[R] Stacking matrix columns

[Eric Berger]

Avi,

I was not trying to provide the most economical solution. I was trying
to anticipate that people (either the OP or others searching for how
to stack columns of a matrix) might be motivated by calculations in
multilinear algebra, in which case they might be interested in the
rTensor package.



On Sun, Aug 6, 2023 at 6:16 PM <avi.e.gross using gmail.com> wrote:
>
> Eric,
>
> I am not sure your solution is particularly economical albeit it works for arbitrary arrays of any dimension, presumably. But it seems to involve converting a matrix to a tensor just to undo it back to a vector. Other solutions offered here, simply manipulate the dim attribute of the data structure.
>
> Of course, the OP may have uses in mind which the package might make easier. We often get fairly specific questions here without the additional context that may help guide a better answer.
>
> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Eric Berger
> Sent: Sunday, August 6, 2023 3:34 AM
> To: Bert Gunter <bgunter.4567 using gmail.com>
> Cc: R-help Mailing List <r-help using r-project.org>; Steven Yen <styen using ntu.edu.tw>
> Subject: Re: [R] Stacking matrix columns
>
> Stacking columns of a matrix is a standard operation in multilinear
> algebra, usually written as the operator vec().
> I checked to see if there is an R package that deals with multilinear
> algebra. I found rTensor, which has a function vec().
> So, yet another way to accomplish what you want would be:
>
> > library(rTensor)
> > vec(as.tensor(x))
>
> Eric
>
>
> On Sun, Aug 6, 2023 at 5:05 AM Bert Gunter <bgunter.4567 using gmail.com> wrote:
> >
> > Or just dim(x) <- NULL.
> > (as matrices in base R are just vectors with a dim attribute stored in
> > column major order)
> >
> > ergo:
> >
> > > x
> >  [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20
> > > x<- 1:20  ## a vector
> > > is.matrix(x)
> > [1] FALSE
> > > dim(x) <- c(5,4)
> > > is.matrix(x)
> > [1] TRUE
> > > attributes(x)
> > $dim
> > [1] 5 4
> >
> > > ## in painful and unnecessary detail as dim() should be used instead
> > > attr(x, "dim") <- NULL
> > > is.matrix(x)
> > [1] FALSE
> > > x
> >  [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20
> >
> > ## well, you get it...
> >
> > -- Bert
> >
> > On Sat, Aug 5, 2023 at 5:21 PM Iris Simmons <ikwsimmo using gmail.com> wrote:
> > >
> > > You could also do
> > >
> > > dim(x) <- c(length(x), 1)
> > >
> > > On Sat, Aug 5, 2023, 20:12 Steven Yen <styen using ntu.edu.tw> wrote:
> > >
> > > > I wish to stack columns of a matrix into one column. The following
> > > > matrix command does it. Any other ways? Thanks.
> > > >
> > > >  > x<-matrix(1:20,5,4)
> > > >  > x
> > > >       [,1] [,2] [,3] [,4]
> > > > [1,]    1    6   11   16
> > > > [2,]    2    7   12   17
> > > > [3,]    3    8   13   18
> > > > [4,]    4    9   14   19
> > > > [5,]    5   10   15   20
> > > >
> > > >  > matrix(x,ncol=1)
> > > >        [,1]
> > > >   [1,]    1
> > > >   [2,]    2
> > > >   [3,]    3
> > > >   [4,]    4
> > > >   [5,]    5
> > > >   [6,]    6
> > > >   [7,]    7
> > > >   [8,]    8
> > > >   [9,]    9
> > > > [10,]   10
> > > > [11,]   11
> > > > [12,]   12
> > > > [13,]   13
> > > > [14,]   14
> > > > [15,]   15
> > > > [16,]   16
> > > > [17,]   17
> > > > [18,]   18
> > > > [19,]   19
> > > > [20,]   20
> > > >  >
> > > >
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