R help - Nov 2010 - force apply not to drop the dimensions of FUN results ?

Dear R users,

Here is my problem:

I have an array with at least four dimensions:

 > dim(myArray)
[1] 20 17  3  6

I'd like to apply a function to each occurrence of the matrix (3x6) 
defined by the last two dimensions. This interpolation function always 
return a matrix of the same dimensions as its argument:

 > interpSecteurs.f(myArray[1, 1, , ])
         secteur
rotation 1     2  3 4 5 6
        1 3  5.25 10 6 6 3
        2 3 10.00 10 7 7 3
        3 3  0.50 10 8 8 3

But when applying this function with apply, these matrices are coerced 
in vectors of length 18:

 > test <- apply(myArray,
+               c(1, 2),
+               interpSecteurs.f)
 > dim(test)
[1] 18 20 17

I read in the help that this is the normal behaviour in apply.
However, I really need to keep the same dimension as the input data.

Do you know any function or method which allows bypassing this behaviour ?
(unfortunately my function seems not suitable for a vectorization using 
sweep)

Alternatively, a method to recover the wished array dimensions afterward 
would be also acceptable.

Many thanks in advance.
Yves

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Dear Yves,

You may not need to do more than set the dim attribute correctly:

dim (test) <- c (dim (myArray) [c (3 : 4, 1 : 2)]
or
dim (test) <- c (dim (myArray) [c (4 : 3, 1 : 2)]

Claudia


-- 
Claudia Beleites
Dipartimento dei Materiali e delle Risorse Naturali
Universit? degli Studi di Trieste
Via Alfonso Valerio 6/a
I-34127 Trieste

phone: +39 0 40 5 58-37 68
email: cbeleites at units.it

Thank you very much Claudia,

That (the first form) works perfectly.
Easily made generic using head and tail on the dim attribute.

All the best,
Yves


Claudia Beleites <cbeleites at units.it> a ?crit?:
> Dear Yves,
>
> You may not need to do more than set the dim attribute correctly:
>
> dim (test) <- c (dim (myArray) [c (3 : 4, 1 : 2)]
> or
> dim (test) <- c (dim (myArray) [c (4 : 3, 1 : 2)]
>
> Claudia
>
>
> -- 
> Claudia Beleites
> Dipartimento dei Materiali e delle Risorse Naturali
> Universit? degli Studi di Trieste
> Via Alfonso Valerio 6/a
> I-34127 Trieste
>
> phone: +39 0 40 5 58-37 68
> email: cbeleites at units.it
>