Pandas, Future Warning: Indexing with multiple keys

Question

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 

Answer 1

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.