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# st: Capturing the date and which something first occurs

 From "Richard T. Campbell" To "statalist-hsphsun2.harvard.edu" Subject st: Capturing the date and which something first occurs Date Fri, 06 Apr 2012 12:28:39 -0500

Suppose I have a data set like that used by Nick Cox in an FAQ which shows how to capture a
```record at which something first occurs. Here is his example.

+---------------------------+
| id   time   state   first |
|---------------------------|
1. |  1      1       0       0 |
2. |  1      2       0       0 |
3. |  1      3       0       0 |
4. |  1      4       1       1 |
5. |  1      5       1       0 |
6. |  1      6       1       0 |
7. |  1      7       1       0 |
8. |  1      8       1       0 |
9. |  1      9       1       0 |
10. |  1     10       1       0 |
|---------------------------|
11. |  2      2       0       0 |
12. |  2      2       0       0 |
13. |  2      3       1       1 |
14. |  2      4       1       0 |
15. |  2      5       1       0 |
16. |  2      6       1       0 |
17. |  2      7       1       0 |
18. |  2      8       1       0 |
19. |  2      9       0       0 |
20. |  2     10       0       0 |
|---------------------------|
21. |  3      1       0       0 |
22. |  3      2       1       1 |
23. |  3      3       0       0 |
+---------------------------+

```
So, for ID 1, the first time at which state = 1 occurs is the fourth record, for ID 2 it is the third record etc. I want to assign a value within an id equal to
```that index. For example, for ID 1 I want a variable that equals 4 for all
```
ten cases, for ID 2 a variable equal to 3 for all cases etc. Put differently,
```I want to assign to all cases within an id, the value of _n when first = 1.
I can't seem to get my head around how to do this.

--
Richard T. Campbell
Professor Emeritus, School of Public Health
Institute for Health Research and Policy
University of Illinois at Chicago
Phone 312-413-0480

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```