R help - Apr 2010 - How to replace all non-maximum values in a row with 0

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!
-- 
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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 at owejessen.de
http://privat.owejessen.de

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 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 Owe Jessen
> Verzonden: vrijdag 9 april 2010 11:08
> Aan: r-help at 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 at owejessen.de
> http://privat.owejessen.de
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> 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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Hi:

This isn't much shorter than the previous solution, but here's another
take,
operating row-wise.

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)

# Write a vector function to apply to each row: begin by initializing a zero
# vector of length = no. columns. Next, find which indices of the row vector
x
# match the maximum. If that number is >1, return a zero vector, else
replace
# the index where the maximum resides to 1.
f <- function(x) {
   o <- rep(0, length(x))
   w <- which(x == max(x))
   r <- if(length(w) > 1) {o} else {
         o[w] <- 1; o}
   r
 }
# Test:
> t(apply(A, 1, f))
     [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    0    0    1
[2,]    0    0    0    0    1
[3,]    0    0    1    0    0
[4,]    0    0    0    0    0

HTH,
Dennis

On Fri, Apr 9, 2010 at 1:04 AM, burgundy <sauburn@yahoo.com> wrote:
>
> 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!
> --
> View this message in context:
>
http://n4.nabble.com/How-to-replace-all-non-maximum-values-in-a-row-with-0-tp1819018p1819018.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> 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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