// first test 

import M2._

def urban_groupById(ratings: List[(String, String)]) = 

  ratings.groupBy(_._1).view.mapValues(_.map(_._2)).toMap 

def urban_get_csv_file(name: String) : List[String] = {

  import io.Source

  import scala.util._

  val csv = Source.fromFile(name)

  csv.mkString.split("\n").toList.drop(1)

}

def urban_process_ratings(lines: List[String]) : List[(String, String)] = {

  for (cols <- lines.map(_.split(",").toList); 

       if (cols(2).toFloat >= 4)) yield (cols(0), cols(1))  

}

val urban_good_ratings = process_ratings(urban_get_csv_file("ratings.csv"))

val urban_ratings_map = urban_groupById(urban_good_ratings)

assert(favourites(urban_ratings_map, "912").length  == 80)

assert(favourites(urban_ratings_map, "858").length  == 158)

assert(favourites(urban_ratings_map, "260").length  == 201)