# [R] repeating rows or columns within a matrix

Achim Zeileis zeileis at ci.tuwien.ac.at
Thu Mar 21 11:45:16 CET 2002

```Juhana Vartiainen wrote:
>
> Hello
>
> Spse I have a matrix, say
>
> 1 2 3
> 4 5 6
> 7 8 9
>
> and I would like to expand it by repeating rows within the matrix, to
> get, if the repeating factor is 2, say:
>
> 123
> 123
> 456
> 456
> 789
> 789
>
> (or columnwise as well) . There must be a smart way of doing that?

You could do something like that:

R> mymatrix <- matrix(1:9, ncol=3)
R> myindex <- rep(1:nrow(mymatrix), rep(2, nrow(mymatrix)))
R> mymatrix[myindex,]
[,1] [,2] [,3]
[1,]    1    4    7
[2,]    1    4    7
[3,]    2    5    8
[4,]    2    5    8
[5,]    3    6    9
[6,]    3    6    9

Best,
Z

> Many thanks
>
> Juhana Vartiainen
> juhana.vartiainen at labour.fi
>
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```