pandas hierarchical indexing unique values

Question

Say I have series:

A  a  1
   b  1
B  c  5
   d  8
   e  5

where first two columns together is the hierarchical index. I want to find how many unique values are for index level=0, e.g., in this output should be A 1; B 2. How can this be done easily? Thanks!

Answer 1

groupby on level 0 and then call .nunique on the column:

>>> df
     val
A a    1
  b    1
B c    5
  d    8
  e    5
>>> df.groupby(level=0)['val'].nunique()
A    1
B    2
Name: val, dtype: int64