scala.collection.mutable.PriorityQueue：与案例类的 2 个或更多属性进行比较

Posted 2023-02-16

【中文标题】scala.collection.mutable.PriorityQueue：与案例类的 2 个或更多属性进行比较

【英文标题】：scala.collection.mutable.PriorityQueue: Comparing with 2 or more attributes of a case class

【发布时间】：2019-10-30 22:10:10

【问题描述】：

这个问题Easy idiomatic way to define Ordering for a simple case class 看起来相似但不一样。这个问题与优先级队列更相关。

import scala.collection.mutable.PriorityQueue

  case class Task(prio: Int, text: String, jobPriority:Int)
    extends Ordered[Task] 
    def compare(that: Task) = that.prio compare this.prio
   // def compare(x: Task, y: Task) = y.prio compare this.prio //&&  y.jobPriority compare this.jobPriority

  

  //test
  var q: mutable.PriorityQueue[Task] = PriorityQueue[Task]() ++ Seq(Task(3, "Clear drains",1), Task(4, "Feed cat",2),
    Task(5, "Make tea",9), Task(1, "Solve RC tasks",5), Task(2, "Tax return",5))
  while (q.nonEmpty) println(q dequeue)

正在给我这个输出：

Task(1,Solve RC tasks,5)
Task(2,Tax return,5)
Task(3,Clear drains,1)
Task(4,Feed cat,2)
Task(5,Make tea,9)

现在我想在进行比较时也考虑jobPriority。就像比较多个属性的自定义 java 比较器一样。

scala 有什么方法可以实现这个吗？

【问题讨论】：

这能回答你的问题吗？ Easy idiomatic way to define Ordering for a simple case class

它仍然是重复的。根据您接受的答案，链接的问题是您问题的准确答案。

【参考方案1】：

你可以这样做：

case class Task(prio: Int, text: String, jobPriority:Int)
    extends Ordered[Task] 
    def prioCompare(that: Task) = that.prio compare this.prio
    def jobPriorityCompare(that: Task) = that.jobPriority compare this.jobPriority
    def compare(that: Task) = 
      val prioC = prioCompare(that)

      if(prioC == 0) jobPriorityCompare(that) else prioC
    

  

  //test
  var q: mutable.PriorityQueue[Task] = PriorityQueue[Task]() ++ Seq(Task(3, "Clear drains",6), Task(4, "Feed cat",2),
    Task(5, "Make tea",9), Task(1, "Solve RC tasks",5), Task(3, "Tax return",5))
  while (q.nonEmpty) println(q dequeue)

/* Output
Task(1,Solve RC tasks,5)
Task(3,Tax return,5)
Task(3,Clear drains,6)
Task(4,Feed cat,2)
Task(5,Make tea,9)
*/

【讨论】：

这可能有效。但链接的问题提供了更惯用的解决方案。

【参考方案2】：

与元组比较：

import scala.collection.mutable.PriorityQueue

  case class Task(prio: Int, text: String, jobPrio: Int)
    extends Ordered[Task] 

    import scala.math.Ordered.orderingToOrdered

    def compare(that: Task) = (that.prio, that.jobPrio) compare(this.prio, this.jobPrio)

  

  //test
  var q: mutable.PriorityQueue[Task] = PriorityQueue[Task]() ++ Seq(Task(3, "Clear drains", 1), Task(4, "Feed cat", 2),
    Task(5, "Make tea", 9), Task(1, "Solve RC tasks", 5), Task(2, "Tax return", 5))
  while (q.nonEmpty) println(q dequeue)

---

结果：

Task(1,Solve RC tasks,5)
Task(2,Tax return,5)
Task(3,Clear drains,1)
Task(4,Feed cat,2)
Task(5,Make tea,9)