While reviewing a recent pull request in Images.jl, I ran across this line : cum_pmf_sq_2 = reverse!(cumsum(reverse!(prob_mass_function_sq))) Using reverse! is better than reverse here, but writing out the loops manually would certainly be more efficient. I’m wondering if it’s worthwhile to tr…

A ReverseView would compose better than extra keywords to functions. If the performance penalty is not too large, it would be my preferred solution, as a middle ground between optimized loops and copying operations.

[image] kevin.squire: @stevengj recently added Iterators.Reverse, but that doesn’t work here, as cumsum (which is based on accumulate) requires an AbstractArray, and Iterators.Reverse isn’t one of those. Is there a fundamental reason why accumulate couldn’t work with any iterator? It looks li…

[image] kevin.squire: Add a ReverseView wrapper to a Vector SubArray already supports this. Try view(a, lastindex(a):-1:firstindex(a)). (using Compat for firstindex and lastindex on 0.6.) Having an accumulate function that works on iterators would be great, though it is tricky to make fast…

Just a side-track: isn’t it possible to use series math to do, for instance, cumsum! on Iterators?

[image] yakir12: isn’t it possible to use series math to do, for instance, cumsum! on Iterators?` The iterator protocol in Julia provides no way to mutate the iterator contents.

[image] kevin.squire: Add a ReverseView wrapper to a Vector, which reverses the indexes (and therefore iteration), but otherwise leaves the data alone. Could it support multi-dimensional arrays too? Via a dim keyword, R = ReverseView(A; dims=(2,4)) would reverse indices along dimensions 2 …

[image] e3c6: Could it support multi-dimensional arrays too? Via a dim keyword, This already works: R = @view A[axes(A,1), reverse(axes(A,2)), axes(A,3), reverse(axes(A,4))] It would be convenient to just do I = CartesianIndices(A) R = @view A[reverse(I, dims=(2,4))] but I noticed that re…

Reverse view of an array

Internals & Design

Topic		Replies	Views
How to `accumulate` from right efficiently? New to Julia	16	3594	September 27, 2018
Cumsum reversed? General Usage	6	984	October 7, 2021
How to create a reversed view that allows for growing arrays? General Usage	3	382	March 16, 2023
Reversed Arrays General Usage	3	658	February 6, 2018
Reverse multidimensional array General Usage array , arrays	6	2143	January 22, 2021

Reverse view of an array

Related topics