st: Using NEARMRG

["MA V" <ma_v@hotmail.com>]

I just came across a very interesting function named "nearmrg" and I have a 
question regarding its use:
If I write:

neamrg region using ageinfo2, nearvar(age) keep

In this case, I have the following questions:
1) "age" must be unique in the using dataset, right?
2) does the variable region need to be unique?
3) how should I sort the variables?

I tried many different things and I always seem to get the message:

"region age not unique in using dataset
something that should be true of your data is not"

Any suggestions?
Thanks for your help!!

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