FlatMap for nested collections in Swift - Mini Project: Build & Apply

FlatMap for nested collections

📖 Scenario: You work at a bookstore that organizes books by genre. Each genre has a list of book titles. You want to create a single list of all book titles from all genres.

🎯 Goal: Build a Swift program that uses flatMap to combine nested lists of book titles into one flat list.

📋 What You'll Learn

Create a dictionary called booksByGenre with genres as keys and arrays of book titles as values

Create a variable called allBooks that uses flatMap on booksByGenre.values to get a single array of all book titles

Print the allBooks array

💡 Why This Matters

🌍 Real World

Combining nested lists of items is common when working with grouped data, like categories of products or genres of books.

💼 Career

Understanding how to flatten nested collections helps in data processing tasks, making it easier to analyze or display combined information.

1

Create the nested dictionary of books

Create a dictionary called booksByGenre with these exact entries: "Fiction": ["The Alchemist", "1984"], "Science": ["A Brief History of Time", "The Selfish Gene"], and "History": ["Sapiens", "Guns, Germs, and Steel"].

Swift

# Create the dictionary booksByGenre with the given genres and book lists
# Your code here

Need a hint?

Use a Swift dictionary with String keys and array of String values.

2

Prepare to flatten the nested arrays

Create a variable called allBooks and set it to an empty array of strings [] to prepare for collecting all book titles.

Swift

let booksByGenre = [
    "Fiction": ["The Alchemist", "1984"],
    "Science": ["A Brief History of Time", "The Selfish Gene"],
    "History": ["Sapiens", "Guns, Germs, and Steel"]
]

// Create an empty array called allBooks to hold all book titles
# Your code here

Need a hint?

Declare allBooks as a variable array of strings starting empty.

3

Use flatMap to combine all book lists

Set the variable allBooks to the result of using flatMap on booksByGenre.values to combine all nested arrays into one flat array.

Swift

let booksByGenre = [
    "Fiction": ["The Alchemist", "1984"],
    "Science": ["A Brief History of Time", "The Selfish Gene"],
    "History": ["Sapiens", "Guns, Germs, and Steel"]
]

var allBooks: [String] = []

// Use flatMap on booksByGenre.values to combine all book arrays into allBooks
# Your code here

Need a hint?

Use flatMap on booksByGenre.values with closure { $0 } to flatten.

4

Print the combined list of all books

Write a print statement to display the allBooks array.

Swift

let booksByGenre = [
    "Fiction": ["The Alchemist", "1984"],
    "Science": ["A Brief History of Time", "The Selfish Gene"],
    "History": ["Sapiens", "Guns, Germs, and Steel"]
]

var allBooks: [String] = []

allBooks = booksByGenre.values.flatMap { $0 }

// Print the allBooks array
# Your code here

Need a hint?

Use print(allBooks) to show the combined list.