1 

     2 // first test 

     3 

     4 val ls1_urban = List(("1", "a"), ("2", "a"), ("1", "c"), ("2", "a"), ("1", "c"))

     5 

     6 val m_urban = groupById(ls1_urban, Map())

     7 

     8 assert(m_urban.getOrElse("1", Nil).count(_ == "c") == 2)

     9 assert(m_urban.getOrElse("1", Nil).count(_ == "a") == 1)

    10 assert(m_urban.getOrElse("2", Nil) == List("a", "a"))

    11 

    12 // second test

    13 

    14 def urban_gb(ratings: List[(String, String)]) = 

    15   ratings.groupBy(_._1).mapValues(_.map(_._2).toSet) 

    16 

    17 def urban_gb2(ratings: List[(String, String)]) = 

    18   ratings.groupBy(_._1).mapValues(_.map(_._2)) 

    19 

    20 def urban_ck(ratings: List[(String, String)]) =

    21   urban_gb(ratings) == groupById(ratings, Map()).mapValues(_.toSet)

    22 

    23 

    24 val ls2_urban = List(("1", "a"), ("1", "b"), ("2", "x"), ("3", "a"), ("2", "y"), ("3", "c"))

    25 

    26 assert(urban_ck(ls2_urban))

    27 

    28 // thrird test

    29 

    30 val ls3_urban = (1 to 1000).map(_.toString).toList

    31 val ls4_urban = ls3_urban zip ls3_urban.tail

    32 val ls5_urban = ls4_urban ::: ls4_urban.reverse

    33 

    34 assert(urban_ck(ls5_urban))

    35 

    36 

    37 /*

    38 import io.Source

    39 import scala.util._

    40 

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

    42   val csv = Source.fromFile(name)

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

    44 }

    45 

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

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

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

    49 }

    50 

    51 val urban_ratings = urban_process_ratings(urban_get_csv_file("ratings.csv").take(1000))

    52 

    53 assert(urban_ck(urban_ratings))

    54 */