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st: Problem looping over spells for an individual


From   Ilona Carneiro <ilonac@orange.es>
To   statalist@hsphsun2.harvard.edu
Subject   st: Problem looping over spells for an individual
Date   Wed, 25 Feb 2009 17:24:11 +0100

Hello all

I am trying to write a programme that will run a command sequentially for observations of an individual. For each individual I have multiple spells and multiple failures. However, the twist is that I also need to exclude a period of time at risk after each treatment (prophylaxis) and after each failure (to prevent double-counting of failures that may actually be the same episode). I managed to do this without any problem for the treatment, but if an episode is disqualified (by a prior treatment or episode) I don't want it to disqualify a subsequent episode. Therefore I need to run the code sequentially for each spell of an individual, but using the marksample touse code to run it "by" individual doesn't seem to be working - the "forvalues" seems to always interpret _N as the last observation in the whole dataset, not the last observation for each individual.

I have the following code:

		program define byid, byable(recall, noheader)
		marksample touse
		sort `id' `start'
		if `touse' {
		forvalues i = 1(1)`=_N' {
replace lagend = (`end' + `lag') if ((`tx' > 0 & `tx' < .) | (`case' > 0 & `case' < .))
		drop if lagend[`i'-1]>`end' & `id'[`i'-1]==`id'
		}
		}
		end
		
		gen lagend=. 	
		qui by id: byid

but I get the error:
2nd by group not found
r(111);

And the programme isn't doing what I need it to.

Any ideas?

Ilona

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