the -by- prefix repeats the command for each possible value of "study".
So, using _N returns the total number of obs. for each value of study.
_n returns the observation index (1,2,3,4..) within each value of study
Finally, _n=_N is true when the index is at its last position.
Sergio
On 11/27/05, b. water <[email protected]> wrote:
> dear listers,
>
> i am trying to understand one of the do-files application for stata. one of
> the lines read:
>
> qui by study: gen last=_n==_N
>
> my understanding so far: this is quietly, sort according to study, and as a
> result, to generate a variable last fulfilling this condition _n==-N.
> although i have the output, i would like to know what in general does gen
> last=_n==_N do?
>
> thank you,
> bw
>
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