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Computing Set Operations on Arrays
CodeExpectedActual
#Union
[1,2,3] | [1,4,5]
 [1, 2, 3, 4, 5] [1, 2, 3, 4, 5] 
#Intersection
[1,2,3] & [1,4,5]
 [1] [1] 
#Difference
[1,2,3] - [1,4,5]
 [2, 3] [2, 3] 
require 'set'
a = [1,2,3]
b = [3,4,5]
a.to_set ^ b.to_set
 #<Set: {5, 1, 2, 4}> #<Set: {5, 1, 2, 4}> 
(a | b) - (a & b)
 [1, 2, 4, 5] [1, 2, 4, 5] 
array = [1,2,3]
set = [3,4,5].to_set
set & array
 #<Set: {3}> #<Set: {3}> 
array & set                 
TypeError: cannot convert Set into Array
 
Error! (Exception?) Here's stdout:
TypeError: can't convert Set into Array
	from (irb):15:in `&'
	from (irb):15

[3,3] & [3,3]
 [3] [3] 
[3,3] | [3,3]
 [3] [3] 
[1,2,3,3] - [1]
 [2, 3, 3] [2, 3, 3] 
[1,2,3,3] - [3]
 [1, 2] [1, 2] 
[1,2,3,3] - [2,2,3]
 [1] [1] 
u = [:red, :orange, :yellow, :green, :blue, :indigo, :violet]
a = [:red, :blue]
u - a
 [:orange, :yellow, :green, :indigo, :violet] [:orange, :yellow, :green, :indigo, :violet] 
def natural_numbers_except(exclude)
  exclude_map = {}
  exclude.each { |x| exclude_map[x] = true } 
  x = 1
  while true
    yield x unless exclude_map[x]
    x = x.succ
  end
end
natural_numbers_except([2,3,6,7]) do |x|
 break if x > 10
 puts x
end
 
1
4
5
8
9
10
 
1
4
5
8
9
10
 
module Enumerable
  def cartesian(other)
    res = []
    each { |x| other.each { |y| res << [x, y] } }
    return res
  end
end
[1,2,3].cartesian(['a',5,6])
 [[1, "a"], [1, 5], [1, 6], [[1, "a"], [1, 5], [1, 6], [2, "a"], [2, 5], [2, 6], [3, "a"], [3, 5], [3, 6]] 
module Enumerable
  def cartesian(other)
    inject([]) { |res, x| other.inject(res) { |res, y| res << [x,y] } }
  end
end
 nil