several bugs (PR#918) lists and matrices

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]

[[1]]
NULL

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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