Issue #16155 has been updated by connorshea (Connor Shea).


shevegen (Robert A. Heiler) wrote:
> You could consider adding this to the upcoming developer meeting:
> 
> https://bugs.ruby-lang.org/issues/16152
> 
> And ask matz whether he would be fine with the functionality 
> itself; or, more importantly, the name for the method
> (#intersection) since the functionality already exists.

Thanks, I will :)

After thinking about the proposal a bit more, one other thing I wanted to ask was about whether we should allow multiple arrays to be passed as arguments. `Array#difference` and `Array#union` both allow this, so it might make sense to have `Array#intersection` also take multiple arguments.

For example:

```ruby
# intersection with multiple arguments.
[ 'a', 'b', 'b', 'z' ].intersection([ 'a', 'b', 'c' ], [ 'b' ])  #=> [ 'b' ]
```

Should we keep `intersection` as a simple alias for `&` or have it allow multiple arrays, to match the `difference` and `union` methods?

----------------------------------------
Feature #16155: Add an Array#intersection method
https://bugs.ruby-lang.org/issues/16155#change-81487

* 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)



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