How to sort an array in Swift

Sorting an Array in Swift

Define a initial names array:

var names = [ "gamma", "Alpha", "alpha", "bravo"]

Method 1:

var sortedNames = sorted(names, {$0 < $1})
// sortedNames becomes "[Alpha, alpha, bravo, gamma]"

This can be further simplified to:

var sortedNames = sorted(names, <)
// ["Alpha", "alpha", "bravo", "gamma"]
var reverseSorted = sorted(names, >)
// ["gamma", "bravo", "alpha", "Alpha"]

Method 2:

names.sort(){$0 < $1}
// names become sorted as this --> "[Alpha, alpha, bravo, gamma]"

If your array does not contain Custom Objects (just a string or number type):

var sortedNames = sorted(names, <)

Otherwise if you create a Custom Data Object Class containing custom properties inside:

customDataObjectArray.sort({ $0.customProperty < $1.customProperty })

Most efficient way of sorting in SWIFT

The use of Operator Overloading is the most efficient way to sort Strings in Swift language.

// OPERATOR OVERLOADING
let names = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
var sortedNames = sorted(names, <)
var reverseOrder = sorted(names, >)

In above code > and < operators are overloaded in Swift to sort Strings.

I have test the code in Playground and conclude that when we use operator overloading it is best for sorting Strings.

Copy below to Playground.

let names = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]

var reversed = sorted (names,
    // This is a closure
    { (s1 : String, s2 : String) -> Bool in
        return s1 > s2
    }
)
println(reversed)

var reverseOrder = sorted(names, {s1, s2 in s1 > s2})

var reverseOrder2 = sorted(names, { $0 > $1} )

// OPERATOR OVERLOADING
var reverseOrder3 = sorted(names, >)

The conclusion from Playground:

From above image you can see that all other ways needs to enumerate loops for sorting 5 strings. Where as when we use Operator overloading it does not required to enumerate loop to sort strings.

Referenced from Swift documentation

If you want to sort your array in ascending order then use below syntax:

var arrayName = sorted(arrayName, <)

as the sorted() is the predefined function in swift and < is used to indicate that the array should be sorted in ascending order. If you want to sort the array in descending order then simply replace < with > as I have shown below:

var arrayName = sorted(arrayName, >)

You can usually use the built-in

func sort<T : Comparable>(inout array: [T])

but if you want to use localizedCaseInsensitiveCompare:, your code can be translated directly using NSArray.

Any method that can be used with Objective-C sortedArrayUsingSelector: can be used with Swift sort (or sorted) provided the type of thing in the array is known. So, in your code:

var arr : [String] = // ...
// it is an array of String, so we can use localizedCaseInsensitiveCompare:
sort(&arr) {return $0.localizedCaseInsensitiveCompare($1) == .OrderedAscending}

Similarly:

var events : [EKEvent] = // ...
sort(&events) {return $0.compareStartDateWithEvent($1) == .OrderedAscending}

In Swift-

let students: Set = ["Kofi", "Abena", "Peter", "Kweku", "Akosua"]
let sortedStudents = students.sorted()
print(sortedStudents)
// Prints "["Abena", "Akosua", "Kofi", "Kweku", "Peter"]"

To sort the elements of your sequence in descending order, pass the greater-than operator (>) to the sorted(isOrderedBefore:) method.

let descendingStudents = students.sorted(isOrderedBefore: >)
print(descendingStudents)
// Prints "["Peter", "Kweku", "Kofi", "Akosua", "Abena"]"