Determine if one array contains all elements of another array

Question

I need to tell if an array contains all of the elements of another array with duplicates.

[1,2,3].contains_all? [1,2]   #=> true
[1,2,3].contains_all         


        

Answer 1

Answering with my own implementation, but definitely want to see if someone can come up with a more efficient way. (I won't accept my own answer)

class Array
  def contains_all?(a2)
    a2.inject(self.dup) do |copy, el|
      if copy.include? el
        index = copy.index el
        copy.delete_at index
      else
        return false
      end
      copy
    end
    true
  end
end

And the tests:

1.9.3p194 :016 > [1,2,3].contains_all? [1,2]   #=> true
 => true 
1.9.3p194 :017 > [1,2,3].contains_all? [1,2,2] #=> false (this is where (a1-a2).empty? fails)
 => false 
1.9.3p194 :018 > [2,1,2,3].contains_all? [1,2,2] #=> true
 => true