[R] rbind for matrices - rep argument

[Gabor Grothendieck]

For matrices you can use kronecker:

> kronecker(rep(1, 6), data.matrix(Xdf))
      [,1] [,2] [,3] [,4]
 [1,]  1.1  2.1  3.1  4.1
 [2,]  1.2  2.2  3.2  4.2
 [3,]  1.1  2.1  3.1  4.1
 [4,]  1.2  2.2  3.2  4.2
 [5,]  1.1  2.1  3.1  4.1
 [6,]  1.2  2.2  3.2  4.2
 [7,]  1.1  2.1  3.1  4.1
 [8,]  1.2  2.2  3.2  4.2
 [9,]  1.1  2.1  3.1  4.1
[10,]  1.2  2.2  3.2  4.2
[11,]  1.1  2.1  3.1  4.1
[12,]  1.2  2.2  3.2  4.2


On Wed, Jan 7, 2009 at 1:08 PM, Ted Harding
<Ted.Harding at manchester.ac.uk> wrote:
> On 07-Jan-09 15:22:57, Niccolò Bassani wrote:
>> Dear R users,I'm facing a trivial problem, but I really can't solve it.
>> I've tried a dozen of codes, but I can't get the result I want.
>> The question is: I have a dataframe like this one
>>
>> [,1] [,2] [,3] [,4] [,5]
>> [1,]    1    2    3    4    5
>> [2,]    2    5    5    4    9
>> [3,]    1    6    8    1    2
>> [4,]    8    6    4    1    5
>>
>> made up of decimal numbers, of course.
>> I want to append this dataframe to itself a number x of times, i.e. 3.
>> That is I want a dataframe like this
>>
>> [,1] [,2] [,3] [,4] [,5]
>> [1,]    1    2    3    4    5
>> [2,]    2    5    5    4    9
>> [3,]    1    6    8    1    2
>> [4,]    8    6    4    1    5
>> [5,]    1    2    3    4    5
>> [6,]    2    5    5    4    9
>> [7,]    1    6    8    1    2
>> [8,]    8    6    4    1    5
>> [9,]    1    2    3    4    5
>> [10,]    2    5    5    4    9
>> [11,]    1    6    8    1    2
>> [12,]    8    6    4    1    5
>>
>> I'm searching for an "authomatic" way to do this (I've already used the
>> rbind re-writing x times the name of the frame...), as it must enter a
>> function where one argument is exactly the number x of times to repeat
>> this frame.
>>
>> Any ideas??
>> Thanks in advance!
>> Niccolò
>
> I don't know whether there is anywhere a ready-made function which
> will implement a "rep" paramater for an rbind, but the following ad-hoc
> function will do it for you efficiently (i.e. with the minimum number
> of applications of the rbind() function).
>
> To produce a result which consists of k replicates of x, row-bound:
>
>
>  Krbind <- function(x,k){
>    y <- x
>    if(k==1) return(x)
>    p <- floor(log2(k))
>    for(i in (1:p)){
>      z <- rbind(y,y)
>      y <- z
>    }
>    k <- (k - 2^p)
>    if(k==0) return(y) else return(rbind(y,Krbind(x,k)))
>  }
>
> ## Example:
>
>  Xdf <- data.frame(X1=c(1.1,1.2),X2=c(2.1,2.2),
>                    X3=c(3.1,3.2),X4=c(4.1,4.2))
>
>  Krbind(Xdf,6)
> #     X1  X2  X3  X4
> # 1  1.1 2.1 3.1 4.1
> # 2  1.2 2.2 3.2 4.2
> # 3  1.1 2.1 3.1 4.1
> # 4  1.2 2.2 3.2 4.2
> # 5  1.1 2.1 3.1 4.1
> # 6  1.2 2.2 3.2 4.2
> # 7  1.1 2.1 3.1 4.1
> # 8  1.2 2.2 3.2 4.2
> # 9  1.1 2.1 3.1 4.1
> # 10 1.2 2.2 3.2 4.2
> # 11 1.1 2.1 3.1 4.1
> # 12 1.2 2.2 3.2 4.2
>
> Of course, if you're not worried by efficiency, then the simple loop
>
>  y <- x
>  for(i in (1:(k-1))){y <- rbind(y,x)}
>
> will do it!
>
> Hoping this helps,
> Ted.
>
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
> Fax-to-email: +44 (0)870 094 0861
> Date: 07-Jan-09                                       Time: 18:08:14
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