datatable.ngroup()

datatable.

ngroup

(

reverse=False

)

sourcetests

Added in version 1.1.0

For each row return a group number it belongs to. 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, groups are numbered in the ascending order. Otherwise, when this parameter is True, groups are numbered in the descending order.

return

FExpr

f-expression that returns group numbers for each row.

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 groups in the ascending order:

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

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

8 rows × 2 columns

Number groups in the descending order:

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

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

8 rows × 2 columns

Number groups in the absence of by():

DT[:, dt.ngroup()]

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

8 rows × 2 columns