Selecting first observation on multiple conditions

[windy]

Hello everyone, 

I need your help in this problem. Suppose I have the data set like that. I have multiple IDs and time periods. The time frame may be different across different IDs (ID1 exists from time 1 to time 5; ID2 exists from time 3 to 20, ID3 exists from time 6 to time 17). Then I have stress time variable receiving value of 1 if it's a stressed time and 0 otherwise. In this example, stress time happens twice (time 8-10 and time 16-17). Finally, I have var 1 where contains the information I want to extract. 

No	ID	time	stress_time	var1
1	1	1	0	100
2	1	2	0	103
3	1	3	0	106
4	1	4	0	109
5	1	5	0	112
6	2	3	0	300
7	2	4	0	310
8	2	5	0	320
9	2	6	0	330
10	2	7	0	340
11	2	8	1	350
12	2	9	1	360
13	2	10	1	370
14	2	11	0	380
15	2	12	0	390
16	2	13	0	400
17	2	14	0	410
18	2	15	0	420
19	2	16	1	430
20	2	17	1	440
21	2	18	0	450
22	2	19	0	460
23	2	20	0	470
24	3	6	0	220
25	3	7	0	230
26	3	8	1	240
27	3	9	1	250
28	3	10	1	260
29	3	11	0	270
30	3	12	0	280
31	3	13	0	290
32	3	14	0	300
33	3	15	0	310
34	3	16	1	320
35	3	17	1	330

What I want to do is that I want to extract all of the first observations for each ID/Stress time frame. I tried with proc sort nodupkey by id stress_time, but it's not the right solution because I can't collect the first observation of the other stress time frame. In specific, I need to create a sample containing observations number 11, 19, 26, and 34. I think I need to use Proc sql for this problem, but I don't know how to do it yet 😞

Please help me out. 

Best regards, 

Windy. 

[PeterClemmensen · Accepted solution]

How about

data have;
input No ID time  stress_time var1;
datalines;
1  1  1  0  100
2  1  2  0  103
3  1  3  0  106
4  1  4  0  109
5  1  5  0  112
6  2  3  0  300
7  2  4  0  310
8  2  5  0  320
9  2  6  0  330
10 2  7  0  340
11 2  8  1  350
12 2  9  1  360
13 2  10 1  370
14 2  11 0  380
15 2  12 0  390
16 2  13 0  400
17 2  14 0  410
18 2  15 0  420
19 2  16 1  430
20 2  17 1  440
21 2  18 0  450
22 2  19 0  460
23 2  20 0  470
24 3  6  0  220
25 3  7  0  230
26 3  8  1  240
27 3  9  1  250
28 3  10 1  260
29 3  11 0  270
30 3  12 0  280
31 3  13 0  290
32 3  14 0  300
33 3  15 0  310
34 3  16 1  320
35 3  17 1  330
;

data want;
   set have;
   by ID stress_time notsorted;
   if first.stress_time and stress_time = 1;
run;

Result:

No  ID  time  stress_time  var1
11  2   8     1            350
19  2   16    1            430
26  3   8     1            240
34  3   16    1            320

[Kurt_Bremser]

You need to have id in the BY, otherwise you miss an event where an old id ends with 1 and the new id also starts with 1.

[PeterClemmensen]

Of Course 🙂

Corrected.

[Kurt_Bremser]

Make sure that the dataset is sorted by id and time, then do:

data want;
set have;
by id time stress_time notsorted;
if stress_time and first.stress_time;
run;

Will extract any first occurence of stress_time = 1.

[windy]

Thank you @PeterClemmensen and @Kurt_Bremser for your help. 

I got what I need now.