# [R] Combining matrices

Daniel Nordlund djnordlund at verizon.net
Mon Aug 24 19:08:14 CEST 2009

```> -----Original Message-----
> From: Marc Schwartz [mailto:marc_schwartz at me.com]
> Sent: Monday, August 24, 2009 9:57 AM
> To: Daniel Nordlund
> Cc: r help
> Subject: Re: [R] Combining matrices
>
>
> On Aug 24, 2009, at 11:46 AM, Marc Schwartz wrote:
>
> >
> > On Aug 24, 2009, at 11:16 AM, Daniel Nordlund wrote:
> >
> >> If I have two matrices like
> >>
> >> x <- matrix(rep(c(1,2,3),3),3)
> >> y <- matrix(rep(c(4,5,6),3),3)
> >>
> >> How can I combine  them to get ?
> >>
> >> 1 1 1 4 4 4
> >> 1 1 1 5 5 5
> >> 1 1 1 6 6 6
> >> 2 2 2 4 4 4
> >> 2 2 2 5 5 5
> >> 2 2 2 6 6 6
> >> 3 3 3 4 4 4
> >> 3 3 3 5 5 5
> >> 3 3 3 6 6 6
> >>
> >> The number of rows and the actual numbers above are unimportant,
> >> they are given so as to illustrate how I want to combine the
> >> matrices.  I.e., I am looking for a general way to combine the
> >> first row of x with each row of y, then the second row of x with
> >> y, ....
> >>
> >> Thanks,
> >>
> >> Dan
> >
> >
> >
> > nr.x <- nrow(x)
> > nr.y <- nrow(y)
> >
> > > cbind(x[rep(1:nr.x, each = nr.x), ], y[rep(1:nr.y, nr.y), ])
> >      [,1] [,2] [,3] [,4] [,5] [,6]
> > [1,]    1    1    1    4    4    4
> > [2,]    1    1    1    5    5    5
> > [3,]    1    1    1    6    6    6
> > [4,]    2    2    2    4    4    4
> > [5,]    2    2    2    5    5    5
> > [6,]    2    2    2    6    6    6
> > [7,]    3    3    3    4    4    4
> > [8,]    3    3    3    5    5    5
> > [9,]    3    3    3    6    6    6
>
>
>
> Actually, correction...that will work in this case, but in
> the general
> case, I believe that it needs to be:
>
> x <- matrix(rep(c(1,2,3),3),3)
> y <- matrix(rep(c(4,5,6,7),3),4)
>
>  > x
>       [,1] [,2] [,3]
> [1,]    1    1    1
> [2,]    2    2    2
> [3,]    3    3    3
>
>  > y
>       [,1] [,2] [,3]
> [1,]    4    4    4
> [2,]    5    5    5
> [3,]    6    6    6
> [4,]    7    7    7
>
>
> nr.x <- nrow(x)
> nr.y <- nrow(y)
>
>
>  > cbind(x[rep(1:nr.x, each = nr.y), ], y[rep(1:nr.y, nr.x), ])
>        [,1] [,2] [,3] [,4] [,5] [,6]
>   [1,]    1    1    1    4    4    4
>   [2,]    1    1    1    5    5    5
>   [3,]    1    1    1    6    6    6
>   [4,]    1    1    1    7    7    7
>   [5,]    2    2    2    4    4    4
>   [6,]    2    2    2    5    5    5
>   [7,]    2    2    2    6    6    6
>   [8,]    2    2    2    7    7    7
>   [9,]    3    3    3    4    4    4
> [10,]    3    3    3    5    5    5
> [11,]    3    3    3    6    6    6
> [12,]    3    3    3    7    7    7
>
>
> We need to replicate each row by the number of rows in the
> other matrix.
>
> HTH,
>
> Marc
>

Thanks to all who responded (including those off-list).  I now have options
to apply to solving my programming task.

Thanks,

Dan

```