```
  val Sparse1 = Map(0 -> 4, 3 -> 7, 6 -> 11, 18 -> 17).withDefaultValue(0)
  val Sparse2 = Map(1 -> 3, 3 -> 3, 11 -> 2,18 -> 3, 20 -> 6).withDefaultValue(0)
  //println(Sparse2.toSeq)//to see what it is....0's missing
  val SparseSum = (Sparse1.toSeq ++ Sparse2.toSeq).groupBy(_._1).mapValues(_.map(_._2).sum)
  //println(SparseSum)
  val productOfValues = ((Sparse1.toSeq ++ Sparse2.toSeq).groupBy(_._1).mapValues(_.map(_._2).reduce(_*_)))
  //println(productOfValues)
  var dotProduct = 0
  for ((h,i) <- productOfValues) {
    dotProduct += i
  }
  //println(dotProduct)
  //If I specify some zero values, lets see what happens:
  val Sparse3 = Map(0 -> 4, 1 -> 0, 3 -> 7, 6 -> 11, 11 -> 0, 18 -> 17, 20 -> 0).withDefaultValue(0)
  val Sparse4 = Map(0 -> 0, 1 -> 3, 3 -> 3, 6 -> 0, 11 -> 2,18 -> 3, 20 -> 6).withDefaultValue(0)
  val productOfValues2 = ((Sparse3.toSeq ++ Sparse4.toSeq).groupBy(_._1).mapValues(_.map(_._2).reduce(_*_)))
  var dotProduct2 = 0
  for ((l, m) <- productOfValues2) {
    dotProduct2 += m
  }
  println(productOfValues2)
  println(dotProduct2)//I get 72

```