Hi guys, I am trying to permute/shuffle columns of a multidimensional array, an example is here: using BenchmarkTools const arra = zeros(Int, 4, 3, 2) arra[:,:, 1] = 1:12 arra[:,:, 2] = 13:24 shuffle_col = [3, 1, 1] @benchmark arra[:, shuffle_col, :] #solution 1 - works but allocates @benchmark…

Did you test your function? I think it must overwrite some elements before they are used.

Thanks it should work now! But my try is now even worse than before as I needed the copy to not overwrite it in a loop.

AFAIK permuting arrays in place in general is not a trivial problem. If allocation (and not copying) is the costly part per se, perhaps you should just preallocate for output .

Preallocation is unfortunately not possible as I need to shuffle the array in a loop and the object of interest is the array itself ( a filtering problem).

Could you elaborate on this ? In place permutations are really difficult to optimize. In 3D you have to compute some permutation cycles… In general out of place (with pre-allocation + ptr swap) permutations are much easier to implement and perform better. If it is simple permutedims you can tile.

Here would be a dummy code of what I have to do: #Input observations = Matrix(T,P) #Algorithm function myproblem(observations, k, ....) #initialize trajectory trajectories = Matrix(T,M,N) for i in 1:T #get column order weights = somefunction(observations[1:i,:], trajec…

(Realize that array[:,i,:] = temp[:,permute,:] allocates an a extra copy of the temp[:,permute,:] slice unless you use @views.) [image] mrVeng: There is a base function permute! in Julia but it only works on vector elements, not on whole columns There actually is an undocumented Base.permute…

[image] stevengj: Base.permutecols!!(A, p) Thank you a lot! I tried to get it to run in Julia 1.2, but failed so far. I will think about how I could extend it to more dimension without copying at least p.

Permute Multidimensional Array without allocation

General Usage

anon92994695 September 25, 2019, 10:48am 4

I’ve been stuck trying to solve this problem too! I have a use case for this kind of mechanism that I haven’t been able to crack: Complex Numbers Wrappers

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Permute Multidimensional Array without allocation

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