Why collection algorithms matter in Swift - See It in Action

Why Collection Algorithms Matter

📖 Scenario: You are managing a small library's book database. The library wants to keep track of books and quickly find books by their genre or author. Using collection algorithms helps organize and retrieve this information efficiently.

🎯 Goal: Build a simple Swift dictionary to store books with their genres, add a filter condition to select books of a specific genre, and then retrieve the filtered list.

📋 What You'll Learn

Create a dictionary called books with these exact entries: "1984": "Dystopian", "To Kill a Mockingbird": "Classic", "The Hobbit": "Fantasy", "Fahrenheit 451": "Dystopian"

Create a variable called selectedGenre and set it to "Dystopian"

Use the filter method on books to create a new dictionary called filteredBooks that contains only books where the genre matches selectedGenre

Add a final line that creates an array called filteredTitles containing only the titles (keys) from filteredBooks

💡 Why This Matters

🌍 Real World

Libraries, bookstores, and many apps use collection algorithms to organize and find data quickly.

💼 Career

Understanding how to filter and manipulate collections is essential for software developers working with databases and user data.

1

Create the books dictionary

Create a dictionary called books with these exact entries: "1984": "Dystopian", "To Kill a Mockingbird": "Classic", "The Hobbit": "Fantasy", "Fahrenheit 451": "Dystopian"

Swift

# Create the books dictionary with the exact entries
# Your code here

Need a hint?

Use a Swift dictionary literal with keys as book titles and values as genres.

2

Set the selected genre

Create a variable called selectedGenre and set it to "Dystopian"

Swift

let books = ["1984": "Dystopian", "To Kill a Mockingbird": "Classic", "The Hobbit": "Fantasy", "Fahrenheit 451": "Dystopian"]
# Create selectedGenre variable and set it to "Dystopian"
# Your code here

Need a hint?

Use let to create a constant string variable.

3

Filter books by genre

Use the filter method on books to create a new dictionary called filteredBooks that contains only books where the genre matches selectedGenre

Swift

let books = ["1984": "Dystopian", "To Kill a Mockingbird": "Classic", "The Hobbit": "Fantasy", "Fahrenheit 451": "Dystopian"]
let selectedGenre = "Dystopian"
# Filter books dictionary to only include entries where the genre equals selectedGenre
# Your code here

Need a hint?

Use filter with a closure that checks if the value equals selectedGenre.

4

Extract filtered book titles

Add a final line that creates an array called filteredTitles containing only the titles (keys) from filteredBooks

Swift

let books = ["1984": "Dystopian", "To Kill a Mockingbird": "Classic", "The Hobbit": "Fantasy", "Fahrenheit 451": "Dystopian"]
let selectedGenre = "Dystopian"
let filteredBooks = books.filter { $0.value == selectedGenre }
# Create filteredTitles array containing keys from filteredBooks
# Your code here

Need a hint?

Use filteredBooks.keys and convert it to an array.