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Re: st: Generating variable that counts number of appearances


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Generating variable that counts number of appearances
Date   Sat, 31 Mar 2012 09:55:15 +0100

Use

. ssc desc countmatch

in a loop across friend variables.

Nick

On Sat, Mar 31, 2012 at 6:29 AM, Timothy Malacarne
<timothy.malacarne@yale.edu> wrote:
> Hello,
>
> I'm attempting to create a variable the counts the number of times a unique id value for existing variable 1 appears across all observations variable two.  In this case, individuals have unique IDs.  They are then asked to name their friends, who appear by their id number in a series of friend variables.  Each value is unique in the "ID" variable, but 3 people might nominate the same ID value under the Friend variable.  I want to count up how often each individual is named a friend by others.
>
> To do so, I wrote this code:
>
> gen NumberFriends=.;
>
> forval k =   90316050/99798989 {;  *the range of ID values
>                egen tot`k' = total(Friend1ID==`k');
>                replace NumberFriends=tot`k' if `k'==ID;
>                drop toad`k';
>        };
>
> Unfortunately, it needs to loop over all values in the ID range for it to work and I don't have the computational power to do this in a reasonable amount of time.  Is there a computationally more efficient way to count up ID cross references in Stata?
>
> Thanks a lot,
> Tim
>
>
>
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