Slides for Ruby Class: Collections & Iterators Original slides by Liah Hansen (edits and additions by Sarah Allen and Wolfram Arnold)

1. Collections & Iterators With Hashes & Arrays

2. Iterators: Conditional Looping “while” allows us to loop through code while a set condition is true x = 1 while x < 10 puts x.to_s + “ iteration” x += 1 end

3. Times 5.times { puts “hello” } 5.times { |num| puts “hi”+num.to_s} 99.times do |beer_num| puts "#{beer_num} bottles of beer” end 99.times do puts "some bottles of beer” end

4. Creating a new array x = [1, 2, 3, 4] => [1, 2, 3, 4] x = %w(1 2 3 4) => [“1”, “2”, “3”, “4”] chef = Array.new(3, “bork”) => [“bork”, “bork”, bork”]

5. Accessing Array Values a = [ "a", "b", "c", "d", "e" ] a[0] #=> "a” a[2] #=> "c” a[6] #=> nil a[1, 2] #=> ["b", "c”] a[1..3] #=> ["b", "c", "d”] a[1…3] #=> ["b", "c"]

7. Creating a Hash h = { "a" => 100, "b" => 200 } h[“a”] h = { 1 => “a”, “b” => “hello” } h[1]

8. Operations on Hashes: Merge h1 = { "a" => 100, "b" => 200 } => {"a"=>100, "b"=>200} h2 = { "b" => 254, "c" => 300 } =>{"b"=>254, "c"=>300} h3 = h1.merge(h2) => {"a"=>100, "b"=>254, "c"=>300} h1 => {"a"=>100, "b"=>200} h1.merge!(h2) => {"a"=>100, "b"=>254, "c"=>300}

9. Operations on Hashes h = { "a" => 100, "b" => 200 } h.delete("a”) h = { "a" => 100, "b" => 200, "c" => 300, "d" => 400 } letters = h.keys h = { "a" => 100, "b" => 200, "c" => 300 } numbers = h.values

10. Each >> superheroes = ["catwoman", "batman", "wonderwoman"] >> superheroes.each { | s | puts "#{ s } save me!" } catwoman save me! batman save me! wonderwomansave me! >> dogs = ["fido", "fifi", "rex", "fluffy"] >> dogs_i_want = [] >> dogs.each do |dog| >? dogs_i_want.push(dog) if dog != "fluffy" >? end >> dogs => ["fido", "fifi", "rex", "fluffy"] >> dogs_i_want => ["fido", "fifi", "rex"]

11. Map superheroes = ["catwoman", "batman", "wonderwoman"] >> superheroes.map { |s| s.upcase } => ["CATWOMAN", "BATMAN", "WONDERWOMAN"] Shorter (available in Rails or Ruby 1.8.7+): >> superheroes.map(&:upcase) => ["CATWOMAN", "BATMAN", ”WONDERWOMAN”]