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scala - For 循环和元组树集的类型不匹配错误

问题描述

我是一个新的 Scala 程序员，我遇到了一个问题。我正在编写一个函数来获取的数量当我尝试从我的 for 循环中获取值时（靠近封装在 If/Else 语句中的底部），它给了我一个类型不匹配错误。我期待一个带有 String 和 Int 的 TreeSet 元组（scala.collection.mutable.TreeSet[(String, Int)]），但它说它返回一个 Unit。

这是我的说明，我相信如果我解决了这个错误，它应该可以工作。

"注意：返回类型是具有 (String, Int) 类型的元组的 TreeSet。例如，给定人员列表 List(“tom”, “ann”, “rob”, “rob”, “ann” , “tom”, “pat”, “rob” “pat”, “tom”) 你的函数应该返回 TreeSet((tom,3), (rob,3))。注意：最大的骗子有一个平局，你必须返回集合中所有最大的骗子。一个名字只出现一次的列表返回一个空的 TreeSet。

***函数“crooks”和“a”都在其他未显示的地方定义。

  def biggestCrooks(people: List[String]): TreeSet[(String,Int)] = {

    val crooksListed = crooks(people).toList //Runs my one function that gives me the
                                         // list of criminals with more than one offense

    var numCounted = new Array[Int](crooksListed.size) // Array to hold the number of times a person name 
                                                       //appears

    for(nameIndex <- 0 until crooksListed.size){ // Counts the number of times a name appears
      val counter = people.count(_.equals(crooksListed(nameIndex))) //Stores that name in the array
      numCounted(nameIndex) = counter //Stores the num in the index associated with the name

     }
    var largestValue = numCounted.max // Largest value in the array
    val numValues = numCounted.count(_ == largestValue) // Number of times the value appears
    var indeces : Set[Int] = Set()
    var completeList : TreeSet[(String, Int)] = TreeSet() // Completed list of all names / values

    if(numValues > 1){// Used JIC there are multiple instances of numValues
    for(i <- 0 until numCounted.length){ //If there are multiple instances, find the indeces of them
      if(numCounted(i) == largestValue)
        indeces(i)                       //add the index to the array
    }
    val wow = indeces.toList //Converts a mutable Set to an immutable list
     for(i <- 0 until wow.size){ //iterate through the indeces and associate with names
       completeList.map(crooksListed(wow(i)), wow(i)) //Maps the values to the completeList TreeSet
       //Supposed to solve problem with mismatched types

     } 
    }
    else{

      completeList.map(i => (crooksListed(numCounted.indexOf(largestValue)), largestValue)) //Maps the values to the TreeSet
    }
  }// end biggestCrook

println(biggestCrooks(a))

标签： scala

解决方案

请记住，scala 中的每个语句都是一个表达式，每个表达式都有一个返回类型，并且应该返回一些东西。在 if else 语句的示例第一个分支中返回nothing，在 scala 中它意味着Unit类型：

if(numValues > 1){// Used JIC there are multiple instances of numValues
  for(i <- 0 until numCounted.length){ //If there are multiple instances, find the indeces of them
    if(numCounted(i) == largestValue)
      indeces(i)                       //add the index to the array
  }
  val wow = indeces.toList //Converts a mutable Set to an immutable list
  for(i <- 0 until wow.size){ //iterate through the indeces and associate with names
    completeList.map(crooksListed(wow(i)), wow(i)) //Maps the values to the completeList TreeSet
    //Supposed to solve problem with mismatched types

  }
// this for loop returns Unit, it just iterates on elements, and you need to add return value for compile
}
else{

  completeList.map(i => (crooksListed(numCounted.indexOf(largestValue)), largestValue)) //Maps the values to the TreeSet
// in this place you return mapped cimpleteList as Tree, but be carefull it's empty
}

我认为这个样本可能是这样的：

if (numValues > 1) { // Used JIC there are multiple instances of numValues
  for (i <- numCounted.indices) { //If there are multiple instances, find the indeces of them
    if (numCounted(i) == largestValue)
      indeces(i) //add the index to the array
  }
  indeces.map(w => crooksListed(w) -> w).foldLeft(TreeSet.empty[(String, Int)]){
    case (tree, pair) => tree + pair
  }
} else {
  completeList.map(i => (crooksListed(numCounted.indexOf(largestValue)), largestValue)) //Maps the values to the TreeSet
}

在这里，我通过 crooksListed 和 wow indeces 成对填充真实分支中的空树，并且该分支像错误分支一样返回 TreeSet。尝试阅读有关表达式的更多信息并尝试使用递归而不是for和while循环。

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