On Wed, 2007-11-21 at 14:30 -0500, Gregory Gentlemen wrote:
> Hello fellow R users,
>
> I have a matrix computation that I imagine should be relatively easy
> to do, however I cannot figure out a nice way to do it. I have two
> matrices, for example
>
> mat1 <- matrix(c(1:5,rep(NA,5), 6:10), nrow=3, byrow=T)
> mat2 <- matrix(c(2:6, 6:10, rep(NA,5)), nrow=3, byrow=T)
>
> I'd like to compute the element-wise average for non-NA entries. Of
> course
>
> (mat1+mat2)/2
>
> does not work for the final two rows because of the NA's. Are there
> any elegant ways to accopmlish this without writing a loop with
> indices?
>
> Thanks in advance for any assistance.
>
> Greg
Is this what you want?
> matrix(colMeans(rbind(as.vector(mat1), as.vector(mat2)),
na.rm = TRUE), dim(mat1))
[,1] [,2] [,3] [,4] [,5]
[1,] 1.5 2.5 3.5 4.5 5.5
[2,] 6.0 7.0 8.0 9.0 10.0
[3,] 6.0 7.0 8.0 9.0 10.0
?
HTH,
Marc Schwartz
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