Re: st: merge: what is the difference between assert(results) and keep(results)?

[Maarten buis <maartenbuis@yahoo.co.uk>]

--- On Wed, 2/3/11, emanuele mazzini wrote:
> I am starting to use Stata right now and I cannot really
> understand the difference between assert(results) and keep
> (results).  The Stata help is not a big aid in this sense.

When you merge two files a couple of things can happen: a 
match exist, a observation can be in the master file but not
in the user or vice versa. After -merge- there will a variable,
called _merge, that will contain a code for each observation 
(=row) that tells you which of these scenarios applies for that 
observation. With the -assert()- option you ask Stata to stop
whatever it is doing when one or more observations fall into
a scenario you did not specify. If that happens -merge- will 
also give you an error message. With the -keep()- option you
ask -merge- to only keep those observations that fall within
the scenarios you specified. It will not issue an error message
and if this is part of a .do file than the .do-file will 
continue running.

Hope this helps,
Maarten

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

http://www.maartenbuis.nl
--------------------------


      

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