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: aprint(vowels[1]) // Prints: eprint(vowels[2]) // Prints: iprint(vowels[3]) // Prints: oprint(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 elementcookieJar.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 elementoddNumbers.remove(2)// Remove all elementsoddNumbers.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: falseif 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: truevar 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"]
