[R] vectorizing a matrix computation

[Liaw, Andy]

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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