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Re: st: RE: putting files together


From   David Kantor <kantor.d@att.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: putting files together
Date   Wed, 28 Mar 2007 10:02:32 -0400

At 08:01 AM 3/28/2007, Maarten L. Buis wrote:
[...]
In other words, -append- adds rows, and -merge-
adds columns.
I would say that the primary purpose of -append- is to add rows, and the primary purpose of -merge-is to add columns, but both of these can add both rows and columns, depending on the circumstances.

Maarten already stated some of this, but I will add my own thoughts:
To the extent that there are variables not common to both datasets, -append- will add columns.
To the extent that there are unmatched observations, -merge- will add rows.

In a -merge-, if there are no matches at all (no _merge==3 cases), then the results of -append- and -merge- are the same.

-merge- may possibly not add columns, if the set of variables are the same. -append- always adds rows.

--David

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