[R] repeating rows or columns within a matrix

[Achim Zeileis]

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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