[Rd] is.matrix
Peter Dalgaard
P.Dalgaard at biostat.ku.dk
Tue Nov 11 19:31:17 CET 2008
Daniel Høyer Iversen wrote:
> a=c(1,1,2);
> is.matrix(a) gives FALSE
> is.matrix(t(a)) gives TRUE
> is.matrix(t(t(a))) gives TRUE
>
> Is this correct? Shouldn't all give FALSE?
> I think is.matrix should give FALSE when dimension is 1*n or n*1.
No this is correct. is.matrix() returns TRUE if and only if the argument
has a two-dimensional 'dim' attribute, and
> dim(a)
NULL
> dim(t(a))
[1] 1 3
> dim(t(t(a)))
[1] 3 1
(And is.array() depends on having a 'dim' attribute of positive length, so
> dim(a) <- 3
> is.matrix(a)
[1] FALSE
> is.array(a)
[1] TRUE
)
--
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