What is the easiest / best way to add entries to a dataframe?
For example, when my algorithm makes a trade, I would like to record the sid and opening price in a custom dataframe, and then later append the price at which the position is exited.
Any help would be greatly appreciated.
# Add a row to df
from pandas import DataFrame as df
mydf = df([1.1, 1.1, 1.1]).T
arow2 = [2.2, 2.2, 2.2]
mydf.loc[len(mydf)] = arow2
print(mydf)
Thanks Dan, but I have not been able to get enlargement with .loc to work.
I get a "Runtime exception: KeyError: 1" on the "mydf.loc[len(mydf)] = arow2" line when using your code.
Any ideas or can you provide a working example/backtest?
Thanks again for the help,
Rob
You should post a screen dump.
Like this:
[email protected] /a/ks/tws/spy $ ipython
Python 2.7.8 |Anaconda 2.1.0 (64-bit)| (default, Aug 21 2014, 18:22:21)
Type "copyright", "credits" or "license" for more information.
IPython 2.2.0 -- An enhanced Interactive Python.
Anaconda is brought to you by Continuum Analytics.
Please check out: http://continuum.io/thanks and https://binstar.org
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
In [1]: from pandas import DataFrame as df
In [2]: mydf = df([1.1, 1.1, 1.1]).T
In [3]: arow2 = [2.2, 2.2, 2.2]
In [4]: mydf.loc[len(mydf)] = arow2
In [5]: print(mydf)
0 1 2
0 1.1 1.1 1.1
1 2.2 2.2 2.2
In [6]:
Try this too:
# Add a row to df
from pandas import DataFrame as df
import numpy as np
mydf = df([1.1, 1.1, 1.1]).T
arow2 = [2.2, 2.2, 2.2]
mynparray = mydf.values
mynparray = np.vstack((mynparray,arow2))
mydf = df(mynparray)
Thanks Dan. The numpy method works like a charm.
I could get .loc enlargement to work in iPython but not in the Quantopian IDE. I read that it is a relatively new feature and thought that might be the reason. Have you used/tested it in a quantopian algorithm?
Thanks again for the help and good luck with your trading.
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