按索引过滤数组 [英] Filter array by indices

问题描述

我有一系列元素。我还有一个IndexSet，它指定需要将数组的哪些索引提取到新数组中。例如：

I have an array of elements. I also have an IndexSet that specifies which indices of the array need to be extracted into a new array. E.g.:

let array = ["sun", "moon", "star", "meteor"]
let indexSet: IndexSet = [2, 3]
// Some magic happens here to get:
let result = ["star", "meteor"]

我正在寻找使用swift 过滤器的功能，但尚未得到答案。我该怎么做？

I'm looking to use the swift filter function, but haven't got the answer yet. How can I do this?

推荐答案

IndexSet 是一个增加的集合整数，因此你可以
map 每个索引到相应的数组元素：

IndexSet is a collection of increasing integers, therefore you can map each index to the corresponding array element:

let array = ["sun", "moon", "star", "meteor"]
let indexSet: IndexSet = [2, 3]

let result = indexSet.map { array[$0] } // Magic happening here!
print(result) // ["star", "meteor"]

这假设所有索引对给定数组都有效。
如果不能保证，那么你可以过滤指数
（正如@dfri正确评论的那样）：

This assumes that all indices are valid for the given array. If that is not guaranteed then you can filter the indices (as @dfri correctly remarked):

let result = indexSet.filteredIndexSet { $0 < array.count }.map { array[$0] }

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