Replicating 2 dimensional matrix to create a 3 dimensional array (in R)

Question

I have a two dimensional matrix that I would like to replicate 10 times to create a three dimensional array where each 'slice' of the array is an identical copy of the two dimensional array.

So, if my 2D array were to be:

a <- matrix(c(1:4),nrow=2)
> a
     [,1] [,2]
[1,]    1    2
[2,]    3    4

I would like as output an array like this:

, , 1

     [,1] [,2]
[1,]    1    2
[2,]    3    4

, , 2

     [,1] [,2]
[1,]    1    2
[2,]    3    4

....

, , 10

     [,1] [,2]
[1,]    1    2
[2,]    3    4

I have seen this page (Duplicate matrix to form list), in which the OP was looking to duplicate matrices to a list, which I adapted to then convert to an array:

b<-rep(list(a), 10) # from original post
array(unlist(b), dim = c(nrow(b[[1]]), ncol(b[[1]]), length(b))) # line I added

This works fine but it's a little roundabout - I was wondering if there were a way to do this in one line without going through the creation of a list.

I tried applying the logic of a do.call in the way that is done with rbind to bind multiple rows together, but using abind instead -

do.call(abind,as.list(c(a,a,a,a,a,a,a,a,a,a))) 

but the output was one long vector and so not what I was looking for.

Any help is greatly appreciated!

Answer 1

you can use replicate, which produces a list by default. To get an array, add simplify = "array".

replicate(10, a, simplify="array")

, , 1

     [,1] [,2]
[1,]    1    3
[2,]    2    4

, , 2

     [,1] [,2]
[1,]    1    3
[2,]    2    4

...

, , 9

     [,1] [,2]
[1,]    1    3
[2,]    2    4

, , 10

     [,1] [,2]
[1,]    1    3
[2,]    2    4