Classify set elements as even or odd

require 'set'

s = (0..3).to_set     # => #<Set: {0, 1, 2, 3}>
s.classify {|x| x%2}  # => {0=>#<Set: {0, 2}>, 1=>#<Set: {1, 3}>}

1.	Create set with Set.new
2.	Create set with constant values
3.	Is it in a set
4.	Is it a subset
5.	Set length, size and empty?
6.	The intersection is the set of values that appear in both
7.	The union is the set of values that appear in either
8.	a-b: is the elements of a except for those also in b
9.	a^b is the set of values that appear in one set but not both: (a\|b)-(a&b)
10.	Add element to a set
11.	merge a range to a set
12.	Remove elements from a set
13.	Set subtraction
14.	Delete elements from a set with block
15.	Reject elements from a set
16.	Do an in-place intersection like this:
17.	Replace a set
18.	Clear a set
19.	Is it empty
20.	Each loop
21.	Map elements in a set
22.	Collect in place
23.	Convert set to array
24.	Inspect a set
25.	Compare two sets
26.	Divide set
27.	Divide with block
28.	Flatten the subsets
29.	Add new method to set
30.	Partitioning or Classifying a Set
31.	Divide a set by value
32.	Divide a set by even and odd value
33.	Divide a set by its element's class
34.	Divide a set by absolute value
35.	Divide set into three sub sets
36.	Classify a set into three
37.	Convert a hash to set and divide
38.	Add set operation to Array
39.	Sort with block
40.	Set includes and membership

Classify set elements as even or odd : Set « Collections « Ruby