Generic function to sort array of class or struct by properties in Swift

Question

I want to create a generic function to sort an array of classes based on a property passed.

For example, I have these classes

public class Car {
    var id: Int
    var manufacturer: String
    var variant: String

    init(id: Int, manufacturer: String, variant: String) {
        self.id = id
        self.manufacturer = manufacturer
        self.variant = variant
    }
}

enum Gender {
    case male
    case female
}

public class Person {
    var id: Int
    var name: String
    var age: Int
    var gender: Gender

    init(id: Int, name: String, age: Int, gender: Gender) {
        self.id = id
        self.name = name
        self.age = age
        self.gender = gender
    }
}

And these arrays,

let cars = [
    Car(id: 1, manufacturer: "Ford", variant: "Focus"),
    Car(id: 2, manufacturer: "Nissan", variant: "Skyline"),
    Car(id: 3, manufacturer: "Dodge", variant: "Charger"),
    Car(id: 4, manufacturer: "Chevrolet", variant: "Camaro"),
    Car(id: 5, manufacturer: "Ford", variant: "Shelby")
]

let persons = [
    Person(id: 1, name: "Ed Sheeran", age: 26, gender: .male),
    Person(id: 2, name: "Phil Collins", age: 66, gender: .male),
    Person(id: 3, name: "Shakira", age: 40, gender: .female),
    Person(id: 4, name: "Rihanna", age: 25, gender: .female),
    Person(id: 5, name: "Bono", age: 57, gender: .male)
]

How to write a generic extension for the array, to sort it based on the property passed? (eg. persons.sort(name) or cars.sort(manufacturer))

Thanks!

Answer 1

edit/update:

For Xcode 13.0+, iOS 15.0+, iPadOS 15.0+, macOS 12.0+, Mac Catalyst 15.0+, tvOS 15.0+, watchOS 8.0+ you can use KeyPathComparator:

let sortedPeople1 = people.sorted(using: KeyPathComparator(\.age))  // [{id 4, name "Rihanna", age 25, female}, {id 1, name "Ed Sheeran", age 26, male}, {id 3, name "Shakira", age 40, female}, {id 5, name "Bono", age 57, male}, {id 2, name "Phil Collins", age 66, male}]
let sortedPeople2 = people.sorted(using: KeyPathComparator(\.age, order: .reverse))  // [{id 2, name "Phil Collins", age 66, male}, {id 5, name "Bono", age 57, male}, {id 3, name "Shakira", age 40, female}, {id 1, name "Ed Sheeran", age 26, male}, {id 4, name "Rihanna", age 25, female}]

You can also use multiple sorting criteria and order:

let sortedPeople3 = people.sorted(using: [KeyPathComparator(\.age, order: .reverse), KeyPathComparator(\.name)])  // [{id 2, name "Phil Collins", age 66, male}, {id 5, name "Bono", age 57, male}, {id 3, name "Shakira", age 40, female}, {id 1, name "Ed Sheeran", age 26, male}, {id 4, name "Rihanna", age 25, female}]
let sortedPeople4 = people.sorted(using: [KeyPathComparator(\.age, order: .reverse), KeyPathComparator(\.name)])  // [{id 2, name "Phil Collins", age 66, male}, {id 5, name "Bono", age 57, male}, {id 3, name "Shakira", age 40, female}, {id 1, name "Ed Sheeran", age 26, male}, {id 4, name "Rihanna", age 25, female}]

---

original answer
Expanding on @MartinR answer and @Sweeper answer to allow increasing (<) or decreasing (>) sort as well as throw and default sort ascending methods:

---

extension MutableCollection where Self: RandomAccessCollection {
    mutating func sort<T: Comparable>(_ predicate: (Element) throws -> T) rethrows {
        try sort(predicate, by: <)
    }
    mutating func sort<T: Comparable>(_ predicate: (Element) throws -> T, by areInIncreasingOrder: ((T, T) throws -> Bool)) rethrows {
        try sort { try areInIncreasingOrder(predicate($0), predicate($1)) }
    }
}

---

extension Sequence {
    func sorted<T: Comparable>(_ predicate: (Element) throws -> T) rethrows -> [Element] {
        try sorted(predicate, by: <)
    }
    func sorted<T: Comparable>(_ predicate: (Element) throws -> T, by areInIncreasingOrder: ((T,T) throws -> Bool)) rethrows -> [Element] {
        try sorted { try areInIncreasingOrder(predicate($0), predicate($1)) }
    }
}

---

people.sorted(\.age)
people.sorted(\.age, by: >)

cars.sorted(\.manufacturer)
cars.sorted(\.manufacturer, by: >)

edit/update:

To suport sorting a custom object by an optional property that conforms to Comparable protocol:

---

extension MutableCollection where Self: RandomAccessCollection {
    mutating func sort<T: Comparable>(_ predicate: (Element) throws -> T?) rethrows {
        try sort(predicate, by: <)
    }

    mutating func sort<T: Comparable>(_ predicate: (Element) throws -> T?, by areInIncreasingOrder: ((T, T) throws -> Bool)) rethrows {
        try sort(by: {
            switch try (predicate($0), predicate($1)) {
            case let (lhs?, rhs?): return try areInIncreasingOrder(lhs, rhs)
            case (.none, _): return false
            case (_, .none): return true
            }
        })
    }
}

---

extension Sequence {
    func sorted<T: Comparable>(_ predicate: (Element) throws -> T?) rethrows -> [Element]  {
        try sorted(predicate, by: <)
    }
    func sorted<T: Comparable>(_ predicate: (Element) throws -> T?, by areInIncreasingOrder: ((T,T) throws -> Bool)) rethrows -> [Element]  {
        try sorted(by: {
            switch try (predicate($0), predicate($1)) {
            case let (lhs?, rhs?): return try areInIncreasingOrder(lhs, rhs)
            case (.none, _): return false
            case (_, .none): return true
            }
        })
    }
}

---

Usage:

array.sort(\.optionalStringProperty) {
    $0.localizedStandardCompare($1) == .orderedAscending
}
print(array)

Answer 2

Here you go:

extension Array {
    mutating func propertySort<T: Comparable>(_ property: (Element) -> T) {
        sort(by: { property($0) < property($1) })
    }
}

Usage:

persons.propertySort({$0.name})

And here is a non-mutating version:

func propertySorted<T: Comparable>(_ property: (Element) -> T) -> [Element] {
    return sorted(by: {property($0) < property($1)})
}

As Leo Dabus pointed out, you can generalise the extension to any MutableCollection that is also a RandomAccessCollection:

extension MutableCollection where Self : RandomAccessCollection {
    ...

Answer 3

Starting with Swift 4 you can define a sorting method which takes a Key-Path Expression as argument. As Leo points out, these methods can be defined more generally as protocols extension methods (for mutable collections and sequences, respectively):

extension MutableCollection where Self: RandomAccessCollection {
    // Mutating in-place sort:
    mutating func sort<T: Comparable>(byKeyPath keyPath: KeyPath<Element, T>) {
        sort(by: { $0[keyPath: keyPath] < $1[keyPath: keyPath] })
    }
}

extension Sequence {
    // Non-mutating sort, returning a new array:
    func sorted<T: Comparable>(byKeyPath keyPath: KeyPath<Element, T>) -> [Element] {
        return sorted(by: { $0[keyPath: keyPath] < $1[keyPath: keyPath] })
    }
}

Example usage:

persons.sort(byKeyPath: \.name)
cars.sort(byKeyPath: \.manufacturer)

For more information about key-path expressions, see SE-0161 Smart KeyPaths: Better Key-Value Coding for Swift.