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

Counting the number of occurrences and comparing them seems to be the obvious way to go.

class Array
   def contains_all? arr
       h = self.inject(Hash.new(0)) {|h, i| h[i] += 1; h}
       arr.each do |i|
           return false unless h.has_key?(i)
           return false if h[i] == 0
           h[i] -= 1
       end
       true
   end
end