Merge pull request #4 from winitzki/feature/exercise_2.1.7.3

add solutions
winitzki · Nov 23, 2023 · 4ea8069 · 4ea8069
2 parents 58cdce0 + cb36cfe
commit 4ea8069
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diff --git a/chapter01/src/test/scala/sofp/unit/Exercises_1_6_1.scala b/chapter01/src/test/scala/sofp/unit/Exercises_1_6_1.scala
@@ -6,7 +6,7 @@ import munit.FunSuite
 
 class Exercises_1_6_1 extends FunSuite {
 
-  test("exercise 1.6.1.1") {
+  test("Exercise 1.6.1.1") {
 
     def staggeredFactorial(n: Int): Int = (n to 1 by -2).product
 

diff --git a/chapter02/src/test/scala/sofp/unit/Exercises_2_1_7.scala b/chapter02/src/test/scala/sofp/unit/Exercises_2_1_7.scala
@@ -5,7 +5,7 @@ import munit.FunSuite
 
 class Exercises_2_1_7 extends FunSuite {
 
-  test("exercise 2.1.7.1") {
+  test("Exercise 2.1.7.1") {
 
     val allPairs      =
       (0 to 9).flatMap { i =>
@@ -19,4 +19,52 @@ class Exercises_2_1_7 extends FunSuite {
     expect(filteredPairs.length == 64)
   }
 
+  test("Exercise 2.1.7.3 solved by Andreas Röhler") {
+    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(_ != (()))
+    expect(d == List("Joe", "Mary"))
+  }
+
+  test("Exercise 2.1.7.3") {
+    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[(String, Boolean)] = b.filter { case (x, y) => y }
+    val d: List[String]            = c.map { case (x, y) => x }
+    expect(d == List("Joe", "Mary"))
+  }
+
+  test("Exercise 2.1.7.3 as function") {
+    def selectTrue(names: List[String], flags: List[Boolean]): List[String] =
+      names.zip(flags).filter { case (name, flag) => flag }.map { case (name, flag) => name }
+
+    def selectTrueShorter(names: List[String], flags: List[Boolean]): List[String] =
+      names.zip(flags).filter(_._2).map(_._1)
+
+    def selectTrueOperatorSyntax(names: List[String], flags: List[Boolean]): List[String] =
+      names zip flags filter (_._2) map (_._1)
+
+    val names    = List("Joe", "Bob", "Mary")
+    val flags    = List(true, false, true)
+    val expected = List("Joe", "Mary")
+
+    expect(selectTrue(names, flags) == expected)
+    expect(selectTrueShorter(names, flags) == expected)
+    expect(selectTrueOperatorSyntax(names, flags) == expected)
+
+    // If all flags are true, the initial list remains unchanged.
+    val allTrue = List(true, true, true)
+    expect(selectTrue(names, allTrue) == names)
+    expect(selectTrueShorter(names, allTrue) == names)
+    expect(selectTrueOperatorSyntax(names, allTrue) == names)
+
+    // If all flags are false, the result is an empty list.
+    val allFalse = List(false, false, false)
+    expect(selectTrue(names, allFalse) == List())
+    expect(selectTrueShorter(names, allFalse) == List())
+    expect(selectTrueOperatorSyntax(names, allFalse) == List())
+  }
 }