Collections: Arrays and Hashes in Ruby

Ruby offers powerful and flexible collections, allowing you to store multiple elements and access them in various ways. Arrays and hashes are two of the most common data structures used to store data in Ruby programs. Understanding their capabilities is crucial for working with data in Ruby.

In this lesson, you will learn:

• How to define and manipulate arrays in Ruby.
• How to define and use hashes for storing key-value pairs.
• How to loop through and modify collections.

Main Concepts in Ruby: Arrays and Hashes

1. Arrays in Ruby:

   • Arrays store ordered collections of elements. You can store any type of object, such as numbers, strings, or even other arrays.

   arr = [1, 2, 3, 'four']
   puts arr[0]  # Output: 1
   puts arr[3]  # Output: 'four'
   

2. Accessing and Modifying Arrays:

   • Access elements using their index, starting from 0.
   • Modify elements by assigning new values at specific indices.

   arr[1] = 5  # Modifies the second element
   puts arr  # Output: [1, 5, 3, 'four']
   

3. Array Methods:

   • Ruby arrays come with several built-in methods such as push, pop, shift, unshift, each, map, and more.

   arr.push(6)  # Adds 6 to the end of the array
   arr.pop()    # Removes the last element
   arr.each { |e| puts e }  # Iterates over each element
   

4. Hashes in Ruby:

   • Hashes store unordered collections of key-value pairs. Each key must be unique, and you can store any type of object as the value.

   person = { name: 'Alice', age: 30 }
   puts person[:name]  # Output: Alice
   puts person[:age]   # Output: 30
   

5. Accessing and Modifying Hashes:

   • Access values using their keys and modify the values by assigning new ones to specific keys.

   person[:age] = 31  # Updates the age
   puts person[:age]   # Output: 31
   

Practical Applications of Arrays and Hashes

Task: Organize Student Scores

1. Create an array of student scores and calculate the average.

   scores = [85, 90, 88, 92]
   average = scores.sum / scores.size.to_f
   puts average  # Output: 88.75
   

Task: Create a Contact Book

1. Use a hash to store a person's name, phone number, and email.

   contact = { name: 'Bob', phone: '123-456-7890', email: 'bob@example.com' }
   puts contact[:email]  # Output: 'bob@example.com'
   

Task: Modify Array Elements

1. Create an array of numbers and square each element.

   numbers = [1, 2, 3, 4]
   squared = numbers.map { |num| num ** 2 }
   puts squared  # Output: [1, 4, 9, 16]
   

Task: Create a Grocery List

1. Use an array to store items in a grocery list and print them.

   groceries = ['apples', 'bananas', 'carrots']
   groceries.each { |item| puts item }
   

Task: Store and Access Product Information

1. Use a hash to store product names as keys and their prices as values.

   products = { apple: 1.2, banana: 0.8, carrot: 1.0 }
   puts products[:banana]  # Output: 0.8
   

Advanced Insights into Arrays and Hashes

1. Nested Arrays and Hashes:

   • Arrays and hashes can contain other arrays or hashes, allowing you to create complex data structures.

   nested_array = [[1, 2], [3, 4]]
   nested_hash = { 'Alice' => { age: 30, city: 'New York' }, 'Bob' => { age: 25, city: 'Los Angeles' } }
   

2. Iterating with each and each_with_index:

   • You can iterate through arrays or hashes using each or each_with_index to access both elements and their indices.

   arr.each_with_index { |value, index| puts "Index #{index}: #{value}" }
   

3. Merging Arrays and Hashes:

   • Use methods like concat and merge to combine arrays and hashes respectively.

   arr1 = [1, 2]
   arr2 = [3, 4]
   arr1.concat(arr2)  # Result: [1, 2, 3, 4]
   

4. Array and Hash Transformations:

   • Use map to transform arrays and transform_values to transform hash values.

   arr = [1, 2, 3]
   transformed = arr.map { |e| e * 2 }  # Result: [2, 4, 6]
   

5. Working with Multi-Dimensional Arrays:

   • You can work with multi-dimensional arrays to represent matrices or grids.

   matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
   puts matrix[1][2]  # Output: 6
   

Additional Resources for Ruby Arrays and Hashes

• Ruby Array Documentation: Ruby Docs - Arrays
• Ruby Hash Documentation: Ruby Docs - Hashes
• Practical Ruby Projects: Ruby Projects

Explore these resources to deepen your understanding of collections in Ruby.