Overwrite duplicate values in Scala List - scala

Question

I have the following Comet server:
object UserServer extends LiftActor with ListenerManager {
private var users: List[UserItem] = Nil
def createUpdate = users
override def lowPriority = {
case UserItem(user, room, active, stamp) => {
users :+= UserItem(user, room, active, stamp);
updateListeners()
}
}
}
Currently each time the form is submitted a new UserItem is added to the users list. What I'm trying to do is each time the server receives a new user, instead of concatenating to the list it should overwrite an existing item with the same user and room handle.
So if the list contains the following:
UserItem("jam_2323", "demo-room", "James", "1320073365")
UserItem("jim_4533", "demo-room", "Jim", "1320073365")
The next time these users submit the form the above two items in the list will be replaced with the new stamp value:
UserItem("jam_2323", "demo-room", "James", "1320073435")
UserItem("jim_4533", "demo-room", "Jim", "1320073435")
Thanks in advance for any help, much appreciated :)

Answer 1

This sounds like a classic case where you need a map, rather than a list. I don't know about the details of Lift / Comet, but I guess you want something like
case class User(id: String)
case class Activity(room: String, active: String, stamp: String)
var lastUserActivity = Map[User, Activity]()
...
case UserItem(id, room, active, stamp) => {
lastUserActivity += User(id) -> Activity(room, active, stamp)
}

Answer 2

If you adjust UserItem from being a straight case class (I assume) to being one where you have overriden equals to ignore the stamp field, then you could make users into a Set.
Alternatively, you could filter the List to remove the old matching values before appending.