从Scala中的Map[List()]返回所有元素

Question

我是Scala的新手，所以如果有什么听起来有点基础的话，我很抱歉。正在做一项大学作业，似乎找不到任何类似的问题。

EDIT：这个函数的思想是，我传递一个数据字符串，并将其分离为各个元素。据我所知，事物被正确地分开，列表中包含了正确的数据类型和正确的信息。

所以我创建了一个函数，它返回Map[String，List[(Int，String，Float(]]

该函数做其他事情，但为了简短起见，一旦我建立了列表，这就是我构建地图并返回它的方式：-

val newMap = Map(name -> newList2.toList)
newMap

我可以使用newMap.foreach循环浏览地图并找到我的所有元素。如预期的那样工作：-

(Sample Key,List((3,PlaceName1,2.7)))
(Sample Key,List((2,PlaceName1,3.8)))
(Sample Key,List((1,PlaceName1,0.75)))

我只是想调用这个函数，并将映射保存到一个新的变量中。我尝试了两种方法：-

val saveMap = separator("1:PlaceName1:0.75,2:PlaceName2:3.8,3:PlaceName3:2.7")

然而，当我尝试循环浏览时，我只得到第一个列表元素：-

(Sample Key,List((1,PlaceName1,0.75)))

我还尝试使用格式为：-的mapBuffer

var mapBuffer: Map[String, List[(Int, String, Float)]] = Map()
mapBuffer = separator("1:PlaceName1:0.75,2:PlaceName2:3.8,3:PlaceName3:2.7")

再次，我在这里返回时得到的是：-

mutated mapBuffer

(Sample Key,List((1,PlaceName1,0.75)))

作为Scala的新手，但在Java和C#方面有一些经验，我很难理解如何返回Map值，将其保存到一个构建相同的Map值中，但它不会成功。尝试了我能找到的地图和列表的每一次迭代，但在搜索中找不到任何内容。

有人能提供帮助吗？

编辑：

以下是函数的全部代码，以及我如何尝试调用它。

def separator(data:String): Map[String, List[(Int, String, Float)]] = {
//Route name will be worked out later. For now, this is a sample.
val sampleRouteName = "First Route"
//Stage list will hold each list entry
val stageList = ListBuffer[(Int, String, Float)]()
//Stage list builder will put all the list entries together
var stageListBuilder = List[(Int, String, Float)]()
if (data.contains(",")) {
//Find index of first comma
val commaIndex = data.indexOf(",")
//Split everything before the comma off
val (firstEntry, restOfPhrase) = data.splitAt(commaIndex)
//Find the index of the colon in the first entry
val colonIndex = firstEntry.indexOf(":")
//Split everything before the colon off to just keep the number
val (number, restOfStage) = firstEntry.splitAt(colonIndex)
//Get rid of the first colon from the rest of the line
val restOfStage2 = restOfStage.replaceFirst(":", "")
//Find the index of the next colon
val colonIndex2 = restOfStage2.indexOf(":")
//Split everything before the colon off to just keep the stage name
val (stageName, restOfStage3) = restOfStage2.splitAt(colonIndex2)
//Get rid of the colon leaving just the stage length
val stageLength = restOfStage3.replaceFirst(":", "")
//Put all of these together into a list line in the builder
stageListBuilder = List((number.toInt,stageName,stageLength.toFloat))
//Add the list line from the builder to the list as an element
stageListBuilder.foreach(line => stageList += line)
//Call recursive function and remove the comma from the start
separator(restOfPhrase.replaceFirst(",", ""))
}
else if (data.length != 0) {
//Find index of first colon
val colonIndex = data.indexOf(":")
//Split everything before the colon off to just keep the number
val (number, restOfStage) = data.splitAt(colonIndex)
//Get rid of the first colon from the rest of the line
val restOfStage2 = restOfStage.replaceFirst(":", "")
//Find the index of the next colon
val colonIndex2 = restOfStage2.indexOf(":")
//Split everything before the colon off to just keep the stage name
val (stageName, restOfStage3) = restOfStage2.splitAt(colonIndex2)
//Get rid of the colon leaving just the stage length
val stageLength = restOfStage3.replaceFirst(":", "")
//Put all of these together into a list line in the builder
stageListBuilder = List((number.toInt,stageName,stageLength.toFloat))
//Add the list line from the builder to the list as an element
stageListBuilder.foreach(line => stageList += line)
}
//This is a map that accurately contains the key (ie. GCU Route) and a list of the routes.
val routeMap = Map(sampleRouteName -> stageList.toList)
//To test that the list has all the elements (CURRENTLY WORKING)
routeMap.foreach(line => println("TEST - " + line))
//Return the map
routeMap
}
//val saveMap = separator("1:City Chambers:0.75,2:Velodrome:3.8,3:People's Palace:2.7")
//Create new map buffer
var mapBuffer: Map[String, List[(Int, String, Float)]] = Map()
//Call separator function
mapBuffer = separator("1:City Chambers:0.75,2:Velodrome:3.8,3:People's Palace:2.7")
//Test that each element is in the list (CURRENTLY NOT WORKING)
mapBuffer.foreach(line => println(line))

Answer 1

正如您所提到的，您使用的键与Map的键相同。假设我们有这样的分离器方法：

val str = "1:PlaceName1:0.75,2:PlaceName2:3.8,3:PlaceName3:2.7"
def separator(str: String): List[(String, (Int, String, Float))] =
str.split(",").map(_.split(":")).toList.map(_.toList).collect {
case ii :: s :: d :: Nil =>
"Sample Key" -> (ii.toInt, s, d.toFloat)
}

separator(str).foearch(println)
// result:
(Sample Key,(1,PlaceName1,0.75))
(Sample Key,(2,PlaceName2,3.8))
(Sample Key,(3,PlaceName3,2.7))

如果我们将结果转换为Map，在这种情况下，我们会丢失一些具有相同密钥的元素示例密钥：

def separator1(str: String): Map[String, List[(Int, String, Float)]] =
str.split(",").map(_.split(":")).toList.map(_.toList).collect {
case ii :: s :: d :: Nil =>
"Sample Key" -> List((ii.toInt, s, d.toFloat))
}.toMap
separator1(str).foreach(println)
// result:
// (Sample Key,List((3,PlaceName3,2.7)))

因此，我们不能拥有与Map的KEY相同的密钥。映射的关键字应该是唯一的。

case class Aname(a: Int, b: String, c: Float)
def separator2(str: String): Map[String, List[Aname]] =
str.split(",").map(_.split(":")).toList.map(_.toList).collect {
case ii :: s :: d :: Nil =>
Aname(ii.toInt, s, d.toFloat)
}.groupBy(_.b)
separator2(str).foreach(println)
// result:
// (PlaceName3,List(Aname(3,PlaceName3,2.7)))
// (PlaceName2,List(Aname(2,PlaceName2,3.8)))
// (PlaceName1,List(Aname(1,PlaceName1,0.75)))

你可以在这里玩