Ruby Hashes - Batch 224

01-recap.rb

"Hello world" # String
1 # Integer
3.14 # Float
true # Boolean
nil # Nil
[1, 3, 6, "Hello"] # Array


# boxes/container to store stuff/data
first_name = "rui"
last_name = "Freitas"


# Contatenation: Adding two or more strings together
# puts first_name + ' ' + last_name

# Interpolation: Injecting ruby expression into strings
#capitalize = false
# puts "#{capitalize ? first_name.capitalize : first_name} #{last_name}"

# Recipe / Set of intructions
def full_name(first_name, last_name) # parameters
  "#{first_name.capitalize} #{last_name.capitalize}"
end

# You are preparing the meal...
# the arguments in this case are defined line 10 and 11
#                     "rui"     "Freitas" => arguments
result = full_name(first_name, last_name)
puts result

02-students.rb

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

#                             element.  index

# students << "John"

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


# students["John"]

# Hashes: Dictionary-like structure
# key/value pairs
students = {
  "Peter" => 24,
  "Mary" => 25,
  "George" => 22,
  "Emma" => 20
}

p students.class

03-lisbon.rb

lisbon = {
  "country" => "Portugal",
  "population" => 504718
}

p lisbon.class
puts lisbon.length

# students[3] Arrays work with indexes
# Hashes work with keys

# Array CRUD
# C: students = ['Peter', 'Mary']
# R: students[1]
# U: students[1] = 'Susan'
# D: students.delete_at(0) / students.delete('Peter')

# Hash CRUD

# Creating
# lisbon = {
#   "country" => "Portugal",
#   "population" => 504718
# }

# Reading
puts lisbon["population"]

# Updating
lisbon["population"] = 604718
p lisbon

# Deleting
puts lisbon.delete("population")
p lisbon

# Adding more entries
# students << "John"

lisbon["monuments"] = ["Torre de Belém", "Jerónimos"]
p lisbon

lisbon["monuments"] << "Castelo de S. Jorge"
p lisbon

04-iterating.rb

lisbon = {
  "country" => "Portugal",
  "population" => 504718
}

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

london = {}
p london.class
p london.length
puts lisbon.empty?
puts london.empty?

puts "============KEYS"
puts lisbon.key?("country")
puts london.key?("country")
p lisbon.keys

puts "===========VALUES"
p lisbon.values

05-hash_map.rb

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

p students

puts "After one year..."
# returns an array
mapped_students = students.map do |name, age|
  "#{name} is now #{age + 1} years old"
end

p mapped_students


aged_students = students.each do |key, age|
  # manually updating each key/value pair
  students[key] = age + 1
end
p aged_students

06-hash_count.rb

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

count_22 = students.count do |_key, age|
  age <= 22
end

puts count_22


students_with_4_letter_names = students.count do |name, _value|
  name.length == 4
end

p students_with_4_letter_names

07-symbols.rb

# paris = {
#   "country" => "France",
#   "population" => 2211000
# }

# london = {
#   "country" => "England",
#   "population" => 8308000
# }

paris = {
  country: "France",
  population: 2211000
}

puts paris[:country]

08-last_hash_argument.rb

def tag(tag_name, attributes = {})
  attr_str = ""
  attributes.each do |key, value|
    attr_str += " #{key}=\"#{value}\""
  end
  content = yield if block_given?
  "<#{tag_name}#{attr_str}>#{content}</#{tag_name}>"
end

attributes = {
  class: "container red button",
  id: "my-card",
  style: "color: red"
}
puts tag("div", attributes) {
  "Hello"
}