try this:

a <- matrix(c(3,4,5,2,3,4,1,1,2), nrow=3, ncol=3)
x <- matrix(c(3, NA, NA, NA, 2, 5, NA, 2, 2), nrow=3, ncol=3)

ind <- is.na(x)
x[ind] <- a[ind]
x


I hope it helps.

Best,
Dimitris


Tom Liptrot wrote:
Hi,

I have two matricies a and x:

a<-matrix(c(3,4,5,2,3,4,1,1,2), nrow=3, ncol=3)

 [,1] [,2] [,3]
[1,]    3    2    1
[2,]    4    3    1
[3,]    5    4    2

x<-matrix(c(3, NA, NA, NA, 2, 5, NA, 2, 2), nrow=3, ncol=3)

 [,1] [,2] [,3]
[1,]    3   NA   NA
[2,]   NA    2    2
[3,]   NA    5    2

I wish to combine these two into one matrix using the values from x where x has 
values, and values from a where x has NA's, giving a new matrix which would 
look like this:

ax<-matrix(c(3,4,5,2,2,5,1,2,2), nrow=3, ncol=3)

    [,1] [,2] [,3]
[1,]    3    2    1
[2,]    4    2    2
[3,]    5    5    2

I want an automatic way of doing this as my actual application is a much larger 
matrix.

Thanks in advance

Tom


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--
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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