Iterators, Hashes, and Arrays

1. COLLECTIONS & ITERATORS
WITH HASHES AND ARRAYS
Sarah Allen

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"]

6. RANGES
Inclusive
1..4# => runs 1 thru 4
(1..4).to_a# => [1,2,3,4]
Exclusive
1...4# => runs 1 thru 3
(1...4).to_a # => [1,2,3]

7. OPERATIONS ON ARRAYS
[ 1, 2, 3 ] * 3
=> [1, 2, 3, 1, 2, 3, 1, 2, 3]
[ 1, 2, 3 ].join(“,”)
⇒ "1,2,3”
[ 1, 2, 3 ] + [ 4, 5 ]
=> [1, 2, 3, 4, 5]
[ 1, 1, 2, 2, 3, 3, 4, 5 ] - [ 1, 2, 4 ]
=> [3, 3, 5]
[ 1, 2 ] << "c" << "d" << [ 3, 4 ]
=> [1, 2, "c", "d", [3, 4]]

8. CREATING A HASH
h = { "a" => 100, "b" => 200 }
h["a"]
h = { 1 => "a", "b" => “hello” }
h[1]

9. 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}

10. 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

11. EACH
>> superheroes = ["catwoman", "batman", "wonderwoman"]
>> superheroes.each { | s | puts "#{ s } save me!" }
catwoman save me!
batman save me!
wonderwoman save 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"]

12. 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)