how to select specific observation

[hjjijkkl]

have a data and I want an outcome where the first cnt is ‘1’

ID	visit	Cnt
1	5/3/20	0
1	7/2/20	0
2	8/9/21	1
3	1/5/20	0
3	4/18/20	1
3	8/23/20	1
4	6/8/20	0
4	10/9/20	1

I want an output like this

ID	visit	cnt
2	7/2/20	1
3	4/18/20	1
4	10/9/20	1

[ballardw]

Does your CNT variable ever decrease after a 1 is encountered?

If not you may be able to use (untested because the example data is not nice)

data want;
    set have;
    by id cnt;
    if first.cnt and cnt=1;
run;

[hjjijkkl]

CNT is either 1 or 0.

[ballardw]

---

@hjjijkkl wrote:
CNT is either 1 or 0.

---

The question is does CNT ever go to 0 after it is 1.

The proposed possible solution using BY group processing and First/ Last processing will not work if you can have something like:

ID   CNT

1   0

1  0

1  1

1  1

1  0

1  0

1 1

because BY requires a specified order, as shown assumes increasing, and would generate a "not sorted by BY variables" error.

Other methods would be needed if the data might have the out of order CNT values.

[Ksharp]

data have;
input 
ID 
visit : mmddyy10. 
Cnt;
format visit mmddyy10.;
cards;
1
5/3/20
0
1
7/2/20
0
2
8/9/21
1
3
1/5/20
0
3
4/18/20
1
3
8/23/20
1
4
6/8/20
0
4
10/9/20
1
;


data want;
 set have;
 by id;
 retain found .;
 if first.id then found=.;
 if not found and cnt=1 then do;output;found=1;end;
 drop found;
run;