scala.collection.mutable.PriorityQueue：比较一个案例的2个或更多属性class

Question

这个问题 Easy idiomatic way to define Ordering for a simple case class 看起来很相似但并不相同。这个问题跟优先级队列比较相关

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)

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)

现在我在做比较的时候也想考虑jobPriority。就像比较多个属性的自定义 java 比较器一样。

scala 中有什么方法可以实现这个吗？

Answer 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)
*/

Answer 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)

scala.collection.mutable.PriorityQueue：比较一个案例的2个或更多属性class

scala.collection.mutable.PriorityQueue: Comparing with 2 or more attributes of a case class

scala

priority-queue

comparator