Or, if you want the standard deviation as a variable you could:
levels class, local(levels)
gen std = .
foreach l of local levels {
qui sum mpg if class == `l'
qui replace std = r(sd) if class == `l'
}
You will need Nick Cox's -levels- (ssc install levels)
Scott
----- Original Message -----
From: "Fraser, Steven" <[email protected]>
To: "Statalist (E-mail)" <[email protected]>
Sent: Sunday, January 19, 2003 2:28 PM
Subject: st: egen .&.. std()
> Statalisters -
>
> I am interested in obtaining the standard deviation for a particular
> variable with groups determined by another variable. Essentially I would
> like to combine the 'egen std()' function with the 'by' construct which is
> not allowed. Is there an alternative to using collapse (I would prefer not
> to change the dataset) or having to introducing a matrix?
>
> Assume:
>
> Manuf Model Class Mpg
> Chevy Tahoe SUV 14
> Toyota Highlander SUV 19
> Toyota Camry Auto 23
> Ford F-150 P/U 17
> etc.
>
> I would like to capture the standard deviation of the mpg within a
> particular class.
>
> i.e.
>
> sort class
> by class: gen (or egen) mpgstd = std(mpg)
>
> The error is:
> . by obj: egen mpgstd = std(mpg)
> egen ... std() may not be combined with by
>
> This however, is not allowed. Any thoughts or comments are greatly
> appreciated.
>
> Steve Fraser
>
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