[R] Trying to avoid nested loop
Dear R users.
I'm trying to avoid using nested loops in the following code but I'm not sure
how to proceed. Any help would be greatly appreciated.
With regards,Phil
X = matrix(rnorm(100), 10, 10)
## Version with nested loopsresult = 0
for(m in 1:nrow(X)){ for(n in 1:ncol(X)){if(X[m,n] != 0){ result
= result + (X[m,n] / (1 + abs(m - n)))} }}
## No loop-sum(ifelse(M 0, M/??? , 0))
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Re: [R] Trying to avoid nested loop
I'm trying to avoid using nested loops in the following code but I'm
not sure how to proceed. Any help would be greatly appreciated.
With regards,Phil
X = matrix(rnorm(100), 10, 10)
result = 0
for(m in 1:nrow(X)){
for(n in 1:ncol(X)){
if(X[m,n] != 0){
result = result + (X[m,n] / (1 + abs(m - n)))
}
}
}
First, you don't need the 'if', do you? If X[m,n]==0 (rare for a floating
point number) (X[m,n] / (1 + abs(m - n)) will be zero anyway.
Then, depending on the matrix size, you can probably do the whole thing using
an index array.
Something like:
idx - as.matrix( expand.grid(1:nrow(X), 1:ncol(X)) )
result - sum( X[idx] / apply(idx,1, function(x) 1+abs(diff(x))) )
#... which seemed to do the identically the same thing as your loop when I
tried it.
S Ellison
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Re: [R] Trying to avoid nested loop
Thank you for your answer. This is what I needed.
From: s.elli...@lgcgroup.com
To: r-help@r-project.org
Date: Fri, 4 Oct 2013 15:13:49 +0100
Subject: Re: [R] Trying to avoid nested loop
I'm trying to avoid using nested loops in the following code but I'm
not sure how to proceed. Any help would be greatly appreciated.
With regards,Phil
X = matrix(rnorm(100), 10, 10)
result = 0
for(m in 1:nrow(X)){
for(n in 1:ncol(X)){
if(X[m,n] != 0){
result = result + (X[m,n] / (1 + abs(m - n)))
}
}
}
First, you don't need the 'if', do you? If X[m,n]==0 (rare for a floating
point number) (X[m,n] / (1 + abs(m - n)) will be zero anyway.
Then, depending on the matrix size, you can probably do the whole thing using
an index array.
Something like:
idx - as.matrix( expand.grid(1:nrow(X), 1:ncol(X)) )
result - sum( X[idx] / apply(idx,1, function(x) 1+abs(diff(x))) )
#... which seemed to do the identically the same thing as your loop when I
tried it.
S Ellison
***
This email and any attachments are confidential. Any use...{{dropped:8}}
__
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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__
R-help@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.
Re: [R] Trying to avoid nested loop
Hi,
set.seed(49)
X = matrix(rnorm(100), 10, 10)
X1- X
result-0
for(m in 1:nrow(X)){ for(n in 1:ncol(X)){ if(X[m,n] != 0){ result
= result + (X[m,n] / (1 + abs(m - n))) } }}
indx-which(X!=0,arr.ind=TRUE)
indx1-1+abs(indx[,1]-indx[,2])
X1[indx]- X1[indx]/indx1
#or
res1- sapply(seq_len(nrow(X)),function(m)
do.call(rbind,lapply(seq_len(ncol(X)),function(n) {if(X[m,n]!=0)
X[m,n]/(1+abs(m-n))})))
res2-t(X1)
identical(res1,res2)
#[1] TRUE
res3- sum(res2)
all.equal(res3,result)
#[1] TRUE
A.K.
- Original Message -
From: philippe massicotte pmassico...@hotmail.com
To: r-help@r-project.org r-help@r-project.org
Cc:
Sent: Friday, October 4, 2013 9:49 AM
Subject: [R] Trying to avoid nested loop
Dear R users.
I'm trying to avoid using nested loops in the following code but I'm not sure
how to proceed. Any help would be greatly appreciated.
With regards,Phil
X = matrix(rnorm(100), 10, 10)
## Version with nested loopsresult = 0
for(m in 1:nrow(X)){ for(n in 1:ncol(X)){ if(X[m,n] != 0){ result
= result + (X[m,n] / (1 + abs(m - n))) } }}
## No loop-sum(ifelse(M 0, M/??? , 0))
[[alternative HTML version deleted]]
__
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.
__
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.
Re: [R] Trying to avoid nested loop
Hi,
set.seed(49)
X = matrix(rnorm(100), 10, 10)
X1- X
result-0
for(m in 1:nrow(X)){ for(n in 1:ncol(X)){ if(X[m,n] != 0){ result
= result + (X[m,n] / (1 + abs(m - n))) } }}
indx-which(X!=0,arr.ind=TRUE)
indx1-1+abs(indx[,1]-indx[,2])
X1[indx]- X1[indx]/indx1
#or
res1- sapply(seq_len(nrow(X)),function(m)
do.call(rbind,lapply(seq_len(ncol(X)),function(n) {if(X[m,n]!=0)
X[m,n]/(1+abs(m-n))})))
res2-t(X1)
identical(res1,res2)
#[1] TRUE
res3- sum(res2)
all.equal(res3,result)
#[1] TRUE
A.K.
- Original Message -
From: philippe massicotte pmassico...@hotmail.com
To: r-help@r-project.org r-help@r-project.org
Cc:
Sent: Friday, October 4, 2013 9:49 AM
Subject: [R] Trying to avoid nested loop
Dear R users.
I'm trying to avoid using nested loops in the following code but I'm not sure
how to proceed. Any help would be greatly appreciated.
With regards,Phil
X = matrix(rnorm(100), 10, 10)
## Version with nested loopsresult = 0
for(m in 1:nrow(X)){ for(n in 1:ncol(X)){ if(X[m,n] != 0){ result
= result + (X[m,n] / (1 + abs(m - n))) } }}
## No loop-sum(ifelse(M 0, M/??? , 0))
[[alternative HTML version deleted]]
__
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.
__
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.
