用分隔符“，"将字符串数组连接起来并添加“和"加入Swift的最后一个元素 [英] Join string array with separator ", " and add ", and " to join the last element in Swift

问题描述

我在一个快速的操场上用SwiftyJSON解析JSON.我的代码如下:

I'm messing around with parsing JSON with SwiftyJSON on a swift playground. My code is as follows:

import UIKit
import SwiftyJSON

var partyList: [String] = []
var firstPresidentList: [String] = []

if let url = URL(string:"http://mysafeinfo.com/api/data?list=presidents&format=json") {
    if let data = try? Data(contentsOf: url) {
        let json = JSON(data: data)
        for i in 1...43 {
            let party = json[i]["pp"].stringValue
            let president = json[i]["nm"].stringValue
            if partyList.contains(party) {
                print("\n")
            } else {
                partyList.append(party)
                firstPresidentList.append(president)
            }
        }
        print("All the different parties of U.S. presidents included "+partyList.joined(separator: ", ")+", in that order. The first presidents of those parties were (repectively) "+firstPresidentList.joined(separator: ", ")+".")
    }
}

在print行上，我想知道如何像我一样用逗号和空格连接数组，但是在最后一个之前添加"and".

On the print line, I was wondering how I could join the arrays with a comma and space like I have, but add "and" before the last one.

谢谢！

推荐答案

添加条件以检查您的String集合是否少于或等于2个元素，如果为true，则仅返回由" and "联接的两个元素否则，请删除集合的最后一个元素，将这些元素与分隔符", "结合在一起，然后用最后一个分隔符", and "重新添加最后一个元素.

Add a condition to check if your String collection has less than or is equal to 2 elements, if true just return the two elements joined by " and " otherwise drop the last element of your collection, join the elements with a separator ", " then re add the last element with the final separator ", and ".

您可以扩展BidirectionalCollection协议，将其元素限制为StringProtocol:

You can extend BidirectionalCollection protocol constraining its elements to the StringProtocol:

双向集合提供了从任何有效路径向后遍历的功能 索引，不包括集合的startIndex.双向的 因此，集合可以提供其他操作，例如 last 属性，可以有效访问最后一个元素和 reversed()方法以相反的顺序显示元素.

Bidirectional collections offer traversal backward from any valid index, not including a collection’s startIndex. Bidirectional collections can therefore offer additional operations, such as a last property that provides efficient access to the last element and a reversed() method that presents the elements in reverse order.

Xcode 11.4•Swift 5.2或更高版本

extension BidirectionalCollection where Element: StringProtocol {
    var sentence: String {
        count <= 2 ?
            joined(separator: " and ") :
            dropLast().joined(separator: ", ") + ", and " + last!
    }
}

---

let elements = ["a", "b", "c"]
let sentenceFromElements = elements.sentence   // "a, b, and c"

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