Group By Task

  abstract class Direction;
  case class Sell() extends Direction;
  case class Buy() extends Direction;
  case class Trade(direction : Direction, amount : Int, security : String);

  val trades = List(
      Trade(Buy(), 100, "AAPL"),
      Trade(Buy(), 200, "MSFT"),
      Trade(Buy(), 150, "INTC"),
      Trade(Buy(), 100, "AAPL"),
      Trade(Sell(), 100, "MSFT"),
      Trade(Sell(), 50, "INTC"),
      Trade(Buy(), 100, "AAPL")
      );