2.1.2 :002 > arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 2.1.2 :003 > arr.each { |e| puts e } 1 2 3 4 5 6 7 8 9 10 => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 2.1.2 :004 > arr.each { |e| puts e if e > 5 } 6 7 8 9 10 => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 2.1.2 :005 > arr.select { |num| num % 2 != 0 } => [1, 3, 5, 7, 9] 2.1.2 :006 > arr.push(11) => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11] 2.1.2 :007 > arr.unshift(0) => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11] 2.1.2 :008 > arr.pop => 11 2.1.2 :009 > arr => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 2.1.2 :010 > arr.push(3) => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 3] 2.1.2 :011 > arr => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 3] 2.1.2 :012 > arr.uniq => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 2.1.2 :013 > arr => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 3] 2.1.2 :014 > arr.uniq! => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 2.1.2 :015 > arr => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Array has "index" start from 0, and every index associate with a element Hash is composed of key value pairs, and the order don't matter

hash = { :name => 'bob' } # old version hash = { name: 'bob' } # new version

h[:b]

h[:e] = 5

h.delete_if { |k, v| v < 3.5 }

hash = { names: ['bob', 'joe', 'susan'] } arr = [ {name: 'bob'}, {name: 'joe'}, {name: 'susan'} ]

http://ruby-doc.org/ is great. I can search any method or class by filter

2.1.2 :005 > contact_data.flatten! => ["joe@email.com", "123 Main st.", "555-123-4567", "sally@email.com", "404 Not Found Dr.", "123-234-3454"] 2.1.2 :006 > contacts.each do |name, hash| 2.1.2 :007 > fields.each do |field| 2.1.2 :008 > hash[field] = contact_data.shift 2.1.2 :009?> end 2.1.2 :010?> end => {"Joe Smith"=>{:email=>"joe@email.com", :address=>"123 Main st.", :phone=>"555-123-4567"}, "Sally Johnson"=>{:email=>"sally@email.com", :address=>"404 Not Found Dr.", :phone=>"123-234-3454"}}

2.1.2 :011 > puts "Joe's email is: #{contacts["Joe Smith"][:email]}" Joe's email is: joe@email.com => nil 2.1.2 :013 > puts "Sally's phone is: #{contacts["Sally Johnson"][:phone]}" Sally's phone is: 123-234-3454 => nil

contacts.each_with_index do |(name, hash), idx| fields.each do |field| hash[field] = contact_data[idx].shift end end

arr.delete_if { |word| word.start_with?("s", "w") }

2.1.2 :001 > a = ['white snow', 'winter wonderland', 'melting ice', 2.1.2 :002 > 'slippery sidewalk', 'salted roads', 'white trees'] => ["white snow", "winter wonderland", "melting ice", "slippery sidewalk", "salted roads", "white trees"] 2.1.2 :003 > a = a.map { |pairs| pairs.split } => [["white", "snow"], ["winter", "wonderland"], ["melting", "ice"], ["slippery", "sidewalk"], ["salted", "roads"], ["white", "trees"]] 2.1.2 :004 > a = a.flatten => ["white", "snow", "winter", "wonderland", "melting", "ice", "slippery", "sidewalk", "salted", "roads", "white", "trees"]

These hashes are the same! # Hashes are not meant to be in a certain order