Re: st: combinations of while, if, by, and foreach commands

[Gary Longton <glongton@fhcrc.org>]

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

- Gary




*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/