如何在 Scala 中创建以下地图的地图

Question

我是 Scala 新手：如何在 Scala 中创建以下 "map of map"：

"Outer" map
+-------------------------+-------------------------------+
|           Key           |             Value             |
+-------------------------+-------------------------------+
| (employeID, currencyID) | (valueDate, set of CashFlow)  |
+-------------------------+-------------------------------+

"outer"图中的值也是一个图：

"Inner" map
+-----------+------------------+
|    Key    |      Value       |
+-----------+------------------+
| valueDate | set of CashFlow  |
+-----------+------------------+

具有以下类型：

员工ID：整数
货币ID：整数
值日期：java.util.Date
现金流集：集[com.company.CashFlow]

以下不会编译（需要覆盖 +=、-= 等）：

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]

要求：

地图必须是可变的
按值日期排序
对于一个 valueDate，我可以有多个现金流量
我想避免检查 (employeeID, currencyID) 上的密钥是否存在，即如果密钥不存在，myMap(emp1, ccy1).addBinding(date1, cashFlow1) 不应失败。相反，它应该自动创建一个新的空排序 MultiMap 并用 (date1, cashFlow1)

Answer 1

不用MultiMap也可以创建：

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 需要，因为 withDefaultValue 将始终 return 与您相同的值。

也可以使用标准包装器从 java 的 TreeMap 创建 MultiMap：

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()

我认为它应该在标准库中，但没有找到。

示例（我使用 Int 而不是 Date 来证明排序有效）：

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))

如何在 Scala 中创建以下地图的地图

how to create the following map of map in Scala

scala

scala-collections