Reorder array compared to another array in Swift [duplicate]

Question

I have one array in Swift containing some ids of objects, and I have another array containing these objects with their ids, so something like this:

class MyObject {
   let id: String
   ...
}

let ids: [String] = ...
let objects: [MyObject] = ...

Now the array of ids is sorted in some custom order, and I need the array of objects to be sorted in the same order. So for example:

let ids: [String] = ["1", "2", "3"]
let objects: [MyObject] = [obj3, obj1, obj2]
// obj1.id = "1"
// obj2.id = "2"
// obj3.id = "3"
objects.reorder(template: ids) 
// Now objects = [obj1, obj2, obj3]

So I basically need to implement this reorder method. Does anyone have a smart suggestion how to do this in Swift? I'm using Swift 3, so all the new APIs are available to me.

Answer 1

You can sort objects in order to follow the order in ids writing

let sorted = objects.sort { ids.indexOf($0.id) < ids.indexOf($1.id) }
// [{id "1"}, {id "2"}, {id "3"}]

Another example

let ids: [String] = ["3", "2", "1"]
let objects: [MyObject] = [MyObject(id: "3"), MyObject(id: "1"), MyObject(id: "2")]

let sorted = objects.sort { ids.indexOf($0.id) < ids.indexOf($1.id) }
// [{id "3"}, {id "2"}, {id "1"}]

This code is in Swift 2.2

---

Swift 4.2 solution

let sorted = objects.sorted { ids.index(of: $0.id)! < ids.index(of: $1.id)! }

Answer 2

A possible solution:

let sorted = objects.flatMap { obj in
    ids.index(of: obj.id).map { idx in (obj, idx) }
}.sorted(by: { $0.1 < $1.1 } ).map { $0.0 }

Explanation:

• First, each object is tied to together with the corresponding position of the id in the array, this gives an array of (object, index) tuples.
• This array is sorted with respect to the index positions.
• Finally, the objects are extracted again.

Possible advantages:

• Each object is searched only once in the array.
• Objects for which no id exists in the array are ignored.