Question

I have a hierarchically indexed data frame:

>>> import pandas as pd
>>> df = pd.DataFrame(np.arange(4),
                      index=[['John', 'John', 'Vicki', 'Vicki'], 
                             ['a','b', 'a','b']],
                      columns=['score'])

         score
John  a      0
      b      1
Vicki a      2
      b      3

and a series with index identical to the first index level in the above data frame:

>>> series = pd.Series([100, 200], index=['John', 'Vicki'])

John     100
Vicki    200

Now I want to merge the data frame with the series, such that the values from the series are broadcasted along the second level index. The resulting data frame should look like this:

         score  salary
John  a      0     100
      b      1     100
Vicki a      2     200
      b      3     200

How can I achieve that in pandas?

Answer 1

This should work:

df['salary'] = series.reindex(df.index, level=0)