如何使用不同的数据类型拆分要添加到 Scala 中的 Map 的列表

Question

I have some raw test data that I need to split into a map of format:

Map[String, List[(Int, String, Float)]]

I have managed to read in the data as a list and will give an example of one line of data below:

Oor Wullie Route (GCU),1:City Chambers:0.75f,2:Sir Chris Hoy Velodrome:3.8f,3:People's Palace:2.7f,4:Riverside Museum:5.4f,5:Botanic Gardens:2.4f,6:GCU:3.4f

The above represents the following: A Route, a stage number:stage name:total distance of stage

So each set of 3 values (ie 1:City Chambers:5) should be added to the [Int, String, Float] section of the map, with the route name being the key.

This is my code so far for reading the file and adding it to a list:

var mapBuffer: Map[String, List[(Int, String, Float)]] = Map()

val fitnessData = "C:\\Users\\josep\\Desktop\\Coursework\\Coursework\\src\\cw.txt"

val lines = Source.fromFile("C:\\Users\\josep\\Desktop\\Coursework\\Coursework\\src\\cw.txt").getLines.toList

I would like to write a funciton for splitting the data up and adding it to a map, essentially doing this:

var key ="Oor Wullie Route (GCU)"
var newList = List((1,"City Chambers",0.75f),(2,"Sir Chris Hoy Velodrome",3.8f),(3,"People's Palace",2.7f),(4,"Riverside Museum",5.4f),(5,"Botanic Gardens",2.4f),(6,"GCU",3.4f))
mapBuffer = mapBuffer ++ Map(key -> newList)

How can I add the data to a map in my desired format?

Answer 1

My suggestion would be to use foldLeft. Something like:

  val resource = Source.fromFile("src/lines.txt")
  val lines = resource.getLines.toList
  resource.close()

  val map = lines.foldLeft(Map[String, List[(Int, String, Float)]]())((map, line) => {
    val keyValuesArray = line.split(",").toList
    val key = keyValuesArray.head
    val listOfValuesAsString = keyValuesArray.tail

    val listOfValues = listOfValuesAsString.map {
      case s"$integer:$string:$float" => (integer.toInt, string, float.toFloat)
    }

    map + (key -> listOfValues)
  })

Start with empty map, and add key->values for each line. Also, try match expressions when you parse data in list (listOfValues part is doing that).

Answer 2

This approach is with pattern matching and tail recursion . I think it works very well.

First I convert the file into a List[Array[String]] .

Second I call loop to go through the list in a recursive way and build the map.

Third inside the loop function I call make List to build the list of tuples in a recursive way.

As an example:

input

Oor Wullie Route (GCU),1:City Chambers:0.75f,2:Sir Chris Hoy Velodrome:3.8f,3:People's Palace:2.7f,4:Riverside Museum:5.4f,5:Botanic Gardens:2.4f,6:GCU:3.4f
Oor Wullie Route2 (GCU),1:City Chambers:0.75f,2:Sir Chris Hoy Velodrome:3.8f,3:People's Palace:2.7f,4:Riverside Museum:5.4f,5:Botanic Gardens:2.4f,6:GCU:3.4f
Oor Wullie Route3 (GCU),1:City Chambers:0.75f,2:Sir Chris Hoy Velodrome:3.8f,3:People's Palace:2.7f,4:Riverside Museum:5.4f,5:Botanic Gardens:2.4f,6:GCU:3.4f

code

import scala.io.Source

object ConverToMap {

  @annotation.tailrec
  def makeList(lst: List[String], acc: List[(Int, String, Float)]):List[(Int, String, Float)] = {
    lst match {
      case Nil => acc
      case (h :: t) => {
        val data = h.split(":")
        val tuple = (data(0).toInt, data(1), data(2).substring(0,data(2).length - 1 ).toFloat)
        makeList(t, tuple :: acc)
      }
    }
  }

  @annotation.tailrec
  def loop(lst: List[Array[String]], acc:  Map[String, List[(Int, String, Float)]]):  Map[String, List[(Int, String, Float)]] = {
    lst match {
      case Nil => acc
      case (h :: t) => {
        val key = h(0)
        val lTuple = makeList(h.toList.tail, List())
        if(acc.contains(key)) loop(t, acc)
        else loop(t, Map(key -> lTuple) ++ acc)
      }
    }
  }

  def main(args: Array[String]): Unit = {
    val fitnessData = "/home/cloudera/files/tests/to_map.csv"

    val lines = Source.fromFile(fitnessData)
      .getLines
      .toList
      .map(line => line.split(","))

    val mp = loop(lines, Map())

    println(mp)
  }
}

expected result

Map(Oor Wullie Route3 (GCU) -> List((6,GCU,3.4), (5,Botanic Gardens,2.4), (4,Riverside Museum,5.4), (3,People's Palace,2.7), (2,Sir Chris Hoy Velodrome,3.8), (1,City Chambers,0.7)), 
    Oor Wullie Route2 (GCU) -> List((6,GCU,3.4), (5,Botanic Gardens,2.4), (4,Riverside Museum,5.4), (3,People's Palace,2.7), (2,Sir Chris Hoy Velodrome,3.8), (1,City Chambers,0.7)), 
    Oor Wullie Route (GCU) -> List((6,GCU,3.4), (5,Botanic Gardens,2.4), (4,Riverside Museum,5.4), (3,People's Palace,2.7), (2,Sir Chris Hoy Velodrome,3.8), (1,City Chambers,0.7)))