[R] permuting dimensions (was do.call("dim<-" , ... ))

[Prof Brian Ripley]

What has this to do with the original subject line?  Replacement functions
are not intended to be used directly, and certainly not in do.call.

See ?aperm, as in

xx <- x
dim(xx) <- c(2,2,3,3)
xx <- aperm(xx, c(1,3,2,4))
dim(xx) <- c(6, 6)
xx

as required.

BTW, you have a broken package `magic' on CRAN: please do us the courtesy
of fixing it so we don't continually have to look at it in tests. See

http://cran.r-project.org/src/contrib/checkSummary.html


On Mon, 13 Sep 2004, Robin Hankin wrote:

>   OK guys
> 
> another problem.  I have a 3D array "x" with dim(x)=c(a,a,b^2)
> and I want to rearrange the elements of x to make a matrix "y"
> with dimensions c(a*b,a*b).  Neither a nor b is known in advance.
> 
> I want the "n-th" a*a submatrix of y to be x[,,n] (where 1 <= n <=
> b^2).  Needless to say, this has gotta be vectorized!
> 
> Toy example with a=2, b=3 follows:
> 
> 
> Given:
> x <- array(1:36,c(2,2,9))
> 
> 
> I require:
> y <- matrix(as.integer(c(
>            1, 2, 5, 6, 9,10,
>            3, 4, 7, 8,11,12,
>           13,14,17,18,21,22,
>           15,16,19,20,23,24,
>           25,26,29,30,33,34,
>           27,28,31,32,35,36
>        )),6,6)
> 
> So
> identical(x[,,1] , y[1:2,1:2])
> identical(x[,,2] , y[3:4,1:2])
> [snip]
> identical(x[,,9] , y[5:6,5:6])
> 
> all return TRUE.
> 
> OBattempts:
> 
> (i)
> dim(x) <- c(4,9);x <- t(x) ; dim(x) <- c(6,6) ; y <- x
> 
> (ii)
> y <- aperm(x,c(2,1,3)) ; dim(y) <- c(6,6)
> 
> Any genius out there with some ideas?
> 
> 
> 

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595