st: reverse lookup

[Jeph Herrin <stata@spandrel.net>]

All,

I've just written the same awkward code for the untoldth time, and I'm 
thinking there must be a better way to do it.
The problem is to get a particular value of a variable into a local 
which corresponds to a particular value of another variable. I think 
this is usally call reverse lookup. For example, I might have -period- 
and -rate- and want to store the value of -rate- which corresponds to 
period = 1. My lazy solution is

 sum rate if period = 1
 local rate1 `=r(mean)'

That is, I summarize a single observation, then put the mean in local. 
Is there a better way to do this?
thanks,
Jeph

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