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Re: st: help with understanding syntax 'gen last=_n==_N'


From   "b. water" <barleywater@hotmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: help with understanding syntax 'gen last=_n==_N'
Date   Mon, 28 Nov 2005 09:13:19 +0000

thank you to both nick (cox) and sergio for the explanations. it was clearer with worked example.

regards,
bw



From: Sergio Correia <sergio.correia@gmail.com>
Reply-To: statalist@hsphsun2.harvard.edu
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: help with understanding syntax 'gen last=_n==_N'
Date: Sun, 27 Nov 2005 22:15:25 -0500

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 <barleywater@hotmail.com> 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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