gistfile1.rb

#!/usr/bin/env ruby

require 'benchmark/ips'
require "set"

X = (0...10000).sort_by{rand}.take(5000)
Y = (0...10000).sort_by{rand}.take(5000)

SET_X = Set.new(X)
SET_Y = Set.new(Y)

def array
  X & Y
end

def set1
  SET_X & SET_Y
end

def set2
  SET_X.intersection SET_Y
end

Benchmark.ips do |x|
  x.report('Union by Array#&')          { array }
  x.report('Union by Set#&')            { set1 }
  x.report('Union by Set#intersection') { set2 }
  x.compare!
end