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RE: st: check for double id-numbers

From   "Nick Cox" <>
To   <>
Subject   RE: st: check for double id-numbers
Date   Thu, 24 Nov 2005 12:10:38 -0000

Thanks for the recommendation, but two 
points of clarification please: 

1. -duplicates- is an official Stata command
added in Stata 8. It certainly draws upon 
-dups- but it does not offer exactly everything
that -dups- does. Conversely, it offers
several things that -dups- does not. 

2. -dups- was written by Thomas J. Steichen 
and myself. The version in STB-41 requires 
Stata 5 and a later version on SSC requires 
Stata 6. 

Raoul does not say what version of Stata he 
is using but in accordance with Statalist 
convention he is presumed to be using Stata 
9.1, in which case -duplicates- is the more
direct of these solutions. 

In addition, Maarten Buis is naturally
correct in drawing attention to -isid- 
as a possible solution to the narrower 
question it focuses on. 


Neil Shephard
> On 11/24/05, Raoul C Reulen <> wrote:

> I have a data file and I want to know whether there are 
> id-numbers that are used twice in the dataset? How can I run 
> a check on this? Thanks.
> Typing...
> . findit duplicates
> ...would have lead you to the -duplicates- command.  See -man
> duplicates- for more information.  Alternatively you may want to use
> Nick Cox's -dups- command which is also listed and is downloadable
> from ssc by typing -ssc install dups-
> There is also a first principle method given in the FAQ's (which are a
> valuable resource) at...
> -findit- and -search- are very useful commands within Stata, check out
> the help pages for them.

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