Swift — Arrays

Creating arrays

let nums = [1, 2, 3, 4, 5]
var mutable = [String]()
mutable.append("Hello")
mutable.append("World")

// Initialize with count and value
let zeros = Array(repeating: 0, count: 5)

Array operations

var nums = [1, 2, 3, 4, 5]

nums.append(6)          // Add to end
nums.insert(0, at: 0)   // Insert at index
nums.remove(at: 0)      // Remove at index
nums.removeFirst()      // Remove first
nums.removeLast()       // Remove last

print(nums) // [2, 3, 4, 5, 6]

Array methods

let nums = [1, 2, 3, 4, 5]

print(nums.count)       // 5
print(nums.isEmpty)     // false
print(nums.contains(3)) // true
print(nums.first ?? 0)  // 1
print(nums.last ?? 0)   // 5
print(nums.sorted())    // [1, 2, 3, 4, 5]
print(nums.reversed())  // [5, 4, 3, 2, 1]

Map, filter, reduce

let nums = [1, 2, 3, 4, 5]

let doubled = nums.map { $0 * 2 }
print(doubled) // [2, 4, 6, 8, 10]

let evens = nums.filter { $0 % 2 == 0 }
print(evens) // [2, 4]

let sum = nums.reduce(0, +)
print(sum) // 15

Chaining

let result = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    .filter { $0 % 2 == 0 }
    .map { $0 * $0 }
    .prefix(3)
    .reduce(0, +)
print(result) // 20

Sets

let set: Set = [1, 2, 3, 2, 1]
print(set) // {1, 2, 3}

let a: Set = [1, 2, 3]
let b: Set = [3, 4, 5]
print(a.union(b))      // {1, 2, 3, 4, 5}
print(a.intersection(b)) // {3}
print(a.subtracting(b))  // {1, 2}

Dictionaries

var ages = ["Alice": 30, "Bob": 25]
ages["Charlie"] = 35
ages.removeValue(forKey: "Bob")

print(ages["Alice"] ?? 0) // 30

for (name, age) in ages {
    print("\(name): \(age)")
}

Mini Practice

Write Swift code that:

1. Creates and manipulates an array
2. Chains filter, map, and reduce
3. Uses set operations
4. Iterates a dictionary with for

Up Next

In the next lesson, you'll learn about Sets — unordered collections.