From: Erik Iverson <iverson_at_biostat.wisc.edu>

Date: Tue, 04 Mar 2008 18:30:33 -0600

> [1] "array"

> [1] "matrix"

*>
*

> [1] 36

> 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???
*

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Wed 05 Mar 2008 - 00:33:59 GMT

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"

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

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