Map, filter, reduce patterns in Swift - Mini Project: Build & Apply

Map, filter, reduce patterns

📖 Scenario: You work at a small fruit store. You have a list of fruit prices and want to do some simple calculations to help with pricing and sales.

🎯 Goal: Learn how to use map, filter, and reduce in Swift to transform, select, and combine data from a list.

📋 What You'll Learn

Create an array of fruit prices

Create a discount rate variable

Use map to apply the discount to all prices

Use filter to find prices above a threshold

Use reduce to calculate the total of filtered prices

Print the final total

💡 Why This Matters

🌍 Real World

Stores and shops often need to update prices, apply discounts, and calculate totals quickly and clearly.

💼 Career

Knowing how to use map, filter, and reduce is useful for data processing tasks in many programming jobs, especially in apps that handle lists of items.

1

Create the fruit prices array

Create an array called fruitPrices with these exact values: 2.5, 3.0, 4.75, 1.25, and 5.0.

Swift

# Create the fruitPrices array with the given values
# Your code here

Need a hint?

Use square brackets [] to create an array and separate values with commas.

2

Add a discount rate variable

Create a variable called discountRate and set it to 0.1 to represent a 10% discount.

Swift

let fruitPrices = [2.5, 3.0, 4.75, 1.25, 5.0]
# Create the discountRate variable and set it to 0.1
# Your code here

Need a hint?

Use let to create a constant variable for the discount rate.

3

Apply discount and filter prices

Use map on fruitPrices to create a new array called discountedPrices where each price is reduced by the discountRate. Then use filter on discountedPrices to create an array called expensivePrices that only contains prices greater than 3.0.

Swift

let fruitPrices = [2.5, 3.0, 4.75, 1.25, 5.0]
let discountRate = 0.1
# Use map to create discountedPrices by reducing each price by discountRate
# Use filter on discountedPrices to create expensivePrices with prices > 3.0
# Your code here

Need a hint?

Use map with a closure to multiply each price by 1 - discountRate. Use filter with a closure to keep prices greater than 3.0.

4

Calculate total and print

Use reduce on expensivePrices to calculate the total sum and store it in a variable called totalPrice. Then print totalPrice.

Swift

let fruitPrices = [2.5, 3.0, 4.75, 1.25, 5.0]
let discountRate = 0.1
let discountedPrices = fruitPrices.map { price in price * (1 - discountRate) }
let expensivePrices = discountedPrices.filter { price in price > 3.0 }
# Use reduce to sum expensivePrices into totalPrice
# Print totalPrice
# Your code here

Need a hint?

Use reduce(0) with a closure that adds each price to the sum. Then print the total.