Tiling or repeating n-dimensional arrays in Julia

11
votes

I am looking for a general function to tile or repeat matrices along an arbitrary number of dimensions an arbitrary number of times. Python and Matlab have these features in NumPy's tile and Matlab's repmat functions. Julia's repmat function only seems to support up to 2-dimensional arrays.

The function should look like repmatnd(a, (n1,n2,...,nk)). a is an array of arbitrary dimension. And the second argument is a tuple specifying the number of times the array is repeated for each dimension k.

Any idea how to tile a Julia array on greater than 2 dimensions? In Python I would use np.tile and in matlab repmat, but the repmat function in Julia only supports 2 dimensions.

For instance, 

x = [1 2 3]
repmatnd(x, 3, 1, 3)

Would result in:

1 2 3
1 2 3
1 2 3

1 2 3
1 2 3
1 2 3

1 2 3
1 2 3
1 2 3

And for

x = [1 2 3; 1 2 3; 1 2 3]
repmatnd(x, (1, 1, 3))

would result in the same thing as before. I imagine the Julia developers will implement something like this in the standard library, but until then, it would be nice to have a fix.

1
matrixjulia
I believe the repeat function may be what you're looking for: docs.julialang.org/en/latest/stdlib/linalg/#Base.repeat. Sorry I keep answering with comments – don't really have the time/energy to write full answers with examples and all that jazz. – StefanKarpinski

1 Answers

14
votes

Use repeat:

julia> X = [1 2 3]
1x3 Array{Int64,2}:
 1  2  3

julia> repeat(X, outer = [3, 1, 3])
3x3x3 Array{Int64,3}:
[:, :, 1] =
 1  2  3
 1  2  3
 1  2  3

[:, :, 2] =
 1  2  3
 1  2  3
 1  2  3

[:, :, 3] =
 1  2  3
 1  2  3
 1  2  3