【Swift】Arrayの操作方法をまとめてみた

はじめに

Arrayから要素を追加・削除・取得する場合に、もっと簡単にできる方法があるのでは？と思うことがよくあるので、ドキュメントを確認しながら追加・削除・取得用途のものを一部まとめてみました。

要素の追加

func append(Element)

：要素を追加

var numbers = [1, 2, 3, 4, 5]
numbers.append(100)
print(numbers)
// Prints "[1, 2, 3, 4, 5, 100]"

func insert(Element, at: Int)　

：指定した位置に要素を追加

var numbers = [1, 2, 3, 4, 5]
numbers.insert(100, at: 3)
numbers.insert(200, at: numbers.endIndex)

print(numbers)
// Prints "[1, 2, 3, 100, 4, 5, 200]"

要素の削除

func remove(at: Int) -> Element

：指定した位置の要素を削除

var measurements: [Double] = [1.1, 1.5, 2.9, 1.2, 1.5, 1.3, 1.2]
let removed = measurements.remove(at: 2)
print(measurements)
// Prints "[1.1, 1.5, 1.2, 1.5, 1.3, 1.2]"

func removeFirst() -> Element

：最初の要素を削除

var bugs = ["Aphid", "Bumblebee", "Cicada", "Damselfly", "Earwig"]
bugs.removeFirst()
print(bugs)
// Prints "["Bumblebee", "Cicada", "Damselfly", "Earwig"]"

func removeLast() -> Element

：最後の要素を削除

var bugs = ["Aphid", "Bumblebee", "Cicada", "Damselfly", "Earwig"]
bugs.removeLast()
print(bugs)
// Prints "["Aphid",　"Bumblebee", "Cicada", "Damselfly"]"

func removeFirst(Int)

：指定した数の要素を最初から削除

var bugs = ["Aphid", "Bumblebee", "Cicada", "Damselfly", "Earwig"]
bugs.removeFirst(3)
print(bugs)
// Prints "["Damselfly", "Earwig"]"

func removeLast(Int)

：指定した数の要素を最後から削除

var bugs = ["Aphid", "Bumblebee", "Cicada", "Damselfly", "Earwig"]
bugs.removeLast(3)
print(bugs)
// Prints "["Aphid", "Bumblebee"]"

func removeSubrange(Range<Int>)

：指定した範囲の要素を削除

var measurements = [1.2, 1.5, 2.9, 1.2, 1.5]
measurements.removeSubrange(1..<4)
print(measurements)
// Prints "[1.2, 1.5]"

func removeAll(where: (Element) -> Bool)

：条件に合った要素を全て削除

var phrase = "The rain in Spain stays mainly in the plain."

let vowels: Set<Character> = ["a", "e", "i", "o", "u"]
phrase.removeAll(where: { vowels.contains($0) })
// phrase == "Th rn n Spn stys mnly n th pln."

func popLast() -> Element?

：最後の要素を削除＆削除した要素の取得

var bugs = ["Aphid", "Bumblebee", "Cicada", "Damselfly", "Earwig"]
print(bugs.popLast())
print(bugs)

// Prints "Earwig"
// Prints "["Aphid",　"Bumblebee", "Cicada", "Damselfly"]"

要素の取得

var first: Element?

：最初の要素を取得

let numbers = [10, 20, 30, 40, 50]
if let firstNumber = numbers.first {
    print(firstNumber)
}
// Prints "10"

var last: Element?

：最後の要素を取得

let numbers = [10, 20, 30, 40, 50]
if let lastNumber = numbers.last {
    print(lastNumber)
}
// Prints "50"

func randomElement() -> Element?

：ランダムな要素を取得

let names = ["Zoey", "Chloe", "Amani", "Amaia"]
let randomName = names.randomElement()!
// randomName == "Amani"

func contains(_ element: Element) -> Bool(Equatableの場合のみ)

：要素が含まれるかどうか(Equatable)

let cast = ["Vivien", "Marlon", "Kim", "Karl"]
print(cast.contains("Marlon"))
// Prints "true"
print(cast.contains("James"))
// Prints "false"

func firstIndex(of: Element) -> Int?(Equatableの場合のみ)

：要素が含まれる最初のIndexを取得(Equatable)

var students = ["Ben", "Ivy", "Jordell", "Maxime"]
if let i = students.firstIndex(of: "Maxime") {
    students[i] = "Max"
}
print(students)
// Prints "["Ben", "Ivy", "Jordell", "Max"]"

func lastIndex(of: Element) -> Int?(Equatableの場合のみ)

：要素が含まれる最後のIndexを取得(Equatable)

var students = ["Ben", "Ivy", "Jordell", "Ben", "Maxime"]
if let i = students.lastIndex(of: "Ben") {
    students[i] = "Benjamin"
}
print(students)
// Prints "["Ben", "Ivy", "Jordell", "Benjamin", "Max"]"

func min() -> Element?(Comparableの場合のみ)

：最小値を取得(Comparable）

let heights = [67.5, 65.7, 64.3, 61.1, 58.5, 60.3, 64.9]
let lowestHeight = heights.min()
print(lowestHeight)
// Prints "Optional(58.5)"

func max() -> Element?(Comparableの場合のみ)

：最大値を取得(Comparable）

let heights = [67.5, 65.7, 64.3, 61.1, 58.5, 60.3, 64.9]
let greatestHeight = heights.max()
print(greatestHeight)
// Prints "Optional(67.5)"

func prefix(Int) -> ArraySlice<Element>

：指定した数の要素を先頭から全て(配列)取得

let numbers = [1, 2, 3, 4, 5]
print(numbers.prefix(2))
// Prints "[1, 2]"
print(numbers.prefix(10))
// Prints "[1, 2, 3, 4, 5]"

func suffix(Int) -> ArraySlice<Element>

：指定した数の要素を最後から全て(配列)取得

let numbers = [1, 2, 3, 4, 5]
print(numbers.suffix(2))
// Prints "[4, 5]"
print(numbers.suffix(10))
// Prints "[1, 2, 3, 4, 5]"

func dropFirst(Int) -> ArraySlice<Element>

：指定した位置以降の全ての要素(配列)を取得

let numbers = [1, 2, 3, 4, 5]
print(numbers.dropFirst(2))
// Prints "[3, 4, 5]"
print(numbers.dropFirst(10))
// Prints "[]"

func dropLast(Int) -> ArraySlice<Element>

：指定した位置までの全ての要素(配列)を取得

let numbers = [1, 2, 3, 4, 5]
print(numbers.dropLast(2))
// Prints "[1, 2, 3]"
print(numbers.dropLast(10))
// Prints "[]"

要素を検索して取得

func contains(where: (Element) -> Bool) -> Bool

：条件に合う要素が含まれるかどうか

let expenses = [21.37, 55.21, 9.32, 10.18, 388.77, 11.41]
let hasBigPurchase = expenses.contains { $0 > 100 }
// 'hasBigPurchase' == true

func allSatisfy((Element) -> Bool) -> Bool

：条件を全ての要素が満たすかどうか

let names = ["Sofia", "Camilla", "Martina", "Mateo", "Nicolás"]
let allHaveAtLeastFive = names.allSatisfy({ $0.count >= 5 })
// allHaveAtLeastFive == true

func first(where: (Element) -> Bool) -> Element?

：条件を満たす最初の要素を取得

let numbers = [3, 7, 4, -2, 9, -6, 10, 1]
if let firstNegative = numbers.first(where: { $0 < 0 }) {
    print("The first negative number is \(firstNegative).")
}
// Prints "The first negative number is -2."

func firstIndex(where: (Element) -> Bool) -> Int?

：条件を満たす最初のIndexを取得

var students = ["Ben", "Ivy", "Jordell", "Maxime"]
if let i = students.firstIndex(of: "Maxime") {
    students[i] = "Max"
}
print(students)
// Prints "["Ben", "Ivy", "Jordell", "Max"]"

func last(where: (Element) -> Bool) -> Element?

：条件を満たす最後の要素を取得

let numbers = [3, 7, 4, -2, 9, -6, 10, 1]
if let lastNegative = numbers.last(where: { $0 < 0 }) {
    print("The last negative number is \(lastNegative).")
}
// Prints "The last negative number is -6."

func lastIndex(where: (Element) -> Bool) -> Int?

：条件を満たす最後のIndexを取得

let students = ["Kofi", "Abena", "Peter", "Kweku", "Akosua"]
if let i = students.lastIndex(where: { $0.hasPrefix("A") }) {
    print("\(students[i]) starts with 'A'!")
}
// Prints "Akosua starts with 'A'!"

func filter((Element) -> Bool) -> [Element]

：条件に合った全ての要素(配列)を取得

let cast = ["Vivien", "Marlon", "Kim", "Karl"]
let shortNames = cast.filter { $0.count < 5 }
print(shortNames)
// Prints "["Kim", "Karl"]"

各要素に処理を加えて取得

func map<T>((Element) -> T) -> [T]

：処理を加えた全ての要素(配列)を取得

let cast = ["Vivien", "Marlon", "Kim", "Karl"]
let lowercaseNames = cast.map { $0.lowercased() }
// 'lowercaseNames' == ["vivien", "marlon", "kim", "karl"]
let letterCounts = cast.map { $0.count }
// 'letterCounts' == [6, 6, 3, 4]

func flatMap<SegmentOfResult>((Element) -> SegmentOfResult) -> [SegmentOfResult.Element]

：処理を加えた全ての要素を一つの配列にしてから取得

let numbers = [1, 2, 3, 4]

let mapped = numbers.map { Array(repeating: $0, count: $0) }
// [[1], [2, 2], [3, 3, 3], [4, 4, 4, 4]]

let flatMapped = numbers.flatMap { Array(repeating: $0, count: $0) }
// [1, 2, 2, 3, 3, 3, 4, 4, 4, 4]

func compactMap<ElementOfResult>((Element) -> ElementOfResult?) -> [ElementOfResult]

：処理を加えた全てのnil以外の要素(配列)を取得

let possibleNumbers = ["1", "2", "three", "///4///", "5"]

let mapped: [Int?] = possibleNumbers.map { str in Int(str) }
// [1, 2, nil, nil, 5]

let compactMapped: [Int] = possibleNumbers.compactMap { str in Int(str) }
// [1, 2, 5]

その他

for-inループとforEachの違い

func forEach((Element) -> Void)

let numberWords = ["one", "two", "three"]
for word in numberWords {
    print(word)
}
// Prints "one"
// Prints "two"
// Prints "three"

numberWords.forEach { word in
    print(word)
}
// Same as above

forEachでは、

• breakやcontinueを使って、ボディクロージャの現在の呼び出しを終了したり、後続の呼び出しをスキップはできない

• ボディクロージャでreturnを使用すると、ボディクロージャの現在の呼び出しのみから終了し、外部スコープからは終了せず、後続の呼び出しもスキップしない

おわりに

多すぎて全てを網羅することはできませんでした。。。必要になったものがあれば、都度追記してみたいと思います。表現が間違っている箇所あるかもしれません。ご指摘いただけると嬉しいです。

参考

ocumentation/swift/sequence

documentation/swift/collection

documentation/swift/sequence/filter