Swift how to sort array of custom objects by property value

Question

lets say we have a custom class named imageFile and this class contains two properties.

class imageFile  {
    var fileName = String()
    var fileID = Int(         


        

Answer 1

Sort using KeyPath

you can sort by KeyPath like this:

myArray.sorted(by: \.fileName, <) /* using `<` for ascending sorting */

By implementing this little helpful extension.

extension Collection{
    func sorted<Value: Comparable>(
        by keyPath: KeyPath<Element, Value>,
        _ comparator: (_ lhs: Value, _ rhs: Value) -> Bool) -> [Element] {
        sorted { comparator($0[keyPath: keyPath], $1[keyPath: keyPath]) }
    }
}

Hope Swift add this in the near future in the core of the language.

Answer 2

Nearly everyone gives how directly, let me show the evolvement:

you can use the instance methods of Array:

// general form of closure
images.sortInPlace({ (image1: imageFile, image2: imageFile) -> Bool in return image1.fileID > image2.fileID })

// types of closure's parameters and return value can be inferred by Swift, so they are omitted along with the return arrow (->)
images.sortInPlace({ image1, image2 in return image1.fileID > image2.fileID })

// Single-expression closures can implicitly return the result of their single expression by omitting the "return" keyword
images.sortInPlace({ image1, image2 in image1.fileID > image2.fileID })

// closure's argument list along with "in" keyword can be omitted, $0, $1, $2, and so on are used to refer the closure's first, second, third arguments and so on
images.sortInPlace({ $0.fileID > $1.fileID })

// the simplification of the closure is the same
images = images.sort({ (image1: imageFile, image2: imageFile) -> Bool in return image1.fileID > image2.fileID })
images = images.sort({ image1, image2 in return image1.fileID > image2.fileID })
images = images.sort({ image1, image2 in image1.fileID > image2.fileID })
images = images.sort({ $0.fileID > $1.fileID })

For elaborate explanation about the working principle of sort, see The Sorted Function.

Answer 3

var students = ["Kofi", "Abena", "Peter", "Kweku", "Akosua"]

students.sort(by: >)

print(students)

Prints : "["Peter", "Kweku", "Kofi", "Akosua", "Abena"]"

Answer 4

[Updated for Swift 3 with sort(by:)] This, exploiting a trailing closure:

images.sorted { $0.fileID < $1.fileID }

where you use < or > depending on ASC or DESC, respectively. If you want to modify the images array, then use the following:

images.sort { $0.fileID < $1.fileID }

If you are going to do this repeatedly and prefer to define a function, one way is:

func sorterForFileIDASC(this:imageFile, that:imageFile) -> Bool {
  return this.fileID > that.fileID
}

and then use as:

images.sort(by: sorterForFileIDASC)

Answer 5

If you are going to be sorting this array in more than one place, it may make sense to make your array type Comparable.

class MyImageType: Comparable, Printable {
    var fileID: Int

    // For Printable
    var description: String {
        get {
            return "ID: \(fileID)"
        }
    }

    init(fileID: Int) {
        self.fileID = fileID
    }
}

// For Comparable
func <(left: MyImageType, right: MyImageType) -> Bool {
    return left.fileID < right.fileID
}

// For Comparable
func ==(left: MyImageType, right: MyImageType) -> Bool {
    return left.fileID == right.fileID
}

let one = MyImageType(fileID: 1)
let two = MyImageType(fileID: 2)
let twoA = MyImageType(fileID: 2)
let three = MyImageType(fileID: 3)

let a1 = [one, three, two]

// return a sorted array
println(sorted(a1)) // "[ID: 1, ID: 2, ID: 3]"

var a2 = [two, one, twoA, three]

// sort the array 'in place'
sort(&a2)
println(a2) // "[ID: 1, ID: 2, ID: 2, ID: 3]"

Answer 6

I do it like this and it works:

var images = [imageFile]() images.sorted(by: {$0.fileID.compare($1.fileID) == .orderedAscending })