benchmark.txt

Ruby version: 2.6.1
Run with: `ruby pirate_combo.rb`

       user     system      total        real
nested map, small array  0.009232   0.000084   0.009316 (  0.009315)
nested map, huge array 27.279118   0.510522  27.789640 ( 27.790889)
flat map, small array  0.002179   0.000043   0.002222 (  0.002219)
flat map, huge array 12.483256   0.087956  12.571212 ( 12.571798)
Array#product, small array  0.001514   0.000000   0.001514 (  0.001513)
Array#product, huge array  5.079583   0.000002   5.079585 (  5.080144)

pirate_combo.rb

require "minitest/autorun"
require "benchmark"

# re: https://twitter.com/funktoriell/status/1111360309598531589

describe "the thing" do
  let(:people) { %w(Guybrush Elaine LeChuck) }
  let(:drinks) { %w(Coffee Water Rum) }
  let(:comboƛ) { lambda { |who, what| { who: who, what: what } } }

  let(:expectation) do
    [
      { who: "Guybrush", what: "Coffee" },
      { who: "Guybrush", what: "Water" },
      { who: "Guybrush", what: "Rum" },
      { who: "Elaine",   what: "Coffee" },
      { who: "Elaine",   what: "Water" },
      { who: "Elaine",   what: "Rum" },
      { who: "LeChuck",  what: "Coffee" },
      { who: "LeChuck",  what: "Water" },
      { who: "LeChuck",  what: "Rum" },
    ]
  end

  describe "with deep nesting" do
    subject do
      people.map { |pirate| drinks.map { |beverage| comboƛ.(pirate, beverage) } }.flatten
    end

    it { subject.must_equal expectation }
  end

  describe "with #flat_map" do
    subject do
      people.flat_map { |pirate| drinks.map { |beverage| comboƛ.(pirate, beverage) } }
    end

    it { subject.must_equal expectation }
  end

  describe "using Array#product" do
    subject do
      people.product(drinks).map { |a, b| comboƛ.(a, b) }
    end

    it { subject.must_equal expectation }
  end
end

iterations = 50
outer_small = ("A".."Z").to_a
inner_small = outer_small.dup
outer_medium  = ("A".."AZZ").to_a
inner_medium  = outer_medium.dup

Benchmark.bm do |bm|
  bm.report("nested map, small array") do
    iterations.times do
      outer_small.map { |a| inner_small.map { |b| [a, b] } }.flatten
    end
  end

  bm.report("nested map, huge array") do
    iterations.times do
      outer_medium.map { |a| inner_medium.map { |b| [a, b] } }.flatten
    end
  end

  bm.report("flat map, small array") do
    iterations.times do
      outer_small.flat_map { |a| inner_small.map { |b| [a, b] } }
    end
  end

  bm.report("flat map, huge array") do
    iterations.times do
      outer_medium.flat_map { |a| inner_medium.map { |b| [a, b] } }
    end
  end

  bm.report("Array#product, small array") do
    iterations.times do
      outer_small.product(inner_small)
    end
  end

  bm.report("Array#product, huge array") do
    iterations.times do
      outer_medium.product(inner_medium)
    end
  end
end