# [R] Trying to avoid nested loop

arun smartpink111 at yahoo.com
Fri Oct 4 16:30:58 CEST 2013

```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 <pmassicotte at hotmail.com>
To: "r-help at r-project.org" <r-help at 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))

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