how to assign grouping seq number

[stataq]

Hello,

I would like to assign seq number for each id's each "stop" activity group .  if two stops are back to back, it will be counted as 1. how can I create "sseq" using example dataset ds1?

data ds1 ;
input id seq stop;
cards ;
1 1 0
1 2 1
1 3 0
1 4 0
1 5 1
1 6 1
2 1 0
2 2 0
2 3 1
2 4 1
2 5 1
2 6 0
2 7 1
2 8 0
2 9 1
;
run;

The expected output:

Thanks.

[A_Kh · Accepted solution]

data step.

data want;
	set ds1;
	by id;
	temp1=lag(stop);
	if 1=stop=temp1 then temp2=0; 
	else temp2=stop; 
	retain temp3; 
	if first.id then temp3 =temp2;
	else temp3= temp3+temp2;
	if stop=0 then sstop=.;
	else sstop=temp3;  
	drop temp:;
proc print; run; 

[FreelanceReinh]

Hello @stataq,

Try this:

data want(drop=_c);
set ds1;
by id seq;
if first.id then _c=0;
_c+(stop & (~lag(stop) | first.id));
if stop then sseq=_c;
run;

and add more test cases, e.g., id=3 beginning with stop=1 (if this is possible in your real data).