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

[Wensui Liu]

How about foreach() run in parallel?
On Oct 9, 2014 1:54 PM, "David L Carlson" <dcarlson at tamu.edu> 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...
> >
> > .
> >
>
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> ______________________________________________
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