[R] do.call() and aperm()

[Robin Hankin]

Hi everyone

I've been playing with do.call() but I'm having problems understanding it.

I have a list of "n" elements, each one of which is "d" dimensional
[actually an n-by-n-by ... by-n array].  Neither n nor d is known in
advance.  I want to bind the elements together in a higher-dimensional
array.

Toy example follows with d=n=3.

f <- function(n){array(n,c(3,3,3))}
x <-  sapply(1:3,f,simplify=FALSE)

Then what I want is

ans <- abind(x[[1]] , x[[2]] , x[[3]]  , along=4)

[abind() is defined in library(abind)].

Note that dim(ans) is c(3,3,3,3), as required.

PROBLEM: how do I do tell do.call() that I want to give abind() the
extra argument along=4 (in general, I want
along=length(dim(x[[1]]))+1)?


Oblig Attempt:

jj <- function(...){abind(... , along=4)}
do.call("jj" , x)

This works, because I know that d=3 (and therefore use along=4), but
it doesn't generalize easily to arbitrary d.  I'm clearly missing
something basic.  Anyone?