This document discusses Ruby arrays and hashes. It covers how to create, access, and manipulate array and hash values using methods like each, map, merge, delete, and more. Loops like while and times are also demonstrated for iterating through 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)