US Equity

Handling Data

Introduction

LEAN passes the data you request to the OnData method so you can make trading decisions. The default OnData method accepts a Slice object, but you can define additional OnData methods that accept different data types. For example, if you define an OnData method that accepts a TradeBar argument, it only receives TradeBar objects. The Slice object that the OnData method receives groups all the data together at a single moment in time. To access the Slice outside of the OnData method, use the CurrentSlice property of your algorithm.

All the data formats use DataDictionary objects to group data by Symbol and provide easy access to information. The plural of the type denotes the collection of objects. For instance, the TradeBars DataDictionary is made up of TradeBar objects. To access individual data points in the dictionary, you can index the dictionary with the security ticker or Symbol, but we recommend you use the Symbol.

Trades

TradeBar objects are price bars that consolidate individual trades from the exchanges. They contain the open, high, low, close, and volume of trading activity over a period of time.

TradeBar objects have the following properties:

To get the TradeBar objects in the Slice, index the Slice or index the Bars property of the Slice with the security Symbol. If the security doesn't actively trade or you are in the same time step as when you added the security subscription, the Slice may not contain data for your Symbol. To avoid issues, check if the Slice contains data for your security before you index the Slice with the security Symbol.

public override void OnData(Slice slice)
{
    if (slice.Bars.ContainsKey(_symbol))
    {
        var tradeBar = slice.Bars[_symbol];
    }
}

public void OnData(TradeBars tradeBars)
{
    if (tradeBars.ContainsKey(_symbol))
    {
        var tradeBar = tradeBars[_symbol];
    }
}
def OnData(self, slice: Slice) -> None:
    if self.symbol in slice.Bars:
        trade_bar = slice.Bars[self.symbol]

You can also iterate through the TradeBars dictionary. The keys of the dictionary are the Symbol objects and the values are the TradeBar objects.

public override void OnData(Slice slice)
{
    foreach (var kvp in slice.Bars)
    {
        var symbol = kvp.Key;
        var tradeBar = kvp.Value;
    }
}

public void OnData(TradeBars tradeBars)
{
    foreach (var kvp in tradeBars)
    {
        var symbol = kvp.Key;
        var tradeBar = kvp.Value;
    }
}
def OnData(self, slice: Slice) -> None:
    for symbol, trade_bar in slice.Bars.items():
        pass

We adjust the daily open and close price of bars to reflect the official auction prices.

Quotes

QuoteBar objects are bars that consolidate NBBO quotes from the exchanges. They contain the open, high, low, and close prices of the bid and ask. The Open, High, Low, and Close properties of the QuoteBar object are the mean of the respective bid and ask prices. If the bid or ask portion of the QuoteBar has no data, the Open, High, Low, and Close properties of the QuoteBar copy the values of either the Bid or Ask instead of taking their mean.

QuoteBar objects have the following properties:

To get the QuoteBar objects in the Slice, index the QuoteBars property of the Slice with the security Symbol. If the security doesn't actively get quotes or you are in the same time step as when you added the security subscription, the Slice may not contain data for your Symbol. To avoid issues, check if the Slice contains data for your security before you index the Slice with the security Symbol.

public override void OnData(Slice slice)
{
    if (slice.QuoteBars.ContainsKey(_symbol))
    {
        var quoteBar = slice.QuoteBars[_symbol];
    }
}

public void OnData(QuoteBars quoteBars)
{
    if (quoteBars.ContainsKey(_symbol))
    {
        var quoteBar = quoteBars[_symbol];
    }
}
def OnData(self, slice: Slice) -> None:
    if self.symbol in slice.QuoteBars:
        quote_bar = slice.QuoteBars[self.symbol]

You can also iterate through the QuoteBars dictionary. The keys of the dictionary are the Symbol objects and the values are the QuoteBar objects.

public override void OnData(Slice slice)
{
    foreach (var kvp in slice.QuoteBars)
    {
        var symbol = kvp.Key;
        var quoteBar = kvp.Value;
    }
}

public void OnData(QuoteBars quoteBars)
{
    foreach (var kvp in quoteBars)
    {
        var symbol = kvp.Key;
        var quoteBar = kvp.Value;
    }
}
def OnData(self, slice: Slice) -> None:
    for symbol, quote_bar in slice.QuoteBars.items():
        pass

QuoteBar objects let LEAN incorporate spread costs into your simulated trade fills to make backtest results more realistic.

Ticks

Tick objects represent a single trade or quote at a moment in time. A trade tick is a record of a transaction for the security. A quote tick is an offer to buy or sell the security at a specific price. Tick objects have the following properties:

Trade ticks have a non-zero value for the Quantity and Price properties, but they have a zero value for the BidPrice, BidSize, AskPrice, and AskSize properties. Quote ticks have non-zero values for BidPrice and BidSize properties or have non-zero values for AskPrice and AskSize properties. To check if a tick is a trade or a quote, use the TickType property.

In backtests, LEAN groups ticks into one millisecond buckets. In live trading, LEAN groups ticks into ~70-millisecond buckets. To get the Tick objects in the Slice, index the Ticks property of the Slice with a Symbol. If the security doesn't actively trade or you are in the same time step as when you added the security subscription, the Slice may not contain data for your Symbol. To avoid issues, check if the Slice contains data for your security before you index the Slice with the security Symbol.

public override void OnData(Slice slice)
{
    if (slice.Ticks.ContainsKey(_symbol))
    {
        var ticks = slice.Ticks[_symbol];
        foreach (var tick in ticks)
        {
            //
        }
    }
}

public void OnData(Ticks ticks)
{
    if (ticks.ContainsKey(_symbol))
    {
        foreach (var tick in ticks[_symbol])
        {
            //
        }
    }
}
def OnData(self, slice: Slice) -> None:
    if self.symbol in slice.Ticks:
        ticks = slice.Ticks[self.symbol]
        for tick in ticks:
            pass

You can also iterate through the Ticks dictionary. The keys of the dictionary are the Symbol objects and the values are the List<Tick>list[Tick] objects.

public override void OnData(Slice slice)
{
    foreach (var kvp in slice.Ticks)
    {
        var symbol = kvp.Key;
        var ticks = kvp.Value;
        foreach (var tick in ticks)
        {
            //
        }
    }
}

public void OnData(Ticks ticks)
{
    foreach (var kvp in ticks)
    {
        var symbol = kvp.Key;
        foreach (var tick in kvp.Value)
        {
            //
        }
    }
}
def OnData(self, slice: Slice) -> None:
    for symbol, ticks in slice.Ticks.items():
        for tick in ticks:
            pass

Tick data is raw and unfiltered, so it can contain bad ticks that skew your trade results. For example, some ticks come from dark pools, which aren't tradable. We recommend you only use tick data if you understand the risks and are able to perform your own online tick filtering.

If we detect a tick that may be suspicious, we set its Suspicious flag to true.

Other Data Formats

For more information about data formats available for US Equities, see Corporate Actions.

You can also see our Videos. You can also get in touch with us via Discord.

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