Re: st: new: collapse2

[Roger Newson <roger.newson@kcl.ac.uk>]

At 16:19 04/08/2004, Dan Blanchette wrote:
> How about adding an option to save id variables during the -collapse-?
> It would be great if you could do this:
>
> . collapse2 (sum) grams kcal fat , by(personid) id(age gender sampwt 
> stratum psu)
>
> because age, gender etc do not vary within a person's set of observations.
>
> I've been cheating -collapse- to get the same result by doing:
>
> . collapse (sum) grams kcal fat , by(age gender sampwt stratum psu personid)
"Cheating" is probably the way to go, rather than adding a superfluous id() 
option. However, I would have typed:

. collapse (sum) grams kcal fat, by(personid age gender samput stratum psu)
. by personid: assert _N==1

That way, I would know that age, gender, samput, stratum and psu really are 
id variables for personid (because otherwise Stata would complain and stop).

Roger


--
Roger Newson
Lecturer in Medical Statistics
Department of Public Health Sciences
King's College London
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Opinions expressed are those of the author, not the institution.

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