pandas.core.groupby.SeriesGroupBy.cumcount#

SeriesGroupBy.cumcount(ascending=True)[source] #

Number each item in each group from 0 to the length of that group - 1.

Essentially this is equivalent to

self.apply(lambda x: pd.Series(np.arange(len(x)), x.index))

Parameters:

ascendingbool, default True

If False, number in reverse, from length of group - 1 to 0.

Returns:

Series

Sequence number of each element within each group.

See also

ngroup

Number the groups themselves.

Examples

>>> df = pd.DataFrame([['a'], ['a'], ['a'], ['b'], ['b'], ['a']],
...  columns=['A'])
>>> df
 A
0 a
1 a
2 a
3 b
4 b
5 a
>>> df.groupby('A').cumcount()
0 0
1 1
2 2
3 0
4 1
5 3
dtype: int64
>>> df.groupby('A').cumcount(ascending=False)
0 3
1 2
2 1
3 1
4 0
5 0
dtype: int64