[R] Assignments inside lapply

[Alaios]

I would like to use lapply as there is a parallel version of lapply called mclapply.

My purpose is to convert 
for (i in c(1:dimx)){
   for (j in c(1:dimy)){
       Powermap[i,j] <- Pr(c(i,j),c(PRX,PRY),f)
 }}

to something that can run in parallel with mclapply:
I am not sure then how to store the results of lapply(mclapply) correctly to Powermap matrix. That is the reason I put the assignment inside the return statement.
For example this does not do what I want to
Powermap[i,j]<-unlist(mclapply(1:nrow(ij),function(rowId) { return (Pr(c(ij$i[rowId],ij$j[rowId]),c(PRX,PRY),f)
How can I try this out?

Best Regards
Alex

--- On Wed, 4/27/11, ONKELINX, Thierry <Thierry.ONKELINX at inbo.be> wrote:

> From: ONKELINX, Thierry <Thierry.ONKELINX at inbo.be>
> Subject: RE: [R] Assignments inside lapply
> To: "Alaios" <alaios at yahoo.com>, "R-help at r-project.org" <R-help at r-project.org>
> Date: Wednesday, April 27, 2011, 11:06 AM
> Dear Alex,
> 
> I think you want to use apply()
> 
> ij <- expand.grid(i = seq_len(dimx),j = seq_len(dimy))
> Powermap <- apply(ij, 1, function(x){
>     Pr(x, c(PRX, PRY), f)
> })
> 
> Best regards,
> 
> Thierry
> 
> ----------------------------------------------------------------------------
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek
> team Biometrie & Kwaliteitszorg
> Gaverstraat 4
> 9500 Geraardsbergen
> Belgium
> 
> Research Institute for Nature and Forest
> team Biometrics & Quality Assurance
> Gaverstraat 4
> 9500 Geraardsbergen
> Belgium
> 
> tel. + 32 54/436 185
> Thierry.Onkelinx at inbo.be
> www.inbo.be
> 
> To call in the statistician after the experiment is done
> may be no more than asking him to perform a post-mortem
> examination: he may be able to say what the experiment died
> of.
> ~ Sir Ronald Aylmer Fisher
> 
> The plural of anecdote is not data.
> ~ Roger Brinner
> 
> The combination of some data and an aching desire for an
> answer does not ensure that a reasonable answer can be
> extracted from a given body of data.
> ~ John Tukey
>   
> 
> > -----Oorspronkelijk bericht-----
> > Van: r-help-bounces at r-project.org
> 
> > [mailto:r-help-bounces at r-project.org]
> Namens Alaios
> > Verzonden: woensdag 27 april 2011 11:37
> > Aan: R-help at r-project.org
> > Onderwerp: [R] Assignments inside lapply
> > 
> > Dear all I would like to ask you if an assignment can
> be done 
> > inside a lapply statement.
> > 
> > For example
> > 
> > I would like to covert a double nested for loop
> > 
> > for (i in c(1:dimx)){
> >   for (j in c(1:dimy)){
> >       Powermap[i,j] <-
> Pr(c(i,j),c(PRX,PRY),f)
> >    }
> > }
> > 
> > to something like that:
> > 
> > 
> > ij<-expand.grid(i=seq(1:dimx),j=(1:dimy))
> > 
> > unlist(lapply(1:nrow(ij),function(rowId) { return 
> >
> (Powermap[i,j]<-Pr(c(ij$i[rowId],ij$j[rowId]),c(PRX,PRY),f))   }))
> > 
> > 
> > as you can see lapply does not return nothing as the 
> > assignment is done inside the function. Would that
> work 
> > correctly? What are the cases such a statement will
> misfunction?
> > 
> > I would like to thank you in advace for your help.
> > 
> > Best Regards
> > Alex
> > 
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> >