Access index in pandas.Series.apply

Question

Lets say I have a MultiIndex Series s:

>>> s
     values
a b
1 2  0.1 
3 6  0.3
4 4  0.7

and I want to apply a functi

Answer 1

Make it a frame, return scalars if you want (so the result is a series)

Setup

In [11]: s = Series([1,2,3],dtype='float64',index=['a','b','c'])

In [12]: s
Out[12]: 
a    1
b    2
c    3
dtype: float64

Printing function

In [13]: def f(x):
    print type(x), x
    return x
   ....: 

In [14]: pd.DataFrame(s).apply(f)
 a    1
b    2
c    3
Name: 0, dtype: float64
 a    1
b    2
c    3
Name: 0, dtype: float64
Out[14]: 
   0
a  1
b  2
c  3

Since you can return anything here, just return the scalars (access the index via the name attribute)

In [15]: pd.DataFrame(s).apply(lambda x: 5 if x.name == 'a' else x[0] ,1)
Out[15]: 
a    5
b    2
c    3
dtype: float64