Re: st: Computing difference of counts within groups

[Phil Schumm <pschumm@uchicago.edu>]

On Nov 1, 2010, at 10:46 AM, Grealy, Patrick J wrote:
> I thought there was a simple way to do what I am attempting using  
> the egen command but I have not gotten that to work right. Can  
> someone make another suggestion? I am trying to check if the  
> difference between two groups within another group exceeds a certain  
> value. For example, using the auto dataset, within the five rep78  
> groups I would like to calculate the difference between Domestic and  
> Foreign and check if it exceeds some limit, say 7.
>
> This code below does what I want but I was hoping to find something  
> simpler:
>
> sysuse auto,clear
> gen fdiff = .
> foreach ix_rep78 of numlist 1/5 {
> quietly count if foreign==0 & rep78==`ix_rep78'
> local foreign0 `r(N)'
> quietly count if foreign==1 & rep78==`ix_rep78'
> local foreign1 `r(N)'
> replace fdiff = abs(`foreign0' - `foreign1') if rep78==`ix_rep78'
> }
> tab rep78 foreign if fdiff > 7


One way to replicate exactly what you have done is the following:

    egen fdiff = total((foreign*2)-1) if !mi(rep78), by(rep78)
    replace fdiff = abs(fdiff)


-- Phil

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