random_iterator.rb

module Enumerable
  
  # Iterate over this array randomly.
  # From: http://stackoverflow.com/questions/2459913/how-can-i-randomly-iterate-through-a-large-range
  # And: http://refactormycode.com/codes/40-is_prime
  def randomized
    return to_enum(:randomized) unless block_given?
    
    def is_prime?(num)
      i = 3
      
      return false if num % 2 == 0 && num != 2
      
      ss = Math.sqrt(num).floor
      return false if ss**2 == num
      
      while i <= ss
        return false if num % i == 0
        i += 2
      end
      
      true
    end
    
    def next_prime(i)
      if i % 2 == 0
        i += 1
      end
      
      until is_prime?(i)
        i += 2
      end
      
      i
    end
    
    n = self.size
    q = next_prime(( 2 * n / (1 + Math.sqrt(5)) ).to_i)
    index = start = Kernel.rand(n)
    
    def next_index(i, q, n)
      (i + q) % n
    end
    
    begin
      yield self[index]
      index = next_index(index, q, n)
    end until index == start
  end
  
end