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st: Programming question


From   Cameron Hooper <chooper@umich.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: Programming question
Date   Fri, 04 Mar 2005 12:00:45 -0500

A novice programming question. Say I have the following data

id x
1 1
1 2
1 4
2 2
2 8
2 6
2 2

I want to write a program to loop through each company (represented by id) and then within each company loop through each observation. Something like:

forvalues i = 1(1)<number of companies> {
for values j = 1(1)<number of observations for company `i'> {
<do stuff>
}
}

To find the number of companies in the sample I've used:

tempvar numco
egen `numco '= max(id)
local nc = `numco'[1]

This is cumbersome, but it (seems) to work. I have not been able to find the <number of observations for company `i'>. I've tried things like

tempvar nobs
by id, sort: generate `nobs' = _N

Placed outside the loop this gets me part of the way there, but I don't know how to use this information to control the inner loop. I'm sure I'm missing something obvious. Thanks.

Cameron

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