[R] Re: Matrix of Elements of Different Types (was Interfacing pre-existing C++ library from R)

[Agustin Lobo]

On Tue, 26 Feb 2002, Gabor Grothendieck wrote:

> - what is the difference between my.list$dim<- and dim(my.list)<- ?

my.list$dim refers to the element called dim in my.list, it's a
piece of your information. 
dim(my.list) refers to the dimension attribute of the object
called my.list, it's an information on how the data are arranged in
the object:

> my.list <- list(a1="1",a2=c(1,2,3),a3=1:5,dim=c(2,2))
Information kept in my.list:
> my.list$a2
[1] 1 2 3
> my.list$dim
[1] 2 2

Instead, information on my.list:

> dim(my.list) <- c(2,2)
> attributes(my.list)
$dim
[1] 2 2
> attributes(my.list)$dim
[1] 2 2

The attributes of an object are organized in a list.


For a matrix it would be equivalent: one thing 
are the cell elements, another the dimension of the matrix (that is,
how you want the elements to be organized).
> x <- matrix(1:12,ncol=3)
> x[1,1]
[1] 1
> dim(x)
[1] 4 3
which is equivalent to:
> attributes(x)$dim
[1] 4 3


> - after creating the matrix with both numbers and my.lm elements in it
>   I tried to convert it to a data frame.  I tried data.frame(my.mat)
>   and as.data.frame(my.mat) but using R 1.4.0 on Windows 2000 I got
> Error in format(unlist(x), trim = trim) : first argument must be atomic
>   for both.  Is it possible to convert my.mat to a data frame?

What's the goal? I mean, what information you have and how you want it
organized? 

Agus


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