[Rd] several bugs (PR#918) lists and matrices

Thomas Lumley tlumley@u.washington.edu
Mon, 23 Apr 2001 15:51:48 -0700 (PDT)

On 24 Apr 2001, Peter Dalgaard BSA wrote:

> Thomas Lumley <tlumley@u.washington.edu> writes:
> > This is a more difficult question.  You can't put a list into a matrix.
> > Matrices handle homogenous data; they are vectors with a dimension
> > attribute.  Lists with an arbitrary dimension attribute are, as Rob
> > pointed out, an unimplemented bug.
> Ummm. I'd have to say that it is an implemented bug if a bug at all.
> tapply() does this all the time (although most often by accident), and
> is even documented to do so. If one can have a list with a dim(), not
> being able to index such a beast does look like a bug to me...

Strange. I had assumed that an array of mode list looked like a vector of
LISTSXPs, but it seems that it looks like a list with dimensions.

You can index it, with [[]]
> a<-list(1,2,3,4)
> dim(a)<-c(2,2)
> a
     [,1]        [,2]
[1,] "Numeric,1" "Numeric,1"
[2,] "Numeric,1" "Numeric,1"
> a[2,1]

> a[[2,1]]
[1] 2
which is weird. The question is then what a[2,1] thinks it's returning.

You still can't stick a list into an array of numbers, which is what Rich
needs, and is better handled with data frames.

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