Grouping in pandas/multi-index data frame

[deanhystad]

You can do something like this:

import pandas as pd

df = pd.read_csv("parties.csv")
df = df.groupby(['COUNTRY', 'PTYNAME'])['YEAR'].count()
print(df)

And get something like this:

Output:
COUNTRY  PTYNAME
Finland  Finns Party                           1
         National Coalition Party              1
         Social Democratic Party of Finland    1
Norway   Centre Party                          1
         Green League                          1

But this is no longer a dataframe, it is a multiindexed series.