Filtering an Array inside a Dictionary - Swift

I am trying to search through a indexed dictionary to return a specific client based on the client's last name. Below are the data structures I am using. Each client object has a name property which is a String.

var clients = Client.loadAllClients()     //Returns client array
var contacts = [String: [Client]]()      //Indexed clients in a dictionary 
var letters: [String] = [] 

var filteredClient = [Client]()
var shouldShowSearchResults = false
var searchController : UISearchController!

When I do my indexing, the contacts dictionary returns:

{A: [Client("Andrew")]}

Letters array returns:

[A]

I am using the UISearchController to display the filtered array of clients.

func updateSearchResults(for searchController: UISearchController) {
    // how to filter the dictionary 
    self.tableView.reloadData()
}

However, I have no idea how to filter the dictionary to return the correct list of clients. I have tried to use

contacts.filter(isIncluded: ((key: String, value: [Client])) throws -> Bool((key: String, value: [Client])) throws -> Bool)

But I was very confused about the implementation. I am using Xcode 8.0 and Swift 3.0.

If anyone could point me in the right direction, that would be much appreciated. Please let me know if I need to clarify anything. Thank you in advance. The full code can be found at my Github

The main problem is that you are using a dictionary as data source array.

My suggestion is to use a custom struct as model

struct Contact {
   let letter : String
   var clients : [Client]

   init(letter: String, clients : [Client] = [Client]()) {
      self.letter = letter
      self.clients = clients
   } 

   mutating func add(client : Client) {
        clients.append(client)
   }
}

Then create your data source array

var contacts = [Contact]()

and the letter array as computed property

var letters : [String] = {
   return contacts.map{ $0.letter }
}

It's easy to sort the array by letter

contacts.sort{ $0.letter < $1.letter }

Now you can search / filter this way (text is the text to be searched for)

 filteredClient.removeAll()
 for contact in contacts {
     let filteredContent = contact.clients.filter {$0.name.range(of: text, options: [.anchored, .caseInsensitive, .diacriticInsensitive]) != nil }
     if !filteredContent.isEmpty {
         filteredClient.append(filteredContent)
     }
 }

You can even keep the sections (letters) if you declare filteredClient also as [Contact] and create temporary Contact instances with the filtered items.

Of course you need to change all table view data source / delegate methods to conform to the Contact array, but it's worth it. An array as data source is more efficient than a dictionary.