Scala: Remove duplicates in list of objects

Question

I've got a list of objects List[Object] which are all instantiated from the same class. This class has a field which must be unique Object.property. What is the cleanest way to iterate the list of objects and remove all objects(but the first) with the same property?

Answer 1

With preserve order:

def distinctBy[L, E](list: List[L])(f: L => E): List[L] =
  list.foldLeft((Vector.empty[L], Set.empty[E])) {
    case ((acc, set), item) =>
      val key = f(item)
      if (set.contains(key)) (acc, set)
      else (acc :+ item, set + key)
  }._1.toList

distinctBy(list)(_.property)

Answer 2

Here is a little bit sneaky but fast solution that preserves order:

list.filterNot{ var set = Set[Property]()
    obj => val b = set(obj.property); set += obj.property; b}

Although it uses internally a var, I think it is easier to understand and to read than the foldLeft-solution.