Re: st: merge

[David Kantor <dkantor@jhu.edu>]

Perhaps they are not mean to be unique.  You need to consider the nature of 
your data to determine that.

But meanwhile, a good rule to follow is that in general, for a matched 
-merge- to be meaningful, either the master or the using should be unique 
in the identifier(s) -- perhaps both, but at least one of them should be 
unique.  In your case, the using data are not unique, but presumably, the 
master data are.  This may be quite okay; that depends on the nature of the 
data.

Assuming that it is meaningful to merge your datasets with these 
conditions, you should specify
-uniqmaster-, rather than -unique-.

(When one dataset is unique and the other isn't, I find it conceptually 
easier to comprehend if it is the master data that are unique.  But it 
really doesn't matter.)

On the other hand, if you truly need for both sets to be unique, then there 
is something wrong with the data.

I hope this helps.
-- David

At 06:43 AM 2/20/2004 -0800,  Anuja wrote:

> Dear Stata users,
>
> I am trying to merge two datasets with 5 unique
> identifyers. The master dataset has 1396 obs, and the
> using one has 8675.
>
>  merge  prov cd cu dwg month using
> "C:\PNG96\Data\hh-merged.dta"
> 1) when i use the option unique i get
> variables prov cd cu dwg month do not uniquely
> identify observations in the using data
>
> I have sorted them, and cann't figure out what how to
> go abt it.
>
> Thanks,
> Anuja
> [...]
David Kantor
Institute for Policy Studies
Johns Hopkins University
dkantor@jhu.edu
410-516-5404

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