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st: AW: RE: Problem looping over spells for an individual

From   "Martin Weiss" <>
To   <>
Subject   st: AW: RE: Problem looping over spells for an individual
Date   Wed, 25 Feb 2009 18:27:39 +0100


I was desperate to find an SJ tip for Ilona on the difference between "if"
and "if"; turns out it is an FAQ:


-----Ursprüngliche Nachricht-----
[] Im Auftrag von Nick Cox
Gesendet: Mittwoch, 25. Februar 2009 18:22
Betreff: st: RE: Problem looping over spells for an individual

Unless you are working under the aegis of -by:- _N will always be
interpreted as the total number of observations. This code doesn't
satisfy that. 

I echo Martin Weiss in suspecting that your -if `touse'- is a bug. You
are almost certainly confusing the two flavours of -if-. 

Otherwise, your code still looks very confused and based on a variety of
misunderstandings. Apart from `touse', which is defined by -marksample-,
all of the local macros you refer to will be treated as empty strings,
as none has been defined earlier in the program. I am surprised to hear
that it is running at all. 

It does not look as if you need a program anyway. My impression is that
all you need is to use -by:- but I don't understand your problem well
enough to suggest better code. Someone else may be able to give better
help. If not, rather than a lengthy word description, you should perhaps
give an example of your data with the intended result. 


Ilona Carneiro

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'
		gen lagend=. 	
		qui by id: byid

but I get the error:
2nd by group not found

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

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