JuliaLang/julia

Make `cumsum(A)` compute a summed-area table

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#26,412 opened on Mar 10, 2018

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 (8 comments) (3 reactions) (0 assignees)Julia (48,709 stars) (5,773 forks)batch import
arraysgood first issue

Description

The idea has been discussed in a few places (e.g. https://github.com/JuliaLang/julia/issues/20041#issuecomment-275938676) to make cumsum(A) return a summed-area table for multidimensional arrays.

The 1D case is already a summed-area table, since that's just the cumulative sum along the one dimension.

Happily, the appropriate deprecation for cumsum — deprecating it for AbstractArrays with no dims argument — is already in place, so this is just a tracking issue for the idea.

cc: @simonbyrne

Contributor guide

Tech stack
None
Domain
data
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
needs investigation
Prerequisites
Understanding of cumsumFamiliarity with summed area tableJulia development environment
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Study the existing `cumsum` implementation in Julia's base library, particularly the files `base/summary.jl` or `base/reduce.jl`. Understand how `cumsum` currently handles dimensions and the deprecation of the no dim argument. Investigate the summed area table algorithm for multidimensional arrays and how it can be implemented efficiently using cumulative sums along each dimension. Explore the linked discussion in issue #20041 for further context and potential design decisions.