how do I sort an NSMutableSet in Swift?

Question

I am trying to use a NSMutableOrderedSet to store some data, but I would like to sort the set by a specific attribute. I tried to look online on how to use the sort(comparator cmptr: (Any, Any) -> ComparisonResult) function of the NSMutableOrderedSet but I am unsure on how to use this. I would like to know if someone could give me a quick example I was unable to find any tutorials or examples on Apples developer documentation.

Currently I have:

jersey.swift:

    struct Jersey{
       var name: String
       var number: Int
}

viewcontroller.swift:

let firstBasemanJersey = Jersey(name: "Bob", number: 5)
let secondBasemanJersey = Jersey(name: "Jim", number: 15)
let thirdBasemanJersey = Jersey(name: "Jon", number: 1)
let catcherJersey = Jersey(name: "Steve", number: 79)

var jerseySet = NSMutableOrderedSet()
jerseySet.addObject(firstBasemanJersey)
jerseySet.addObject(secondBasemanJersey)
jerseySet.addObject(thirdBasemanJersey)
jerseySet.addObject(catcherJersey)

I would like to sort the set by the jersey.number would someone be able to show me how would I use the

self.something.sort { (<#Any#>, <#Any#>) -> ComparisonResult in
            <#code#>
        }

Since `OrderedSet` is using `Any` as element type, it's not a good structure to be used in Swift. Also note that you should start by declaring `Jersey` to be `Hashable`, otherwise the `Set` part of `OrderedSet` won't really work (that is, the `contains` method won't work and you will be able to insert the same object multiple times). — Sulthan, Mar 07 '20 at 22:58
@Sulthan I totally agree with that. I was on the fence about providing an answer but did so only for helping clarifying the use of the api. — Alladinian, Mar 07 '20 at 23:01
@Alladinian The real usage for an `OrderedSet` is to have a combination of a `Set` and an `Array`, where all operations are automatically performed on both substructures. For example, `add` does not happen if `Set` already contains the item. If the ultimate aim is to sort the items, there is no need to keep items ordered while updating. Instead of an `OrderedSet`, I would probably create my own Swift generic struct doing the same. — Sulthan, Mar 07 '20 at 23:27
@Sulthan Once again, fully agree... hence the second part of my answer. Having said that, I tried to make as little assumptions as possible about the intentions of the OP. What if this is for a UI that adds unique items in a list and there is a button to let you sort them (in place) by number for example? That would be a valid case for an ordered set & a (possible) sort. If we got more details about the use of this code then a more insightful answer on this would be more appropriate, I agree. — Alladinian, Mar 07 '20 at 23:43

Alladinian · Answer 1 · 2020-03-07T23:15:52.563

In the most basic form you just have to compare the two arguments (a pair of Any objects since the Set doesn't 'know' what objects is currently holding) and return a ComparisonResult that can be either orderedAscending, orderedDescending or orderedSame:

jerseySet.sort(comparator: { lhs, rhs in
    guard let (l, r) = (lhs, rhs) as? (Jersey, Jersey) else { return .orderedSame }
    guard l.number != r.number else { return .orderedSame }
    return l.number < r.number  ? .orderedAscending : .orderedDescending
})

now if you print(jerseySet.array):

[Jerseys.Jersey(name: "Jon", number: 1), Jerseys.Jersey(name: "Bob", number: 5), Jerseys.Jersey(name: "Jim", number: 15), Jerseys.Jersey(name: "Steve", number: 79)]

And (for the reasons mentioned in the question comments) here is a "Swiftier" version of this:

struct Jersey: Hashable {
   let name: String
   let number: Int
}

let firstBasemanJersey  = Jersey(name: "Bob", number: 5)
let secondBasemanJersey = Jersey(name: "Jim", number: 15)
let thirdBasemanJersey  = Jersey(name: "Jon", number: 1)
let catcherJersey       = Jersey(name: "Steve", number: 79)

// Kept as var assuming that you will later `.insert` things in the set
var jerseySet = Set([
    firstBasemanJersey,
    secondBasemanJersey,
    thirdBasemanJersey,
    catcherJersey
])

let sortedByNumber = jerseySet.sorted { lhs, rhs in
    lhs.number < rhs.number
}

how do I sort an NSMutableSet in Swift?

1 Answers1