pandas.core.groupby.SeriesGroupBy.cumcount

SeriesGroupBy.cumcount(ascending=True)

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