If I'm reading the original post correctly, dropping b1 may not be a
solution because there are two merges happening (production and investment
data), each adding a b1 as needed. If this guess is correct, then I think
that the solution would be to use the update option to merge, which will
replace missing b1 with b1 from the using data. An alternative would be to
name b1 something else in the second file being merged (b2?) and then
compare b1 and b2 for any observations where both are present, just to be
sure that there agreement. Then one could replace b1=b2 if b1==. and then
drop b2.
Michael Blasnik
[email protected]
----- Original Message -----
From: "William Gould, Stata" <[email protected]>
To: <[email protected]>
Sent: Tuesday, April 29, 2003 10:07 AM
Subject: Re: st: Merge problem
> Julian Fennema <[email protected]> is having difficulty merging
datasets.
> To summarize (and put words in his mouth), he has a dataset
>
> p1992.dta containing identifying vars r1 r2 and other vars x1, x2,
..
>
> and he has
>
> link.dta containing variables r1, r2, and b1
>
> He claims that in link.dta, r1, r2, and b1 are never missing.
>
> He merges the two datasets,
>
> . use p1992, clear
> . merge r1 r2 using link
>
> and he discovers that
>
> _merge==1 observations:
> look fine; have b1==.
>
> _merge==2 observations:
> look fine, have b1<. (i.e., not missing, has correct values
> obtained from link.dta)
>
> _merge==3 observations:
> look fine in one sense, but have b1==., rather than the correct
> values from link.dta
>
> I have a suspicion as to the problem:
>
> dataset p1992.dta already has a variable named b1 in it, and that
> variable has b1==.
>
> If I am right, then dropping the b1 variable before the merge will solve
> the problem.
>
> When Stata joins two observations, it never replaces values in the master
> dataset, the dataset in memory. Rather, it uses only the new values
> associated with the new variables.
>
> -- Bill
> [email protected]
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