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Re: st: question about egen


From   Shige Song <sgsong@ucla.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: question about egen
Date   Fri, 18 Apr 2003 00:24:18 -0700

Hi Gary,

This is exactly what I need, thanks!

Shige


The "(exp)" just indicates that Stata is looking for a valid Stata
expression here.  The logical expressions you have used are valid.

The problem is that the egen count() function is not doing what you
might logically expect: it is not counting the number of observations
for which the expression is "true".  Rather it is counting the number of
observations for which the expression evaluates to a non-missing result
(look closely at either the help or the manual for the egen count
function.).  When the logical expression evaluates to "false" (i.e.
zero) the result is nevertheless non-missing, and is thus "counted".

However, you should be able to achieve the result you want using the
egen -sum()- function using an argument which is a logical expression
evaluating to either 1 (true) or 0 (false) as in your example.

I.e.
        egen nm = sum(GENDER == 1), by(CITY)
        egen nw = sum(GENDER == 2), by(CITY)
        egen np = sum(GENDER ~= .), by(CITY)

- Gary
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