Find min / max value in Swift Array
ArraysSwiftArrays Problem Overview
Given an array of Swift numeric values, how can I find the minimum and maximum values?
I've so far got a simple (but potentially expensive) way:
var myMax = sort(myArray,>)[0]
And how I was taught to do it at school:
var myMax = 0
for i in 0..myArray.count {
if (myArray[i] > myMax){myMax = myArray[i]}
}
Is there a better way to get the minimum or maximum value from an integer Array in Swift? Ideally something that's one line such as Ruby's .min
and .max
.
Arrays Solutions
Solution 1 - Arrays
Given:
let numbers = [1, 2, 3, 4, 5]
Swift 3:
numbers.min() // equals 1
numbers.max() // equals 5
Swift 2:
numbers.minElement() // equals 1
numbers.maxElement() // equals 5
Solution 2 - Arrays
To calculate an array's min and max values yourself, you can use reduce
. This was a key solution prior to .min()
and .max()
appearing in Swift.
Use the almighty reduce
:
let nums = [1, 6, 3, 9, 4, 6];
let numMax = nums.reduce(Int.min, { max($0, $1) })
Similarly:
let numMin = nums.reduce(Int.max, { min($0, $1) })
reduce
takes a first value that is the initial value for an internal accumulator variable, then applies the passed function (here, it's anonymous) to the accumulator and each element of the array successively, and stores the new value in the accumulator. The last accumulator value is then returned.
Solution 3 - Arrays
With Swift 5, Array
, like other Sequence
Protocol conforming objects (Dictionary
, Set
, etc), has two methods called max()
and max(by:)
that return the maximum element in the sequence or nil
if the sequence is empty.
Array
's max()
method
#1. Using If the element type inside your sequence conforms to Comparable
protocol (may it be String
, Float
, Character
or one of your custom class or struct), you will be able to use max()
that has the following declaration:
@warn_unqualified_access func max() -> Element?
>Returns the maximum element in the sequence.
The following Playground codes show to use max()
:
let intMax = [12, 15, 6].max()
let stringMax = ["bike", "car", "boat"].max()
print(String(describing: intMax)) // prints: Optional(15)
print(String(describing: stringMax)) // prints: Optional("car")
class Route: Comparable, CustomStringConvertible {
let distance: Int
var description: String { return "Route with distance: \(distance)" }
init(distance: Int) {
self.distance = distance
}
static func ==(lhs: Route, rhs: Route) -> Bool {
return lhs.distance == rhs.distance
}
static func <(lhs: Route, rhs: Route) -> Bool {
return lhs.distance < rhs.distance
}
}
let routes = [
Route(distance: 20),
Route(distance: 30),
Route(distance: 10)
]
let maxRoute = routes.max()
print(String(describing: maxRoute)) // prints: Optional(Route with distance: 30)
Array
's max(by:)
method
#2. Using If the element type inside your sequence does not conform to Comparable
protocol, you will have to use max(by:)
that has the following declaration:
@warn_unqualified_access func max(by areInIncreasingOrder: (Element, Element) throws -> Bool) rethrows -> Element?
>Returns the maximum element in the sequence, using the given predicate as the comparison between elements.
The following Playground codes show to use max(by:)
:
let dictionary = ["Boat" : 15, "Car" : 20, "Bike" : 40]
let keyMaxElement = dictionary.max(by: { (a, b) -> Bool in
return a.key < b.key
})
let valueMaxElement = dictionary.max(by: { (a, b) -> Bool in
return a.value < b.value
})
print(String(describing: keyMaxElement)) // prints: Optional(("Car", 20))
print(String(describing: valueMaxElement)) // prints: Optional(("Bike", 40))
class Route: CustomStringConvertible {
let distance: Int
var description: String { return "Route with distance: \(distance)" }
init(distance: Int) {
self.distance = distance
}
}
let routes = [
Route(distance: 20),
Route(distance: 30),
Route(distance: 10)
]
let maxRoute = routes.max(by: { (a, b) -> Bool in
return a.distance < b.distance
})
print(String(describing: maxRoute)) // prints: Optional(Route with distance: 30)
Solution 4 - Arrays
The other answers are all correct, but don't forget you could also use collection operators, as follows:
var list = [1, 2, 3, 4]
var max: Int = (list as AnyObject).valueForKeyPath("@max.self") as Int
you can also find the average in the same way:
var avg: Double = (list as AnyObject).valueForKeyPath("@avg.self") as Double
This syntax might be less clear than some of the other solutions, but it's interesting to see that -valueForKeyPath:
can still be used :)
Solution 5 - Arrays
You can use with reduce
:
let randomNumbers = [4, 7, 1, 9, 6, 5, 6, 9]
let maxNumber = randomNumbers.reduce(randomNumbers[0]) { $0 > $1 ? $0 : $1 } //result is 9
Solution 6 - Arrays
Swift 3.0
You can try this code programmatically.
func getSmallAndGreatestNumber() -> Void {
let numbers = [145, 206, 116, 809, 540, 176]
var i = 0
var largest = numbers[0]
var small = numbers[0]
while i < numbers.count{
if (numbers[i] > largest) {
largest = numbers[i]
}
if (numbers[i] < small) {
small = numbers[i]
}
i = i + 1
}
print("Maximum Number ====================\(largest)")// 809
print("Minimum Number ====================\(small)")// 116
}
Solution 7 - Arrays
With Swift 1.2 (and maybe earlier) you now need to use:
let nums = [1, 6, 3, 9, 4, 6];
let numMax = nums.reduce(Int.min, combine: { max($0, $1) })
For working with Double values I used something like this:
let nums = [1.3, 6.2, 3.6, 9.7, 4.9, 6.3];
let numMax = nums.reduce(-Double.infinity, combine: { max($0, $1) })
Solution 8 - Arrays
In Swift 2.0, the minElement
and maxElement
become methods of SequenceType
protocol, you should call them like:
let a = [1, 2, 3]
print(a.maxElement()) //3
print(a.minElement()) //1
Using maxElement
as a function like maxElement(a)
is unavailable now.
The syntax of Swift is in flux, so I can just confirm this in Xcode version7 beta6.
It may be modified in the future, so I suggest that you'd better check the doc before you use these methods.
Solution 9 - Arrays
var numbers = [1, 2, 7, 5];
var val = sort(numbers){$0 > $1}[0];
Solution 10 - Arrays
Here's a performance test for the solutions posted here. https://github.com/tedgonzalez/MaxElementInCollectionPerformance
This is the fastest for Swift 5
array.max()
Solution 11 - Arrays
> Updated for Swift 3/4:
Use below simple lines of code to find the max from array;
var num = [11, 2, 7, 5, 21]
var result = num.sorted(){
$0 > $1
}
print("max from result: \(result[0])") // 21
Solution 12 - Arrays
Just curious why you think the way it was taught in school is potentially expensive? You're running a for loop which has the time complexity of O(N). That's actually better than most sorting algorithms and equivalent to the performance of higher-order methods like reduce
.
So I would think that in terms of performance, a for loop is as good as it gets. I don't think you'll find anything better than O(N) for finding max.
Of course, just use the .max()
method provided by apple is the way to go.
Solution 13 - Arrays
If both minimum and maximum values are desired, an efficient approach could be to use a single reduce
operation with a tuple:
let values = [11, 2, 7, 5, 21]
let (minimum, maximum) = values.reduce((Int.max, Int.min)) {
(min($0.0, $1), max($0.1, $1))
}
print(minimum, maximum) // 2, 21
Solution 14 - Arrays
You can also sort your array and then use array.first
or array.last