[R] another matrix question

[Julien Barnier]

Hi,

> Given matrix m and matrix n, I would like to compute mn[i,,j]= m[i,,j]
> + n[i,,j] if either of these elements is 0. (In other words, whichever
> number is nonzero.)
> Else I want mn[i,,j]=(m[i,,j] + n[i,,j])/2
> I need a fast method.

m <- matrix(c(0,1,2,3,4,0,5,6,0),nrow=3,ncol=3)
n <- matrix(c(1,2,0,3,0,4,0,5,6),nrow=3,ncol=3)

mn <- ifelse(m==0 | n==0, m+n,(m+n)/2)

Hope that helps,
-- 
Julien Barnier
Groupe de recherche sur la socialisation
ENS-LSH - Lyon, France