datatable.cumcount()

datatable.

cumcount

(

reverse=False

)

sourcetests

Added in version 1.1.0

Number rows within each group. In the absence of by() the frame is assumed to consist of one group only.

Parameters

reverse

bool

By default, when this parameter is False, the numbering is performed in the ascending order. Otherwise, when this parameter is True, the numbering is done in the descending order.

return

FExpr

f-expression that returns row numbers within each group.

Examples

Create a sample datatable frame:

from datatable import dt, f, by DT = dt.Frame(['a', 'a', 'a', 'b', 'b', 'c', 'c', 'c']) DT

	C0
	str32
0	a
1	a
2	a
3	b
4	b
5	c
6	c
7	c

8 rows × 1 column

Number rows within each group in the ascending order:

DT[:, dt.cumcount(), f.C0]

	C0	C1
	str32	int64
0	a	0
1	a	1
2	a	2
3	b	0
4	b	1
5	c	0
6	c	1
7	c	2

8 rows × 2 columns

Number rows within each group in the descending order:

DT[:, dt.cumcount(reverse = True), f.C0]

	C0	C1
	str32	int64
0	a	2
1	a	1
2	a	0
3	b	1
4	b	0
5	c	2
6	c	1
7	c	0

8 rows × 2 columns

Number rows in the absence of by():

DT[:, [f.C0, dt.cumcount()]]

	C0	C1
	str32	int64
0	a	0
1	a	1
2	a	2
3	b	3
4	b	4
5	c	5
6	c	6
7	c	7

8 rows × 2 columns