[R] How to replace all non-maximum values in a row with 0

[ONKELINX, Thierry]

It can be done faster and more elegant with apply and rowSums

rows <- 100000
A <- matrix(rpois(n = rows * 20, lambda = 100), nrow = rows)
A[4, c(1,3)] <- 1000

system.time({
	y <- t(apply(A, 1, function(z){
		1 * (z == max(z))
	}))
	y[rowSums(y) > 1, ] <- 0
})

system.time({
	nr <- nrow(A)
	nc <- ncol(A)
	B <- matrix(0,nrow=nr, ncol=nc)
	for(i in 1:nr){
		x <- which(A[i,]==max(A[i,]))
		B[i,x] <- 1
		if(sum(B[i,])>1) B[i,] <- as.vector(rep(0,nc))
	}
})
all.equal(y, B)

HTH,

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 op inbo.be
www.inbo.be

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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 op r-project.org 
> [mailto:r-help-bounces op r-project.org] Namens Owe Jessen
> Verzonden: vrijdag 9 april 2010 11:08
> Aan: r-help op r-project.org
> Onderwerp: Re: [R] How to replace all non-maximum values in a 
> row with 0
> 
> Am 09.04.2010 10:04, schrieb burgundy:
> > Hi,
> >
> > I would like to replace all the max values per row with "1" 
> and all other
> > values with "0". If there are two max values, then "0" for 
> both. Example:
> >
> > from:
> > 2  3  0  0  200
> > 30 0  0  2  50
> > 0  0  3  0  0
> > 0  0  8  8  0
> >
> > to:
> > 0  0  0  0  1
> > 0  0  0  0  1
> > 0  0  1  0  0
> > 0  0  0  0  0
> >
> > Thanks!
> >    
> Nice little homework to get the day started. :-)
> 
> This worked for me, but is probably not the shortest possible answer
> 
> A <- matrix (c(2,  3,  0,  0,  200, 30, 0,  0,  2,  50, 0,  
> 0,  3,  0,  
> 0, 0,  0,  8,  8,  0), nrow = 4, byrow=T)
> nr <- nrow(A)
> nc <- ncol(A)
> B <- matrix(0,nrow=nr, ncol=nc)
> for(i in 1:nr){
> x <- which(A[i,]==max(A[i,]))
> B[i,x] <- 1
> if(sum(B[i,])>1) B[i,] <- as.vector(rep(0,nc))
> }
> 
> -- 
> Owe Jessen
> Nettelbeckstr. 5
> 24105 Kiel
> post op owejessen.de
> http://privat.owejessen.de
> 
> ______________________________________________
> R-help op r-project.org mailing list
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> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 

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