【Swift】配列を整理するときに便利な関数まとめ

配列を整理するときに便利な関数をまとめました。

map

配列の要素を１つずつ変換する。

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]

https://developer.apple.com/documentation/swift/array/3017522-map より

compactMap

クロージャーでnilだったものを除外して処理する。

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]

https://developer.apple.com/documentation/swift/array/2957701-compactmap より

flatMap

配列の要素を１つずつ分解して配列に追加する。

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]

https://developer.apple.com/documentation/swift/sequence/2905332-flatmap より

reduce

配列の要素を１つの値にまとめる。

let numbers = [1, 2, 3, 4]
let numberSum = numbers.reduce(0, { x, y in
    x + y
})
// numberSum == 10

https://developer.apple.com/documentation/swift/array/2298686-reduce より

allSatisfy

配列の全要素がクロージャーの条件を満たすか判別。

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

https://developer.apple.com/documentation/swift/array/2994715-allsatisfy より

sort

配列を昇順あるいは降順に並び替える。

var students = ["Kofi", "Abena", "Peter", "Kweku", "Akosua"]
students.sort()
print(students)
// Prints "["Abena", "Akosua", "Kofi", "Kweku", "Peter"]"

students.sort(by: >)
print(students)
// Prints "["Peter", "Kweku", "Kofi", "Akosua", "Abena"]"

https://developer.apple.com/documentation/swift/array/1688499-sort より

filter

クロージャーの条件を満たす要素のみ抜き出す。

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

https://developer.apple.com/documentation/swift/sequence/3018365-filter より

forEach

配列の中身を繰り返す。

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

numberWords.forEach { word in
    print(word)
}
// Prints "one"
// Prints "two"
// Prints "three"

https://developer.apple.com/documentation/swift/array/1689783-foreach より

joined

要素の間に指定した区切り文字を追加した上で配列の中身を連結する。

let cast = ["Vivien", "Marlon", "Kim", "Karl"]
let list = cast.joined(separator: ", ")
print(list)
// Prints "Vivien, Marlon, Kim, Karl"

https://developer.apple.com/documentation/swift/sequence/1641243-joined より

prefix

配列の頭からの範囲を指定して分割。

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

https://developer.apple.com/documentation/swift/array/1689487-prefix より

suffix

配列の後ろからの範囲を指定して分割。

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

https://developer.apple.com/documentation/swift/array/1687909-suffix より

minElement

配列の最小要素を取得。

let scores = [84, 76, 91, 62 ,80]
scores.minElement() // 62

https://qiita.com/motokiee/items/cf83b22cb34921580a52 より

maxElement

配列の最大要素を取得。

let scores = [84, 76, 91, 62 ,80]
scores.maxElement() // 91

https://qiita.com/motokiee/items/cf83b22cb34921580a52 より

dropFirst

配列の最初から指定した個数分の要素を削除。

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

https://developer.apple.com/documentation/swift/array/1688675-dropfirst より

dropLast

配列の最後から指定した個数分の要素を削除。

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

https://developer.apple.com/documentation/swift/array/1689751-droplast より

reverse

配列の順番を逆にする。

var characters: [Character] = ["C", "a", "f", "é"]
characters.reverse()
print(characters)
// Prints "["é", "f", "a", "C"]

https://developer.apple.com/documentation/swift/array/2943836-reverse より

shuffle

配列の順番をランダムに並び替える。

var names = ["Alejandro", "Camila", "Diego", "Luciana", "Luis", "Sofía"]
names.shuffle(using: myGenerator)
// names == ["Luis", "Camila", "Luciana", "Sofía", "Alejandro", "Diego"]

https://developer.apple.com/documentation/swift/array/2994753-shuffle より

insert

配列の特定の位置に要素を追加する。

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]"

https://developer.apple.com/documentation/swift/array/3126951-insert より

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