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Re: st: make a program byable


From   Gary Longton <glongton@fhcrc.org>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: make a program byable
Date   Sun, 23 Jun 2002 23:36:40 -0700

Katsuhide Isa wrote:

> Recently I wrote the following simple program
> titled 'coefvar.ado' for the purpose of calculating
> coefficients of variation.
> 
> ----------coefvar.ado----------
> program define coefvar, rclass byable(recall)
>  version 7
>  qui summ `1', det
>  local coefvar = r(mean)/r(sd)
>  di in green _col(8) `coefvar'
> end
> ----------coefvar.ado----------
> 
> But somehow it doesn't work as expected.
> More specifically, when typing like

  <cut>

> . . . 
> Namely, they are all the same for
> each year when they should vary from year
> to year.
> I guess something is wrong or missing with this
> program,  . . .

See -help byable- or the manual: [P] byable

Your program is missing a -marksample- or -mark- command, the means by which a -byable(recall)- program keeps track of and restricts to each by-group.

Eg.:

----------coefvar2.ado----------
program define coefvar2, byable(recall)
   version 7
   marksample touse        /* added line.
                              marksample knows to mark wrt by-group
                              in addition to handling -syntax [if] [in]-
                              restrictions if included */
   qui summ `1' if `touse'   /* restrict to marked sample with the marker variable `touse' */
   local coefvar = r(mean)/r(sd)
   di in green _col(8) `coefvar'
end
----------coefvar2.ado----------

additional notes:
The -rclass- program option is not necessary as your program does not return any results.
The -,detail- option of -summarize- is not necessary to obtain mean and sd

Consider adding a -syntax- command, as -marksample- will neatly handle any sample restrictions included there in additions to keeping track of the by-groups.

Eg.:
----------coefvar3.ado----------
program define coefvar3, byable(recall)
   version 7
   syntax varname [if] [in]
   marksample touse
   qui summ `1' if `touse' 
   local coefvar = r(mean)/r(sd)
   di in gr "  coef. of variation: " in yel _col(8) `coefvar'
end
----------coefvar3.ado----------

- Gary
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