#61, Solution2.2.6.4.scala provided

chapter02/worksheets/solution2.2.6.4.scala

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+/** 
+  Exercise 2.2.6.4
+  Use foldLeft to implement a function filterMap that combines map and
+  filter for sequences. The predicate is applied to the elements of
+  the initial sequence, and values that pass the predicate are mapped.
+
+  The required type signature and a sample test:
+
+  def filterMap[A, B](xs: Seq[A])(pred: A => Boolean)(f: A => B): Seq[B] = ???
+
+  scala> filterMap(Seq(1, 2, 3, 4)) { x => x > 2 } { x => x * 10 }
+  res0: Seq[Int] = List(30, 40)
+  */
+
+def filterMap[A, B](xs: Seq[A])(pred: A => Boolean)(f: A => B): Seq[B] = {
+  xs.filter(pred).map(f)
+}
+
+val result =  filterMap(Seq(1, 2, 3, 4)) { x => x > 2 } { x => x * 10 }
+val expected =  Seq[Int] = List(30, 40)
+assert(result == expected)
+
+// scala> filterMap(Seq(1, 2, 3, 4)) { x => x > 2 } { x => x * 10 }
+// filterMap(Seq(1, 2, 3, 4)) { x => x > 2 } { x => x * 10 }
+// val res1: Seq[Int] = List(30, 40)
+