Compute daily climatology using pandas python

Question

I am trying to use pandas to compute daily climatology. My code is:

import pandas as pd

dates      = pd.date_range(\'1950-01-01\', \'1953-12-31\', freq=\'D\         


        

Answer 1

You can groupby the day of the year, and the calculate the mean for these groups:

cum_data.groupby(cum_data.index.dayofyear).mean()

However, you have the be aware of leap years. This will cause problems with this approach. As alternative, you can also group by the month and the day:

In [13]: cum_data.groupby([cum_data.index.month, cum_data.index.day]).mean()
Out[13]:
1  1     462.25
   2     631.00
   3     615.50
   4     496.00
...
12  28    378.25
    29    427.75
    30    528.50
    31    678.50
Length: 366, dtype: float64