Rebuild an NSArray by grouping objects that have matching id numbers?

Question

I have an NSArray and each object in the array has a groupId and a name. Each object is unique but there are many with the same groupId. Is there a way i can tear the arra

Answer 1

Swift implementation of Sergery's answer for my fellow noobs.

class People: NSObject {
    var groupId: String
    var name : String
    init(groupId: String, name: String){
        self.groupId = groupId
        self.name = name
    }
}


let matt = People(groupId: "1", name: "matt")
let john = People(groupId: "2", name: "john")
let steve = People(groupId: "3", name: "steve")
let alice = People(groupId: "4", name: "alice")
let bill = People(groupId: "1", name: "bill")
let bob = People(groupId: "2", name: "bob")
let jack = People(groupId: "3", name: "jack")
let dan = People(groupId: "4", name: "dan")
let kevin = People(groupId: "1", name: "kevin")
let mike = People(groupId: "2", name: "mike")
let daniel = People(groupId: "3", name: "daniel")

let arrayOfPeople = NSArray(objects: matt, john, steve, alice, bill, bob, jack, dan, kevin, mike, daniel)

var resultArray = NSMutableArray()
let groups = arrayOfPeople.valueForKeyPath("@distinctUnionOfObjects.groupId") as [String]


for groupId in groups {
    var entry = NSMutableDictionary()
    entry.setObject(groupId, forKey: "groupId")
    let predicate = NSPredicate(format: "groupId = %@", argumentArray: [groupId])
    var groupNames = arrayOfPeople.filteredArrayUsingPredicate(predicate)
    for i in 0..

Note the @ sign in valueForKeyPath. that tripped me up a little :)