solution2.1.7.3_AR.scala provided

chapter02/worksheets/solution2.1.7.3_AR.scala

@@ -0,0 +1,18 @@
+/** author: Andreas Röhler */
+
+/** Exercise 2.1.7.3
+Given two sequences p: Seq[String] and q: Seq[Boolean] of equal length, compute a
+Seq[String] with those elements of p for which the corresponding element of q is true.
+Hint: use zip, map, filter. */ 
+
+// val names: List[String]        = List("Joe", "Bob", "Mary")
+// val a: List[Boolean]           = List(true, false, true)
+// val b: List[(String, Boolean)] = names.zip(a)
+// val c: List[Any]               = b.map { case (x, y) => if (y == true) x }
+// val d: List[Any]               = c.filter(_ != (()))
+
+List("Joe", "Bob", "Mary").zip(List(true, false, true)).map { case (x, y) => if (y == true) x }.filter(_ != (()))
+
+// scala> :load solution2.1.7.3_AR.scala
+// Loading solution2.1.7.3_AR.scala...
+// res17: List[Any] = List(Joe, Mary)

chapter02/worksheets/solution2.1.7.3_as_function_SW.scala

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+/** author: Sergei Winitzki */
+
+/** Exercise 2.1.7.3
+Given two sequences p: Seq[String] and q: Seq[Boolean] of equal length, compute a
+Seq[String] with those elements of p for which the corresponding element of q is true.
+Hint: use zip, map, filter. */ 
+
+val names:  List[String]        = List("Joe", "Bob", "Mary")
+val a:  List[Boolean]           = List(true, false, true)
+
+def selectTrueOperatorSyntax(names: List[String], flags: List[Boolean]): List[String] =
+  names zip flags filter (_._2) map (_._1)
+
+selectTrueOperatorSyntax(names, a)
+
+// scala> :load solution2.1.7.3_as_function_SW.scala
+// Loading solution2.1.7.3_as_function_SW.scala...
+// names: List[String] = List(Joe, Bob, Mary)
+// a: List[Boolean] = List(true, false, true)
+// selectTrueOperatorSyntax: (names: List[String], flags: List[Boolean])List[String]
+// res27: List[String] = List(Joe, Mary)