Count with multiple conditions

[Myurathan]

Dear SAS community,

I am having trouble counting and resetting the count with conditions and your help would be much appreciated.

Suppose that I have data below; Count is the variable I am after. 

ID	Flag	Count
A	0	0
A	0	0
A	1	1
A	1	2
A	0	0
A	1	1
A	1	2
B	1	1
B	1	2
B	0	0
B	1	1
B	1	2

I need the count variable to perform as displayed above. 

Whenever flag=0 the count has to reset to 0. 

How can I achieve this? Please help. Thank you!

Regards,

Myu

[andreas_lds · Accepted solution]

What have you tried? Can you post the code? If not: please post the data in usable form.

Untested:

data want;
	set have;
	by ID;
	
	retain count;
	
	if first.ID then count = 0;
	
	if Flag = 1 then Count = Count + 1;
	else Count = 0;
run;

[Myurathan]

You are a real saviour. Thank you so much.

[PeterClemmensen]

data have;
input ID $ Flag;
datalines;
A 0
A 0
A 1
A 1
A 0
A 1
A 1
B 1
B 1
B 0
B 1
B 1
;

data want;
    set have;
    by ID;
    if first.ID | flag=0 then Count=0;
    if flag then Count+1;
run;