Avoid duplicates in Swift array

Question

I created this singleton to access a shared array throughout my app:

class TranslationItems {
    var delegate: TranslationItemsDelegate?

    static let shared = TranslationItems()

    var array = [Translation]() {
        didSet {
            delegate?.newItemAdded()
        }
    }
}

The problem is that this allows for duplication (the array may contain multiple items with the same hashValue). If I check for duplication inside the didSet setter and then change the array there (for example by doing array = Array(Set(array))) that leads to an infinite loop.

How do I remove duplicates in my class?

Translation has to be hashable`

ielyamani
– ielyamani

2018-12-25 11:41:28 +00:00
Commented Dec 25, 2018 at 11:41 — ielyamani
– ielyamani, Commented Dec 25, 2018 at 11:41
I confirm it is hashable already

Cesare
– Cesare

2018-12-25 11:59:20 +00:00
Commented Dec 25, 2018 at 11:59 — Cesare
– Cesare, Commented Dec 25, 2018 at 11:59
stackoverflow.com/a/46519116/2303865

Leo Dabus
– Leo Dabus

2018-12-25 12:33:39 +00:00
Commented Dec 25, 2018 at 12:33 — Leo Dabus
– Leo Dabus, Commented Dec 25, 2018 at 12:33

vadian · Accepted Answer · 2018-12-25 11:39:30Z

4

If you want to avoid duplicates why don't you use a Set anyway (Translation must conform to Hashable)?

var set = Set<Translation>()

However if you want to keep the array a more efficient way is to add an add method which filters the duplicates, Translation must conform to Equatable

func add(object: Translation) {
    if !array.contains(object) {
       array.append(object)
       delegate?.newItemAdded()
    }
}

Making a Set from the Array and then convert it back to Array is unnecessarily expensive.

answered Dec 25, 2018 at 11:39

vadian

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6 Comments

ielyamani Over a year ago

array.contains will become expensive for a large number of elements.

vadian Over a year ago

@Carpsen90 Not as expensive as Array(Set(array)) 😉

ielyamani Over a year ago

Yes, that's like reaching for your ear with the wrong hand 😜Not sure why such answers are upvoted...

vadian Over a year ago

@Carpsen90 Most people especially the newbies are looking for the easiest/shortest solution which is not necessarily the most efficient.

vadian Over a year ago

[OT] @Cesare Marry is sposare 😉 Buon Natale.

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