Removing Duplicates From Array of Custom Objects Swift

I have a custom class defined as follows :

class DisplayMessage : NSObject {
var id : String?
var partner_image : UIImage?
var partner_name : String?
var last_message : String?
var date : NSDate?
}

Now I have an array `myChats = [DisplayMessage]?`. The `id` field is unique for each `DisplayMessage` object. I need to check my array and remove all duplicates from it, essentially ensure that all objects in the array have a unique `id`. I have seen some solutions using `NSMutableArray` and `Equatable` however I'm not sure how to adapt them here; I also know of `Array(Set(myChats))` however that doesn't seem to work for an array of custom objects.

Here is an `Array` extension to return the unique list of objects based on a `keyPath`:

```
extension Array {

func uniques<T: Hashable>(by keyPath: KeyPath<Element, T>) -> [Element] {
return reduce([]) { result, element in
let alreadyExists = (result.contains(where: { $0[keyPath: keyPath] == element[keyPath: keyPath] }))
return alreadyExists ? result : result + [element]
}
}
}

```


Usage:
```
myChats.uniques(by: \.id)
```

Create a free duplicate version of an Array, using equality comparisons based on a given key



public extension Sequence {

public func uniq<Id: Hashable >(by getIdentifier: (Iterator.Element) -> Id) -> [Iterator.Element] {
var ids = Set<Id>()
return self.reduce([]) { uniqueElements, element in
if ids.insert(getIdentifier(element)).inserted {
return uniqueElements + CollectionOfOne(element)
}
return uniqueElements
}
}


public func uniq<Id: Hashable >(by keyPath: KeyPath<Iterator.Element, Id>) -> [Iterator.Element] {
return self.uniq(by: { $0[keyPath: keyPath] })
}
}

public extension Sequence where Iterator.Element: Hashable {

var uniq: [Iterator.Element] {
return self.uniq(by: { (element) -> Iterator.Element in
return element
})
}

}

**Usage**


let numbers = [1,2,3,4,5,6,7,1,1,1,]
let cars = [Car(id:1), Car(id:1), Car(id:2)]

numbers.uniq
cars.uniq(by: { $0.id})
cars.uniq(by: \Car.id)
cars.uniq(by: \.id)

Here is an Array extension to return the unique list of objects based on a given key:

extension Array {
func unique<T:Hashable>(map: ((Element) -> (T))) -> [Element] {
var set = Set<T>() //the unique list kept in a Set for fast retrieval
var arrayOrdered = [Element]() //keeping the unique list of elements but ordered
for value in self {
if !set.contains(map(value)) {
set.insert(map(value))
arrayOrdered.append(value)
}
}

return arrayOrdered
}
}

for your example do:

let uniqueMessages = messages.unique{$0.id ?? ""}

You can do it with a set of strings, like this:

var seen = Set<String>()
var unique = [DisplayMessage]
for message in messagesWithDuplicates {
if !seen.contains(message.id!) {
unique.append(message)
seen.insert(message.id!)
}
}

The idea is to keep a set of all IDs that we've seen so far, go through all items in a loop, and add ones the IDs of which we have not seen.