[Rd] is.matrix

[Christos Hatzis]

The point was that c(1, 1, 2) is not a matrix but a vector, two distinct
things in R.

> a <- c(1, 1, 2)
> class(a)
[1] "numeric"
> ta <- t(a)
> class(ta)
[1] "matrix"
> class(t(ta))
[1] "matrix"

The transpose operation is only defined for matrices, so if you insist to
apply it to a vector, it first needs to be coersed to a matrix and then
transposed.  The result of this operation is a matrix. The result of
transposing this matrix will still be a matrix.

-Christos 

> -----Original Message-----
> From: r-devel-bounces at r-project.org 
> [mailto:r-devel-bounces at r-project.org] On Behalf Of Daniel 
> Høyer Iversen
> Sent: Tuesday, November 11, 2008 2:36 PM
> To: hadley wickham
> Cc: Tony Plate; r-devel at r-project.org
> Subject: Re: [Rd] is.matrix
> 
> > That's confusing!  In what situations is x a matrix but 
> does not have 
> > a dim attribute?
> 
> That was my point. I don't find it logical that
> is.matrix(a) gives FALSE but
> is.matrix(t( t(a) )) gives TRUE.
> 
> I also think it would be more logical that
> a=c(1,1,2)
> dim(a) gives 3 1 instead of NULL,
> 
> 
> 
> Daniel
> 
> 
> 
> On Tue, Nov 11, 2008 at 8:21 PM, hadley wickham 
> <h.wickham at gmail.com> wrote:
> >> |  is.matrix| returns |TRUE| if |x| is a matrix and has a |dim 
> >> | <dim.html>|
> >> attribute of length 2) and |FALSE| otherwise
> >
> > That's confusing!  In what situations is x a matrix but 
> does not have 
> > a dim attribute?
> >
> > Hadley
> >
> > --
> > http://had.co.nz/
> >
> >
> 
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