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st: RE: RE: ifelse mata function


From   philippe van kerm <philippe.vankerm@ceps.lu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: ifelse mata function
Date   Tue, 12 May 2009 13:53:49 +0200

Sorry, I realize the conditional operator will not help as it only takes a scalar as condition. Then, one can probably do the switch 'manually' with something like

z = (y:>=x) :* (y:-x)   +   (1:-(y:>=x)) :* (x:-y)


Philippe


> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-
> statalist@hsphsun2.harvard.edu] On Behalf Of philippe van kerm
> Sent: Tuesday, May 12, 2009 1:29 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: RE: ifelse mata function
>
> 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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>
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*
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