[R] replicate matrix blocks different numbers of times into new matrix

[Peter Dalgaard]

Ralph S. wrote:
> Hi,
>
> I am trying to replicate blocks of a matrix (defined by factors) into another matrix, but an unequal, consecutive number of times for each factor. 
>
> I need to find an elegant and fast way to do this, so loops will not work.
>
> An example of what I am trying to do is the following:
>
> # the data - first column entries are both data and the two factors
> x<-matrix(c(1,2,3,4),2,2)
>   
>> x
>>     
>      [,1] [,2]
> [1,]    1    3
> [2,]    2    4
>
> # the number of repetitions of the first and second factor
> n<-c(1,3)
>
> This is what I want as output:
>
>      [,1] [,2]
> [1,]    1    3
> [2,]    2    4
> [3,]    2    4
> [4,]    2    4
>
>
> Any ideas how to get there? I have tried using tapply with combination of rep, but this does not work (I need 1 and then 3 replications).
>
> Any help would be great!
>   
Will this do?

x[rep(1:2,n),]

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