# [R] Odp: Matrix

Petr PIKAL petr.pikal at precheza.cz
Mon Feb 2 17:05:10 CET 2009

```Hi

r-help-bounces at r-project.org napsal dne 02.02.2009 16:52:06:

>
> Hi,
>
> I have a very basic question on merging two matrices by alternating the
> rows. For illustration, assume two matrices -
>
> A looks like:
>
> 10 10
> 10 10
>
> B looks like:
>
> 20 20
> 20 20
>
> How do I combine them such that I get alternating rows from A and B? My
> final result should be C which looks like:
>
> 10 10
> 20 20
> 10 10
> 20 20

I would rbind both matrices and then indexed the resulting matrix.

x<-rep(10,4)
y<-rep(20,4)
dim(x)<-c(2,2)
dim(y)<-c(2,2)
z<-rbind(x,y)
> z
[,1] [,2]
[1,]   10   10
[2,]   10   10
[3,]   20   20
[4,]   20   20

ind<-c(seq(1,4,2), seq(2,4,2))
z[ind,]

> z[ind,]
[,1] [,2]
[1,]   10   10
[2,]   20   20
[3,]   10   10
[4,]   20   20

Regards
Petr

>
> Thanks very much, and I am sorry for such a newbie question.
>
> Shruthi
> --
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http://www.nabble.com/Matrix-tp21792064p21792064.html
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