st: Propensity score matching within the same group

[qhuang@umn.edu]

Dear all, 
I was told by a friend that Stata can do propensity score matching within a 
group. That is, only allow matching of two observations within the same 
village or within the same township or within the same county.

Does anyone know what is the Stata command/option?  Thanks! 
Qiuqiong 
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