Many thanks to both Gary and Nick for their help. I used Gary's suggestion and it worked perfectly.
Paul
-----Original Message-----
From: Nick Cox [mailto:[email protected]]
Sent: Friday, September 19, 2003 12:49 AM
To: [email protected]
Subject: RE: st: combinations of while, if, by, and foreach commands
Gary Longton
>
> Metcalfe, Paul wrote:
>
> > Using Stata 8.1 SE, I'm trying to put together a loop for
> what I imagine should be quite a straightforward task.
> >
> > The relevant part of my data looks like the following:
> >
> > id cons time
> > 5001574 32
> > 5001574 31
> > 5001574 0.278548 30
> > 5001574 0.271683 29
> > 5001574 0.378903 28
> > 5001574 0.291933 27
> > 5001574 0.319807 26
> > 5001574 25
> > 5001574 24
> > 5001574 23
> > 5001574 22
> > 5001574 21
> > 5001574 0.348804 20
> > 5001574 0.247645 19
> > 5001574 0.306516 18
> > 5001574 0.303717 17
> > 5001574 0.310532 16
> >
> > I have about 8000 different id values in the full
> dataset, observed for different stretches of time with
> different numbers of gaps in the cons variable in different
> places across the set of ids.
> >
> > What I would like to do is drop the observations at the
> end of the time series where cons=., but keep the
> observations in the middle. There are varying numbers of
> gaps in the cons time series for different ids, and I want
> to keep all of them except the observations at the end of
> the time series for each id. I've tried a number of
> different combinations of the while, if and foreach
> commands, but none of them has worked, so I hoped that
> someone on the list could help.
>
> I think this can be done without looping. -bysort- is your
> friend here.
>
> gen t_neg = -time
> bysort id (t_neg) : drop if sum(cons ~= .) == 0
Yes, it's pretty clear I misread the problem!
I suppose my excuse is that I didn't imagine that
blocks of missings at the beginning could be of
use or interest.
Nick
[email protected]
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