[R] storing matrices in a list or vector and preserve dimensions

[Gabor Csardi]

Bram,

On Tue, Jan 08, 2008 at 03:11:07PM +0100, Bram Kuijper wrote:
> Hi all,
> 
> As an R newbie, I wonder how I can store multiple matrices in a list() 
> or vector() object without losing their structure. I should be able to 
> retrieve the matrix from the list later on.
> 
> If I just append() the matrices to a list() object, they automatically 
> lose their dimensions, whereas I would like to preserve the dimensions 
> of the matrices.

append concatenates two list (as far as i can remember), but not a 
list and a list element. A simple workaround is to use 

l <- append(l, list(e))

instead of 

l <- append(l, e)

> Is there any function in R which allows me to store a _fully preserved_ 
> object inside a list() or vector() structure?

You can also do things like 

l <- list(1,2,3)
l[[2]] <- 5
l[[10]] <- matrix(runif(100), 10, 10)

etc. For more you should really read 'Introduction to R', 
see the documentation links on the R homepage.

Gabor

> thanks in advance,
> 
> Bram Kuijper
> 
> 
> 
> 
> PS: this is what I do:
> 
> # two matrices, which are my objects to be put in the list
> my_matrix_object1 <- matrix(data=rep(1,times=9),nrow=3,ncol=3);
> my_matrix_object2 <- matrix(data=rep(0,times=9),nrow=3,ncol=3);
> 
> my_list <- list()
> # note that I explicitly want to append the object to the list
> # instead of directly inserting it from the beginning
> # (e.g., code to be used in a for-loop)
> my_list <- append(my_list,as.matrix(my_matrix_object1));
> my_list <- append(my_list,as.matrix(my_matrix_object2));
> 
> However, this results in the following list structure...
> [[1]]
> [1] 1
> 
> [[2]]
> [1] 1
> 
> [[3]]
> [1] 1
> 
> ... etcetera,
> 
> whereas I just want to preserve the matrix structure in my list:
> 
> my_matrix_object1;
>       [,1] [,2] [,3]
> [1,]    1    1    1
> [2,]    1    1    1
> [3,]    1    1    1
> ,
>       [,1] [,2] [,3]
> [1,]    0    0    0
> [2,]    0    0    0
> [3,]    0    0    0
> 
> I guess I need a more sophisticated function then append, but I do not 
> know which one?
> 
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-- 
Csardi Gabor <csardi at rmki.kfki.hu>    MTA RMKI, ELTE TTK