Feature #15198



Added by c4am95 (Travis Hunter) over 5 years ago. Updated about 3 years ago.

Target version:


I frequently find myself needing to determine if two arrays intersect but not actually caring about the intersection, so I write code like:

(a1 & a2).any?

It would be nice to have an intersect? convenience method on Array to perform this query.

ruby#1972: Add Array#intersect?

Related issues 2 (1 open1 closed)

Related to Ruby master - Feature #16928: Array#include_all? & Array#include_any?OpenActions
Has duplicate Ruby master - Feature #15976: Add Array#overlap? for whether the intersection of 2 arrays is non empty?ClosedActions

Updated by shyouhei (Shyouhei Urabe) over 5 years ago

  • Interesting. Can you share a bit more detail about your "if two arrays intersect but not actually caring about the intersection" use case? For instance if you have open sourced such code, a URL for it helps us a lot.

  • If you have zero interest to the intersection itself I think you can avoid creating the temporary array.

Updated by c4am95 (Travis Hunter) over 5 years ago

The most recent example I encountered was authorizing a user in a Rails endpoint. Each user has a list of abilities, and each endpoint has a list of abilities that is authorized to perform the action. We just need to check if there is an intersection between the two lists.

I updated the PR to avoid creating the intermediate array.

Updated by shevegen (Robert A. Heiler) over 5 years ago

Demonstrated use cases helps the core team & matz assess on the usefulness of a proposed
change, which can help in accepting issue requests ultimately in the long run (if the
use case is considered sufficiently useful). :)

Updated by c4am95 (Travis Hunter) over 5 years ago

I threw together an example in a gist which is very similar to the use case I described. I have also run into numerous other situations where this functionality would have been useful.

I added some comments in the gist but I'll cross-post them here for reference:

The current behavior creates an intermediate array for both intersection tests when the resulting array is clearly not needed. With the desired behavior, we could avoid creating the intermediate array and produce a faster best case runtime.

Actions #6

Updated by matz (Yukihiro Matsumoto) over 4 years ago

  • Has duplicate Feature #15976: Add Array#overlap? for whether the intersection of 2 arrays is non empty? added

Updated by Dan0042 (Daniel DeLorme) over 4 years ago

It might make sense to use ary1.to_set.intersect?(ary2). That way it makes explicit the fact that ary1 must be converted to a set. But Set#intersect? would have to support any Enumerable.

Updated by c4am95 (Travis Hunter) over 4 years ago

I tried setting that up here:

I ignored infinite ranges for now

Actions #9

Updated by marcandre (Marc-Andre Lafortune) almost 4 years ago

  • Related to Feature #16928: Array#include_all? & Array#include_any? added

Updated by c4am95 (Travis Hunter) about 3 years ago

Matz/Marc-Andre: anything I can do to help here as far as documentation or providing more use cases? I/my colleagues would love to see this make it into Ruby.

Updated by marcandre (Marc-Andre Lafortune) about 3 years ago

  • Assignee set to matz (Yukihiro Matsumoto)

I am positive on the feature as has valid use cases, it can be optimized in C and as a bonus adds no cognitive load.

I believe we just need a final "yay" from Matz. I'll add it to the next meeting's agenda.

Updated by knu (Akinori MUSHA) about 3 years ago

We discussed this in today's developer meeting. Here are some remarks:

  • It takes one argument for now.
  • It means !(a & b).empty? instead of (a & b).any? so [nil].intersect?([nil]) evaluates to true.
  • The implementation will internally use a hash to match the behavior of Array#&.
Actions #14

Updated by nobu (Nobuyoshi Nakada) about 3 years ago

  • Status changed from Open to Closed

Applied in changeset git|b6bb4623ebcf1335cf0a81d279cde24a9e97bcce.

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