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RE: st: how to identify unique id variables within groups?


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   stata list <statalist@hsphsun2.harvard.edu>
Subject   RE: st: how to identify unique id variables within groups?
Date   Wed, 20 May 2009 10:12:48 +0000 (GMT)

--- Jia Xiangping wrote:
> For a datafile like :
> id                    var1
> 1			1
> 1			2
> 1			3
> 2			1
> 2			2
> 2  		        1
> 
> I expect to check whether the value of "var1" within
>  one group of "id" is unique -- i.e. in group 2, the
> values are not unique. 

_N in combination with -bys- gives the total number of 
observations withing each group defined by the variables
in -bys-. So if var1 uniquely identifies individuals 
within id, than _N within -bys id var1- should always be 
1, and any duplicates will be identified with _N larger 
than 1. So you can do something like this:

bys id var1: gen byte duplicates = _N > 1
list id var1 if duplicates == 1

Hope this helps,
Maarten

-----------------------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://home.fsw.vu.nl/m.buis/
-----------------------------------------


      

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