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st: RE: ifelse mata function


From   philippe van kerm <philippe.vankerm@ceps.lu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: ifelse mata function
Date   Tue, 12 May 2009 13:29:24 +0200

See under 'conditional operator':

 help m2_op_conditional (http://www.stata.com/help.cgi?m2_op_conditional)

Philippe


> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-
> statalist@hsphsun2.harvard.edu] On Behalf Of Nicola Orsini
> Sent: Tuesday, May 12, 2009 1:21 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: ifelse mata function
>
> Mata users,
>
> do you know any mata function similar to ifelse implemented in R or
> the cond() programming function in Stata?
>
> http://www.iiap.res.in/astrostat/School07/R/library/base/html/ifelse.ht
> ml
>
> I know I can loop across observations but it's not really fast with
> large dataset in an optimization process where this process has to be
> repeated many times.
>
> Here is a simple example
>
> mata
> mata clear
> y =  runiform(10,1)
> x =  runiform(10,1)
> z =  J(10,1,.)
> for (i=1; i<=rows(y); i++) {
>             if (y[i]>= x[i]) z[i] = y[i]-x[i]
>                   else       z[i] = x[i]-y[i]
>       }
> y, x, z
> end
>
> Wouldn't be great to have a mata function like -ifelse-?
>
> ifelse(y>=x, z=y-x, z=x-y)
>
> Nicola
>
>
>
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