如何过滤具有唯一属性的对象数组？

Question

请原谅下面这个人为的例子，但我怎样才能像这样过滤？使用 Set 去重不是一种选择，因为我的真实数据对象有另一个属性，每个对象都是唯一的。

struct MyDataObject {
    var startDate: Date
    var endDate: Date
}

let dataObject1 = MyDataObject(startDate: Date().startOfDay(), endDate: Date().startOfDay())
let duplicateDataObject = MyDataObject(startDate: Date().startOfDay(), endDate: Date().startOfDay())

let array = [dataObject1, duplicateDataObject]

//How to filter to end up with an array of data objects with a unique start date?

Answer 1

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

import Algorithms

array.uniqued(on: \.startDate)

或者，如果您需要更多地控制选择哪些元素：

array.uniqued(on: \.startDate) { [[=11=], ].max(by: \.endDate)! }

import struct OrderedCollections.OrderedDictionary

public extension Sequence {
  @inlinable func uniqued<Subject: Hashable>(
    on projection: (Element) throws -> Subject,
    uniquingWith combine: (Element, Element) throws -> Element
  ) rethrows -> [Element] {
    try OrderedDictionary(keyed(by: projection), uniquingKeysWith: combine)
      .values
      .elements
  }

  @inlinable func max<Comparable: Swift.Comparable>(
    by getComparable: (Element) throws -> Comparable
  ) rethrows -> Element? {
    try self.max {
      try getComparable([=12=]) < getComparable()
    }
  }
}

public extension Sequence {
  @inlinable func keyed<Key: Hashable>(
    by key: (Element) throws -> Key
  ) rethrows -> [KeyValuePairs<Key, Element>.Element] {
    try map { (try key([=13=]), [=13=]) }
  }
}

Answer 2

您的意思是过滤以便只保留在原始集合中恰好出现一次的元素吗？

import OrderedCollections

struct A {
    let id: String
    let thing: String
}

let things: [A] = [
    .init(id: "1", thing: "thing"),
    .init(id: "2", thing: "thing"),
    .init(id: "3", thing: "thing"),
    .init(id: "2", thing: "thing"),
    .init(id: "1", thing: "thing"),
    .init(id: "4", thing: "thing"),
    .init(id: "2", thing: "thing"),
]

let uniqueThings = OrderedDictionary<String, [A]>(grouping: things, by: \.id)
    .filter { [=10=].value.count == 1 }
    .values

仅给出具有唯一 ID（在此示例中为 3 和 4）的 A

或者你的意思只是去重，比如 https://github.com/apple/swift-algorithms/blob/main/Guides/Unique.md uniqued(on:) 如果是的话，如果有多个元素，应该保留哪个元素，第一个看到的，最后一个等等？

如何过滤具有唯一属性的对象数组？

How to filter an array of objects with unique properties?

arrays

filter

ios

swift