如何交换字符串数组中的第一项和第二项？

Question

我有一个字符串格式的坐标列表，分别有经度和纬度。 我想拥有纬度和经度：

var str = "POLYGON ((-97.7157864909859 30.406523563068, -97.7165355983688 30.4068866173208, -97.7167879301601 30.406495457696, -97.7168046574092 30.4065112735542, -97.7168203607564 30.406527859154, -97.7168349935064 30.4065451649171))

我删除了格式的字符串：

let formattedString = str.replacingOccurrences(of: "POLYGON ((", with: "").replacingOccurrences(of: "))", with: "").replacingOccurrences(of: ",", with: "")
var token = formattedString.components(separatedBy: " ")

现在我试图翻转经度和纬度的位置，以便它：

30.406523563068, -97.7157864909859, 30.4068866173208, -97.7157864909859

我尝试了以下但它似乎没有改变数组的配置：

var coordinateArray = [String]()
for (index, coordinate) in token.enumerated() {
    if index % 2 == 0 {
        coordinateArray.insert(coordinate, at: index)
    } else {
        coordinateArray.insert(coordinate, at: index)
    }
}

任何帮助将不胜感激。

Answer 1

这是一个更实用的方法：

let str = "POLYGON ((-97.7157864909859 30.406523563068, -97.7165355983688 30.4068866173208, -97.7167879301601 30.406495457696, -97.7168046574092 30.4065112735542, -97.7168203607564 30.406527859154, -97.7168349935064 30.4065451649171))"
let formattedString = str.replacingOccurrences(of: "POLYGON ((", with: "").replacingOccurrences(of: "))", with: "")

// split by commas, not spaces, because in the original string, pairs of 
// coordinates are separated by commas
let coordianates = formattedString.components(separatedBy: ", ")

// Here I transform each pair of coordinate into an array with two elements, 
// reverse it, and flatten the whole array
let flipped = coordianates.flatMap { $0.components(separatedBy: " ").reversed() }
print(flipped)

Answer 2

您可能想使用swapAt函数尝试此操作，

var arr = [30.406523563068, -97.7157864909859, 30.4068866173208, -54.881838371711]
    for(index, _) in arr.enumerated() {
        if index % 2 == 0 && index + 1 < arr.count {
             arr.swapAt(index, index + 1)
        }
    }
print(arr)

Answer 3

使用swapAt(_:_:)

例：

var names = ["Paul", "John", "George", "Ringo"]
names.swapAt(0, 1)

这将在阵列中交换"Paul"和"John" 。

满足您的特殊需求

var str = "POLYGON ((-97.7157864909859 30.406523563068, -97.7165355983688 30.4068866173208, -97.7167879301601 30.406495457696, -97.7168046574092 30.4065112735542, -97.7168203607564 30.406527859154, -97.7168349935064 30.4065451649171))"

let formattedString = str.replacingOccurrences(of: "POLYGON ((", with: "").replacingOccurrences(of: "))", with: "").replacingOccurrences(of: ",", with: "")
var coordinateArray = formattedString.components(separatedBy: " ")

for i in stride(from: 0, to: coordinateArray.endIndex - 1, by: 2) {
    coordinateArray.swapAt(i, i+1)
}

Answer 4

如果您的coordinateArray看起来像这样

[-97, 30, -97, 30]

然后你可以说你要刷每两个元素。 然后你需要stride方法，它给你数组中每个元素的第二个索引（从0开始），然后你可以使用swapAt方法，它将每个第二个索引和带有索引的元素交换元素。

for index in stride(from: coordinateArray.startIndex, to: coordinateArray.endIndex - 1, by: 2) {
     coordinateArray.swapAt(index, index + 1)
}