st: merge: "variable does not uniquely identify observations in the masterdata"

[Jeff Pflueger <jeff@infouse.com>]

I am having problems with merge. I am running Stata 10.0 on a Mac (powerPC)

I am merging a dataset of variables pertaining to individuals within 
households to a dataset of variables pertaining to the households that 
they are within. The Households are identified by a unique key in the 
household dataset. In the people dataset, the household key exists, but 
is clearly not unique.


If I do this, I get the error I would expect:

use "$people", clear
merge householdno using "$household", uniqmaster sort

the error is in red on the command line and it terminates my do-file.
It says: "variable householdno does not uniquely identify observations 
in the master data"

Makes sense, the master dataset does not contain unique householdno's  
but the household dataset does.

But if I do this:

use "$people", clear
merge householdno using "$household", uniqusing sort

I get the same error: "variable householdno does not uniquely identify 
observations in the master data" but in this case, the do-file continues 
to run, and the error message is in green, not red.

But householdno is unique in the master dataset....

When I:
use "$household", clear
duplicates list householdno

I get this:

Duplicates in terms of householdno

(0 observations are duplicates)

Any ideas about what I am doing wrong here? The error message is 
certainly disconcerting.


Thanks,
Jeff


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