Pandas, Future Warning: Indexing with multiple keys

Issue

Pandas throws a Future Warning when I apply a function to multiple columns of a groupby object. It suggests to use a list as index instead of tuples. How would one go about this?

>>> df = pd.DataFrame([[1,2,3],[4,5,6],[7,8,9]])
>>> df.groupby([0,1])[1,2].apply(sum)
<stdin>:1: FutureWarning: Indexing with multiple keys (implicitly converted to a tuple of keys) will be deprecated, use a list instead.
     1  2
0 1      
1 2  2  3
4 5  5  6
7 8  8  9

Solution

This warning was introduced in pandas 1.0.0, following a discussion on GitHub. So best use what was suggested there:

df.groupby([0, 1])[[1, 2]].apply(sum)

It’s also possible to move the slicing operation to the end, but that is not as efficient:

df.groupby([0, 1]).apply(sum).loc[:, 1:]

Thanks @ALollz and @cmosig for helpful comments.

Answered By – Arne

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