Aggregate By Repeated Values In A Column In A Data Frame In Pandas

I have a data frame as follows: value identifier 2007-01-01 0.781611 55 2007-01-01 0.766152 56 2007-01-01 0.766152 57 2007-02-01 0.705615 5

Solution 1:

If your index is a datetime then you can access the .date attribute, if not you can convert it using df.index = pd.to_datetime(df.index) and then perform a groupby on the date and calc the mean:

In [214]:

df.groupby(df.index.date)['value'].mean()
Out[214]:
2007-01-01    0.771305
2007-02-01    0.256628
2008-01-01    0.670920
2008-02-01    0.098047
Name: value, dtype: float64