Sorting arrays is a very common task. Swift has a built-in feature that is fast and easy to use. In this article you’ll learn all the details.
Hint: This post is using Swift 3
sort and sorted
Imagine we have an array of integers:
var intArray = [ 34 , 13 , 14 , 584 , 1 , 34 , 69 , 3 , 596 , 2 ]
If the members of the array have a type that confirms to the
Comparable sorted ( ) Comparable
let result = intArray . sorted ( )
print ( result ) //[1, 2, 3, 13, 14, 34, 34, 69, 584, 596]
So, that was very easy! Alternatively, we can also use the function
sort ( ) sorted ( )
intArray . sort ( )
print ( intArray ) //[1, 2, 3, 13, 14, 34, 34, 69, 584, 596]
However, not all types confirm to the
Comparable
Sorting arrays of dates
A good example for a type that doesn’t confirm to the
Comparable Date Date
public func sorted ( by areInIncreasingOrder : ( Element , Element ) -> Bool ) -> [ Element ]
or
public mutating func sort ( by areInIncreasingOrder : ( Element , Element ) -> Bool )
The only difference to the functions in the previous paragraph is, that we have to hand over a closure that has two array elements as parameters and returns a boolean. If the two elements are already in the right order, we have to return
true
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
var dateArray = [ Date ] ( )
let dateFormatter = DateFormatter ( )
dateFormatter . dateFormat = "MM/dd/yyyy"
dateArray . append ( dateFormatter . date ( from : "02/03/1985" ) ! )
dateArray . append ( dateFormatter . date ( from : "12/01/2025" ) ! )
dateArray . append ( dateFormatter . date ( from : "07/08/1964" ) ! )
dateArray . append ( dateFormatter . date ( from : "09/04/2016" ) ! )
dateArray . append ( dateFormatter . date ( from : "01/01/2000" ) ! )
dateArray . append ( dateFormatter . date ( from : "12/12/1903" ) ! )
dateArray . append ( dateFormatter . date ( from : "04/23/2222" ) ! )
dateArray . append ( dateFormatter . date ( from : "08/06/1957" ) ! )
dateArray . append ( dateFormatter . date ( from : "11/11/1911" ) ! )
dateArray . append ( dateFormatter . date ( from : "02/05/1961" ) ! )
dateArray . sort { ( date1 , date2 ) -> Bool in
return date1 . compare ( date2 ) == ComparisonResult . orderedAscending
}
for date in dateArray {
print ( dateFormatter . string ( from : date ) )
}
And indeed, the result is as expected:
Performance
How is the performance? Is the build-in algorithm a good choice for sorting arrays? Yes, it is! As you can see in this article , a self implemented sort algorithm could be quicker in some situations, but generally speaking the performance is very good.
Differences between Swift 2 and Swift 3
It’s worth to mention that there’s a difference between Swift 2 and Swift 3. All the examples in this post are written in Swift 3. In Swift 2, the functions have different names.
Swift 2:
sort ( ) sorted ( )
Swift 2:
sortInPlace ( ) sort ( )
For more details about the changed API naming, you can take a look at this Swift evolution proposal: Apply API Guidelines to the Standard Library .
Video
Check out this video as well:
VIDEO
References
Image: @ S.Pytel / shutterstock.com
