Find values in common between two arrays

Question

If I want to compare two arrays and create an interpolated output string if an array variable from array y exists in x how can I get an output for each

Answer 1

OK, so the & operator appears to be the only thing you need to do to get this answer.

But before I knew that I wrote a quick monkey patch to the array class to do this:

class Array
  def self.shared(a1, a2)
    utf = a1 - a2 #utf stands for 'unique to first', i.e. unique to a1 set (not in a2)
    a1 - utf
  end
end

The & operator is the correct answer here though. More elegant.