counting 1s in each group

[Masoumeh Sanagou]

Hi STATALIST,

I have variables group and order. I want a new variable which is counting 1s in the variable order in each group.

could you please help me to create the new variable ("wanted-counting 1s in each group")?

group	order	wanted-counting 1s in each group
a	1	1
a	2
a	3
a	1	2
a	2
a	3
a	1	3
a	2
a	1	4
a	2
a	3
a	4
b	1	1
b	1	2
b	2
b	3
b	1	3
b	2

Regards,
Masoumeh

[Nick Cox]

sort group, stable 

by group : gen count1 = sum(order == 1) if order == 1

where if order == 1 may or may not be what you want.