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

With Swift 5, Array has two methods called sorted() and sorted(by:). The first method, sorted(), has the following declaration:

Returns the elements of the collection, sorted.

func sorted() -> [Element]

The second method, sorted(by:), has the following declaration:

Returns the elements of the collection, sorted using the given predicate as the comparison between elements.

func sorted(by areInIncreasingOrder: (Element, Element) throws -> Bool) rethrows -> [Element]

---

#1. Sort with ascending order for comparable objects

If the element type inside your collection conforms to Comparable protocol, you will be able to use sorted() in order to sort your elements with ascending order. The following Playground code shows how to use sorted():

class ImageFile: CustomStringConvertible, Comparable {

    let fileName: String
    let fileID: Int
    var description: String { return "ImageFile with ID: \(fileID)" }

    init(fileName: String, fileID: Int) {
        self.fileName = fileName
        self.fileID = fileID
    }

    static func ==(lhs: ImageFile, rhs: ImageFile) -> Bool {
        return lhs.fileID == rhs.fileID
    }

    static func <(lhs: ImageFile, rhs: ImageFile) -> Bool {
        return lhs.fileID < rhs.fileID
    }

}

let images = [
    ImageFile(fileName: "Car", fileID: 300),
    ImageFile(fileName: "Boat", fileID: 100),
    ImageFile(fileName: "Plane", fileID: 200)
]

let sortedImages = images.sorted()
print(sortedImages)

/*
 prints: [ImageFile with ID: 100, ImageFile with ID: 200, ImageFile with ID: 300]
 */

---

#2. Sort with descending order for comparable objects

If the element type inside your collection conforms to Comparable protocol, you will have to use sorted(by:) in order to sort your elements with a descending order.

class ImageFile: CustomStringConvertible, Comparable {

    let fileName: String
    let fileID: Int
    var description: String { return "ImageFile with ID: \(fileID)" }

    init(fileName: String, fileID: Int) {
        self.fileName = fileName
        self.fileID = fileID
    }

    static func ==(lhs: ImageFile, rhs: ImageFile) -> Bool {
        return lhs.fileID == rhs.fileID
    }

    static func <(lhs: ImageFile, rhs: ImageFile) -> Bool {
        return lhs.fileID < rhs.fileID
    }

}

let images = [
    ImageFile(fileName: "Car", fileID: 300),
    ImageFile(fileName: "Boat", fileID: 100),
    ImageFile(fileName: "Plane", fileID: 200)
]

let sortedImages = images.sorted(by: { (img0: ImageFile, img1: ImageFile) -> Bool in
    return img0 > img1
})
//let sortedImages = images.sorted(by: >) // also works
//let sortedImages = images.sorted { $0 > $1 } // also works
print(sortedImages)

/*
 prints: [ImageFile with ID: 300, ImageFile with ID: 200, ImageFile with ID: 100]
 */

---

#3. Sort with ascending or descending order for non-comparable objects

If the element type inside your collection DOES NOT conform to Comparable protocol, you will have to use sorted(by:) in order to sort your elements with ascending or descending order.

class ImageFile: CustomStringConvertible {

    let fileName: String
    let fileID: Int
    var description: String { return "ImageFile with ID: \(fileID)" }

    init(fileName: String, fileID: Int) {
        self.fileName = fileName
        self.fileID = fileID
    }

}

let images = [
    ImageFile(fileName: "Car", fileID: 300),
    ImageFile(fileName: "Boat", fileID: 100),
    ImageFile(fileName: "Plane", fileID: 200)
]

let sortedImages = images.sorted(by: { (img0: ImageFile, img1: ImageFile) -> Bool in
    return img0.fileID < img1.fileID
})
//let sortedImages = images.sorted { $0.fileID < $1.fileID } // also works
print(sortedImages)

/*
 prints: [ImageFile with ID: 300, ImageFile with ID: 200, ImageFile with ID: 100]
 */

---

Note that Swift also provides two methods called sort() and sort(by:) as counterparts of sorted() and sorted(by:) if you need to sort your collection in-place.