Concatenating 2D generator of arrays

New to Julia
1

Hi, I’m trying to concatenate an 2D generator that generate an 2D array of 2x2 arrays, such as this one
iter = (rand(2,2) for i in 1:d1, j in 1:d2 )
I would need to concatenate these arrays into a 2 by d1 by 2 by d2 array, ideally w/o first generating an array of wrong permutation and then permute. I tried cat(iter..., dims=(1,3)) or cat(iter..., dims=(2,4)), neither worked.

I also read a little about this thread, however, I don’t want to collect(iter) before the concatenation or use LazyArrays as the latter is probably not as efficient when later used for LA operations. In other words, I want the memory to be allocated exactly as specified dimensions.

So what is the right way to generate this concatenation correctly?

Thank you!

2

If you can afford collecting your iter generator:

julia> using SplitApplyCombine

julia> combinedims([rand(2,2) for i in 1:3, j in 1:5], (2, 4))
2×3×2×5 Array{Float64, 4}:
...

If you need to keep the generator lazy and only materialize the final array:

julia> using SplitApplyCombine, GeneratorArrays

julia> combinedims(array(rand(2,2) for i in 1:3, j in 1:5), (2, 4))
2×3×2×5 Array{Float64, 4}:
...

Alternatively, see mapview() in SplitApplyCombine.jl for lazy arrays.

Note that the first - eager - approach can be faster than the lazy one.