grouper_example3.py

gitcsv = 'https://raw.githubusercontent.com/justinhchae/medium/main/sample.csv'
df = pd.read_csv(gitcsv, index_col=0)

df['dates'] = pd.to_datetime(df['dates'])

freq='M'

df = df.groupby(['types', pd.Grouper(key='dates', freq=freq)])['types'].agg(['count']).reset_index()


print(df)

"""
   types      dates  count
0      b 2016-01-31      1
1      a 2016-01-31      5
2      b 2016-02-29      3
3      a 2016-02-29      4
4      b 2016-03-31      3
5      a 2016-03-31      6
6      b 2016-04-30      1
...
"""