how to create the following map of map in Scala - scala

Question

I am a Scala newbie: how can I create the following "map of map" in Scala:
"Outer" map
+-------------------------+-------------------------------+
| Key | Value |
+-------------------------+-------------------------------+
| (employeID, currencyID) | (valueDate, set of CashFlow) |
+-------------------------+-------------------------------+
The value in the "outer" map is also a map:
"Inner" map
+-----------+------------------+
| Key | Value |
+-----------+------------------+
| valueDate | set of CashFlow |
+-----------+------------------+
with the following types:
employeeID: Int
currencyID: Int
valueDate: java.util.Date
set of CashFlow: Set[com.company.CashFlow]
The following won't compile (need to override +=, -=, etc):
myMap = new mutable.HashMap[(Int, Int), java.util.TreeMap[Date, mutable.Set[CashFlow]] with mutable.MultiMap[Date, CashFlow].withDefaultValue(new util.TreeMap[Date, mutable.Set[CashFlow]] with mutable.MultiMap[Date, CashFlow]
Requirements:
map must be mutable
sorted by valueDate
for one valueDate, I can have multiple cash flows
I would like to avoid checking for key existence on (employeeID, currencyID), i.e. myMap(emp1, ccy1).addBinding(date1, cashFlow1) shouldn't fail if the key doesn't exist.
Instead, it should automatically create a new empty sorted MultiMap and initialize it with (date1, cashFlow1)

Answer 1

You can create it without MultiMap:
import scala.collection.mutable._, JavaConverters._, java.util.TreeMap
val myMap = new mutable.HashMap[(Int, Int), mutable.Map[Date, Set[CashFlow]]]{
override def apply(k: (Int, Int)) =
getOrElseUpdate(k, new TreeMap[Date, mutable.Set[CashFlow]].asScala)
}
myMap: scala.collection.mutable.Map[(Int, Int),scala.collection.mutable.Map[java.util.Date,scala.collection.mutable.Set[CashFlow]]] = Map()
override def apply needed as withDefaultValue will always return you the same value.
It's also possible to create MultiMap from java's TreeMap using standard wrappers:
import scala.collection.convert.Wrappers._
//This wrapper will hold your Java's TreeMap inside, and delegate all operations to it
scala> def newTreeMultiMap[K, V]: MultiMap[K, V] = new JMapWrapper(new TreeMap[K, Set[V]]) with MultiMap[K, V]
newTreeMultiMap: [K, V]=> scala.collection.mutable.MultiMap[K,V]
scala> val myMap = new HashMap[(Int, Int), MultiMap[Int, String]]{ override def apply(k: (Int, Int)) = getOrElseUpdate(k, newTreeMultiMap[Int, String]) }
myMap: scala.collection.mutable.Map[(Int, Int),scala.collection.mutable.MultiMap[java.util.Date,CashFlow]] = Map()
I think it should be in standard library but didn't find any.
Examples (I used Int instead of Date to show that ordering works):
scala> val myMap = new HashMap[(Int, Int), MultiMap[Int, String]]{ override def apply(k: (Int, Int)) = getOrElseUpdate(k, newTreeMultiMap[Int, String]) }
myMap: scala.collection.mutable.Map[(Int, Int),scala.collection.mutable.MultiMap[Int,String]] = Map()
scala> myMap(0 -> 0).addBinding(4, "aaa") //no exceptions on myMap(0 -> 0) with empty Map
res27: scala.collection.mutable.MultiMap[Int,String] = Map(4 -> Set(aaa))
scala> myMap(0 -> 0).addBinding(2, "aaa") //should be before 4
res28: scala.collection.mutable.MultiMap[Int,String] = Map(2 -> Set(aaa), 4 -> Set(aaa))
scala> myMap(0 -> 0).addBinding(5, "aaa") //should be after 4
res29: scala.collection.mutable.MultiMap[Int,String] = Map(2 -> Set(aaa), 4 -> Set(aaa), 5 -> Set(aaa))
scala> myMap(0 -> 0).addBinding(4, "bbb")
res30: scala.collection.mutable.MultiMap[Int,String] = Map(2 -> Set(aaa), 4 -> Set(aaa, bbb), 5 -> Set(aaa))
scala> myMap(0 -> 0).toList //finally use the order
res31: List[(Int, scala.collection.mutable.Set[String])] = List((2,Set(aaa)), (4,Set(aaa, bbb)), (5,Set(aaa)))
scala> myMap(0 -> 1).addBinding(2, "aaa")
res18: scala.collection.mutable.MultiMap[Int,String] = Map(2 -> Set(aaa))