JuliaLang/julia

Ellipsis slicing

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#5,405 opened on Jan 15, 2014

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 (29 comments) (8 reactions) (0 assignees)Julia (48,709 stars) (5,773 forks)batch import
arrayshelp wantedparser

Description

Numpy has this ellipsis notation for filling index tuples up to dimension, where in A[..., i, k] ... is interpreted as shorthand for the number of colons :, :, : etc needed to fill the indexing tuple up to dimension n.

http://docs.scipy.org/doc/numpy/reference/arrays.indexing.html

This gives nice access to contiguous subarrays in the dense array case and would be not more harmful than the : notation itself.

Was this feature already considered? It was mentioned by @toivoh on the mailing list, but did not trigger discussion.

Contributor guide

Tech stack
None
Domain
backend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
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.
clear
Prerequisites
Julia array indexingJulia parser internalsNumpy ellipsis notation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
15
Research direction
Investigate how Julia currently handles array indexing with ':' and n dimensional slices. Look at the parser and indexing implementation in Julia's source (e.g., `src/julia parser.scm` or `base/abstractarray.jl`). Consider how to parse '...' as an operator that expands to appropriate number of colons. Study numpy's implementation for reference. Check existing comments in the issue for suggested approaches.