diff -r ef5f62bf5987 -r 9a04eb6a2291 marking2/danube_test3.scala
--- a/marking2/danube_test3.scala	Tue Oct 29 23:56:13 2019 +0000
+++ b/marking2/danube_test3.scala	Wed Oct 30 11:28:44 2019 +0000
@@ -1,3 +1,5 @@
+import CW7b._
+
 
 // first test 
 
@@ -12,13 +14,13 @@
 // second test
 
 def urban_gb(ratings: List[(String, String)]) = 
-  ratings.groupBy(_._1).mapValues(_.map(_._2).toSet) 
+  ratings.groupBy(_._1).view.mapValues(_.map(_._2).toSet).toMap 
 
 def urban_gb2(ratings: List[(String, String)]) = 
-  ratings.groupBy(_._1).mapValues(_.map(_._2)) 
+  ratings.groupBy(_._1).view.mapValues(_.map(_._2)).toMap 
 
 def urban_ck(ratings: List[(String, String)]) =
-  urban_gb(ratings) == groupById(ratings, Map()).mapValues(_.toSet)
+  urban_gb(ratings) == groupById(ratings, Map()).view.mapValues(_.toSet).toMap
 
 
 val ls2_urban = List(("1", "a"), ("1", "b"), ("2", "x"), ("3", "a"), ("2", "y"), ("3", "c"))