# [R] Ask for help: find corresponding elements between matrix

arun smartpink111 at yahoo.com
Thu Feb 21 16:17:16 CET 2013

```Hi,

I guess this is what you wanted:
seq1<-matrix(c(1,-1,0,1,1,-1,0,0,-1,1,1,NA),3,4)
seq1
#     [,1] [,2] [,3] [,4]
#[1,]    1    1    0    1
#[2,]   -1    1    0    1
#[3,]    0   -1   -1   NA

set.seed(15)
mat1<-matrix(rnorm(12),3)

mat1
#           [,1]       [,2]       [,3]       [,4]
#[1,]  0.2588229  0.8971982  0.0227882 -1.0750013
#[2,]  1.8311207  0.4880163  1.0907732  0.8550108
#[3,] -0.3396186 -1.2553858 -0.1321224 -0.3649801

m<-sapply(seq_len(ncol(mat1)),function(i) ifelse(seq1[,i]==1|seq1[,i]==-1,mat1[,i],NA))
m
#          [,1]       [,2]       [,3]       [,4]
#[1,] 0.2588229  0.8971982         NA -1.0750013
#[2,] 1.8311207  0.4880163         NA  0.8550108
#[3,]        NA -1.2553858 -0.1321224         NA
A.K.

----- Original Message -----
From: JiangZhengyu <zhyjiang2006 at hotmail.com>
To: r-help at r-project.org
Cc:
Sent: Thursday, February 21, 2013 9:39 AM
Subject: [R] Ask for help: find corresponding elements between matrix

Dear R experts,

I have two matrix (seq & mat) & I want to retrieve in a new matrix all the numbers from mat that =1 (corresponding to the same row/ column position) in seq, or all the numbers in mat that =-1 in seq. - Replace all the numbers with NA if it's not 1/-1 in seq.  There are some "NA"s in seq.

seq=matrix(c(1,-1,0,1,1,-1,0,0,-1,1,1,NA),3,4)
mat=matrix(rnorm(12),3)
I made this code but I don't know where's the problem..

seq=matrix(c(1,-1,0,1,1,-1,0,0,-1,1,1,NA),3,4)
mat=matrix(rnorm(12),3)

m=rep(NA,nrow(seq))
for(i in 1:nrow(seq))
{m[i]=mat[seq[i]==1]
}

Error in m[i] = mat[seq[i] == 1] : replacement has length zero
In m[i] = mat[seq[i] == 1] :
number of items to replace is not a multiple of replacement length
>

I was wondering if anyone can help me with this.
Zhengyu
eg. here is what I want

[,1] [,2] [,3] [,4]
[1,]    1    1    0    1
[2,]   -1    1    0    1
[3,]    0   -1   -1   NA

[,1]       [,2]       [,3]      [,4]
[1,]  0.1006950  0.3354360  0.1796888 1.3198761
[2,]  1.0948252  0.5350797 -0.5739454 0.2744478
[3,] -0.5409936 -0.3820084 -0.5601096 0.9239680

This is a new new matrix.
[,1]       [,2]       [,3]      [,4]
[1,]  0.1006950  0.3354360  NA 1.3198761
[2,]  NA  0.5350797 NA 0.2744478
[3,]  NA NA NA NA

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