout points.

    Useful for identifying support/resistance breaks and
    supply/demand shifts without time noise.
    """

    def __init__(self, reversal_amount: float = 10.0):
        self.reversal_amount = reversal_amount
        self.lines: list[dict] = []
        self.current_direction: int = 0  # 1=up, -1=down
        self.current_price: float | None = None
        self.extreme_price: float | None = None
        self.prev_high: float | None = None
        self.prev_low: float | None = None
        self.line_type: str = 'yang'  # 'yang' (thick) or 'yin' (thin)

    def on_price(self, timestamp: int, price: float):
        if self.current_price is None:
            self.current_price = price
            self.extreme_price = price
            return None

        if self.current_direction == 0:
            if price - self.current_price >= self.reversal_amount:
                self.current_direction = 1
                self.extreme_price = price
            elif self.current_price - price >= self.reversal_amount:
                self.current_direction = -1
                self.extreme_price = price
            return None

        if self.current_direction == 1:
            if price > self.extreme_price:
                self.extreme_price = price
                if self.prev_high is not None and price > self.prev_high:
                    self.line_type = 'yang'
            elif self.extreme_price - price >= self.reversal_amount:
                line = {
                    'timestamp': timestamp,
                    'start': self.current_price,
                    'end': self.extreme_price,
                    'direction': 'up',
                    'type': self.line_type,
                }
                self.lines.append(line)
                self.prev_high = self.extreme_price
                self.current_price = self.extreme_price
                self.extreme_price = price
                self.current_direction = -1
                if self.prev_low is not None and price < self.prev_low:
                    self.line_type = 'yin'
                return line
        else:
            if price < self.extreme_price:
                self.extreme_price = price
                if self.prev_low is not None and price < self.prev_low:
                    self.line_type = 'yin'
            elif price - self.extreme_price >= self.reversal_amount:
                line = {
                    'timestamp': timestamp,
                    'start': self.current_price,
                    'end': self.extreme_price,
                    'direction': 'down',
                    'type': self.line_type,
                }
                self.lines.append(line)
                self.prev_low = self.extreme_price
                self.current_price = self.extreme_price
                self.extreme_price = price
                self.current_direction = 1
                if self.prev_high is not None and price > self.prev_high:
                    self.line_type = 'yang'
                return line

        return None

10. Line Break Charts

Line break charts draw a new line (box) only when the closing price exceeds the high or low of the previous N lines (typically 3). No new line is drawn if the price stays within the range.

class LineBreakGenerator:
    """
    Generates Line Break bars (Three Line Break by default).

    A new bar is drawn only when the close exceeds the high or low
    of the last N bars. Filters out minor noise by requiring price
    to break through a multi-bar range.

    The 'N' parameter (line_count) controls sensitivity:
    - N=2: more sensitive, more bars, more noise
    - N=3: standard (Three Line Break)
    - N=4+: less sensitive, fewer bars, stronger signals
    """

    def __init__(self, line_count: int = 3):
        self.line_count = line_count
        self.lines: list[dict] = []

    def on_close(self, timestamp: int, close: float) -> dict | None:
        if not self.lines:
            self.lines.append({
                'timestamp': timestamp,
                'open': close,
                'close': close,
                'high': close,
                'low': close,
                'direction': 0,
            })
            return None

        lookback = self.lines[-self.line_count:] if len(self.lines) >= self.line_count else self.lines

        highest = max(l['high'] for l in lookback)
        lowest = min(l['low'] for l in lookback)
        last = self.lines[-1]

        new_line = None

        if close > highest:
            new_line = {
                'timestamp': timestamp,
                'open': last['close'],
                'close': close,
                'high': close,
                'low': last['close'],
                'direction': 1,
            }
        elif close < lowest:
            new_line = {
                'timestamp': timestamp,
                'open': last['close'],
                'close': close,
                'high': last['close'],
                'low': close,
                'direction': -1,
            }

        if new_line:
            self.lines.append(new_line)
            return new_line

        return None

11. Point & Figure Charts

class PointAndFigureGenerator:
    """
    Generates Point & Figure chart data.

    X column: price rising by box_size increments.
    O column: price falling by box_size increments.
    Column switch: requires reversal_boxes * box_size movement
    in the opposite direction.

    Classic setting: box_size based on ATR, reversal_boxes = 3.
    """

    def __init__(self, box_size: float = 10.0, reversal_boxes: int = 3):
        self.box_size = box_size
        self.reversal_boxes = reversal_boxes
        self.reversal_amount = box_size * reversal_boxes

        self.columns: list[dict] = []
        self.current_direction: int = 0
        self.current_top: float | None = None
        self.current_bottom: float | None = None

    def on_price(self, timestamp: int, price: float):
        if self.current_top is None:
            box_price = self._round_to_box(price)
            self.current_top = box_price
            self.current_bottom = box_price
            self.current_direction = 1
            return None

        events = []

        if self.current_direction == 1:
            while price >= self.current_top + self.box_size:
                self.current_top += self.box_size
                events.append(('X', self.current_top, timestamp))

            if price <= self.current_top - self.reversal_amount:
                col = {
                    'type': 'X',
                    'top': self.current_top,
                    'bottom': self.current_bottom,
                    'boxes': int((self.current_top - self.current_bottom) / self.box_size) + 1,
                    'timestamp': timestamp,
                }
                self.columns.append(col)
                self.current_direction = -1
                self.current_top = self.current_top - self.box_size
                self.current_bottom = self._round_to_box(price)
                events.append(('new_column', 'O', timestamp))

        else:
            while price <= self.current_bottom - self.box_size:
                self.current_bottom -= self.box_size
                events.append(('O', self.current_bottom, timestamp))

            if price >= self.current_bottom + self.reversal_amount:
                col = {
                    'type': 'O',
                    'top': self.current_top,
                    'bottom': self.current_bottom,
                    'boxes': int((self.current_top - self.current_bottom) / self.box_size) + 1,
                    'timestamp': timestamp,
                }
                self.columns.append(col)
                self.current_direction = 1
                self.current_bottom = self.current_bottom + self.box_size
                self.current_top = self._round_to_box(price)
                events.append(('new_column', 'X', timestamp))

        return events if events else None

    def _round_to_box(self, price: float) -> float:
        return round(price / self.box_size) * self.box_size

12–14. Information-Driven Bars

Information-driven bars Imbalance bars, run bars, CUSUM filters, and entropy bars: sampling when the market tells us something has changed.

12. Tick Imbalance Bars (TIB)

If the market is in equilibrium, buyer-initiated and seller-initiated trades should roughly balance. When the imbalance exceeds our expectation, something has changed. Sample a bar at that moment.

Each trade is classified as buyer-initiated (+1) or seller-initiated (-1) using the tick rule. We track cumulative imbalance θ and sample when |θ| exceeds a dynamic threshold.

class TickImbalanceBarGenerator:
    """
    Generates bars when the cumulative tick imbalance exceeds
    expected levels — i.e., when "new information" arrives.

    Based on Lopez de Prado (2018), Chapter 2.
    """

    def __init__(
        self,
        expected_ticks_init: int = 1000,
        ewma_window: int = 100,
        min_ticks: int = 100,
        max_ticks: int = 50000,
    ):
        self.expected_ticks_init = expected_ticks_init
        self.ewma_window = ewma_window
        self.min_ticks = min_ticks
        self.max_ticks = max_ticks

        self.theta = 0.0
        self.prev_price: float | None = None
        self.prev_sign = 1
        self.trades: list[tuple[int, float, float]] = []

        self.bar_lengths: list[int] = []
        self.imbalances: list[float] = []
        self.expected_ticks = float(expected_ticks_init)
        self.expected_imbalance = 0.0

        self.bars: list[OHLCV] = []

    def _tick_sign(self, price: float) -> int:
        """Classify trade as buy (+1) or sell (-1) using tick rule."""
        if self.prev_price is None:
            self.prev_price = price
            return 1

        if price > self.prev_price:
            sign = 1
        elif price < self.prev_price:
            sign = -1
        else:
            sign = self.prev_sign

        self.prev_price = price
        self.prev_sign = sign
        return sign

    def on_trade(self, timestamp: int, price: float, qty: float):
        sign = self._tick_sign(price)
        self.theta += sign
        self.trades.append((timestamp, price, qty))

        threshold = self.expected_ticks * abs(self.expected_imbalance)
        if threshold == 0:
            threshold = self.expected_ticks_init * 0.5

        if abs(self.theta) >= threshold and len(self.trades) >= self.min_ticks:
            return self._close_bar()

        if len(self.trades) >= self.max_ticks:
            return self._close_bar()

        return None

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)

        self.bar_lengths.append(len(self.trades))
        self.imbalances.append(self.theta / len(self.trades))

        if len(self.bar_lengths) >= 2:
            alpha = 2.0 / (self.ewma_window + 1)
            self.expected_ticks = (
                alpha * self.bar_lengths[-1]
                + (1 - alpha) * self.expected_ticks
            )
            self.expected_ticks = max(
                self.min_ticks,
                min(self.max_ticks, self.expected_ticks)
            )
            self.expected_imbalance = (
                alpha * self.imbalances[-1]
                + (1 - alpha) * self.expected_imbalance
            )

        self.theta = 0.0
        self.trades = []
        return bar

13. Volume Imbalance Bars (VIB)

class VolumeImbalanceBarGenerator:
    """
    Like TIBs, but uses signed volume instead of signed ticks.

    Captures the insight that a 100-BTC buy signal is 100x more
    informative than a 1-BTC buy signal.
    """

    def __init__(
        self,
        expected_ticks_init: int = 1000,
        ewma_window: int = 100,
    ):
        self.expected_ticks_init = expected_ticks_init
        self.ewma_window = ewma_window

        self.theta = 0.0
        self.prev_price: float | None = None
        self.prev_sign = 1
        self.trades: list[tuple[int, float, float]] = []

        self.bar_lengths: list[int] = []
        self.volume_imbalances: list[float] = []
        self.expected_ticks = float(expected_ticks_init)
        self.expected_vol_imbalance = 0.0

        self.bars: list[OHLCV] = []

    def _tick_sign(self, price: float) -> int:
        if self.prev_price is None:
            self.prev_price = price
            return 1
        if price > self.prev_price:
            sign = 1
        elif price < self.prev_price:
            sign = -1
        else:
            sign = self.prev_sign
        self.prev_price = price
        self.prev_sign = sign
        return sign

    def on_trade(self, timestamp: int, price: float, qty: float):
        sign = self._tick_sign(price)
        self.theta += sign * qty
        self.trades.append((timestamp, price, qty))

        threshold = self.expected_ticks * abs(self.expected_vol_imbalance)
        if threshold == 0:
            threshold = self.expected_ticks_init * 0.5

        if abs(self.theta) >= threshold and len(self.trades) >= 10:
            return self._close_bar()
        return None

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)

        self.bar_lengths.append(len(self.trades))
        self.volume_imbalances.append(self.theta / len(self.trades))

        alpha = 2.0 / (self.ewma_window + 1)
        if len(self.bar_lengths) >= 2:
            self.expected_ticks = (
                alpha * self.bar_lengths[-1] + (1 - alpha) * self.expected_ticks
            )
            self.expected_vol_imbalance = (
                alpha * self.volume_imbalances[-1]
                + (1 - alpha) * self.expected_vol_imbalance
            )

        self.theta = 0.0
        self.trades = []
        return bar

The Explosion Problem

A known issue with imbalance bars: the EWMA-based threshold can enter a positive feedback loop. The solution: clamp with min_ticks and max_ticks bounds.


self.expected_ticks = max(
    self.min_ticks,    # Floor: never less than 100 ticks
    min(
        self.max_ticks,  # Ceiling: never more than 50000 ticks
        new_expected_ticks
    )
)

14. Run Bars

class TickRunBarGenerator:
    """
    Generates bars when the length of a directional run exceeds expectations.

    Based on Lopez de Prado (2018), Chapter 2.

    Difference from imbalance bars:
    - Imbalance bars track NET imbalance (buys minus sells)
    - Run bars track the MAXIMUM run length (consecutive buys OR sells)
    """

    def __init__(
        self,
        expected_ticks_init: int = 1000,
        ewma_window: int = 100,
        min_ticks: int = 100,
        max_ticks: int = 50000,
    ):
        self.expected_ticks_init = expected_ticks_init
        self.ewma_window = ewma_window
        self.min_ticks = min_ticks
        self.max_ticks = max_ticks

        self.prev_price: float | None = None
        self.prev_sign = 1
        self.trades: list[tuple[int, float, float]] = []

        self.buy_run = 0
        self.sell_run = 0
        self.max_buy_run = 0
        self.max_sell_run = 0

        self.bar_lengths: list[int] = []
        self.max_runs: list[float] = []
        self.expected_ticks = float(expected_ticks_init)
        self.expected_max_run = 0.0

        self.bars: list[OHLCV] = []

    def _tick_sign(self, price: float) -> int:
        if self.prev_price is None:
            self.prev_price = price
            return 1
        if price > self.prev_price:
            sign = 1
        elif price < self.prev_price:
            sign = -1
        else:
            sign = self.prev_sign
        self.prev_price = price
        self.prev_sign = sign
        return sign

    def on_trade(self, timestamp: int, price: float, qty: float):
        sign = self._tick_sign(price)
        self.trades.append((timestamp, price, qty))

        if sign == 1:
            self.buy_run += 1
            self.sell_run = 0
        else:
            self.sell_run += 1
            self.buy_run = 0

        self.max_buy_run = max(self.max_buy_run, self.buy_run)
        self.max_sell_run = max(self.max_sell_run, self.sell_run)

        theta = max(self.max_buy_run, self.max_sell_run)
        threshold = self.expected_ticks * self.expected_max_run if self.expected_max_run > 0 else self.expected_ticks_init * 0.3

        if theta >= threshold and len(self.trades) >= self.min_ticks:
            return self._close_bar()

        if len(self.trades) >= self.max_ticks:
            return self._close_bar()

        return None

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)

        max_run = max(self.max_buy_run, self.max_sell_run) / len(self.trades)
        self.bar_lengths.append(len(self.trades))
        self.max_runs.append(max_run)

        alpha = 2.0 / (self.ewma_window + 1)
        if len(self.bar_lengths) >= 2:
            self.expected_ticks = alpha * self.bar_lengths[-1] + (1 - alpha) * self.expected_ticks
            self.expected_ticks = max(self.min_ticks, min(self.max_ticks, self.expected_ticks))
            self.expected_max_run = alpha * self.max_runs[-1] + (1 - alpha) * self.expected_max_run

        self.trades = []
        self.buy_run = 0
        self.sell_run = 0
        self.max_buy_run = 0
        self.max_sell_run = 0

        return bar

Run bars can be extended to volume runs and dollar runs.

15. CUSUM Filter Bars

class CUSUMFilterBarGenerator:
    """
    Symmetric CUSUM filter for event-based sampling.

    Based on Lopez de Prado (2018), Chapter 2.5.

    Key advantage over Bollinger Bands: CUSUM requires a FULL
    run of threshold magnitude before triggering. Bollinger Bands
    trigger repeatedly when price hovers near the band.

    Can be applied to 1m OHLCV data — no tick data required.
    """

    def __init__(self, threshold: float = 0.01):
        self.threshold = threshold
        self.s_pos = 0.0
        self.s_neg = 0.0
        self.prev_price: float | None = None
        self.buffer: list[OHLCV] = []
        self.bars: list[OHLCV] = []

    def on_candle_1m(self, candle: OHLCV) -> OHLCV | None:
        self.buffer.append(candle)

        if self.prev_price is None:
            self.prev_price = candle.close
            return None

        import math
        log_ret = math.log(candle.close / self.prev_price)
        self.prev_price = candle.close

        self.s_pos = max(0.0, self.s_pos + log_ret)
        self.s_neg = min(0.0, self.s_neg + log_ret)

        triggered = False

        if self.s_pos > self.threshold:
            self.s_pos = 0.0
            triggered = True

        if self.s_neg < -self.threshold:
            self.s_neg = 0.0
            triggered = True

        if triggered and len(self.buffer) >= 2:
            bars = self.buffer
            bar = OHLCV(
                timestamp=bars[-1].timestamp,
                open=bars[0].open,
                high=max(b.high for b in bars),
                low=min(b.low for b in bars),
                close=bars[-1].close,
                volume=sum(b.volume for b in bars),
            )
            self.bars.append(bar)
            self.buffer = []
            return bar

        return None

16. Entropy Bars

The most theoretically elegant approach: sample when the information content (Shannon entropy) of the intra-bar price series exceeds a threshold.

class EntropyBarGenerator:
    """
    Generates bars when the entropy of intra-bar returns exceeds
    a threshold.

    Based on Shannon's information theory: bars are sampled when
    "new information" arrives, measured as the entropy of the
    return distribution within the current bar.

    This is the most theoretically "pure" information-driven bar.
    """

    def __init__(
        self,
        entropy_threshold: float = 2.0,
        min_trades: int = 50,
        n_bins: int = 10,
    ):
        self.entropy_threshold = entropy_threshold
        self.min_trades = min_trades
        self.n_bins = n_bins
        self.trades: list[tuple[int, float, float]] = []
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float):
        self.trades.append((timestamp, price, qty))

        if len(self.trades) < self.min_trades:
            return None

        entropy = self._compute_entropy()

        if entropy >= self.entropy_threshold:
            return self._close_bar()

        return None

    def _compute_entropy(self) -> float:
        import math

        prices = [t[1] for t in self.trades]
        if len(prices) < 2:
            return 0.0

        returns = [
            math.log(prices[i] / prices[i-1])
            for i in range(1, len(prices))
            if prices[i-1] > 0
        ]

        if not returns:
            return 0.0

        min_r = min(returns)
        max_r = max(returns)

        if max_r == min_r:
            return 0.0

        bin_width = (max_r - min_r) / self.n_bins
        bins = [0] * self.n_bins

        for r in returns:
            idx = min(int((r - min_r) / bin_width), self.n_bins - 1)
            bins[idx] += 1

        total = sum(bins)
        entropy = 0.0
        for count in bins:
            if count > 0:
                p = count / total
                entropy -= p * math.log2(p)

        return entropy

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        self.bars.append(bar)
        self.trades = []
        return bar

17. Delta Bars (Order Flow)

Delta bars and order flow Cumulative delta: measuring the net force of aggressive buyers vs sellers in real time.

class DeltaBarGenerator:
    """
    Generates bars based on cumulative order flow delta.

    Delta = Buy Volume - Sell Volume (classified by aggressor side).

    Requires trade-level data with side classification
    (available from Binance aggTrades, Bybit trades, etc.)
    """

    def __init__(self, threshold: float = 500.0):
        self.threshold = threshold
        self.cumulative_delta = 0.0
        self.trades: list[tuple[int, float, float, int]] = []
        self.bars: list[OHLCV] = []

    def on_trade(self, timestamp: int, price: float, qty: float, is_buyer_maker: bool):
        side = -1 if is_buyer_maker else 1
        signed_qty = side * qty

        self.cumulative_delta += signed_qty
        self.trades.append((timestamp, price, qty, side))

        if abs(self.cumulative_delta) >= self.threshold:
            return self._close_bar()

        return None

    def _close_bar(self):
        prices = [t[1] for t in self.trades]
        volumes = [t[2] for t in self.trades]

        bar = OHLCV(
            timestamp=self.trades[-1][0],
            open=prices[0],
            high=max(prices),
            low=min(prices),
            close=prices[-1],
            volume=sum(volumes),
        )
        bar.delta = self.cumulative_delta  # type: ignore
        bar.buy_volume = sum(t[2] for t in self.trades if t[3] == 1)  # type: ignore
        bar.sell_volume = sum(t[2] for t in self.trades if t[3] == -1)  # type: ignore

        self.bars.append(bar)
        self.cumulative_delta = 0.0
        self.trades = []
        return bar

Rolling window aggregation A circular buffer of base bars: new data enters, old data exits, and the aggregated candle is always valid.

Aggregation methods determine how base bars are composed into higher-timeframe (HTF) candles. They are independent of the bar type — you can apply any aggregation method to any base bar type.

Method A: Calendar-Aligned Aggregation

Aggregate all base bars that fall within a fixed calendar boundary. The "1-hour" candle covers all bars from 14:00:00 to 14:59:59.

Properties:

All market participants see the same boundaries — essential for market structure analysis, support/resistance, PIQ triggers
Cold start problem: partial candle after restart
Natural for time bars (this is what exchanges provide natively)
Also works for non-time bars: "all volume bars that closed between 14:00 and 15:00" = a calendar-aligned hourly candle from volume bars

Method B: Rolling Window Aggregation

Aggregate the last N closed base bars, recomputed on every new bar. A "1-hour" rolling candle = the last 60 closed 1-minute time bars, updated every minute.

The atomic unit is the closed base bar. This design choice gives:

No cold start. After N bars, the candle is valid. No partial-candle noise.
Backtest parity. If live trading uses the same atomic unit as the backtest engine, signals are identical.
Simple validation. One rule: if buffer not full: skip.

import numpy as np

class RollingCandleAggregator:
    """
    Produces rolling higher-timeframe candles from closed base bars.

    Works with ANY bar type: time bars, tick bars, volume bars,
    dollar bars, delta bars — anything that produces OHLCV output.

    Example: RollingCandleAggregator(window=60) with 1m time bars
    produces a "1h" candle updated every minute.

    Example: RollingCandleAggregator(window=24) with volume bars
    produces a candle spanning the last 24 volume bars.
    """

    def __init__(self, window: int):
        self.window = window
        self.buffer: deque[OHLCV] = deque(maxlen=window)

    def push(self, bar: OHLCV) -> OHLCV | None:
        """
        Add a closed base bar. Returns aggregated candle
        only when buffer is full (= candle is valid).
        """
        self.buffer.append(bar)

        if len(self.buffer) < self.window:
            return None

        return self._aggregate()

    def _aggregate(self) -> OHLCV:
        bars = list(self.buffer)
        return OHLCV(
            timestamp=bars[-1].timestamp,
            open=bars[0].open,
            high=max(b.high for b in bars),
            low=min(b.low for b in bars),
            close=bars[-1].close,
            volume=sum(b.volume for b in bars),
        )

    @property
    def is_valid(self) -> bool:
        return len(self.buffer) == self.window

Method C: Adaptive Rolling Aggregation

Like rolling, but the window size adapts to current volatility. Calm markets → wider window (more smoothing). Volatile markets → narrower window (faster reaction).

class AdaptiveRollingAggregator:
    """
    Rolling window where the window size adapts to volatility.

    Works with any base bar type. Uses ATR of recent bars
    as the volatility measure.

    Low volatility → wider window (more smoothing, fewer signals)
    High volatility → narrower window (faster reaction)
    """

    def __init__(
        self,
        base_window: int = 60,
        min_window: int = 15,
        max_window: int = 240,
        atr_period: int = 14,
        atr_base: float | None = None,
    ):
        self.base_window = base_window
        self.min_window = min_window
        self.max_window = max_window
        self.atr_period = atr_period
        self.atr_base = atr_base

        self.all_candles: deque[OHLCV] = deque(maxlen=max_window)
        self.atr_values: deque[float] = deque(maxlen=atr_period * 2)
        self.current_window = base_window

    def push(self, bar: OHLCV) -> OHLCV | None:
        self.all_candles.append(bar)

        tr = bar.high - bar.low
        self.atr_values.append(tr)

        if len(self.atr_values) < self.atr_period:
            return None

        current_atr = sum(list(self.atr_values)[-self.atr_period:]) / self.atr_period

        if self.atr_base is None and len(self.atr_values) >= self.atr_period * 2:
            self.atr_base = sum(self.atr_values) / len(self.atr_values)

        if self.atr_base is None or self.atr_base == 0:
            return None

        vol_ratio = current_atr / self.atr_base
        self.current_window = int(self.base_window / vol_ratio)
        self.current_window = max(self.min_window, min(self.max_window, self.current_window))

        if len(self.all_candles) < self.current_window:
            return None

        bars = list(self.all_candles)[-self.current_window:]
        return OHLCV(
            timestamp=bars[-1].timestamp,
            open=bars[0].open,
            high=max(b.high for b in bars),
            low=min(b.low for b in bars),
            close=bars[-1].close,
            volume=sum(b.volume for b in bars),
        )

Every base bar type can be combined with every aggregation method. Some combinations are standard (calendar time bars = what exchanges give you), others are exotic but powerful.

Combination Examples

Base Bar Type	Calendar	Rolling	Adaptive
Time	Standard exchange candles	Always-valid HTF, no cold start	Vol-adaptive timeframe
Volume	"All volume bars this hour"	Last 24 volume bars	Wider window in calm markets
Dollar	Hourly dollar-bar aggregate	Last N dollar bars	Adaptive dollar windows
Tick Imbalance	Hourly imbalance aggregate	Last N imbalance events	Fast reaction in volatile regimes
Delta	Hourly net order flow	Rolling delta snapshot	Adaptive flow window
Renko	"Bricks this hour"	Last N bricks	Adaptive brick count

Hybrid Engine: Calendar + Rolling

In practice, you want both calendar and rolling aggregation simultaneously. The memory overhead is negligible — two deque buffers per timeframe per symbol.

class HybridCandleEngine:
    """
    Maintains both calendar-aligned and rolling candles
    for any base bar type.

    Calendar candles: for market structure, support/resistance, PIQ.
    Rolling candles: for indicators, signal generation, entries/exits.
    """

    def __init__(self):
        self.rolling = {
            '1h': RollingCandleAggregator(60),
            '4h': RollingCandleAggregator(240),
        }
        self.calendar: dict[str, list[OHLCV]] = {
            '1h': [],
            '4h': [],
        }
        self._calendar_buffer: dict[str, list[OHLCV]] = {
            '1h': [],
            '4h': [],
        }

    def on_bar(self, bar: OHLCV):
        """Process any base bar type — time, volume, tick, delta, etc."""
        rolling_results = {}
        for tf, agg in self.rolling.items():
            rolling_results[tf] = agg.push(bar)

        self._update_calendar(bar)

        return rolling_results

    def _update_calendar(self, bar: OHLCV):
        from datetime import datetime
        ts = datetime.utcfromtimestamp(bar.timestamp)

        for tf, minutes in [('1h', 60), ('4h', 240)]:
            self._calendar_buffer[tf].append(bar)

            total_minutes = ts.hour * 60 + ts.minute
            if (total_minutes + 1) % minutes == 0:
                bars = self._calendar_buffer[tf]
                if bars:
                    agg = OHLCV(
                        timestamp=bars[-1].timestamp,
                        open=bars[0].open,
                        high=max(b.high for b in bars),
                        low=min(b.low for b in bars),
                        close=bars[-1].close,
                        volume=sum(b.volume for b in bars),
                    )
                    self.calendar[tf].append(agg)
                    self._calendar_buffer[tf] = []

Time-Volume Hybrid: Calendar with Volume Splits

A special aggregation variant: calendar-aligned candles that force-close early when volume exceeds a threshold. Maintains time synchronization while adapting to activity spikes.

class TimeVolumeHybridGenerator:
    """
    Calendar-aligned candles that split when volume spikes.

    Rule: close the candle at the calendar boundary OR when
    accumulated volume exceeds vol_threshold, whichever comes first.

    Works with any base bar type — the volume trigger adds an
    extra split dimension on top of calendar alignment.
    """

    def __init__(
        self,
        interval_minutes: int = 60,
        vol_threshold: float = 5000.0,
    ):
        self.interval_minutes = interval_minutes
        self.vol_threshold = vol_threshold

        self.buffer: list[OHLCV] = []
        self.accumulated_volume = 0.0
        self.bars: list[OHLCV] = []

    def on_bar(self, bar: OHLCV) -> OHLCV | None:
        self.buffer.append(bar)
        self.accumulated_volume += bar.volume

        from datetime import datetime
        ts = datetime.utcfromtimestamp(bar.timestamp)
        total_minutes = ts.hour * 60 + ts.minute
        at_boundary = (total_minutes + 1) % self.interval_minutes == 0

        vol_spike = self.accumulated_volume >= self.vol_threshold

        if at_boundary or vol_spike:
            return self._close_bar(split_reason='volume' if vol_spike else 'time')

        return None

    def _close_bar(self, split_reason: str) -> OHLCV:
        bars = self.buffer
        bar = OHLCV(
            timestamp=bars[-1].timestamp,
            open=bars[0].open,
            high=max(b.high for b in bars),
            low=min(b.low for b in bars),
            close=bars[-1].close,
            volume=sum(b.volume for b in bars),
        )
        bar.split_reason = split_reason  # type: ignore
        bar.num_bars = len(bars)  # type: ignore

        self.bars.append(bar)
        self.buffer = []
        self.accumulated_volume = 0.0
        return bar

Practical Aggregation: Cascading Preload

Cascading aggregation Cascading preload: composing daily candles from hourly, and hourly from minute — bypassing API limits.

The solution: cascading aggregation — build higher timeframes from the highest resolution available at each depth, then stitch them together.

Rolling 1W candle:
├── 6 completed 1D candles ← fetch from REST /klines?interval=1d
├── 1 partial day:
│   ├── 23 completed 1h candles ← fetch from REST /klines?interval=1h
│   └── 1 partial hour:
│       └── N completed 1m candles ← fetch from REST /klines?interval=1m
└── Live: each new closed 1m candle updates the entire chain

This works because OHLCV aggregation is composable: the high of a 1D candle is the max of 24 1h highs, which is the max of 1440 1m highs.

Multi-Exchange Limits

Exchange	Max 1m Candles	Max 1h Candles	Notable Intervals
Binance	1,000	1,000	1m–1M, full range
Bybit	1,000	1,000	1–720, D/W/M
OKX	300	300	1m–1M (more restrictive)
Gate.io	1,000	1,000	10s–30d

Aggregation Consistency Check

The 1h candle from a REST API might not match what you'd compute from 60 1m candles. Always validate:

def validate_aggregation(
    candle_htf: OHLCV,
    candles_ltf: list[OHLCV],
    tolerance_pct: float = 0.001,
) -> dict[str, bool]:
    agg = OHLCV(
        timestamp=candles_ltf[-1].timestamp,
        open=candles_ltf[0].open,
        high=max(c.high for c in candles_ltf),
        low=min(c.low for c in candles_ltf),
        close=candles_ltf[-1].close,
        volume=sum(c.volume for c in candles_ltf),
    )

    def close_enough(a: float, b: float) -> bool:
        if a == 0 and b == 0:
            return True
        return abs(a - b) / max(abs(a), abs(b)) < tolerance_pct

    return {
        'open': close_enough(candle_htf.open, agg.open),
        'high': close_enough(candle_htf.high, agg.high),
        'low': close_enough(candle_htf.low, agg.low),
        'close': close_enough(candle_htf.close, agg.close),
        'volume': close_enough(candle_htf.volume, agg.volume),
    }

If validation fails consistently, always aggregate from 1m yourself — never trust the exchange's HTF candle for backtesting parity.

Comparison Matrix

Axis 1: Base Bar Types

#	Bar Type	Trigger	Tick Data Required	Best For
1	Time	Fixed interval	No	Market structure, crowd behavior
2	Tick	N trades	Yes	ML features, equal-opinion sampling
3	Volume	N units traded	Yes	Normalized activity analysis
4	Dollar	$N notional	Yes	Cross-asset comparison
5	Renko	Price ± N units	No	Trend following, noise filtering
6	Range	High-Low ≥ N	Yes	Breakout detection
7	Volatility	Adaptive range	Yes	Regime-adaptive analysis
8	Heikin-Ashi	Transformation	No	Trend confirmation (synthetic prices!)
9	Kagi	Price reversal	No	Supply/demand structure
10	Line Break	N-line breakout	No	Macro trend filter
11	Point & Figure	Box + reversal	No	Support/resistance mapping
12	TIB	Tick imbalance	Yes	Informed flow detection
13	VIB	Volume imbalance	Yes	Large order detection
14	Run	Run length	Yes	Order splitting detection
15	CUSUM	Cumulative return	No (1m closes)	Structural break events
16	Entropy	Shannon entropy	Yes	ML research, feature purity
17	Delta	Order flow delta	Yes (aggTrades)	Aggressor flow analysis

Axis 2: Aggregation Methods

Method	Alignment	Cold Start	Phase Shift	Best For
Calendar	Wall clock	Partial bar risk	None (crowd-aligned)	Market structure, PIQ, S/R
Rolling	N bars	None (after warmup)	Yes (shifted from :00)	Indicators, signals
Adaptive	Volatility-driven N	After ATR calibration	Yes	Vol-adaptive strategies

Practical Recommendations

Layered architecture Four-layer candle architecture: rolling signals, calendar structure, microstructure flow, and trend filters.

If your backtest engine runs on 1m OHLCV data:

Rolling time bars — simplest upgrade. Zero additional data. Eliminates cold start.
Hybrid (rolling + calendar) time bars — calendar for market structure, rolling for signals.
CUSUM filter — works on 1m closes, no tick data. "Something moved enough to be interesting."

If you have tick/trade data:

Dollar bars + rolling — recommended default from quant finance literature.
Volume imbalance bars + rolling — detects informed flow, samples more during significant events.
Delta bars + calendar — if you have aggressor-side classification, the most direct view of who is pushing the market.

As filters (apply Heikin-Ashi or Line Break on top of any base+aggregation combination):

Heikin-Ashi over rolling volume bars — clean trend signals on activity-normalized data.
Line Break / Kagi over daily calendar bars — macro trend filter.

For Marketmaker.cc specifically — a layered approach:

Layer 1 (signals): Rolling aggregation of time bars for indicators and entry/exit signals. No cold start, perfect backtest parity.
Layer 2 (market structure): Calendar-aligned time bars for support/resistance, hourly close analysis, and PIQ triggers.
Layer 3 (microstructure): Volume imbalance bars + delta bars from the raw trade stream for detecting informed flow, order splitting, and anticipating large moves. See also Digital Fingerprint: Trader Identification for behavioral pattern recognition on order flow data.
Layer 4 (trend filter): Heikin-Ashi transformation on rolling bars, or Line Break on 4h calendar closes, to keep signals aligned with macro direction.

Conclusion

Candle construction is not a single choice — it's two independent decisions:

What kind of bar? Time captures clock intervals. Activity (tick, volume, dollar) captures market participation. Price (Renko, range, volatility) captures movements. Information (imbalance, runs, CUSUM, entropy) captures arrivals of new information. Order flow (delta) captures aggressive pressure.
How to aggregate into higher timeframes? Calendar aligns with the crowd. Rolling eliminates cold start. Adaptive reacts to volatility.

The atomic unit — the closed base bar — remains the foundation. Everything else is aggregation.

Useful Links

Citation

@article{soloviov2026bartypes,
  author = {Soloviov, Eugen},
  title = {Bar Types and Aggregation Methods for Algorithmic Trading},
  year = {2026},
  url = {https://marketmaker.cc/en/blog/post/beyond-time-bars-candle-construction},
  description = {Two-axis classification of candle construction: 17 base bar types × 3 aggregation methods = 51 combinations, with implementation code and practical recommendations for crypto algotrading.}
}

TL;DR

Two Axes of Candle Construction

1. Time Bars (Standard)

2–4. Activity-Based Bars

2. Tick Bars

3. Volume Bars

4. Dollar Bars

Choosing the Threshold

5–7. Price-Based Bars

5. Renko Bars

6. Range Bars

7. Volatility Bars

8. Heikin-Ashi (Smoothed Transformation)

9–11. Japanese Reversal Charts

9. Kagi Charts

10. Line Break Charts

11. Point & Figure Charts

12–14. Information-Driven Bars

12. Tick Imbalance Bars (TIB)

13. Volume Imbalance Bars (VIB)

The Explosion Problem

14. Run Bars

15. CUSUM Filter Bars

16. Entropy Bars

17. Delta Bars (Order Flow)

Method A: Calendar-Aligned Aggregation

Method B: Rolling Window Aggregation

Method C: Adaptive Rolling Aggregation

Combination Examples

Hybrid Engine: Calendar + Rolling

Time-Volume Hybrid: Calendar with Volume Splits

Practical Aggregation: Cascading Preload

Multi-Exchange Limits

Aggregation Consistency Check

Comparison Matrix

Axis 1: Base Bar Types

Axis 2: Aggregation Methods

Practical Recommendations

Conclusion

Useful Links

Citation

Read More

Trading Candles Demystified: How Raw Trades Become the Foundation of Market Analysis

Queue Inside the Wall: Analyzing Order Position in Order Book Density

Digital Fingerprint of a Trader: How to Identify a Market Maker by Their Order Book Behavior

बाज़ार से आगे रहें

TL;DR

Two Axes of Candle Construction

1. Time Bars (Standard)

2–4. Activity-Based Bars

2. Tick Bars

3. Volume Bars

4. Dollar Bars

Choosing the Threshold

5–7. Price-Based Bars

5. Renko Bars

6. Range Bars

7. Volatility Bars

8. Heikin-Ashi (Smoothed Transformation)

9–11. Japanese Reversal Charts

9. Kagi Charts

10. Line Break Charts

11. Point & Figure Charts

12–14. Information-Driven Bars

12. Tick Imbalance Bars (TIB)

13. Volume Imbalance Bars (VIB)

The Explosion Problem

14. Run Bars

15. CUSUM Filter Bars

16. Entropy Bars

17. Delta Bars (Order Flow)

Method A: Calendar-Aligned Aggregation

Method B: Rolling Window Aggregation

Method C: Adaptive Rolling Aggregation

Combination Examples

Hybrid Engine: Calendar + Rolling

Time-Volume Hybrid: Calendar with Volume Splits

Practical Aggregation: Cascading Preload

Multi-Exchange Limits

Aggregation Consistency Check