python - Select only one index of multiindex DataFrame

Question

I am trying to create a new DataFrame using only one index from a multi-indexed DataFrame.

                   A         B         C
first second                              
bar   one     0.895717  0.410835 -1.413681
      two     0.805244  0.813850  1.607920
baz   one    -1.206412  0.132003  1.024180
      two     2.565646 -0.827317  0.569605
foo   one     1.431256 -0.076467  0.875906
      two     1.340309 -1.187678 -2.211372
qux   one    -1.170299  1.130127  0.974466
      two    -0.226169 -1.436737 -2.006747

Ideally, I would like something like this:

In: df.ix[level="first"]

and:

Out:

               A         B         C
first                               
bar        0.895717  0.410835 -1.413681
           0.805244  0.813850  1.607920
baz       -1.206412  0.132003  1.024180
           2.565646 -0.827317  0.569605
foo        1.431256 -0.076467  0.875906
           1.340309 -1.187678 -2.211372
qux       -1.170299  1.130127  0.974466
          -0.226169 -1.436737 -2.006747
`

Essentially I want to drop all the other indexes of the multi-index other than level first. Is there an easy way to do this?

Answer 1

One way could be to simply rebind df.index to the desired level of the MultiIndex. You can do this by specifying the label name you want to keep:

df.index = df.index.get_level_values('first')

or use the level's integer value:

df.index = df.index.get_level_values(0)

All other levels of the MultiIndex would disappear here.