How to slice one MultiIndex DataFrame with the MultiIndex of another

Question

I have a pandas dataframe with 3 levels of a MultiIndex. I am trying to pull out rows of this dataframe according to a list of values that correspond to two of the levels.

Answer 1

I find it interesting that this doesn't work:

In [45]: df.loc[(idx[:, 'foo', 'can'], idx[:, 'bar', 'baz']), ]
Out[45]: 
           hi
a b   c      
1 bar baz   2
      can   3
  foo baz   0
      can   1
2 bar baz   6
      can   7
  foo baz   4
      can   5
3 bar baz  10
      can  11
  foo baz   8
      can   9

It sort of looks like it "should", somehow. In any case, here's a reasonable workaround:

Let's assume the tuples you want to slice by are in the index of another DataFrame (since it sounds like they probably are in your case!).

In [53]: ix_use = pd.MultiIndex.from_tuples([('foo', 'can'), ('bar', 'baz')], names=['b', 'c'])
In [55]: other = pd.DataFrame(dict(a=1), index=ix_use)
In [56]: other
Out[56]: 
         a
b   c     
foo can  1
bar baz  1

Now to slice df by the index of other we can use the fact that .loc/.ix allow you to give a list of tuples (see the last example here).

First let's build the list of tuples we want:

In [13]: idx = [(x, ) + y for x in df.index.levels[0] for y in other.index.values]
In [14]: idx
Out[14]: 
[(1, 'foo', 'can'),
 (1, 'bar', 'baz'),
 (2, 'foo', 'can'),
 (2, 'bar', 'baz'),
 (3, 'foo', 'can'),
 (3, 'bar', 'baz')]

Now we can pass this list to .ix or .loc:

In [17]: df.ix[idx]
Out[17]: 
           hi
a b   c      
1 foo can   1
  bar baz   2
2 foo can   5
  bar baz   6
3 foo can   9
  bar baz  10