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Arrays, Loops, and Sets

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Swift Sets

We can use a set to store unique elements of the same data type.

var paintingsInMOMA: Set = ["The Dream", "The Starry Night", "The False Mirror"]

Empty Sets

An empty set is a set that contains no values inside of it.

var team = Set<String>()
// Prints: []

Populated Sets

To create a set populated with values, use the Set keyword before the assignment operator.

The values of the set must be contained within brackets [] and separated with commas ,.

var vowels: Set = ["a", "e", "i", "o", "u"]


To insert a single value into a set, append .insert() to a set and place the new value inside the parentheses ().

var cookieJar: Set = ["Chocolate Chip", "Oatmeal Raisin"]
// Add a new element
cookieJar.insert("Peanut Butter Chip")

.remove() and .removeAll() Methods

To remove a single value from a set, append .remove() to a set with the value to be removed placed inside the parentheses ().

To remove every single value from a set at once, append .removeAll() to a set.

var oddNumbers: Set = [1, 2, 3, 5]
// Remove an existing element
// Remove all elements


Appending .contains() to an existing set with an item in the parentheses () will return a true or false value that states whether the item exists within the set.

var names: Set = ["Rosa", "Doug", "Waldo"]
print(names.contains("Lola")) // Prints: false
if names.contains("Waldo"){
print("There's Waldo!")
} else {
print("Where's Waldo?")
// Prints: There's Waldo!

Iterating Over a Set

A for-in loop can be used to iterate over each item in a set.

var recipe: Set = ["Chocolate chips", "Eggs", "Flour", "Sugar"]
for ingredient in recipe {
print ("Include \(ingredient) in the recipe.")

.isEmpty Property

Use the built-in property .isEmpty to check if a set has no values contained in it.

var emptySet = Set<String>()
print(emptySet.isEmpty) // Prints: true
var populatedSet: Set = [1, 2, 3]
print(populatedSet.isEmpty) // Prints: false

.count Property

The property .count returns the number of elements contained within a set.

var band: Set = ["Guitar", "Bass", "Drums", "Vocals"]
print("There are \(band.count) players in the band.")
// Prints: There are 4 players in the band.

.intersection() Operation

The .intersection() operation populates a new set of elements with the overlapping elements of two sets.

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D", "E", "F"]
var setC = setA.intersection(setB)
print(setC) // Prints: ["D", "C"]

.union() Operation

The .union() operation populates a new set by taking all the values from two sets and combining them.

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D", "E", "F"]
var setC = setA.union(setB)
// Prints: ["B", "A", "D", "F", "C", "E"]

.symmetricDifference() Operation

The .symmetricDifference() operation creates a new set with all the non-overlapping values between two sets.

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D", "E", "F"]
var setC = setA.symmetricDifference(setB)
// Prints: ["B", "E", "F", "A"]

.subtracting() Operation

The .subtracting() operation removes the values of one second set from another set and stores the remaining values in a new set.

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D"]
var setC = setA.subtracting(setB)
// Prints: ["B", "A"]


An array stores an ordered collection of values of the same data type.

Use the initializer syntax, [Type](), to create an empty array of a certain type.

var scores = [Int]()
// The array is empty: []

Initialize with Array Literal

An array can be initialized with an array literal, which is a short-hand method of writing one or more values as an array collection.

An array literal is written as a list of values, separated by commas, and surrounded by a pair of square brackets.

// Using type inference:
var snowfall = [2.4, 3.6, 3.4, 1.8, 0.0]
// Being explicit with the type:
var temp: [Int] = [33, 31, 30, 38, 44]


An index refers to an item’s position within an ordered list. Use the subscript syntax, array[index], to retrieve an individual element from an array.

Note: Swift arrays are zero-indexed, meaning the first element has index 0.

var vowels = ["a", "e", "i", "o", "u"]
print(vowels[0]) // Prints: a
print(vowels[1]) // Prints: e
print(vowels[2]) // Prints: i
print(vowels[3]) // Prints: o
print(vowels[4]) // Prints: u

.count Property

The .count property returns the number of elements in an array.

var grocery = ["πŸ₯“", "πŸ₯ž", "πŸͺ", "πŸ₯›", "🍊"]
// Prints: 5

.append() Method and += Operator

The .append() method can be called on an array to add an item to the end of the array.

The += addition assignment operator can be used to add the elements of another array to the existing array.

var gymBadges = ["Boulder", "Cascade"]
gymBadges += ["Rainbow", "Soul"]
// ["Boulder", "Cascade", "Thunder", "Rainbow", "Soul"]

.insert() and .remove() Methods

The .insert() method can be called on an array to add an element at a specified index. It takes two arguments: value and at: index.

The .remove() method can be called on an array to remove an element at a specified index. It takes one argument: at: index.

var moon = ["πŸŒ–", "πŸŒ—", "🌘", "πŸŒ‘"]
moon.insert("πŸŒ•", at: 0)
// ["πŸŒ•", "πŸŒ–", "πŸŒ—", "🌘", "πŸŒ‘"]
moon.remove(at: 4)
// ["πŸŒ•", "πŸŒ–", "πŸŒ—", "🌘"]

Iterating Over an Array

In Swift, a for-in loop can be used to iterate through the items of an array.

This is a powerful tool for working with and manipulating a large amount of data.

var employees = ["Michael", "Dwight", "Jim", "Pam", "Andy"]
for person in employees {
// Prints: Michael
// Prints: Dwight
// Prints: Jim
// Prints: Pam
// Prints: Andy


Ranges created by the ... operator will include the numbers from the lower bound to (and includes) the upper bound.

let zeroToThree = 0...3
// zeroToThree: 0, 1, 2, 3

stride() Function

Calling stride() with the 3 necessary arguments creates a collection of numbers; the arguments decide the starting number to, the (excluded) ending number, and how to increment/decrement from the start to the end.

for oddNum in stride(from: 1, to: 5, by: 2) {
// Prints: 1
// Prints: 3

for-in Loop

The for-in loop is used to iterate over collections, including strings and ranges.

for char in "hehe" {
// Prints: h
// Prints: e
// Prints: h
// Prints: e

continue Keyword

The continue keyword will force the loop to move on to the next iteration.

for num in 0...5 {
if num % 2 == 0 {
// Prints: 1
// Prints: 3
// Prints: 5

break Keyword

To terminate a loop before its completion, use the break keyword.

for char in "supercalifragilisticexpialidocious" {
if char == "c" {
// Prints: s
// Prints: u
// Prints: p
// Prints: e
// Prints: r

Using Underscore

Use _ instead of a placeholder variable if the variable is not referenced in the for-in loop body.

for _ in 1...3 {
// Prints: OlΓ©
// Prints: OlΓ©
// Prints: OlΓ©

while Loop

A while loop accepts a condition and continually executes its body’s code for as long as the provided condition is true.

If the condition is never false then the loop continues to run and the program is stuck in an infinite loop.

var counter = 1
var stopNum = Int.random(in: 1...10)
while counter < stopNum {
counter += 1
// The loop prints until the stop condition is met