Ruby 04 - Hash and Symbols

01-recap.rb

# Built-int Objects
34 # Integer
"Hello world!" # String
3.14 # Float
true # Boolean
(1..10) # Range
[1, 2, "hello", ["a"]] # Array
nil # Nil

# box/container where stuff/information/data
# can be stored
first_name = "rui"
last_name = "freitas"

# this is a recipe
# or set of instructions
# (ruby will put this in memory for future user)
#            parameters -> ingredients
def full_name(first_name, last_name)
  # ruby has implicit returns
  # (last line will be returned)
  #first_name.capitalize + " " + last_name.capitalize # <= return
  "#{first_name.capitalize} #{last_name.capitalize}"
end

# here I am preparing the meal/recipe
# using the in-memory instructions
# puts full_name("beatrix", "kiddo")
puts full_name(first_name, last_name)

02-students.rb

# From Arrays to Hashes

#                   0        1      2         3
students =     [ "Peter", "Mary", "George", "Emma" ]
student_ages = [ 24     , 25    , 22      ,  20    ]

# "Peter is 24 years old"
# "Mary is 25 years old"
# ...

#     will iterate from 0 to 3
# for index in (0...students.size)
#   name = students[index]
#   age = student_ages[index]
#   puts "#{name} is #{age} years old"
# end

# students << "John"

# each_with_index : Iterator
 students.each_with_index do |student, index|
  age = student_ages[index]
  puts "#{student} is #{age} years old"
 end

students["Peter"]


students_age = {
  "Peter" => 24,
  "Mary" => 25,
  "George" => 22,
  "Emma" => 20
}

03-melbourne.rb

# Hashes
# { "key" => "value" }

melbourne = {
  "country" => "Australia",
  "population" => 4936000,
}

puts melbourne.class
puts melbourne.size
p melbourne

# CRUD
# Arrays
# C: students = ["Peter", "Mary"]
# R: students[1]
# U: students << "Susan"
# D: students.delete_at(0)

# Hashes CRUD
# Create
{ "key" => "value" }

# Read
population = melbourne["population"]
puts "Melbourne's population is #{population}"

# Update
melbourne["suburbs"] = ["Richmond", "South Yarra"]
# melbourne["population"] = melbourne["population"] + 1
melbourne["population"] += 1
p melbourne

suburbs = melbourne["suburbs"]
suburbs.each do |suburb|
  puts suburb
end

# Delete
suburbs = melbourne["suburbs"]
puts suburbs.class
suburbs.delete("Richmond")
p melbourne

# melbourne.delete("suburbs")
# p melbourne

04-iterating.rb

# Iteration
# Hashes are part of the Enumerable family

students = {
  "Peter" => 24,
  "Mary" => 25,
  "George" => 22,
  "Emma" => 20
}

# hash#map => array (of the same size)
# mapped_students = students.map do |student|
#   name = student[0]
#   age = student[1]
#   "#{name} is #{age} years old"
# end

#                                   key , value
mapped_students = students.map do |name, age|
  "#{name} is #{age} years old"
end

p mapped_students


# Each
aged_students = {}
students.each do |key, age|
  aged_students[key] = age + 1
end

p aged_students
p students


# Count => integer
count_22 = students.count do |_key, age|
  age <= 22
end
p count_22

count_m = students.count do |name, _v|
  name.start_with?("M")
end
p count_m

05-methods.rb

# Hash methods


melbourne = {
  "country" => "Australia",
  "population" => 4936000,
}

melbourne.each do |key, value|
  puts "The value of #{key} is #{value},"
end

london = {}
# melbourne has 2 key/value pairs
puts melbourne.size
puts london.size

# if london.size == 0
#   puts "The hash is empty"
# else
#   puts "The hash is not empty"
# end

if london.empty?
  puts "The hash is empty"
else
  puts "The hash is not empty"
end

puts "============= KEYS"
# keys => array of keys
p melbourne.keys
p melbourne.key?("suburbs")
p melbourne.key?("country")

puts "============= VALUES"
# .values => array of values
p melbourne.values
p melbourne.value?("abc")
p melbourne.value?("Australia")

06-symbols.rb

# Symbols as keywords

# melbourne = {
#   "country" => "Australia",
#   "population" => 4936000,
# }

melbourne = {
  country: "Australia",
  population: 4936000
}

puts melbourne[:country]
puts melbourne["country"]

07-last_argument.rb

# => <h1>Hello world</h1>
# => <h1 class='bold'>Hello world</h1>
# => <a href='http://lewagon.org' class='btn'>Le Wagon</a>

def tag(tag_name, attributes = {})
  attr_html = ""
  attributes.each do |key, value|
    attr_html << "#{key}=\"#{value}\" "
  end

  "<#{tag_name} #{attr_html.strip}>#{yield}</#{tag_name}>"
  "<#{tag_name} #{attr_html}>#{yield}</#{tag_name}>"
end

attributes = {
  class: "bold",
  id: "heading",
  style: "color: red; font-size: 14px"
}

html = tag("h1", attributes) do
  "Hello world"
end

puts html