Re: [R] repeating rows or columns within a matrix

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From: Achim Zeileis (zeileis@ci.tuwien.ac.at)
Date: Thu 21 Mar 2002 - 21:45:16 EST 

Message-id: <3C99B9BC.7DF7C0F6@ci.tuwien.ac.at>

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@labour.fi
>
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