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

Another simple routine.

def flatten_columns(df, sep='.'):
    def _remove_empty(column_name):
        return tuple(element for element in column_name if element)
    def _join(column_name):
        return sep.join(column_name)

    new_columns = [_join(_remove_empty(column)) for column in df.columns.values]
    df.columns = new_columns