Re: [R] How to make a 2-dim array being "interpreted" as an array rather than as a matrix

From: Erik Iverson <>
Date: Tue, 04 Mar 2008 18:30:33 -0600

Hello -

Søren Højsgaard 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?

Erik Iverson mailing list PLEASE do read the posting guide and provide commented, minimal, self-contained, reproducible code. Received on Wed 05 Mar 2008 - 00:33:59 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Wed 05 Mar 2008 - 01:30:20 GMT.

Mailing list information is available at Please read the posting guide before posting to the list.

list of date sections of archive