Rando - Speaker Deck

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Rando # Ruby v2.1.1 Random.srand 123 1

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four random things 2

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pick a random number between 100 and 200 3

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(rand * 100 + 100).to_i => 169 4

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(rand * 100 + 100).to_i => 169 NO! 5

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rand(100..200) => 166 6

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rand(*args) 7

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how many kinds of random does Ruby have? 8

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ObjectSpace .each_object .select { |obj| obj.respond_to?(:rand) } 9

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Kernel Random # 10

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Kernel Random # Random::DEFAULT => # 11

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Kernel Random # 12

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rand == Kernel.rand Random.rand == Random::DEFAULT.rand Kernel.rand != Random.rand 13

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Kernel.rand => 0.6964691855978616 Random.rand => 0.6964691855978616 14

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Kernel.rand(100) => 66 Random.rand(100) => 66 15

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Kernel.rand(0..100) => 66 Random.rand(0..100) => 66 16

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Kernel.rand(100.0) => 66 Random.rand(100.0) => 69.64691855978616 17

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Kernel.rand(-100.0) => 66 Random.rand(-100.0) => ArgumentError 18

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know your rand 19

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generate a list of random numbers 20

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(0..20).map { rand } => [0.696469, 0.286139, ...] 21

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(0..20).map { rand } => [0.696469, 0.286139, ...] NO! 22

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Array.new(20) { rand } => [0.696469, 0.286139, ...] 23

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Array.new(*args) 24

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Array.new(size, obj, &generator) 25

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Array.new(3) => [nil, nil, nil] 26

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Array.new(3, 0) => [0, 0, 0] 27

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Array.new(3) { |n| n } => [0, 1, 2] 28

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know your primitives 29

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pick a random subset of elements from an array 30

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users = %w[alice bob carol] subset = Array.new(2) { users[rand * users.length] } => ['bob', 'alice'] 31

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users = %w[alice bob carol] subset = Array.new(2) { users[rand * users.length] } => ['bob', 'alice'] NO! 32

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users = %w[alice bob carol] users.sample(2) => ['bob', 'carol'] 33

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Array#sample(*args) 34

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Array#sample(size, random: rng) 35

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a = [1,2,3,4,5] a.sample => 3 36

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a = [1,2,3,4,5] a.sample(3) => [3, 1, 5] 37

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a = [1,2,3,4,5] a.sample(1) => [3] 38

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a = [1,2,3,4,5] rng = Random.new(234) a.sample(random: rng) => 1 39

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a = [1,2,3,4,5] rng = Random.new(234) a.sample(3, random: rng) => [1, 5, 2] 40

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a = [1,2,3,4,5] rng = Random.new(234) a.shuffle(random: rng) => [3, 2, 5, 4, 1] 41

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know your primitives (seriously) 42

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generate a secure token from random values 43

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token = '' 40.times do token << rand(0..255).to_s(16) end => 'fe6d7e42dc62e6115...' 44

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token = '' 40.times do token << rand(0..255).to_s(16) end => 'fe6d7e42dc62e6115...' NO! 45

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require 'securerandom' token = SecureRandom.hex(40) => '6011e8861f024cb75...' 46

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require 'securerandom' token = SecureRandom.hex(40) => '6011e8861f024cb75...' => '8f90ea2187b50cb52...' => 'cad2eb20a39939601...' => '272a822296de5b249...' => 'ad65839e646c27252...' 47