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Re: st: Capturing the date and which something first occurs

 From Nick Cox To statalist@hsphsun2.harvard.edu Subject Re: st: Capturing the date and which something first occurs Date Sat, 7 Apr 2012 07:21:28 +0100

```Also consider

gsort id -state time
by id: gen date_first = time[1] if state[1] == 1
gen is_first = time == date_first

Nick

On Fri, Apr 6, 2012 at 6:41 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> When the first occurrence occurred is discussed in the same FAQ
>
> http://www.stata.com/support/faqs/data/firstoccur.html
>
> Here is another way to do it.
>
> egen date_first = min(time / state), by(id)
>
> Explanation: This is the trick that dividing by zero can be useful.
> time / 0 is returned as missing and thus ignored in the calculation of
> the minimum, as long as the -state- did occur.
>
> Nick
>
> On Fri, Apr 6, 2012 at 6:28 PM, Richard T. Campbell <dcamp@uic.edu> wrote:
>
>> 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.
>>

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