[R] Stacking matrix columns

[@vi@e@gross m@iii@g oii gm@ii@com]

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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