Pandas - How to flatten a hierarchical index in columns

Question

I have a data frame with a hierarchical index in axis 1 (columns) (from a groupby.agg operation):

     USAF   WBAN  year  month  day  s_PC  s_CL         


        

Answer 1

A bit late maybe, but if you are not worried about duplicate column names:

df.columns = df.columns.tolist()