'Functional' CSV parsing: http://stackoverflow.com/questions/22846375/a-more-functional-implementation

CsvParsing.scala

import java.io.ByteArrayInputStream

import scalaz.stream.io

import scalaz.std.map._
import scalaz.std.vector._

object CsvParsing extends App {

  val csv =
    """|0,2014-01-01,1
       |0,2014-01-02,2
       |1,2014-01-01,3
       |1,2014-01-01,4""".stripMargin

  val is = new ByteArrayInputStream(csv.getBytes)

  val process = io.linesR(is).
    map(_.split(",")).               // split to columns
    map(arr => (arr(0), arr(2))).    // pick id & number columns
    runFoldMap { case (id, number) => Map(id -> Vector(number)) }

  val output = process.run
  println(s"Output: ")
  output.foreach(println)
}