From: "marcandre (Marc-Andre Lafortune)" <ruby-core@...>
Date: 2012-11-13T00:38:30+09:00
Subject: [ruby-core:49258] [ruby-trunk - Feature #6588] Set#intersect?


Issue #6588 has been updated by marcandre (Marc-Andre Lafortune).


alexeymuranov (Alexey Muranov) wrote:
> +1.  

Thanks for the +1

> It can be argued that any set intersects any other, just the intersection is sometimes empty :).

No, I believe it would be wrong to argue that. From wikipedia: "We say that A intersects B if A intersects B at some element"

Moreover: "We say that A and B are disjoint if A does not intersect B. In plain language, they have no elements in common"

I believe that both `intersect?` and `disjoint?` are the established terms for the concept I'm proposing.

----------------------------------------
Feature #6588: Set#intersect?
https://bugs.ruby-lang.org/issues/6588#change-32818

Author: marcandre (Marc-Andre Lafortune)
Status: Assigned
Priority: Normal
Assignee: knu (Akinori MUSHA)
Category: lib
Target version: next minor


There is `Set#superset?`, `Set#subset?` with their `proper` variants, but there is no `Set#intersect?` nor `Set#disjoint?`

To check if two sets intersect, one can do

  set.intersection(other).empty?

This cycles through all elements, though. To be efficient, one can instead do the iteration manually:

  other.any? { |x| set.include?(x) }

I think it would be natural to add `Set#intersect?` and its reverse `Set#disjoint?`

  class Set
    def intersect?(enum)
      enum.any? { |x| include?(x) }
    end
  end

Maybe it would be worth it to optimize it if enum is a larger Set by starting it with

      return any? { |x| enum.include?(x) } if enum.is_a?(Set) && enum.size > size



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