Swift 4-如何从数组中返回重复值的计数？

Question

我有一个具有多个值（双精度）的数组，其中许多是重复的。我想返回或打印所有唯一值的列表，以及给定值在数组中出现多少次的计数。我对Swift来说还很陌生，我尝试了几种不同的方法，但是我不确定实现此目的的最佳方法。

像这样的内容：[65.0、65.0、65.0、55.5、55.5、30.25、30.25、27.5]

将打印（例如）：“ 3 at 65.0、2 at 55.5、2 at 30.25、1 at 27.5”。

我不太关心输出，而不是实现此目的的方法。

谢谢！

Answer 1

正如@rmaddy已经评论的那样，您可以按以下方式使用Foundation NSCountedSet：

import Foundation // or iOS UIKit or macOS Cocoa

let values = [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]
let countedSet = NSCountedSet(array: values)
print(countedSet.count(for: 65.0))   // 3
for value in countedSet {
    print("Element:", value, "count:", countedSet.count(for: value))
}

Xcode 11•Swift 5.1

您还可以扩展NSCountedSet以返回元组数组或字典：

extension NSCountedSet {
    var occurences: [(object: Any, count: Int)] { map { ($0, count(for: $0))} }
    var dictionary: [AnyHashable: Int] {
        reduce(into: [:]) {
            guard let key = $1 as? AnyHashable else { return }
            $0[key] = count(for: key)
        }
    }
}

let values = [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]
let countedSet = NSCountedSet(array: values)
for (key, value) in countedSet.dictionary {
    print("Element:", key, "count:", value)
}

对于Swift本机解决方案，我们可以将Sequence其元素的约束扩展到Hashable：

extension Sequence where Element: Hashable {
    var frequency: [Element: Int] { reduce(into: [:]) { $0[$1, default: 0] += 1 } }
}

let values = [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]
let frequency = values.frequency
frequency[65] // 3
for (key, value) in frequency {
    print("Element:", key, "count:", value)
}

那些会打印

Element: 27.5 count: 1
Element: 30.25 count: 2
Element: 55.5 count: 2
Element: 65 count: 3

Answer 2

您可以枚举数组并将值添加到字典中。

var array: [CGFloat] =  [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]
var dictionary = [CGFloat: Int]()

for item in array {
   dictionary[item] = dictionary[item] ?? 0 + 1
}

print(dictionary)

或者你可以在数组上执行 foreach ：

array.forEach { (item) in
  dictionary[item] = dictionary[item] ?? 0 + 1
}

print(dictionary)

或者正如@rmaddy 所说：

var set: NSCountedSet =  [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]
var dictionary = [Float: Int]()
set.forEach { (item) in
  dictionary[item as! Float] = set.count(for: item)
}

print(dictionary)