









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 addition: Warning message:
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.
Thanks in advance, 
Zhengyu
eg. here is what I want
 
 
 > head(seq)
     [,1] [,2] [,3] [,4]
[1,]    1    1    0    1
[2,]   -1    1    0    1
[3,]    0   -1   -1   NA

> head(mat)
           [,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.
> head(mat1)
           [,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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