Calling data by date
Is it possible to call data by date in the next() loop?
Namely, I would like to perform some computations in the next() operation to check if last close value is higher/lower than its value at some specific date.
Data feeds offer you the
datetimeline which conveys timestamps. And lines can be converted to python
datetimeinstances (of course it only makes sense for the
You just have to decide how to perform the accounting.
Maybe my question was not so clear. I don't have problem getting the date from a line by its index. E.g.:
My problem is how do I get the price associated with a date? e.g. how do I recover the close for 2017-01-31?
In pure pandas dataframe I would do something like this to get the line:
It was crystal clear. by keeping the accounting as to when (in terms of data length) that specific timestamp happened (i.e.:
This is far easier done as this, which also takes care of timezone management:
In any case and although it may make sense to refer to something like
2017-01-31for specific price research around a set of dates, the background in backtrader is:
- You throw something in, and you don't really care about the date
This isn't 100% true, because an algorithm could be looking into:
- Is it the last day of the month?
- Is it 15 minutes before the closing time on the 24th of December? (which happens earlier as other closing times)
- Is it already
2017-01-31because Trump is going to tweet something and the algorithm has to stop trading on that day?
But those things, as stated, are checked when one is at instant
0(the pivot index which in backtrader always refers to the current instant) during live trading or walk-forward-like actions.
In the backtrader ecosystem,
datetimeis not an index, the index is the number of instants that have elapsed (number of bars if you wish), in which you can always refer to the current instant as
0keeps moving forward, because from the point of view of the system, it doesn't know in advance when the action is going to terminate (even if you are backtesting with a fixed amount of data, the system makes no assumption about it)
pandas.DataFrameis mostly a static structure and that's why an
appendis a very expensive operation, but keeping an index and finding things is easy (things like
daskbuild on it by managing multiple
Dataframeas chunks of a larger structure to offer dynamic
That's why the indexing in backtrader refers to the length of the data (later you have to look backwards from instant
Thanks for this explanation! Much clearer in my mind.
I am indeed in the need of knowing the exact date to get the return between two end of month business days.
I am trying to replicate a simple tactical asset allocation paper with monthly rebalancing and I need to compute the 1 year return each month. At first, I did it by using the
PercentChangefunction with a period of 252 days but my results are not in line with the source I am following for comparison. This is probably due to the fact that I am not using exactly the same window to compute returns. Hence, I would like to compute the exact percent change over a year.
I was looking into
resamplebut I don't want to resample my daily data to monthly as I am
cheating-on-openand by resampling I would lose the next open (correct?).
I actually didn't know about it! Still some learning to do!
I have been trying
TimeReturnwith no luck. I have added the analyzer:
cerebro.addanalyzer(btanalyzers.TimeReturn, timeframe=TimeFrame.Years, data=data, _name='myret')
But how do I catch the returns computed in the
next()of my strategy?
myret = self.analyzers.myretwill get you to the analyzer. The strategy has some attributes holding things like that
- See Docs - Strategy (under Member attributes)
And then ... the
TimeFrameAnalyzerBaseis not documented ... and probably should ... being the base class for analyzers that calculate things on a regular basis based on a given timeframe. Quickly:
Canonically you would call
analysis = myanalyzer.get_analysis()
The answer will be a
collections.OrderedDictwith the keys being
- You know that the current results (the
OrderedDict) are held in an attribute of the analyzer named
- You know that the current key for the insertion in the dictionary is held in an attributed named:
And you play with it
- You know that the current results (the
Getting much clearer thanks!
I could make it work but came across something strange.
I am on the 31st of January 2011 after the close according to this line in my
I get my analyzer details like so:
tmp = self.analyzers.ret_spy.get_analysis() for i in tmp.items()[-12:]: print i
and get the following results (ticker is SPY):
(datetime.datetime(2010, 2, 28, 0, 0), 0.031194710866933484) (datetime.datetime(2010, 3, 31, 0, 0), 0.05652880621275069) (datetime.datetime(2010, 4, 30, 0, 0), 0.015470085470085548) (datetime.datetime(2010, 5, 31, 0, 0), -0.07945459136436328) (datetime.datetime(2010, 6, 30, 0, 0), -0.05623114199506263) (datetime.datetime(2010, 7, 31, 0, 0), 0.06830071691532646) (datetime.datetime(2010, 8, 31, 0, 0), -0.04498050240319207) (datetime.datetime(2010, 9, 30, 0, 0), 0.08375273003513439) (datetime.datetime(2010, 10, 31, 0, 0), 0.03820205029352497) (datetime.datetime(2010, 11, 30, 0, 0), 0.0) (datetime.datetime(2010, 12, 31, 0, 0), 0.06127099333277064) (datetime.datetime(2011, 1, 31, 0, 0), 0.01566600397614315)
I manually cross-checked the number and they seem fine for all dates but the last , i.e. 31st of January 2011. To get to the result given by the analyzer I need to compute the result from the close of 31/12/2010 to the close of 28/01/2011. Why the last day isn't taken into account? I
cheat-on-openso everything should be after the close.
Side question: is there a way to compute
TimeReturnon each ticker without having to call
addanalyzer(TimeReturn, data=cerebro.datas[x])for each one of them?
Thanks again for your help!
Side question: is there a way to compute TimeReturn on each ticker without having to call addanalyzer(TimeReturn, data=cerebro.datas[x]) for each one of them?
I manually cross-checked the number and they seem fine for all dates but the last , i.e. 31st of January 2011. To get to the result given by the analyzer I need to compute the result from the close of 31/12/2010 to the close of 28/01/2011. Why the last day isn't taken into account? I cheat-on-open so everything should be after the close.
It seems your data would end on
2011-01-28. The analyzer doesn't know your data ends there ... and the end of the montha and/or next month has not been seen. It can only calculate it when stopping (
stopmethod) and you can therefore only see that in the corresponding strategy