[R] cbind in a loop...better way?

[Evan Cooch]

That works as well. I'll collate your response and a couple of others, 
and post tomorrow.

On 10/8/2014 4:17 PM, David L Carlson wrote:
> How about
>
>> do.call(cbind, lapply(env, as.vector))
>         [,1]  [,2]
>   [1,]  0.00  0.00
>   [2,]  0.05  0.15
>   [3,]  0.00  0.00
>   [4,] 20.00 15.00
>   [5,]  0.00  0.00
>   [6,]  0.10  0.20
>   [7,] 50.00 45.00
>   [8,]  0.00  0.00
>   [9,]  0.00  0.00
>
> -------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77840-4352
>
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Evan Cooch
> Sent: Wednesday, October 8, 2014 2:13 PM
> To: r-help at r-project.org
> Subject: [R] cbind in a loop...better way?
>
> ...or some such. I'm trying to work up a function wherein the user
> passes a list of matrices to the function, which then (1) takes each
> matrix, (2) performs an operation to 'vectorize' the matrix (i.e., given
> an (m x n) matrix x, this produces the vector Y of length  m*n that
> contains the columns of the matrix x, stacked below each other), and
> then (3) cbinds them together.
>
> Here is an example using the case where I know how many matrices I need
> to cbind together. For this example, 2 square (3x3) matrices:
>
>    a <- matrix(c,0,20,50,0.05,0,0,0,0.1,0),3,3,byrow=T)
>    b <- matrix(c(0,15,45,0.15,0,0,0,0.2,0),3,3,byrow=T)
>
> I want to vec them, and then cbind them together. So,
>
> result  <- cbind(matrix(a,nr=9), matrix(b,nr=9))
>
> which yields the following:
>
>         [,1]  [,2]
>    [1,]  0.00  0.00
>    [2,]  0.05  0.15
>    [3,]  0.00  0.00
>    [4,] 20.00 15.00
>    [5,]  0.00  0.00
>    [6,]  0.10  0.20
>    [7,] 50.00 45.00
>    [8,]  0.00  0.00
>    [9,]  0.00  0.00
>
> Easy enough. But, I want to put it in a function, where the number and
> dimensions  of the matrices is not specified. Something like
>
> Using matrices (a) and (b) from above, let
>
>     env <- list(a,b).
>
> Now, a function (or attempt at same) to perform the desired operations:
>
>     vec=function(matlist) {
>
>         n_mat=length(matlist);
>         size_mat=dim(matlist[[1]])[1];
>
>         result=cbind()
>
>          for (i in 1:n_mat) {
>            result=cbind(result,matrix(matlist[[i]],nr=size_mat^2))
>                             }
>
>        return(result)
>
>      }
>
>
> When I run vec(env), I get the *right answer*, but I am wondering if
> there is a *better* way to get there from here than the approach I use
> (above). I'm not so much interested in 'computational efficiency' as I
> am in stability, and flexibility.
>
> Thanks...
>
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