Getting element with max property from array

Question

If I have a struct...

struct MyStruct {
    let number: Int
}

and I have an array of them...

var array = [MyStruct]()
// populate array with MyStructs

Then I can do this to get the maximum number...

var maxNumber = 0

for tempStruct in array where tempStruct.number > maxNumber {
    maxNumber = tempStruct.number
}

However, I can't use...

let maxStruct = array.maxElement()

because MyStruct is not comparable. I could make it comparable but then I might also have a date stamp that I want to compare by so making it Comparable isn't ideal.

Is there another way I could do this that is more elegant?

....

I just thought, I could also do this...

let maxStruct = array.sort{$0.number > $1.number}.first()

But this will take more time. I'm not sure which sort method it uses but it'll prob be n log(n) whereas my initial method will just be n.

Martin R · Accepted Answer · 2016-10-19 12:07:51Z

6

As with sort()/sortInPlace(), there are also two variants of min/maxElement(): The first requires that the sequence elements are comparable:

extension SequenceType where Generator.Element : Comparable {

    public func minElement() -> Self.Generator.Element?
    public func maxElement() -> Self.Generator.Element?
}

The second has no such restriction and takes the comparator as an argument instead:

extension SequenceType {

    public func minElement(@noescape isOrderedBefore: (Self.Generator.Element, Self.Generator.Element) throws -> Bool) rethrows -> Self.Generator.Element?
    public func maxElement(@noescape isOrderedBefore: (Self.Generator.Element, Self.Generator.Element) throws -> Bool) rethrows -> Self.Generator.Element?
}

In your case, you can use maxElement() with a comparator function:

// Swift 2:
let maxStruct = array.maxElement { $0.number < $1.number }
// Swift 3:
let maxStruct = array.max { $0.number < $1.number }

edited Oct 19, 2016 at 12:07

answered Jan 4, 2016 at 14:59

Martin R

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1 Comment

Fogmeister Over a year ago

Ah! Awesome, I didn't know I could use maxElement() that way. Thanks

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