set.rb

require 'benchmark'
require 'set'

array = (1..10000).to_a
set = array.to_set
probes = 10000.times.map { rand(20000) }

Benchmark.bmbm do |bm|
  bm.report("Array") { probes.each { |p| array.include? p } }
  bm.report("Set") { probes.each { |p| set.include? p } }
end

set.txt

~/ ruby set.rb
Rehearsal -----------------------------------------
Array   3.050000   0.000000   3.050000 (  3.060505)
Set     0.010000   0.000000   0.010000 (  0.002117)
-------------------------------- total: 3.060000sec

            user     system      total        real
Array   2.400000   0.000000   2.400000 (  2.406458)
Set     0.000000   0.000000   0.000000 (  0.001736)

~/ rbx set.rb
Rehearsal -----------------------------------------
Array   0.889865   0.001000   0.890865 (  0.892081)
Set     0.007998   0.000000   0.007998 (  0.007734)
-------------------------------- total: 0.898863sec

            user     system      total        real
Array   0.861869   0.000000   0.861869 (  0.863451)
Set     0.006999   0.000000   0.006999 (  0.007077)

~/ jruby set.rb
Rehearsal -----------------------------------------
Array   0.189000   0.000000   0.189000 (  0.189000)
Set     0.030000   0.000000   0.030000 (  0.029000)
-------------------------------- total: 0.219000sec

            user     system      total        real
Array   0.117000   0.000000   0.117000 (  0.117000)
Set     0.024000   0.000000   0.024000 (  0.024000)