Create set with Set.new
require 'set' p Set.new(1..5) # => #<Set: {5, 1, 2, 3, 4}> p Set.new([1,2,3]) # => #<Set: {1, 2, 3}> p Set.new([1,2,3]) {|x| x+1} # => #<Set: {2, 3, 4}>