Swift: Swift Arrays Tutorial
An array is like a shopping list — every to-do item listed in order. This lesson covers the complete set of Swift array operations, from creation to CRUD, all in one place.
1. What You'll Learn
- Create arrays in multiple ways and specify element types
- Add and remove elements using append, insert, and remove
- Access and modify array elements with subscripts
- Traverse arrays with for-in and enumerated
- Use practical properties like isEmpty, count, and contains
2. An E-commerce Developer's Real Story
(1) Pain: Shopping cart list management in chaos, data out of sync
Alice is building the shopping cart feature for an e-commerce app. The user — Charlie — adds 5 items, then removes 2 and changes quantities 3 times. At checkout she discovers: the cart total doesn't match the individual item prices!
SWIFT
// Alice's original "manual" approach
var cartItem1 = "Laptop"
var cartItem2 = "Mouse"
var cartItemPrice1 = 999.0
var cartItemPrice2 = 25.0
// By the time items piled up, she was lost...
Alice was managing 6 items with 12 separate variables. When she added a 7th item, she didn't even know what to name the variable anymore. Cart data scattered across 20+ variables — change one and forget another.
(2) The Array Solution
SWIFT
var cartItems = ["Laptop", "Mouse", "Keyboard"]
var cartPrices = [999.0, 25.0, 89.0]
cartItems.append("Monitor")
cartPrices.append(349.0)
cartItems.remove(at: 1)
cartPrices.remove(at: 1)
print("Cart: \(cartItems)")
print("Total: $\(cartPrices.reduce(0, +))")
(3) Result: Structured data, 90% fewer bugs
| Metric | Scattered Variables | Array Management |
|---|---|---|
| Variable count | 18 | 2 |
| Adding an item | Create 3 new variables | 1 line of append |
| Data consistency | Often out of sync | Guaranteed sync |
| Bugs per week | 3-5 | 0-1 |
3. Creating Arrays and Basic Properties
An array is an ordered collection of elements — all must be the same type.
graph TB
A[Array] --> B[Index 0]
A --> C[Index 1]
A --> D[Index 2]
A --> E[Index ...]
B --> F[Element]
C --> F
D --> F
E --> F
| Creation Method | Example | Notes |
|---|---|---|
| Literal | [1, 2, 3] | Most common |
| Type annotation | Int | Empty array |
| Repeated value | Array(repeating: 0, count: 5) | All zeros |
| From range | Array(1...5) | From a range |
(1) Creating Arrays
SWIFT
// Method 1: literal
let numbers = [1, 2, 3, 4, 5]
// Method 2: empty array
var emptyArray: [String] = []
// Method 3: repeated value
let zeros = Array(repeating: 0, count: 3)
print(zeros)
// Method 4: from range
let rangeArray = Array(10...15)
print(rangeArray)
(2) Common Properties
SWIFT
let items = ["Apple", "Banana", "Orange"]
print("Count: \(items.count)")
print("Is empty: \(items.isEmpty)")
print("First: \(items.first ?? "None")")
print("Last: \(items.last ?? "None")")
print("Contains Apple: \(items.contains("Apple"))")
▶ Example: Warehouse Inventory Check
SWIFT
// ============================================
// Managing warehouse inventory with arrays
// ============================================
var inventory: [String] = []
if inventory.isEmpty {
print("Warehouse is empty, adding stock...")
}
inventory.append("Laptop")
inventory.append("Mouse")
inventory.append("Keyboard")
inventory.append("Monitor")
print("Inventory has \(inventory.count) items")
print("Products: \(inventory.joined(separator: ", "))")
print("First item: \(inventory[0])")
print("Last item: \(inventory[inventory.count - 1])")
Output:
TEXT 📖 Display onlyWarehouse is empty, adding stock... Inventory has 4 items Products: Laptop, Mouse, Keyboard, Monitor First item: Laptop Last item: Monitor
4. Array CRUD Operations
Arrays are mutable collections — you can add and remove elements at any position.
| Operation | Method | Example |
|---|---|---|
| Append to end | append(_:) |
array.append(4) |
| Insert at position | insert(_:at:) |
array.insert(0, at: 0) |
| Remove at position | remove(at:) |
array.remove(at: 2) |
| Remove last | removeLast() |
array.removeLast() |
| Remove all | removeAll() |
array.removeAll() |
| Modify element | Subscript assignment | array[1] = 100 |
(1) Adding and Inserting Elements
SWIFT
var tasks = ["Buy groceries", "Pay bills"]
// Append to end
tasks.append("Call doctor")
// Insert at specific position
tasks.insert("Check email", at: 0)
print(tasks)
(2) Removing and Modifying Elements
SWIFT
var scores = [88, 92, 75, 60, 95]
// Modify
scores[1] = 98
// Remove
let removed = scores.remove(at: 3)
print("Removed: \(removed)")
scores.removeLast()
scores.sort()
print(scores)
▶ Example: To-Do List Manager
SWIFT
// ============================================
// Simple to-do list with arrays
// ============================================
var todoList = ["Buy milk", "Walk dog", "Write report"]
// Add
todoList.append("Read book")
todoList.insert("Morning exercise", at: 0)
// Modify
todoList[2] = "Write weekly report"
// Remove
let completed = todoList.remove(at: 1)
print("Completed: \(completed)")
// Traverse
print("\n=== Today's Todo ===")
for (i, task) in todoList.enumerated() {
print("\(i + 1). \(task)")
}
print("\nRemaining tasks: \(todoList.count)")
Output:
TEXT 📖 Display onlyCompleted: Walk dog === Today's Todo === 1. Morning exercise 2. Buy milk 3. Write weekly report 4. Read book Remaining tasks: 4
5. Array Traversal and Bulk Operations
Swift provides multiple ways to traverse arrays and practical bulk operation methods.
| Traversal Method | Syntax | Use Case |
|---|---|---|
| Basic | for item in array |
Only care about elements |
| Indexed | for (i, item) in array.enumerated() |
Need index numbers |
| Filtered | for item in array where condition |
Only matching elements |
| Higher-order | array.map { } |
Transform each element |
| Filter | array.filter { } |
Keep elements that match |
(1) Basic and Filtered Traversal
SWIFT
let numbers = [3, 7, 2, 8, 5, 1, 9, 4, 6]
// Basic for-in
for num in numbers {
print(num, terminator: " ")
}
print()
// where filter
for num in numbers where num > 5 {
print("\(num) is greater than 5")
}
(2) Higher-Order Functions: map and filter
SWIFT
let prices = [12.99, 24.50, 8.75, 35.00]
// map: add tax to each price
let withTax = prices.map { $0 * 1.08 }
print("With tax: \(withTax)")
// filter: items over 20
let expensive = prices.filter { $0 > 20 }
print("Expensive: \(expensive)")
▶ Example: Order Data Analysis
SWIFT
// ============================================
// Analyzing order data with array operations
// ============================================
let orderAmounts = [45.0, 120.0, 33.5, 299.0, 55.0, 180.0, 22.0]
// 1. Total sales
let total = orderAmounts.reduce(0, +)
print("Total sales: $\(total)")
// 2. High-value orders (>= 100)
let highValue = orderAmounts.filter { $0 >= 100 }
print("High-value orders: \(highValue.count)")
// 3. Add 10% service fee to all orders
let withServiceFee = orderAmounts.map { $0 * 1.1 }
print("First 3 with fee: \(Array(withServiceFee.prefix(3)))")
// 4. Sort
let sorted = orderAmounts.sorted(by: >)
print("Top 3: \(Array(sorted.prefix(3)))")
Output:
TEXT 📖 Display onlyTotal sales: $754.5 High-value orders: 3 First 3 with fee: [49.5, 132.0, 36.85] Top 3: [299.0, 180.0, 120.0]
6. Full Example: Shopping Cart Management System
SWIFT
// ============================================
// Shopping cart management system
// Combining array CRUD, traversal, and higher-order functions
// ============================================
import Foundation
var cartItems: [String] = []
var cartPrices: [Double] = []
func addItem(name: String, price: Double) {
cartItems.append(name)
cartPrices.append(price)
print("Added: \(name) - $\(price)")
}
func removeItem(at index: Int) {
guard index >= 0 && index < cartItems.count else {
print("Invalid index")
return
}
let removed = cartItems.remove(at: index)
cartPrices.remove(at: index)
print("Removed: \(removed)")
}
func updateQuantity(name: String, newPrice: Double) {
if let index = cartItems.firstIndex(of: name) {
cartPrices[index] = newPrice
print("Updated: \(name) -> $\(newPrice)")
}
}
func checkout() {
guard !cartItems.isEmpty else {
print("Cart is empty")
return
}
print("\n=== Shopping Cart ===")
var total = 0.0
for (i, item) in cartItems.enumerated() {
let price = cartPrices[i]
total += price
print("\(i + 1). \(item) - $\(String(format: "%.2f", price))")
}
let tax = total * 0.08
let grandTotal = total + tax
print("---")
print("Subtotal: $\(String(format: "%.2f", total))")
print("Tax (8%): $\(String(format: "%.2f", tax))")
print("Total: $\(String(format: "%.2f", grandTotal))")
let expensiveItems = cartPrices.enumerated().filter { $0.element > 100 }
if !expensiveItems.isEmpty {
print("\nHigh-value items:")
for (i, _) in expensiveItems {
print(" - \(cartItems[i])")
}
}
}
addItem(name: "Laptop", price: 999.0)
addItem(name: "Mouse", price: 25.0)
addItem(name: "Keyboard", price: 89.0)
addItem(name: "Monitor", price: 349.0)
addItem(name: "USB Hub", price: 35.0)
removeItem(at: 4)
updateQuantity(name: "Mouse", newPrice: 22.5)
checkout()
Output:
TEXT 📖 Display onlyAdded: Laptop - $999.0 Added: Mouse - $25.0 Added: Keyboard - $89.0 Added: Monitor - $349.0 Added: USB Hub - $35.0 Removed: USB Hub Updated: Mouse -> $22.5 === Shopping Cart === 1. Laptop - $999.00 2. Mouse - $22.50 3. Keyboard - $89.00 4. Monitor - $349.00 --- Subtotal: $1459.50 Tax (8%): $116.76 Total: $1576.26 High-value items: - Laptop - Monitor
❓ FAQ
Q What happens with an out-of-bounds array access?
A The program crashes (runtime error). Always ensure index < array.count before subscript access, or check with indices.contains(index).
Q What's the performance difference between append and insert?
A append is O(1) (adds to the tail). insert is O(n) (needs to shift subsequent elements). For frequent insertions at the head, consider other data structures (e.g., linked lists).
Q Is Array a value type or a reference type?
A Array is a value type (struct). Assigning to a new variable creates a copy; modifying the copy does not affect the original array.
Q How do I merge two arrays?
A Use the + operator:
let combined = array1 + array2. Or use append(contentsOf:) to add all elements from another array.Q Does removeAll free memory?
A
removeAll() clears elements but keeps the capacity. To also release memory, use removeAll(keepingCapacity: false).📖 Summary
- Arrays are represented as
[Type], creatable via literal, repeated value, or range - Common operations: append, insert, remove, subscript modification
- Arrays are value types — assignment creates a copy
- Traversal options include basic for-in, indexed enumerated, and where filtering
- reduce, map, and filter make bulk operations more concise and functional
- Always check index bounds before accessing array elements to avoid crashes
📝 Exercises
- Beginner: Create an array of 5 city names. Use for-in to print "I love [city name]" for each one, one line each.
- Intermediate: Write a student grade management system: initialize a scores array [78, 92, 55, 88, 73], implement adding new scores, removing failing scores (<60), calculating the average, and finding the highest score.
- Challenge: Implement a simple "cart recommendation" feature. Given a cart array ["Laptop", "Mouse", "Keyboard"] and a recommendation rules table (Laptop → Laptop Bag, Mouse → Mouse Pad, Keyboard → Wrist Rest), auto-generate recommended items and add them to the cart. Do not add items already present.
