Given an array of indexes, how can I filter an array in swift?

Question

Given an array of indexes I would like to get a subarray of myArray, with the items at those indexes. I'm currently iterating the indexes array to create a subarray, but I'm wondering if this can be achieved by using the .filter function.

var indexes = [3,4,9,11]
myArray.filter(...)

Answer 1

Assuming that

• the given indices are in increasing order, and
• all indices are valid for the array (i.e. less than the number of elements),

then a simple map operation would work:

let indexes = [2, 4, 7]
let myArray = ["a", "b", "c", "d", "e", "f", "g", "h"]

let filtered = indexes.map { myArray[$0] }
print(filtered) //["c", "e", "h"]

Remark: In earlier Swift releases, there was a PermutationGenerator exactly for this purpose:

let filtered = Array(PermutationGenerator(elements: myArray, indices: indexes))
print(filtered) //["c", "e", "h"]

However, this has been deprecated in Swift 2.2 and will be removed in Swift 3. I haven't seen a Swift 3 replacement yet.