如何根据预定义的元素顺序对数组排序? [英] How to sort an array based on a predefined element order?

问题描述

我想基于定义元素顺序的自定义数组对数组的元素进行排序.例如，假定以下数组:

I would like to sort the elements of an array based on a custom array that defines the element order. For example, assume the following array:

let arr = ["second", "first", "second", "fourth", "third", "second"]

我试图创建一个数组扩展名，以便能够通过以下方式对该数组进行排序:

I tried to create an Array extension to be able to sort this array by:

let sortedArr = arr.sortBy(orderArray: ["first","second","third","fourth"])
// desired output: ["first", "second", "second", "second", "third", "fourth": 

但是，该扩展名无法正常工作:

However, the extension does not work correctly:

extension Array {
    public func sortBy<T: Comparable>(orderArray: [T]) -> [T]? {
        guard self.count > 0,
            self.first! as? T != nil else {
                return nil
        }

        let indices = self.map {orderArray.index(of: $0 as! T)! }

        return self.sorted { indices[$0] > indices[$1] } // This doesn’t work
    }
}

有什么想法吗?

推荐答案

您的代码的一个问题是self.sorted期望 封闭比较数组 elements 而不是索引.

One problem with your code is that self.sorted expects a closure comparing array elements, not indices.

这是一个可能的解决方案，也避免了不必要的操作 键入强制转换和展开(内嵌解释):

Here is a possible solution which also avoids unnecessary type casts and unwrappings (explanations inline):

extension Array where Element: Equatable {
    public func sortBy(orderArray: [Element]) -> [Element]? {

        // Index of each element in `orderArray`:
        let targetIndices = self.flatMap { orderArray.index(of: $0) }
        // Verify that each array element occurs in `orderArray`:
        guard targetIndices.count == self.count else {
            return nil
        }
        // Sort array indices according to their index in `orderArray`:
        let sortedIndices = self.indices.sorted { targetIndices[$0] < targetIndices[$1] }
        // Rearrange elements accordingly:
        return sortedIndices.map { self[$0] }
    }
}

示例:

let arr = ["second", "first", "second", "fourth", "third", "second"]

if let sortedArr = arr.sortBy(orderArray: ["first","second","third","fourth"]) {
    print(sortedArr)
    // ["first", "second", "second", "second", "third", "fourth"]
}

---

移动orderArray中不包含的数组元素 到排序结果的末尾(但保留它们的相对顺序)，将代码略微修改为

---

To move array elements which are not contained in orderArray to the end of the sorted result (but preserve their relative order), modify the code slightly to

extension Array where Element: Equatable {
    public func sortBy(orderArray: [Element]) -> [Element] {

        // Index of each element in `orderArray`:
        let targetIndices = self.enumerated().map {
            orderArray.index(of: $1) ?? orderArray.count + $0
        }
        // Sort array indices according to their index in `orderArray`:
        let sortedIndices = self.indices.sorted { targetIndices[$0] < targetIndices[$1] }
        // Rearrange elements accordingly:
        return sortedIndices.map { self[$0] }
    }
}

示例:

let arr = ["x", "second", "first", "y", "second", "fourth", "third", "second", "z"]
let sortedArr = arr.sortBy(orderArray: ["first","second","third","fourth"])
print(sortedArr)
// ["first", "second", "second", "second", "third", "fourth", "x", "y", "z"]

这篇关于如何根据预定义的元素顺序对数组排序?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！