Grouping DataFrame by start of decade using pandas Grouper

Question

I have a dataframe of daily observations from 01-01-1973 to 12-31-2014.

Have been using Pandas Grouper and everything has worked fine for each frequency until now:

Answer 1

You can do a little arithmetic on the year to floor it to the nearest decade:

df.groupby(df.index.year // 10 * 10).mean()