.count()

The .count() method produces a new Series or DataFrame with counts of the values for each group in a in a GroupBy object.

groupbyobject.count()

The following example produces a GroupBy object from a DataFrame and executes the .count() method on it.

import pandas as pd

df = pd.DataFrame({'Key' : ['A', 'A', 'A', 'B', 'B', 'C'],
                   'Value' : [15., 23., 17., 5., 8., 12.]})
print(df, end='\n\n')

group = df.groupby(['Key'], as_index=False)

print(group.count())

This example produces the following output:

  Key  Value
0   A   15.0
1   A   23.0
2   A   17.0
3   B    5.0
4   B    8.0
5   C   12.0

  Key  Value
0   A      3
1   B      2
2   C      1