Exploring and Manipulating Ruby Hashes

Introduction to Ruby Hashes

Welcome to our exploration of data structures in Ruby! Today, we will delve into Ruby Hashes . Similar to a dictionary or an address book, hashes store data in key-value pairs, allowing for efficient data retrieval and modification. Hashes are essential in Ruby for managing and organizing data with unique identifiers. Let's dive into Ruby hashes to understand these concepts clearly.

Ruby Hashes

Ruby hashes are key-value collections that store data in pairs. They allow you to quickly access a value using its key. For example, a hash can store a friend's contact information, where their name (key) maps to their phone number (value). Ruby contacts = {"Alice" => "123-456-7890", "Bob" => "234-567-8901"} puts contacts["Alice"] # Output: "123-456-7890" puts contacts["Carol"] # Output: nil (key not found) contacts = {"Alice" => "123-456-7890", "Bob" => "234-567-8901"} puts contacts["Alice"] # Output: "123-456-7890" puts contacts["Carol"] # Output: nil (key not found) In this example, we create a simple hash with names as keys and phone numbers as values. Trying to access a nonexistent key, like "Carol," returns nil .

Operations with Hashes

Ruby hashes offer several operations for adding, updating, and accessing key-value pairs, making data management efficient. Let's explore how each of these operations works one by one.

Adding or Updating Entries

You can add or update entries by assigning a value to a key. If the key exists, the value is updated; if it doesn’t, a new key-value pair is added. Ruby contacts = {} contacts["Alice"] = "123-456-7890" contacts["Bob"] = "234-567-8901" puts contacts.inspect # Output: {"Alice"=>"123-456-7890", "Bob"=>"234-567-8901"} contacts = {} contacts["Alice"] = "123-456-7890" contacts["Bob"] = "234-567-8901" puts contacts.inspect # Output: {"Alice"=>"123-456-7890", "Bob"=>"234-567-8901"} This example demonstrates adding key-value pairs to a hash by directly assigning values.

Accessing Values with fetch

The fetch method retrieves the value associated with a key and lets you specify a default return value if the key doesn’t exist. This is useful to avoid exceptions when accessing keys that may not be present. Ruby also provides the .key? method to check if a key exists in the hash. Using .key? can be helpful to verify a key’s presence before performing operations. Ruby puts contacts.fetch("Alice", "Not found") # Output: "123-456-7890" puts contacts.fetch("Carol", "Not found") # Output: "Not found" puts contacts.key?("Alice") # Output: true puts contacts.key?("Carol") # Output: false puts contacts.fetch("Alice", "Not found") # Output: "123-456-7890" puts contacts.fetch("Carol", "Not found") # Output: "Not found" puts contacts.key?("Alice") # Output: true puts contacts.key?("Carol") # Output: false The fetch method provides a fallback value, making it safer than direct key access, while .key? checks for the presence of a key and returns a boolean value. Here are the key differences between fetch and direct access: fetch Method : Retrieves the value for a given key. Allows specifying a default value if the key is not found. Raises an error if the key is missing and no default is provided. Direct Access or [] Method : Retrieves the value for a given key. Returns nil if the key is not found. Does not provide a way to specify a default value directly.

Join the 1M+ learners on CodeSignal

Be a part of our community of 1M+ users who develop and demonstrate their skills on CodeSignal

Ruby

contacts = {
  "Alice" => "123-456-7890",
  "Bob" => "234-567-8901"
}

puts contacts["Alice"]  # Output: "123-456-7890"
puts contacts["Carol"]  # Output: nil (key not found)

Ruby

contacts = {}
contacts["Alice"] = "123-456-7890"
contacts["Bob"] = "234-567-8901"
puts contacts.inspect  # Output: {"Alice"=>"123-456-7890", "Bob"=>"234-567-8901"}

Ruby

puts contacts.fetch("Alice", "Not found")  # Output: "123-456-7890"
puts contacts.fetch("Carol", "Not found")  # Output: "Not found"
puts contacts.key?("Alice")                # Output: true
puts contacts.key?("Carol")                # Output: false

Ruby

contacts.delete("Bob")
puts contacts.inspect  # Output: {"Alice"=>"123-456-7890"}

contacts.delete("Bob")
puts contacts.inspect  # Output: {"Alice"=>"123-456-7890"}

Ruby

tasks = { "Buy milk" => "Pending", "Pay bills" => "Completed" }

tasks.each do |task, status|
  puts "#{task}: #{status}"
end
# Output:
# Buy milk: Pending
# Pay bills: Completed

tasks = { "Buy milk" => "Pending", "Pay bills" => "Completed" }

tasks.each do |task, status|
  puts "#{task}: #{status}"
end
# Output:
# Buy milk: Pending
# Pay bills: Completed

Ruby

tasks.each_key { |task| puts "Task: #{task}" }
# Output:
# Task: Buy milk
# Task: Pay bills

tasks.each_key { |task| puts "Task: #{task}" }
# Output:
# Task: Buy milk
# Task: Pay bills

Ruby

class StudentDatabase
  def initialize
    @students = {}
  end

  def add_student(name, subjects)
    # Adds students and their subjects with grades
    @students[name] = subjects
  end

  def get_mark(name, subject)
    @students.fetch(name, {}).fetch(subject, "N/A")
  end

  def print_database
    # Prints each student's name along with their subjects and grades
    @students.each do |name, subjects|
      puts "Student: #{name}"
      subjects.each do |subject, grade|
        puts "  Subject: #{subject}, Grade: #{grade}"
      end
    end
  end
end

# Example usage
student_db = StudentDatabase.new
student_db.add_student("Alice", {"Math" => "A", "English" => "B"})
student_db.add_student("Bob", {"Math" => "C", "Science" => "B+"})

puts student_db.get_mark("Alice", "English") # Output: "B"
puts student_db.get_mark("Alice", "History") # Output: "N/A"
student_db.print_database
# Output:
# Student: Alice
#   Subject: Math, Grade: A
#   Subject: English, Grade: B
# Student: Bob
#   Subject: Math, Grade: C
#   Subject: Science, Grade: B+

class StudentDatabase
  def initialize
    @students = {}
  end

  def add_student(name, subjects)
    # Adds students and their subjects with grades
    @students[name] = subjects
  end

  def get_mark(name, subject)
    @students.fetch(name, {}).fetch(subject, "N/A")
  end

  def print_database
    # Prints each student's name along with their subjects and grades
    @students.each do |name, subjects|
      puts "Student: #{name}"
      subjects.each do |subject, grade|
        puts "  Subject: #{subject}, Grade: #{grade}"
      end
    end
  end
end

# Example usage
student_db = StudentDatabase.new
student_db.add_student("Alice", {"Math" => "A", "English" => "B"})
student_db.add_student("Bob", {"Math" => "C", "Science" => "B+"})

puts student_db.get_mark("Alice", "English") # Output: "B"
puts student_db.get_mark("Alice", "History") # Output: "N/A"
student_db.print_database
# Output:
# Student: Alice
#   Subject: Math, Grade: A
#   Subject: English, Grade: B
# Student: Bob
#   Subject: Math, Grade: C
#   Subject: Science, Grade: B+

Ruby

inventory = Hash.new(0)
inventory["Apples"] += 10
inventory["Oranges"] += 5

puts inventory["Apples"]   # Output: 10
puts inventory["Bananas"]  # Output: 0 (default value)

inventory = Hash.new(0)
inventory["Apples"] += 10
inventory["Oranges"] += 5

puts inventory["Apples"]   # Output: 10
puts inventory["Bananas"]  # Output: 0 (default value)

Ruby

class ShoppingCart

  def initialize
    # Initialize cart as an empty hash
    @cart = Hash.new(0)
  end

  def add_product(product_name, quantity)
    # Add or update the quantity of a product in the cart
    @cart[product_name] += quantity
  end

  def remove_product(product_name)
    # Remove a product from the cart if it exists
    if @cart.key?(product_name)
      @cart.delete(product_name)
    else
      puts "#{product_name} is not in the cart."
    end
  end

  def show_cart
    # Display the products and their quantities in the cart
    if @cart.empty?
      puts "Your shopping cart is empty."
    else
      @cart.each { |product, quantity| puts "#{product}: #{quantity}" }
    end
  end
end

# Example usage
my_cart = ShoppingCart.new
my_cart.add_product("Apples", 5)
my_cart.add_product("Bananas", 2)
my_cart.add_product("Apples", 3)  # Updates quantity of Apples to 8

my_cart.show_cart
# Output:
# Apples: 8
# Bananas: 2

my_cart.remove_product("Bananas")
my_cart.show_cart
# Output:
# Apples: 8

class ShoppingCart

  def initialize
    # Initialize cart as an empty hash
    @cart = Hash.new(0)
  end

  def add_product(product_name, quantity)
    # Add or update the quantity of a product in the cart
    @cart[product_name] += quantity
  end

  def remove_product(product_name)
    # Remove a product from the cart if it exists
    if @cart.key?(product_name)
      @cart.delete(product_name)
    else
      puts "#{product_name} is not in the cart."
    end
  end

  def show_cart
    # Display the products and their quantities in the cart
    if @cart.empty?
      puts "Your shopping cart is empty."
    else
      @cart.each { |product, quantity| puts "#{product}: #{quantity}" }
    end
  end
end

# Example usage
my_cart = ShoppingCart.new
my_cart.add_product("Apples", 5)
my_cart.add_product("Bananas", 2)
my_cart.add_product("Apples", 3)  # Updates quantity of Apples to 8

my_cart.show_cart
# Output:
# Apples: 8
# Bananas: 2

my_cart.remove_product("Bananas")
my_cart.show_cart
# Output:
# Apples: 8

Ruby

contacts.delete("Bob")
puts contacts.inspect  # Output: {"Alice"=>"123-456-7890"}

Ruby

tasks = { "Buy milk" => "Pending", "Pay bills" => "Completed" }

tasks.each do |task, status|
  puts "#{task}: #{status}"
end
# Output:
# Buy milk: Pending
# Pay bills: Completed

Ruby

tasks.each_key { |task| puts "Task: #{task}" }
# Output:
# Task: Buy milk
# Task: Pay bills

Ruby

class StudentDatabase
  def initialize
    @students = {}
  end

  def add_student(name, subjects)
    # Adds students and their subjects with grades
    @students[name] = subjects
  end

  def get_mark(name, subject)
    @students.fetch(name, {}).fetch(subject, "N/A")
  end

  def print_database
    # Prints each student's name along with their subjects and grades
    @students.each do |name, subjects|
      puts "Student: #{name}"
      subjects.each do |subject, grade|
        puts "  Subject: #{subject}, Grade: #{grade}"
      end
    end
  end
end

# Example usage
student_db = StudentDatabase.new
student_db.add_student("Alice", {"Math" => "A", "English" => "B"})
student_db.add_student("Bob", {"Math" => "C", "Science" => "B+"})

puts student_db.get_mark("Alice", "English") # Output: "B"
puts student_db.get_mark("Alice", "History") # Output: "N/A"
student_db.print_database
# Output:
# Student: Alice
#   Subject: Math, Grade: A
#   Subject: English, Grade: B
# Student: Bob
#   Subject: Math, Grade: C
#   Subject: Science, Grade: B+

Ruby

inventory = Hash.new(0)
inventory["Apples"] += 10
inventory["Oranges"] += 5

puts inventory["Apples"]   # Output: 10
puts inventory["Bananas"]  # Output: 0 (default value)

Ruby

class ShoppingCart

  def initialize
    # Initialize cart as an empty hash
    @cart = Hash.new(0)
  end

  def add_product(product_name, quantity)
    # Add or update the quantity of a product in the cart
    @cart[product_name] += quantity
  end

  def remove_product(product_name)
    # Remove a product from the cart if it exists
    if @cart.key?(product_name)
      @cart.delete(product_name)
    else
      puts "#{product_name} is not in the cart."
    end
  end

  def show_cart
    # Display the products and their quantities in the cart
    if @cart.empty?
      puts "Your shopping cart is empty."
    else
      @cart.each { |product, quantity| puts "#{product}: #{quantity}" }
    end
  end
end

# Example usage
my_cart = ShoppingCart.new
my_cart.add_product("Apples", 5)
my_cart.add_product("Bananas", 2)
my_cart.add_product("Apples", 3)  # Updates quantity of Apples to 8

my_cart.show_cart
# Output:
# Apples: 8
# Bananas: 2

my_cart.remove_product("Bananas")
my_cart.show_cart
# Output:
# Apples: 8

Introduction to Ruby Hashes

Ruby Hashes

Operations with Hashes

Adding or Updating Entries

Accessing Values with fetch

Join the 1M+ learners on CodeSignal

Deleting Entries

Iterating Through Hashes

Nested Hashes

Hash Defaults

Practical Example: Managing a Shopping Cart

Lesson Summary and Practice