转换数组

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最近项目中，非持久化部分使用了数组来暂存数据，涉及到去重。一直以来都是 for in 循序遍历来处理数组，比较了函数式编程，还是后者的模块化组装性比较有优势。

《Advanced Swift》中 Transforming Arrays 一节讲解了一些数组的基本映射转换方法。其中主要是重新实现了部分方法，以及推荐我们自己写一些拓展标准库的方法。

以下是标准库中13个独立的方法，可以随意组合使用：

  • map and flatMap — how to transform an element 映射：如何转换每一个元素
  • filter — should an element be included? 过滤：是否应该包含该元素
  • reduce — how to fold an element into an aggregate value 归纳：如何折叠元素到一个总值
  • sort and lexicographicCompare — in what order should two elements come? 排序和字典顺序比较：两个元素如何排序
  • indexOf and contains — does this element match? 索引/下标 和 包含：是否与该元素匹配
  • minElement and maxElement — which is the min/max of two elements? 最小元素和最大元素：两个元素中最小/最大的那个
  • elementsEqual and startsWith — are two elements equivalent? 元素等于和开始于：两个元素是否是对等
  • split — is this element a separator? 分割：该元素是否是分隔符

编程毕竟是操作性的语言，以上都有表意很明确的方法，只要在实际调用几次也就理解了。下面是我写的 Demo ：

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// : Playground - noun: a place where people can play

import UIKit

var fibs = [2, 3, 45, 53, 32, 12, 32, 1, 0, 1]

fibs.map {
    Double($0 * 3)
}

let suits = ["♠", "♥", "♣", "♦"]

let ranks = ["J", "Q", "K", "A"]

let allCombinations = suits.flatMap { suit in
    ranks.map { rank in
        (suit, rank)
    }
}

suits.flatMap { (suit) -> [String]? in
    [suit, suit]
}

suits.flatMap { (suit) -> [String] in
    if suit != "♥" {
        return [suit]
    } else {
        return []
    }
}

fibs.flatMap { (num) in
    print(num)
}

fibs.sort {
    $0 > $1
}

fibs.lexicographicalCompare([3])
fibs.lexicographicalCompare([1])
fibs.lexicographicalCompare([3]) { (num0, num1) -> Bool in
    num0 > num1
}
fibs.lexicographicalCompare([1]) { (num0, num1) -> Bool in
    num0 > num1
}

fibs.reduce(0) { (total, num) -> Int in
    total + num
}

fibs.filter { (num) -> Bool in
    num % 3 == 0
}

fibs.indexOf(4)
fibs.indexOf(1)
fibs.contains(4)
fibs.contains(1)

fibs.minElement()
fibs.minElement { (num0, num1) -> Bool in
    num0 < num1
}
fibs.minElement { (num0, num1) -> Bool in
    num0 > num1
}
fibs.maxElement()
fibs.maxElement { (num0, num1) -> Bool in
    print("num0: \(num0), num1: \(num1)")
    return num0 < num1
}

fibs.maxElement { (num0, num1) -> Bool in
    num0 > num1
}

var strs = ["Lee", "Bee", "Will", "10", ""]
strs.maxElement { (str0, str1) -> Bool in
    str0 < str1
}
strs.maxElement { (str0, str1) -> Bool in
    str0 > str1
}

strs.elementsEqual(["Lee", "Bee", "Will", "10"])
strs.elementsEqual(["Lee", "Bee", "Will", "10", ""])

strs.startsWith(["Lee"])
strs.startsWith(["10"])
strs.startsWith(["Lee"]) { (str0, str1) -> Bool in
    str0 == str1
}

strs.split("10")
strs.split("3")
fibs.split(1)

fibs.split(1, maxSplit: 2, allowEmptySlices: true)
fibs.split(1, maxSplit: 2, allowEmptySlices: false)
fibs.split(1, maxSplit: 3, allowEmptySlices: true)
fibs.split(1, maxSplit: 6, allowEmptySlices: false)
fibs.split(3333, maxSplit: 2, allowEmptySlices: true)
fibs.split(44444, maxSplit: 2, allowEmptySlices: false)

fibs.split(32, maxSplit: 0, allowEmptySlices: true)
fibs.split(32, maxSplit: 1, allowEmptySlices: false)
fibs.split(32, maxSplit: 2, allowEmptySlices: true)
fibs.split(32, maxSplit: 3, allowEmptySlices: false)

fibs.split { (num) -> Bool in
    num % 2 == 0
}

fibs.split(1, allowEmptySlices: true) { (num) -> Bool in
    num % 2 == 1
}

fibs.split(66, allowEmptySlices: true) { (num) -> Bool in
    num % 2 == 1
}

fibs.forEach { (num) in
    print(num - 44)
}

Demo 下载地址：https://github.com/gewill/test-projects/tree/master/collections%20transform.playground