Swift how to sort array of custom objects by prope

Question

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

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

lots of them stored in Array

var images : Array = []

var aImage = imageFile()
aImage.fileName = "image1.png"
aImage.fileID = 101
images.append(aImage)

aImage = imageFile()
aImage.fileName = "image1.png"
aImage.fileID = 202
images.append(aImage)

question is: how can i sort images array by 'fileID' ASC or DESC?

Answer 1

With Swift 4, 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.

Answer 2

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 3

[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 4

Swift 4.0, 4.1 & 4.2 First, I created mutable array of type imageFile() as shown below

var arr = [imageFile]()

Create mutable object image of type imageFile() and assign value to properties as shown below

   var image = imageFile()
   image.fileId = 14
   image.fileName = "A"

Now, append this object to array arr

    arr.append(image)

Now, assign the different properties to same mutable object i.e image

   image = imageFile()
   image.fileId = 13
   image.fileName = "B"

Now, again append image object to array arr

    arr.append(image)

Now, we will apply Ascending order on fileId property in array arr objects. Use < symbol for Ascending order

 arr = arr.sorted(by: {$0.fileId < $1.fileId}) // arr has all objects in Ascending order
 print("sorted array is",arr[0].fileId)// sorted array is 13
 print("sorted array is",arr[1].fileId)//sorted array is 14

Now, we will apply Descending order on on fileId property in array arr objects. Use > symbol for Descending order

 arr = arr.sorted(by: {$0.fileId > $1.fileId}) // arr has all objects in Descending order
 print("Unsorted array is",arr[0].fileId)// Unsorted array is 14
 print("Unsorted array is",arr[1].fileId)// Unsorted array is 13

In Swift 4.1. & 4.2 For sorted order use

let sortedArr = arr.sorted { (id1, id2) -> Bool in
  return id1.fileId < id2.fileId // Use > for Descending order
}

Answer 5

If you want to sort original array of custom objects. Here is another way to do so in Swift 2.1

var myCustomerArray = [Customer]()
myCustomerArray.sortInPlace {(customer1:Customer, customer2:Customer) -> Bool in
    customer1.id < customer2.id
}

Where id is an Integer. You can use the same < operator for String properties as well.

You can learn more about its use by looking at an example here: Swift2: Nearby Customers

Answer 6

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

students.sort(by: >)

print(students)

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