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Re: st: re: data management


From   "Raphael Fraser" <raphael.fraser@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: re: data management
Date   Thu, 27 Mar 2008 22:34:36 -0500

Thank you all

I thought bysort id: gen x = cond( _n < 4, 1, 2) was rather elegant. I
don't have an obs variable but it appears to be stable.

On Thu, Mar 27, 2008 at 8:07 PM, Kit Baum <baum@bc.edu> wrote:
> Sergiy said
>
>   > Raphael said
>   >
>   > I have 100 subjects with 6 obs each. I would like to create a new
>   > variable containing 1s for the first three obs and 2s for the
>   > remaining obs for each id.
>   >
>   >
>   > bysort id: gen x = cond( _n < 4, 1, 2)
>
>  and this raises the question, is _bysort_ stable? Because if it is
>  not, then not the first three of Raphael's observations get 1s, but
>  three random of each six get 1s. Stata's manual is silent about it,
>  but it seems to be the case. Quote:
>
>  "sort specifies that if the data are not already sorted by varlist, by
>  sort them."
>
>  Does anybody have more precise info? Is bysort stable?
>
>
>
>  This can be dealt with, presuming Raphael has an obs number for each
>  reading on a subject, by doing
>
>  bysort id (obs): gen x ...
>
>  which will ensure that the observations for each ID are ordered
>  1,2,...,6.
>
>
>
>  Kit Baum, Boston College Economics and DIW Berlin
>  http://ideas.repec.org/e/pba1.html
>  An Introduction to Modern Econometrics Using Stata:
>  http://www.stata-press.com/books/imeus.html
>
>
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