st: question on keeping observations - selecting substitute instituions for sampled institutions

[Gáti Annamária <annamaria.gati@tarki-tudok.hu>]

Dear List users,

I am trying to collect a sample out of schools. I have successfully 
sampled 300 institutions out of 4000. I have now a dataset containing 
4000 observations and a variable named sample indicating whether a given 
institution is part of my sample (code=1) or not (code=0).

As I also need 2 substitutes for each institutions I would like to chose 
the ones that are right above and under the sampled school. Is there a 
simple way to do this with stata? I was browsing through the Keep 
observations commands but didn’t manage to find out how to do this.

Thank U in advance

Annamaria
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