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Re: st: new: collapse2

From   Roger Newson <>
Subject   Re: st: new: collapse2
Date   Wed, 04 Aug 2004 16:50:14 +0100

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 Newson
Lecturer in Medical Statistics
Department of Public Health Sciences
King's College London
5th Floor, Capital House
42 Weston Street
London SE1 3QD
United Kingdom

Tel: 020 7848 6648 International +44 20 7848 6648
Fax: 020 7848 6620 International +44 20 7848 6620
or 020 7848 6605 International +44 20 7848 6605

Opinions expressed are those of the author, not the institution.

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