union-array-ampersand-vs-set.rb

require "set"
require 'benchmark/ips'

X = [5, 5, 1, 1]
Y = [1, 2, 5]

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

def fast
  X & Y
end

def slow
  SET_X & SET_Y
end

def slowest
  SET_X.intersection SET_Y
end

Benchmark.ips do |x|
  x.report('Union by Array#&')          { fast    }
  x.report('Union by Set#&')            { slow    }
  x.report('Union by Set#intersection') { slowest }
  x.compare!
end

Calculating -------------------------------------
    Union by Array#&    73.415k i/100ms
      Union by Set#&    23.392k i/100ms
Union by Set#intersection
                        23.274k i/100ms
-------------------------------------------------
    Union by Array#&      1.410M (±10.2%) i/s -      6.974M
      Union by Set#&    289.687k (± 3.2%) i/s -      1.450M
Union by Set#intersection
                        279.034k (± 9.3%) i/s -      1.396M

Comparison:
    Union by Array#&:  1410069.9 i/s
      Union by Set#&:   289686.6 i/s - 4.87x slower
Union by Set#intersection:   279033.8 i/s - 5.05x slower