Collection Types
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Creating an Empty Array
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var someInts = [Int]()
print("someInts is of type [Int] with \(someInts.count) items.")
// Prints "someInts is of type [Int] with 0 items."
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someInts.append(3)
// someInts now contains 1 value of type Int
someInts = []
// someInts is now an empty array, but is still of type [Int]
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Creating an Array with a Default Value
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var threeDoubles = Array(repeating: 0.0, count: 3)
// threeDoubles is of type [Double], and equals [0.0, 0.0, 0.0]
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Creating an Array by Adding Two Arrays Together
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var anotherThreeDoubles = Array(repeating: 2.5, count: 3)
// anotherThreeDoubles is of type [Double], and equals [2.5, 2.5, 2.5]
var sixDoubles = threeDoubles + anotherThreeDoubles
// sixDoubles is inferred as [Double], and equals [0.0, 0.0, 0.0, 2.5, 2.5, 2.5]
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Creating an Array with an Array Literal
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[value 1, value 2, value 3]
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var shoppingList: [String] = ["Eggs", "Milk"]
// shoppingList has been initialized with two initial items
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var shoppingList = ["Eggs", "Milk"]
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Accessing and Modifying an Array
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print("The shopping list contains \(shoppingList.count) items.")
// Prints "The shopping list contains 2 items."
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if shoppingList.isEmpty {
print("The shopping list is empty.")
} else {
print("The shopping list is not empty.")
}
// Prints "The shopping list is not empty."
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shoppingList.append("Flour")
// shoppingList now contains 3 items, and someone is making pancakes
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shoppingList += ["Baking Powder"]
// shoppingList now contains 4 items
shoppingList += ["Chocolate Spread", "Cheese", "Butter"]
// shoppingList now contains 7 items
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var firstItem = shoppingList[0]
// firstItem is equal to "Eggs"
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shoppingList[0] = "Six eggs"
// the first item in the list is now equal to "Six eggs" rather than "Eggs"
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shoppingList[4...6] = ["Bananas", "Apples"]
// shoppingList now contains 6 items
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shoppingList.insert("Maple Syrup", at: 0)
// shoppingList now contains 7 items
// "Maple Syrup" is now the first item in the list
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let mapleSyrup = shoppingList.remove(at: 0)
// the item that was at index 0 has just been removed
// shoppingList now contains 6 items, and no Maple Syrup
// the mapleSyrup constant is now equal to the removed "Maple Syrup" string
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firstItem = shoppingList[0]
// firstItem is now equal to "Six eggs"
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let apples = shoppingList.removeLast()
// the last item in the array has just been removed
// shoppingList now contains 5 items, and no apples
// the apples constant is now equal to the removed "Apples" string
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Iterating Over an Array
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for item in shoppingList {
print(item)
}
// Six eggs
// Milk
// Flour
// Baking Powder
// Bananas
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for (index, value) in shoppingList.enumerated() {
print("Item \(index + 1): \(value)")
}
// Item 1: Six eggs
// Item 2: Milk
// Item 3: Flour
// Item 4: Baking Powder
// Item 5: Bananas
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Creating and Initializing an Empty Set
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var letters = Set<Character>()
print("letters is of type Set<Character> with \(letters.count) items.")
// Prints "letters is of type Set<Character> with 0 items."
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letters.insert("a")
// letters now contains 1 value of type Character
letters = []
// letters is now an empty set, but is still of type Set<Character>
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Creating a Set with an Array Literal
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var favoriteGenres: Set<String> = ["Rock", "Classical", "Hip hop"]
// favoriteGenres has been initialized with three initial items
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var favoriteGenres: Set = ["Rock", "Classical", "Hip hop"]
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Accessing and Modifying a Set
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print("I have \(favoriteGenres.count) favorite music genres.")
// Prints "I have 3 favorite music genres."
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if favoriteGenres.isEmpty {
print("As far as music goes, I'm not picky.")
} else {
print("I have particular music preferences.")
}
// Prints "I have particular music preferences."
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favoriteGenres.insert("Jazz")
// favoriteGenres now contains 4 items
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if let removedGenre = favoriteGenres.remove("Rock") {
print("\(removedGenre)? I'm over it.")
} else {
print("I never much cared for that.")
}
// Prints "Rock? I'm over it."
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if favoriteGenres.contains("Funk") {
print("I get up on the good foot.")
} else {
print("It's too funky in here.")
}
// Prints "It's too funky in here."
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Iterating Over a Set
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for genre in favoriteGenres {
print("\(genre)")
}
// Classical
// Jazz
// Hip hop
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for genre in favoriteGenres.sorted() {
print("\(genre)")
}
// Classical
// Hip hop
// Jazz
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Fundamental Set Operations
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let oddDigits: Set = [1, 3, 5, 7, 9]
let evenDigits: Set = [0, 2, 4, 6, 8]
let singleDigitPrimeNumbers: Set = [2, 3, 5, 7]
oddDigits.union(evenDigits).sorted()
// [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
oddDigits.intersection(evenDigits).sorted()
// []
oddDigits.subtracting(singleDigitPrimeNumbers).sorted()
// [1, 9]
oddDigits.symmetricDifference(singleDigitPrimeNumbers).sorted()
// [1, 2, 9]
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Set Membership and Equality
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let houseAnimals: Set = ["🐶", "🐱"]
let farmAnimals: Set = ["🐮", "🐔", "🐑", "🐶", "🐱"]
let cityAnimals: Set = ["🐦", "🐭"]
houseAnimals.isSubset(of: farmAnimals)
// true
farmAnimals.isSuperset(of: houseAnimals)
// true
farmAnimals.isDisjoint(with: cityAnimals)
// true
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Creating an Empty Dictionary
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var namesOfIntegers = [Int: String]()
// namesOfIntegers is an empty [Int: String] dictionary
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namesOfIntegers[16] = "sixteen"
// namesOfIntegers now contains 1 key-value pair
namesOfIntegers = [:]
// namesOfIntegers is once again an empty dictionary of type [Int: String]
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Creating a Dictionary with a Dictionary Literal
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[key 1: value 1, key 2: value 2, key 3: value 3]
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var airports: [String: String] = ["YYZ": "Toronto Pearson", "DUB": "Dublin"]
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var airports = ["YYZ": "Toronto Pearson", "DUB": "Dublin"]
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Accessing and Modifying a Dictionary
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print("The airports dictionary contains \(airports.count) items.")
// Prints "The airports dictionary contains 2 items."
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if airports.isEmpty {
print("The airports dictionary is empty.")
} else {
print("The airports dictionary is not empty.")
}
// Prints "The airports dictionary is not empty."
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airports["LHR"] = "London"
// the airports dictionary now contains 3 items
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airports["LHR"] = "London Heathrow"
// the value for "LHR" has been changed to "London Heathrow"
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if let oldValue = airports.updateValue("Dublin Airport", forKey: "DUB") {
print("The old value for DUB was \(oldValue).")
}
// Prints "The old value for DUB was Dublin."
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if let airportName = airports["DUB"] {
print("The name of the airport is \(airportName).")
} else {
print("That airport is not in the airports dictionary.")
}
// Prints "The name of the airport is Dublin Airport."
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airports["APL"] = "Apple International"
// "Apple International" is not the real airport for APL, so delete it
airports["APL"] = nil
// APL has now been removed from the dictionary
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if let removedValue = airports.removeValue(forKey: "DUB") {
print("The removed airport's name is \(removedValue).")
} else {
print("The airports dictionary does not contain a value for DUB.")
}
// Prints "The removed airport's name is Dublin Airport."
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Iterating Over a Dictionary
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for (airportCode, airportName) in airports {
print("\(airportCode): \(airportName)")
}
// LHR: London Heathrow
// YYZ: Toronto Pearson
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for airportCode in airports.keys {
print("Airport code: \(airportCode)")
}
// Airport code: LHR
// Airport code: YYZ
for airportName in airports.values {
print("Airport name: \(airportName)")
}
// Airport name: London Heathrow
// Airport name: Toronto Pearson
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let airportCodes = [String](airports.keys)
// airportCodes is ["LHR", "YYZ"]
let airportNames = [String](airports.values)
// airportNames is ["London Heathrow", "Toronto Pearson"]
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