val data = List(("PO123", "P001", "Item 1", 10),
                ("PO123", "P001", "Item 1", 10),
                ("PO123", "P002", "Item 2", 30),
                ("PO123", "P002", "Item 2", 10))

 data.groupBy( product => (product._1, product._2, product._3))
      .map {
         case (productInfo, products) => {
         val total = products.foldLeft(0)((sum,elt) => sum + elt._4)
         (productInfo._1,productInfo._2,productInfo._3,total)
          }
 }

scala.collection.immutable.Iterable[(String, String, String, Int)] =
    List((PO123,P001,Item 1,20), (PO123,P002,Item 2,40))

case class Document(poID: String, productID: String, name: String, qty: Int)

var list2 = list.groupBy(doc => doc.productID)

list2.map(stringListTuple => stringListTuple._2.foldLeft(Document("","","",0)){
   (acc: Document,curr: Document) => Document(curr.poID, curr.productID, curr.name,curr.qty + acc.qty)
}).toList.sortBy(el => el.productID)

val in = Array(("PO123", "P001", "Item 1", 10), ("PO123", "P001", "Item 1", 10),
               ("PO123", "P002", "Item 2", 30), ("PO123", "P002", "Item 2", 10))

in groupBy (p=>(p._1,p._2,p._3)) map { case(k,v) =>
  (k._1, k._2, k._3, (v map (_._4) sum )) }

List((PO123,P001,Item 1,20), (PO123,P002,Item 2,40))