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Re: st: counting unique ids


From   Richard Williams <Richard.A.Williams.5@nd.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: counting unique ids
Date   Tue, 07 Sep 2004 21:30:49 -0500

At 08:47 PM 9/7/2004 -0500, Kang, Eugene wrote:
Hi,

I have a cross-section panel data that is unbalanced. For instance:
id      year            x1
111     1999            3
111     2000            5
111     2001            6
123     2000            4
123     2001            2

For the above example, there are 2 unique ids (111 and 123). Since my
dataset has over 6000 observations, what commands should I use to generate a
count of unique ids?
One of many possible approaches:

. egen x = group(id)

. sum x

    Variable |       Obs        Mean    Std. Dev.       Min        Max
-------------+--------------------------------------------------------
           x |         5         1.4    .5477226          1          2

The value for Max is the # of unique ids.


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Richard Williams, Notre Dame Dept of Sociology
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