bysort id (date) : gen visitno = sum(date != date[_n-1])
does it in one line.
Nick
[email protected]
Joseph Coveney replied to Richard Hiscock
> I have the following data structure
>
> id date var1 var2
>
> 1 16267 x 53
> 1 16267 y 106
> 1 16267 y 84
> 1 16267 y 90
> 1 16267 z 76
> 1 16267 z 65
> 1 16298 x 87
> 1 16298 y 76
> 2 15678 x 98
> 2 15678 y 98
> 2 16541 x 150
>
> etc
> I wish to create identifier (visitno) 1,2,3,... for each
> sequential date
> within id.
> I have tried to use :
> sort id date
> by id date: gen visitno = [_n] which obviously doesnt produce the
> required variable
> I would be greatful for solution & ?or direction to FAQ dealing with
> this
> How about:
>
> -by id date: generate byte visitno = _n == 1-
>
> and then
>
> -by id: replace visitno = sum(visitno)-
>
> Or, in one line:
>
> -bysort id (date): generate byte visitno = ///
> sum( (_n == 1) | (date > date[_n-1]) )-
>
> As I recall, Nick Cox wrote a posted a more elegant one-line
> command for
> this task recently on the list, but I cannot seem to find it.
>
> You mention that your final aim is to generate summary
> statistics each date
> within id. For this, check out -egen-.
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