Combining 3 arrays by row number

Question

Is there a way to combine three arrays in R so that the first row of the first array is followed by the first row of the second array and that is followed by the third row of the third array? So, if I ran the following code:

> number1<-rbind(rep("A",3), rep("B",3), rep("C",3))
> number1
     [,1] [,2] [,3]
[1,] "A"  "A"  "A" 
[2,] "B"  "B"  "B" 
[3,] "C"  "C"  "C" 
> number2<-rbind(rep(1,3), rep(2,3), rep(3,3))
> number2
     [,1] [,2] [,3]
[1,]    1    1    1
[2,]    2    2    2
[3,]    3    3    3
> number3<-rbind(rep("X",3), rep("Y",3), rep("Z",3))
> number3
     [,1] [,2] [,3]
[1,] "X"  "X"  "X" 
[2,] "Y"  "Y"  "Y" 
[3,] "Z"  "Z"  "Z"

The result would look like this:

      [,1] [,2] [,3]
 [1,] "A"  "A"  "A" 
 [2,] "1"  "1"  "1" 
 [3,] "X"  "X"  "X" 
 [4,] "B"  "B"  "B" 
 [5,] "2"  "2"  "2" 
 [6,] "Y"  "Y"  "Y" 
 [7,] "C"  "C"  "C" 
 [8,] "3"  "3"  "3" 
 [9,] "Z"  "Z"  "Z"

I have tried melt but I can't get it to work.

score 18 · Accepted Answer · answered Aug 26 '15 at 18:11

18

You could try this:

> matrix(t(cbind(number1,number2,number3)),ncol=3, byrow=T)
#      [,1] [,2] [,3]
# [1,] "A"  "A"  "A" 
# [2,] "1"  "1"  "1" 
# [3,] "X"  "X"  "X" 
# [4,] "B"  "B"  "B" 
# [5,] "2"  "2"  "2" 
# [6,] "Y"  "Y"  "Y" 
# [7,] "C"  "C"  "C" 
# [8,] "3"  "3"  "3" 
# [9,] "Z"  "Z"  "Z"

answered Aug 26 '15 at 18:11

RHertel

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Now, this is just some impressive deep understanding of `matrix` – Vlo Aug 26 '15 at 18:16
wow, I never would have guessed that. working from the inside out, I understand how it works until you get to the most outer function. How did you know it would do that? – user3390169 Aug 26 '15 at 18:26
I don't know how I came up with that. Probably just experience and some intuition. – RHertel Aug 26 '15 at 18:30

score 4 · Answer 2 · edited May 23 '17 at 10:29

Copying Arun's approach to interleaving two lists...

intermat <- function(...) 
  do.call(rbind,list(...))[ 
    order(sapply(list(...),function(x) 1:nrow(x))), ]

intermat(number1,number2,number3)

      [,1] [,2] [,3]
 [1,] "A"  "A"  "A" 
 [2,] "1"  "1"  "1" 
 [3,] "X"  "X"  "X" 
 [4,] "B"  "B"  "B" 
 [5,] "2"  "2"  "2" 
 [6,] "Y"  "Y"  "Y" 
 [7,] "C"  "C"  "C" 
 [8,] "3"  "3"  "3" 
 [9,] "Z"  "Z"  "Z"

This also "works" (i.e., does something sensible) for matrices with different numbers of rows.

score 0 · Answer 3 · answered Aug 26 '15 at 18:17

Kind of hacky, but since I'd typed it out before @RHertel posted a superior solution:

wrong_order <- rbind (number1, number2, number3)
row_n <- nrow (wrong_order)

right_order <- wrong_order[ 
  c(seq (1, row_n, by=3),
    seq (2, row_n, by=3),
    seq (3, row_n, by=3)
    ),
  ]

Combining 3 arrays by row number

3 Answers3