从数组中删除重复项的简单方法

extension Array where Element: Equatable {
mutating func removeDuplicates() {
    var result = [Element]()
    for value in self {
        if !result.contains(value) {
            result.append(value)
        }
    }
    self = result
}}

我认为这是更好的理解逻辑的方法

var arrayOfInts = [2, 2, 4, 4]
var mainArray = [Int]()

for value in arrayOfInts {

if mainArray.contains(value) != true  {
    
    mainArray.append(value)
    print("mainArray:\(mainArray)")
}}

如果你把两个扩展都放在你的代码中，更快的Hashable版本将在可能的情况下使用，Equatable版本将用作备用版本。

public extension Sequence where Element: Hashable {
  /// The elements of the sequence, with duplicates removed.
  /// - Note: Has equivalent elements to `Set(self)`.
  @available(
  swift, deprecated: 5.4,
  message: "Doesn't compile without the constant in Swift 5.3."
  )
  var firstUniqueElements: [Element] {
    let getSelf: (Element) -> Element = \.self
    return firstUniqueElements(getSelf)
  }
}

public extension Sequence where Element: Equatable {
  /// The elements of the sequence, with duplicates removed.
  /// - Note: Has equivalent elements to `Set(self)`.
  @available(
  swift, deprecated: 5.4,
  message: "Doesn't compile without the constant in Swift 5.3."
  )
  var firstUniqueElements: [Element] {
    let getSelf: (Element) -> Element = \.self
    return firstUniqueElements(getSelf)
  }
}

public extension Sequence {
  /// The elements of the sequences, with "duplicates" removed
  /// based on a closure.
  func firstUniqueElements<Hashable: Swift.Hashable>(
    _ getHashable: (Element) -> Hashable
  ) -> [Element] {
    var set: Set<Hashable> = []
    return filter { set.insert(getHashable($0)).inserted }
  }

  /// The elements of the sequence, with "duplicates" removed,
  /// based on a closure.
  func firstUniqueElements<Equatable: Swift.Equatable>(
    _ getEquatable: (Element) -> Equatable
  ) -> [Element] {
    reduce(into: []) { uniqueElements, element in
      if zip(
        uniqueElements.lazy.map(getEquatable),
        AnyIterator { [equatable = getEquatable(element)] in equatable }
      ).allSatisfy(!=) {
        uniqueElements.append(element)
      }
    }
  }
}

如果顺序不重要，那么你总是可以使用这个Set初始化式。

现在不需要写扩展了。

Apple终于在其算法包中引入了unique()方法，可以在符合Sequence协议的任何类型上使用。

import Algorithms

let numbers = [1, 2, 3, 3, 2, 3, 3, 2, 2, 2, 1]
print(numbers.uniqued()) // prints [1, 2, 3]

更多信息https://github.com/apple/swift-algorithms/blob/main/Guides/Unique.md

Daniel Krom的Swift 2答案的更简洁的语法版本，使用了一个尾随闭包和简写参数名，这似乎是基于Airspeed Velocity的原始答案:

func uniq<S: SequenceType, E: Hashable where E == S.Generator.Element>(source: S) -> [E] {
  var seen = [E: Bool]()
  return source.filter { seen.updateValue(true, forKey: $0) == nil }
}

实现一个可以与uniq(_:)一起使用的自定义类型的示例(必须符合Hashable，因此符合Equatable，因为Hashable扩展了Equatable):

func ==(lhs: SomeCustomType, rhs: SomeCustomType) -> Bool {
  return lhs.id == rhs.id // && lhs.someOtherEquatableProperty == rhs.someOtherEquatableProperty
}

struct SomeCustomType {

  let id: Int

  // ...

}

extension SomeCustomType: Hashable {

  var hashValue: Int {
    return id
  }

}

在上面的代码中…

在==重载中使用的id可以是任何Equatable类型(或返回Equatable类型的方法，例如someMethodThatReturnsAnEquatableType())。注释掉的代码演示了扩展相等性检查，其中someOtherEquatableProperty是Equatable类型的另一个属性(但也可以是返回Equatable类型的方法)。

在hashValue计算属性中使用的id(必须符合Hashable)可以是任何Hashable(因此是Equatable)属性(或返回Hashable类型的方法)。

使用uniq(_:)的示例:

var someCustomTypes = [SomeCustomType(id: 1), SomeCustomType(id: 2), SomeCustomType(id: 3), SomeCustomType(id: 1)]

print(someCustomTypes.count) // 4

someCustomTypes = uniq(someCustomTypes)

print(someCustomTypes.count) // 3

这只是一个非常简单和方便的实现。具有相等元素的数组扩展中的计算属性。

extension Array where Element: Equatable {
    /// Array containing only _unique_ elements.
    var unique: [Element] {
        var result: [Element] = []
        for element in self {
            if !result.contains(element) {
                result.append(element)
            }
        }

        return result
    }
}