I think this should do:
z <- apply(my.matrix, 1:3, scale)
z <- aperm(z, c(2:4, 1))
Andy
> From: Christoph Lehmann
>
> 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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