Removing Duplicates From Array of Custom Objects Swift

Question

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.

Answer 1

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 ?? ""} 

Answer 2

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.