R help - Mar 2008 - How to make a 2-dim array being "interpreted" as an array rather than as a matrix

Dear List
 
A 2-dimensional array seems to be "interpreted" as a matrix whereas
higher dimensional arrays are interpreted as arrays, e.g.
 
> a1 <- array(1:8,c(2,2,2))
> class(a1)
[1] "array"
> a2 <- array(1:4,c(2,2))
> class(a2)
[1] "matrix"

If I write a generic function (apologies if this is the wrong word) on arrays as
 
foo <- function(x) UseMethod("foo")
foo.array <- function(x) sum(x)

then this fails on a 2-dimensional array:
 
> foo(a1)
[1] 36
> foo(a2)
Error in UseMethod("foo") : no applicable method for "foo"
 
Is there any way in which I can "force" a2 to being
"interpreted" as having class "array" rather than
"matrix" so that foo will work on a2???
 
Thanks in advance
S?ren

I don't know if is the best way:

a3 <- array(a2, dim=c(nrow(a2), ncol(a2), 1))

foo(a3)

On 04/03/2008, S?ren H?jsgaard <Soren.Hojsgaard at agrsci.dk>
wrote:
> Dear List
>
>  A 2-dimensional array seems to be "interpreted" as a matrix
whereas higher dimensional arrays are interpreted as arrays, e.g.
>
>  > a1 <- array(1:8,c(2,2,2))
>  > class(a1)
>  [1] "array"
>  > a2 <- array(1:4,c(2,2))
>  > class(a2)
>  [1] "matrix"
>
>  If I write a generic function (apologies if this is the wrong word) on
arrays as
>
>  foo <- function(x) UseMethod("foo")
>  foo.array <- function(x) sum(x)
>
>  then this fails on a 2-dimensional array:
>
>  > foo(a1)
>  [1] 36
>  > foo(a2)
>  Error in UseMethod("foo") : no applicable method for
"foo"
>
>  Is there any way in which I can "force" a2 to being
"interpreted" as having class "array" rather than
"matrix" so that foo will work on a2???
>
>  Thanks in advance
>  S?ren
>
>
>
>
>
>
>
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>

-- 
Henrique Dallazuanna
Curitiba-Paran?-Brasil
25? 25' 40" S 49? 16' 22" O

Hello -

S?ren H?jsgaard wrote:
> Dear List
> 
> A 2-dimensional array seems to be "interpreted" as a matrix
whereas
> higher dimensional arrays are interpreted as arrays, e.g.
> 
>> a1 <- array(1:8,c(2,2,2)) class(a1)
> [1] "array"
>> a2 <- array(1:4,c(2,2)) class(a2)
> [1] "matrix"
> 
Note that is.matrix(a2) and is.array(a2) are both TRUE though.
> If I write a generic function (apologies if this is the wrong word)
> on arrays as
> 
> foo <- function(x) UseMethod("foo") foo.array <-
function(x) sum(x)
> 
> then this fails on a 2-dimensional array:
> 
>> foo(a1)
> [1] 36
>> foo(a2)
> Error in UseMethod("foo") : no applicable method for
"foo"
> 
> Is there any way in which I can "force" a2 to being
"interpreted" as
> having class "array" rather than "matrix" so that foo
will work on
> a2???
I don't know about that.  However, I see that both of the functions
duplicated.matrix and unique.matrix are copies of duplicated.array and 
unique.array, respectively.

Perhaps that's all you need to do?

foo.matrix <- foo.array

Maybe there is a better suggestion?

Best,
Erik Iverson

One more note:

>> Is there any way in which I can "force" a2 to being
"interpreted" as
>> having class "array" rather than "matrix" so that
foo will work on
>> a2???
> 
Maybe try?

a3 <- structure(1:10, dim = c(2,5), class = "array")

Then class(a3) gives "array", and is.matrix and is.array are both
still
TRUE.

Erik