Append unique values to an array in swift

Question

I haven't found anything on that in Swift. Have found how to find unique values on an array, but not this. Sorry if it sounds quite basic...

But I have the following array

var selectedValues = [String]()

And the following value that comes from a Parse query

 var objectToAppend = object.objectForKey("description")! as! String

this is how I'am doing it at the moment.

self.selectedHobbies.append(objectToAppend)

But because the query happens repeated times, it ends up appending repeated values. It works, but I just want to not waste memory and only keep unique values.

Any ideas on how to solve that in swift?

Mundi · Accepted Answer · 2017-03-10 06:24:11Z

33

You can use a Set which guarantees unique values.

var selectedValues = Set<String>()
// ...
selectedValues.insert(newString) // will do nothing if value exists

Of course, the elements of a Set are not ordered.

If you want to keep the order, just continue with the Array but check before you insert.

if !selectedValues.contains("Bar") { selectedValues.append("Bar") }

edited Mar 10, 2017 at 6:24

answered Aug 20, 2015 at 0:26

Mundi

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5 Comments

GuiSoySauce Over a year ago

is it possible to maintain your code syntax but use a [String] instead of a Set<String>? A Set<String> do not have much use for me as I can convert it to a [String]. I tried much haven't got much luck with it.

Alexander Over a year ago

@Mundi You don't need to do a contains check. If you insert and the element already exists, nothing will happen.

Mundi Over a year ago

@Alexander Agree. Changed it.

kevin Over a year ago

You can also ignore what you put into the array and just use .unique when you need only the unique values. In some cases this might be preferable, like if the unique check is costly and saving the data isn't.

Gargo Over a year ago

Set works with Hashable types only. So for example Set<String> works but Set<SomeProtocol> doesn't

BEN MESSAOUD Mahmoud · Accepted Answer · 2019-02-18 10:31:37Z

9

I guess that your problem was resolved but I add my answer for next developers who's facing same problem :)

My solution is to write an extension of Array to add elements from an array with a distinct way:

here the code :

extension Array{
    public mutating func appendDistinct<S>(contentsOf newElements: S, where condition:@escaping (Element, Element) -> Bool) where S : Sequence, Element == S.Element {
      newElements.forEach { (item) in
        if !(self.contains(where: { (selfItem) -> Bool in
            return !condition(selfItem, item)
        })) {
            self.append(item)
        }
    }
  }
}

example:

var accounts: [Account]
let arrayToAppend: [Account]
accounts.appendDistinct(contentsOf: arrayToAppend, where: { (account1, account2) -> Bool in
        return account1.number != account2.number
})

answered Feb 18, 2019 at 10:31

BEN MESSAOUD Mahmoud

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3 Comments

Kaaaaai Over a year ago

Hi, I have a question. I customized your code like this: public mutating func appendDistinct<T>(_ newElement: T, where condition: @escaping (Element) -> Bool) where T == Element { if !(self.contains(where: { (newElement) -> Bool in return !condition(newElement) })) { self.append(newElement) } } However, it shows a warning: "Same-type requirement makes generic parameters 'T' and 'Element' equivalent; this is an error in Swift 6." How can I fix this issue and get the correct code?

BEN MESSAOUD Mahmoud Over a year ago

Hi @Kaaaaai, I think in this case we don't need to use generic type in this method. The method could be simply like this: ` public mutating func appendDistinct(_ newElement: Element, where condition: @escaping (Element) -> Bool) { if !(self.contains(where: { (newElement) -> Bool in return !condition(newElement) })) { self.append(newElement) } } `

Kaaaaai Over a year ago

that's helpful,thank you~

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