Extending rep to matrices?

Question

If you call rep on a matrix, it repeats its elements rather than the entire matrix. The traditional fix is to call rep(list(theMatrix),...). I want to extend rep so that it does this automatically.

I attempted to use

rep.matrix<-function(x,...) rep(list(x),...)

which did indeed add rep.matrix to methods(rep)

> methods(rep)
[1] rep.bibentry*       rep.Date            rep.factor          rep.matrix         
[5] rep.numeric_version rep.POSIXct         rep.POSIXlt         rep.roman*         
see '?methods' for accessing help and source code

However, calling rep on a matrix did not appear to dispatch to rep.matrix.

> rep(diag(5),3)
 [1] 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0
[42] 0 0 1 0 0 0 0 0 1 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1

Although direct calls to rep.matrix worked without error.

> rep.matrix(diag(5),3)
[[1]]
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    0    0    0    0
[2,]    0    1    0    0    0
[3,]    0    0    1    0    0
[4,]    0    0    0    1    0
[5,]    0    0    0    0    1

[[2]]
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    0    0    0    0
[2,]    0    1    0    0    0
[3,]    0    0    1    0    0
[4,]    0    0    0    1    0
[5,]    0    0    0    0    1

[[3]]
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    0    0    0    0
[2,]    0    1    0    0    0
[3,]    0    0    1    0    0
[4,]    0    0    0    1    0
[5,]    0    0    0    0    1

I get the same outcomes if I create and use rep.array instead of rep.matrix.

Where is my error? Why isn't rep dispatching to rep.matrix? Did I use the wrong object system somehow?

Looks like a bug in `rep()`. You should report it. – user2554330 Feb 19 '21 at 22:43 — user2554330, Feb 19 '21 at 22:43
@user2554330 How did you come to that conclusion? – J. Mini Feb 20 '21 at 01:11 — J. Mini, Feb 20 '21 at 01:11

score 3 · Accepted Answer · answered Mar 11 '21 at 19:25

This cannot be done. The documentation is not too forthcoming about this fact, but rep is an internal generic function, as explained here. This means that it will only dispatch to things where is.object returns TRUE. Matrices are not such a thing, so you cannot extend rep to matrices and have it dispatch to them.

Extending rep to matrices?

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