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Arrays & Sets

Array

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]

Index

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 = ["🥓", "🥞", "🍪", "🥛", "🍊"]


print(grocery.count)


// 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.append("Thunder")
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 = ["🌖", "🌗", "🌘", "🌑"]


moon.insert("🌕", at: 0)


// ["🌕", "🌖", "🌗", "🌘", "🌑"]


moon.remove(at: 4)


// ["🌕", "🌖", "🌗", "🌘"]

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 {
  print(person)
}


// Prints: Michael
// Prints: Dwight
// Prints: Jim
// Prints: Pam
// Prints: Andy

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>()


print(team)
// 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"]

.insert()

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
oddNumbers.remove(2)


// Remove all elements
oddNumbers.removeAll()

.contains()

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)
print(setC) 
// 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)
print(setC) 
// 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)
print(setC) 
// Prints: ["B", "A"]
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