Map multi-index column to new values in Pandas DataFrame

Question

I have a multi-index dataframe in Pandas with two index values like this:

week_of_year    day_of_week

 1              0
 1              1
 .              .
 1              6

 2              0
 .              .
 .              .
 2              6
 .              .

I want to map the day_of_week index to {'0': 'Monday', '1': 'Tuesday', ...} but not sure how to access and map the second index.

Answer 1

Use Index.get_level_values :

d = {0: 'Monday', 1: 'Tuesday', ..., 6: 'Sunday'}

df.index.get_level_values(level='day_of_week').map(d)

output:

Index(['Monday', 'Tuesday', 'Sunday', 'Monday', 'Sunday'], dtype='object', name='day_of_week')