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st: RE: Re: How to list just the first case meeting a selection criterion?


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Re: How to list just the first case meeting a selection criterion?
Date   Tue, 28 Jun 2005 00:40:46 +0100

Agreed, with one wrinkle: 

gen long obs = _n 
bysort county precinct (obs) : keep if _n == 1

keeps the original observation numbers if they 
are important to you. 

Nick 
n.j.cox@durham.ac.uk 

Michael Blasnik
 
> Given the large dataset, I would just drop all of the cases 
> after the first 
> for each criteria grouping, the you can list whatever you 
> like quickly and 
> easily:
> 
> bysort county precinct: keep if _n==1
> 
> Then you could:
> 
> list if county==xxx & precinct==y
> 
> It will be much faster working with the reduced dataset.  
> Just remember not 
> to save,replace.
 
paul gronke

> >I am dealing with an extremely large (2 gig) dataset and wish to list
> > just the first case that meets a set of criteria.  There 
> are about 200
> > separate sets of criteria (county and precinct values).
> >
> > Thus, I'd like a command that does something like:
> >
> > list name address1 address2 county precinct city state
> >     if [first one of] county=VALUE & precinct=VALUE
> >
> > repeated about 200 times.
> >
> > I could do this with
> >     sample 1 if CRITERIA
> >
> > but that seems needless complex, especially since all I want is the
> > first case that meets 200 combinations of county and precinct.

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