Assignments inside lapply

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
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Belgium

Research Institute for Nature and Forest
team Biometrics & Quality Assurance
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tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be
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? 

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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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reproducible code.