From: sin@... Date: 2019-10-07T06:57:11+00:00 Subject: [ruby-core:95257] [Ruby master Feature#16155] Add an Array#intersection method Issue #16155 has been updated by prajjwal (Prajjwal Singh). Implementation is currently based on `Array#&`, which is elegant but might end up allocating a whole bunch of arrays holding intermediate results. If needed I can implement `Array#intersection` so it only allocates the result array once, but then I would like to rewrite `Array#&` in terms of `Array#intersection` to keep things DRY. ```ruby static VALUE rb_ary_intersection_multi(int argc, VALUE *argv, VALUE ary) { VALUE result = rb_ary_dup(ary); int i; for (i = 0; i < argc; i++) { result = rb_ary_and(result, argv[i]); } return result; } ``` Let me know what you think. ---------------------------------------- Feature #16155: Add an Array#intersection method https://bugs.ruby-lang.org/issues/16155#change-81934 * Author: connorshea (Connor Shea) * Status: Open * Priority: Normal * Assignee: * Target version: ---------------------------------------- `Array#union` and `Array#difference` were added in Ruby 2.6 ([see this bug](https://bugs.ruby-lang.org/issues/14097)), but an equivalent for `&` (intersection) was not. I'd like to propose `Array#intersection`. This would essentially just be a more readable alias for `Array#&`, in the same way that `Array#|` and `Array#-` have `Array#union` and `Array#difference`. I think it'd make sense for Ruby to have a more readable name for this method :) Current syntax: ``` ruby [ 1, 1, 3, 5 ] & [ 3, 2, 1 ] #=> [ 1, 3 ] [ 'a', 'b', 'b', 'z' ] & [ 'a', 'b', 'c' ] #=> [ 'a', 'b' ] ``` What I'd like to see added: ```ruby [ 1, 1, 3, 5 ].intersection([ 3, 2, 1 ]) #=> [ 1, 3 ] [ 'a', 'b', 'b', 'z' ].intersection([ 'a', 'b', 'c' ]) #=> [ 'a', 'b' ] ``` mame asks about `intersection` [in this comment](https://bugs.ruby-lang.org/issues/14097#note-26) on the `union`/`difference` bug, but as far as I can tell it was never addressed. [`Set#intersection`](http://ruby-doc.org/stdlib-2.6.2/libdoc/set/rdoc/Set.html#method-i-intersection) already exists and is an alias for `Set#&`, so there's precedent for such a method to exist. Thanks for Ruby, I enjoy using it a lot! :) Related links: - [PR for `union`](https://github.com/ruby/ruby/pull/1747) - [PR for `difference`](https://github.com/ruby/ruby/pull/1758) - [Bug for adding `union` and `difference` methods](https://bugs.ruby-lang.org/issues/14097) -- https://bugs.ruby-lang.org/ Unsubscribe: