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RE: Matching data, Files A &B [Was: Re: st: Picking from a matrix ]


From   Joly.Patrick@ic.gc.ca
To   statalist@hsphsun2.harvard.edu
Subject   RE: Matching data, Files A &B [Was: Re: st: Picking from a matrix ]
Date   Thu, 28 Nov 2002 10:57:11 -0500

Benoit.Laplante@inrs-UCS.uquebec.ca wrote
> Maybe things are simpler that I think they are but, for what
> I understand of -merge-, it would merge observations that would
> have similar values on one or several variables both in File A
> and File B. The three variables Year, Age and Area do not exist
> as such in File B: Year defines lines while columns are
> combinations of Age within Area. Furthermore, there will not be
> unique combinations of Year, Age and Area in A: some elements of
> B will have to be copied several times to different lines of A.
> Also I need to copy only one value from File B on any given line
> of A, not all 770 values of a given line of B.

Use Jeroen Weesie -mmerge- (available on SSC).  Type -ssc desc mmerge- to
see a description.  The routine allows you to specify different names for
the match variables in the _using_ dataset with option -umatch()-.  For
example, to match variables a, b, and c from the master data (your File A)
with variables, d, e, and f of the using data (your File B), invoke

   mmerge a b c, umatch(d e f)

Note that you must specify the same number of match variables in umatch() as
mmerge's varlist.

To handle the fact that the match variables may not form a key in the using
data (File B), you can use option type() with parameter 1:n,  i.e.

   mmerge a b c, umatch(d e f) type(1:n)

the initial 1 in type() specifies that variables a b c form a key in the
master data, while the n after the colon states that variables d e f do not
form a key in the using data.

Finally, since you are only interested in observations in the using data
that are a match with the master file, specify option -unmatch(master)-.
(This is not a typo, -umatch()- and -unmatch()- are different options.)


Patrick Joly
joly.patrick@ic.gc.ca
pat.joly@utoronto.ca
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