R help - Jan 2012 - Difference across the Nth dimension of an array

I have a multidimensional array - in this case with 4 dimensions of x,y,z
and time.  I'd like to take the time derivative of this matrix, i.e.
perform the diff operator along dimension number 4.

In Matlab, there is a simple option to specify which dimension the
difference is to be taken across., but I can't see this in R.

I realise I can use aperm to rotate my array so that time is in the 1st
dimension, then do the difference, but this seems a little messy.

Surely I can't be the first person wanting to do this, but I can't find
any
answers after doing a (what I thought was thorough) search.

Thanks in advance,

Phil.

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On 9 January 2012 08:53, Phil Wiles <philip.wiles at gmail.com>
wrote:
> I have a multidimensional array - in this case with 4 dimensions of x,y,z
> and time. ?I'd like to take the time derivative of this matrix, i.e.
> perform the diff operator along dimension number 4.
"apply" can do that, but you may need to reorder the dimensions of the
result.

  a <- array(1:81,dim=c(3,3,3,3))
  b <- apply(a, 1:3, diff)
  b <- aperm(b,c(2:4,1))
  dim(b)

-- Vincent