This works fine for integers and letters. It should work for anything though, so long as Ruby can form an range from the first and last array items.
class Array def missing_items return [] if self.length <= 1 self.uniq! self.sort! rescue nil begin (self.first..self.last).to_a - self rescue [] end end end
>> [1, 3, 4, 10].missing_items.join(', ') => 2, 5, 6, 7, 8, 9 >> [1, 2, 7, 7.5, 8.2].missing_items.join(', ') => 3, 4, 5, 6, 8 >> %w(a b c f g j).missing_items.join(', ') => d, e, h, i >> [2.5, {:test => 'value'}].missing_items.join(', ') =>
