My (non strident) assertion was about

matrices, not about matrix lists (which nobody said that would not exist).

In your example you omit the fact that

is.list(m) also results in TRUE:

m <- list(a1=1:3, a2=4:6, a3=pi, a4=c("a","b","c"))

dim(m) <- c(2,2)

is.matrix(m) [1] TRUE

is.list(m) [1] TRUE

m[1,1]

[[1]]dim(m) <- c(2,2)

is.matrix(m) [1] TRUE

is.list(m) [1] TRUE

m[1,1]

NULL

So it's a matrix and it's a list.

The NULL result of m[1,1] (that I pointed to you), might be, as you say, a

bug. But in any case, objects such as m in the example

are not what most people would understand as a matrix.

It's a different type of object. And the original message said

" ...I tried to create a matrix from a list..."

The "normal" matrix would yield FALSE for is.list():

m <- list(a1=1:2, a2=4:5)

m <- unlist(m)

dim(m) <- c(2,2)

is.matrix(m) [1] TRUE

is.list(m) [1] FALSE

m[1,1]

[1] 1m <- unlist(m)

dim(m) <- c(2,2)

is.matrix(m) [1] TRUE

is.list(m) [1] FALSE

m[1,1]

On Tue, 26 Feb 2002, Prof Brian D Ripley wrote:

Perhaps the following example will help demonstrate that matrix lists do

exist and do work up to a point, despite strident assertions on R-help to

the contrary:

[1,] "Numeric,3" "Numeric,1"

[2,] "Numeric,3" "Character,3"

In S m[2,2] extracts a sub-list, but that seems not to work correctly in R:

neither does m[,2]. I am reporting that as a bug.

--

Brian D. Ripley, ripley at stats.ox.ac.uk

Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/

University of Oxford, Tel: +44 1865 272861 (self)

1 South Parks Road, +44 1865 272860 (secr)

Oxford OX1 3TG, UK Fax: +44 1865 272595

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Perhaps the following example will help demonstrate that matrix lists do

exist and do work up to a point, despite strident assertions on R-help to

the contrary:

m <- list(a1=1:3, a2=4:6, a3=pi, a4=c("a","b","c"))

dim(m) <- c(2,2)

m

[,1] [,2]dim(m) <- c(2,2)

m

[1,] "Numeric,3" "Numeric,1"

[2,] "Numeric,3" "Character,3"

is.matrix(m) [1] TRUE

m[[1,2]]

[1] 3.141593

m[[2,2]]

[1] "a" "b" "c"m[[1,2]]

[1] 3.141593

m[[2,2]]

In S m[2,2] extracts a sub-list, but that seems not to work correctly in R:

neither does m[,2]. I am reporting that as a bug.

--

Brian D. Ripley, ripley at stats.ox.ac.uk

Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/

University of Oxford, Tel: +44 1865 272861 (self)

1 South Parks Road, +44 1865 272860 (secr)

Oxford OX1 3TG, UK Fax: +44 1865 272595

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