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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   Sun, 1 Apr 2012 09:14:22 +0100

This is just to underline that the help for -countmatch- explains how
to do this.


On Sat, Mar 31, 2012 at 9:55 AM, Nick Cox <njcoxstata@gmail.com> wrote:
> 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?
>>

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