Summing over a multiindex level in a pandas series

Question

Using the Pandas package in python, I would like to sum (marginalize) over one level in a series with a 3-level multiindex to produce a series with a 2 level multiindex. For exa

Answer 1

If you know you always want to aggregate over the first two levels, then this is pretty easy:

In [27]: data.groupby(level=[0, 1]).sum()
Out[27]:
A  B    277
   b     37
a  B    159
   b     16
dtype: int64