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RE: st: repeated values of a variable


From   Richard Williams <Richard.A.Williams.5@nd.edu>
To   statalist@hsphsun2.harvard.edu
Subject   RE: st: repeated values of a variable
Date   Wed, 17 Mar 2004 07:02:53 -0500

At 10:17 AM 3/17/2004 +0000, Nick Cox wrote:
Note that

. bysort id : drop if _N == 1

is (nearly) equivalent. It's more direct;
but note the side-effect of -sort-ing.
That is good. In general, data sets should have id numbers; sort commands can be a little scary without them, and ado files may sort your data without your knowledge. It would be sort of a shame if you had thousands of survey questionnaires coded and then couldn't link the data back to their original sources.

If missing data on id is a concern, modify the above to

bysort id : drop if _N == 1 | missing(id)


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Richard Williams, Notre Dame Dept of Sociology
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