[R] vectorizing a matrix computation
Christoph Lehmann
christoph.lehmann at gmx.ch
Tue Jul 20 11:31:04 CEST 2004
Dear R users
I have a 4-dimensional matrix (actually several 3d (x,y, slices)
matrices appended over time (volumes))
say, e.g. I want to z-transform the data (subtract the mean and divide
by the std-deviation)
for (slice in 1:slices) {
for (x in 1:x.dim) {
for (y in 1:y.dim) {
t <- as.matrix(my.matrix[x,y,slice,1:volumes])
for (vol in 1:volumes) {
my.matrix.transformed[x,y,slice,vol] <-
(my.matrix[x,y,slice,vol] - mean(t))/sqrt(var(t))
}
}
}
}
how can I vectorize such a function using, one of the *apply functions?
many thanks
Cheers
Christoph
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