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st: counting unique ids


From   "Kang, Eugene" <EKang@cgsb.tamu.edu>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: counting unique ids
Date   Tue, 7 Sep 2004 20:47:53 -0500

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?

Any help would be appreciated. Thanks!

SoonLee
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