How can I check if a Ruby array includes one of several values?

Question

I have two Ruby arrays, and I need to see if they have any values in common. I could just loop through each of the values in one array and do include?() on the other, but I'm sure there's a better way. What is it? (The arrays both hold strings.)

Thanks.

Answer 1

Set intersect them:

a1 & a2

Here's an example:

> a1 = [ 'foo', 'bar' ]
> a2 = [ 'bar', 'baz' ]
> a1 & a2
=> ["bar"]

Answer 2

Any value in common ? you can use the intersection operator : &

[ 1, 1, 3, 5 ] & [ 1, 2, 3 ]   #=> [ 1, 3 ]

If you are looking for a full intersection however (with duplicates) the problem is more complex there is already a stack overflow here : http://stackoverflow.com/questions/1600168/how-to-return-a-ruby-array-intersection-with-duplicate-elements-problem-with-bi

Or a quick snippet which defines "real_intersection" and validates the following test

class ArrayIntersectionTests < Test::Unit::TestCase    
  def test_real_array_intersection
    assert_equal [2], [2, 2, 2, 3, 7, 13, 49] & [2, 2, 2, 5, 11, 107]
    assert_equal [2, 2, 2], [2, 2, 2, 3, 7, 13, 49].real_intersection([2, 2, 2, 5, 11, 107])
    assert_equal ['a', 'c'], ['a', 'b', 'a', 'c'] & ['a', 'c', 'a', 'd']
    assert_equal ['a', 'a', 'c'], ['a', 'b', 'a', 'c'].real_intersection(['a', 'c', 'a', 'd'])
  end
end