First of each distinct value

gistfile1.txt

 class LordeSandwich
 {
  static List<E> firstOfEach<E, L>(Iterable<E> sourceIterable, ConsumerSupplierFunction<E, L> strategy)
  {
    Set<L> seenPrimaryKeys = new Set<L>();

    List<E> list = new List<E>();

    for (E element in sourceIterable)
    {
      L primaryKey = strategy(element);
      if ( !seenPrimaryKeys.contains(primaryKey) ) {
        seenPrimaryKeys.add(primaryKey);
        list.add(element);
      }
    }

    return list;
  }
}