List Comprehensions In Ruby

Taken from: http://www.ruby-forum.com/topic/89416
Author: Phrogz

To avoid reinventing the wheel check out the built-in methods described in:
http://www.ruby-doc.org/core/classes/Array.html and
http://www.ruby-doc.org/core/classes/Enumerable.html.




#class Array 
module Enumerable
  def comprehend(&block) 
    block ? map(&block).compact : self 
  end 
end 


old_data = *(1..5)          # alternatives to the splat operator: (1..5).to_a or (1..5).collect
new_data = *(3..9)


# some reinventing going on here ...
added = new_data.comprehend { |x| x if not old_data.include?(x) } 
removed = old_data.comprehend { |x| x if not new_data.include?(x) } 
same = new_data.comprehend { |x| x if old_data.include?(x) } 
modified = new_data.comprehend { |x| x**2 if not x % 2 == 0 }

p added                                            #=> [6, 7, 8, 9]
p added = new_data - old_data                      #=> [6, 7, 8, 9]

p removed                                         #=> [1, 2]
p removed = old_data - new_data                   #=> [1, 2]

p same                                              #=> [3, 4, 5]
p same = old_data & new_data                        #=> [3, 4, 5]
 
p modified                                        #=> [9, 25, 49, 81]


new_data = [[5, 9], [22, 3], [99, 564]]
bool_vals = new_data.comprehend { |x, y| x <= y }
p bool_vals                                      #=> [true, false, true]