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Re: st: loop with egen


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: loop with egen
Date   Fri, 8 Feb 2013 13:38:20 +0000

I don't believe that was your code.

I suspect that you wrote something of the form

foreach v of var <varlist> {
      egen mean = mean(`v')
      egen sd = sd(`v')
}

where instead of <varlist> you had a list of variable names.

Second time around the loop, the problem is that -mean- already
exists, and so the loop fails.

You could make this loop legal by ensuring that each new variable has
a different name

foreach v of var <varlist> {
      egen mean_`v' = mean(`v')
      egen sd_`v'  = sd(`v')
}

but that would still be a bad idea. There is usually little point in
generating lots of variables that just contain constants.

su <varlist> will give you a list of means and standard deviations.

For more precise control, consider

. sysuse auto
(1978 Automobile Data)

. tabstat mpg weight, s(mean sd) c(s) format(%2.1f)

    variable |      mean        sd
-------------+--------------------
         mpg |      21.3       5.8
      weight |    3019.5     777.2
----------------------------------

Nick

On Fri, Feb 8, 2013 at 1:29 PM, Nahla Betelmal <nahlaib@gmail.com> wrote:

> I am trying to generate the mean and standard deviation for more than
> 30 variables. I tried to do that using the following loop
>
> foreach v of var {
> egen mean = mean(`v')
> egen sd = sd(`v')
> }
>
> however, it only generate the mean and standard deviation for the
> first variable only.
>
> I got this message :mean already defined
> r(110);
>
> what should I add to the loop , so it can generate the mean and
> standard deviation for each variable in separate column?
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