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Re: st: about deleting variables


From   Ricardo Ovaldia <ovaldia@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: about deleting variables
Date   Tue, 10 Dec 2002 17:47:18 -0800 (PST)

--- Hailing Zang <hlzang@yahoo.com> wrote:

> I have a question about deleting variables that have
> 
> a certain character. I know if I want to drop, then
> simply use
> .drop if<character>
> 
> But if I want to keep the first observation that has
> that character, what should I do?

Remember that the observations are indexed by _n. That
is, the first observation is _n=1, the second _n=2 and
so on. 

When you sort observations and use the -by- statement
the first observation in each of the possible values
of the "by-variable" is index by _n=1 and so on.

So if you are able to sort your data by the variable,
say x,  you can keep the first occurrence of each of
the x values with the statement:

. by x: keep if _n==1

Best,
Ricardo.

=====
Ricardo Ovaldia, MS
Statistician 
Oklahoma City, OK

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