[R] matrix subsetting assignment with logical mask

[Ross Boylan]

If m is a matrix and s is a logical matrix of the same dimensions, I'd
like to be able to update m with
m[s] <- 0
If m2 is another matrix, I'd also like to be able to do
m[s] <- m2
where elements of m for which s is TRUE get the corresponding element of
m2.

However, this doesn't work in R 2.7.1.  The best I've been able to come
up with is
> s
     [,1]  [,2]  [,3]
[1,] TRUE FALSE FALSE
[2,] TRUE  TRUE  TRUE
[3,] TRUE FALSE  TRUE
> x
     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9
> ifelse(s, x, 0) # x[s] <- 0
     [,1] [,2] [,3]
[1,]    1    0    0
[2,]    2    5    8
[3,]    3    0    9

Is there a better way?

Ross Boylan