Question

What’s the most efficient way to test if an array contains any element from a second array?

Two examples below, attempting to answer the question does foods contain any element from cheeses:

cheeses = %w(chedder stilton brie mozzarella feta haloumi reblochon)
foods = %w(pizza feta foods bread biscuits yoghurt bacon)

puts cheeses.collect{|c| foods.include?(c)}.include?(true)

puts (cheeses - foods).size < cheeses.size

Answer 1

(cheeses & foods).empty?

As Marc-André Lafortune said in comments, & works in linear time while any? + include? will be quadratic. For larger sets of data, linear time will be faster. For small data sets, any? + include? may be faster as shown by Lee Jarvis’ answer — probably because & allocates a new Array while another solution does not and works as a simple nested loop to return a boolean.