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

[Evan Cooch]

Thanks!

On 10/9/2014 1:52 PM, David L Carlson wrote:
> Actually Jeff Laake's can be made even shorter with
>
> sapply(mat_list, as.vector)
>
> David C
>
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Evan Cooch
> Sent: Thursday, October 9, 2014 7:37 AM
> To: Evan Cooch; r-help at r-project.org
> Subject: Re: [R] cbind in a loop...better way? | summary
>
> Two solutions proposed -- not entirely orthogonal, but both do the
> trick. Instead of nesting cbin in a loop (as I did originally -- OP,
> below),
>
> 1\   do.call(cbind, lapply(mat_list, as.vector))
>
> or
>
> 2\   sapply(mat_list,function(x) as.vector(x))
>
>
> Both work fine. Thanks to Jeff Laake (2) + David Carlson (1) for their
> suggestions.
>
>
> On 10/8/2014 3:12 PM, Evan Cooch wrote:
>> ...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...
>>
>> .
>>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> .
>