Cumulative sum of another variable

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Hi,

I would like to create the variable "CumVar" which adds up a value of 1 each time Var=1 (and also retains the same value until the next time Var is 1).

Var is binary (1/0).

Please see below an example of what I mean.

Thanks very much in advance!

ID	Visit	Var	CumVar
1	1	0	0
1	2	0	0
1	3	0	0
1	4	1	1
1	5	0	1
1	6	1	2
1	7	1	3
1	8	1	4
1	9	0	4
2	1	0	0
2	2	0	0
2	3	0	0
2	4	0	0
2	5	1	1
2	6	1	2
2	7	0	2
2	8	1	3
3	1	1	1
3	2	0	1
3	3	1	2
3	4	0	2

[novinosrin · Accepted solution]

data have;
input ID	Visit	Var;	
cards;
1	1	0	0
1	2	0	0
1	3	0	0
1	4	1	1
1	5	0	1
1	6	1	2
1	7	1	3
1	8	1	4
1	9	0	4
2	1	0	0
2	2	0	0
2	3	0	0
2	4	0	0
2	5	1	1
2	6	1	2
2	7	0	2
2	8	1	3
3	1	1	1
3	2	0	1
3	3	1	2
3	4	0	2
;

data want;
set have;
by id;
if first.id then cum_var=0;
if var then cum_var+1;
run;