[R] matrix indexing

[toka tokas]

Dear R-users,

I was wondering for the following:

Let 'x' be a matrix and 'ind' and indicator matrix,
i.e.,

x <- array(1:20, dim = c(4, 5))
ind <- array(c(1:3, 3:1), dim = c(3, 2))

I'd like to get (as a vector) the elements of 'x'
which are not indexed by 'ind'. Since negative indices
are not allowed in index matrices I thought of using
something like:

x[ind] <- NA
x[!is.na(x)]

but are there any more elegant solutions.

Thanks in advance,
toka