solution2.1.7.9_as_function added

Signed-off-by: Andreas Roehler <[email protected]>

chapter02/worksheets/solution2.1.7.9_as_function.scala

@@ -0,0 +1,19 @@
+/** author: Andreas Röhler */
+/** author: Sergei Winitzki */ 
+
+/** 
+  Exercise 2.1.7.9
+  Given a Seq[(String, Int)] showing a list of purchased items (where item names
+may repeat), compute a Map[String, Int] showing the total counts. So, for the input:
+Seq(("apple", 2), ("pear", 3), ("apple", 5), ("lemon", 2), ("apple", 3))
+
+the output must be Map("apple" -> 10, "pear" -> 3, "lemon" -> 2).
+Hint: use groupBy, map, sum.
+ */
+
+def totalCount(arg: Seq[(String, Int)]) = {
+  // val a: Seq[(String, Int)] =  Seq(("pear", 2), ("apple", 2), ("apple", 6), ("pear", 1), ("lemon", 4), ("apple", 2), ("apple", 2))
+  arg.groupBy(s => s._1).map { case (x, y) => (x, y.map(_._2).sum) }
+
+// scala> totalCount(Seq(("pear", 2), ("apple", 2), ("apple", 6), ("pear", 1), ("lemon", 4), ("apple", 2), ("apple", 2)))
+// res37: scala.collection.immutable.Map[String,Int] = Map(pear -> 3, apple -> 12, lemon -> 4)