From c9409048134f41548a5cf960f3754243dc706420 Mon Sep 17 00:00:00 2001
From: Andreas Roehler <andreas.roehler@online.de>
Date: Mon, 18 Mar 2024 07:29:25 +0100
Subject: [PATCH 1/3] solution2.2.6.1_flatMap provided

Signed-off-by: Andreas Roehler <andreas.roehler@online.de>
---
 .../worksheets/solution2.2.6.1_flatMap.scala  | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 chapter02/worksheets/solution2.2.6.1_flatMap.scala

diff --git a/chapter02/worksheets/solution2.2.6.1_flatMap.scala b/chapter02/worksheets/solution2.2.6.1_flatMap.scala
new file mode 100644
index 0000000..2ca8a9b
--- /dev/null
+++ b/chapter02/worksheets/solution2.2.6.1_flatMap.scala
@@ -0,0 +1,43 @@
+/**
+  Exercise 2.2.6.1
+
+  Implement a function fromPairs that performs the inverse
+  transformation to the toPairs function defined in Example 2.2.5.6.
+
+  The required type signature and a sample test are:
+
+  def fromPairs[A](xs: Seq[(A, A)]): Seq[A] = ???
+
+  scala> fromPairs(List((1,2), (3,4)))
+  res1: Seq[Int] = List(1, 2, 3, 4)
+
+  scala> fromPairs(List((a,b), (c,<nothing>)))
+  res1: Seq[(String, String)] = List("a", "b", "c", "<nothing>")
+
+  Hint: This can be done with foldLeft or with flatMap.
+  */
+
+object FromPairs {
+  def fromPairs[A](xs: Seq[(A, A)]): Seq[A] = {
+    xs.flatMap { x => x.toList }
+  }
+  def main(args: Array[String]) = {
+    val result: Seq[String] = fromPairs(List(("a","b"), ("c","<nothing>")))
+    val expected: Seq[String] = List("a", "b", "c", "<nothing>")
+      println("result: %s".format(result))
+    assert(result == expected)
+    val a: Seq[Int] = fromPairs(List((1, 2), (3, 4)))
+    val b: Seq[Int] = List(1, 2, 3, 4)
+      println("a: %s".format(a))
+    assert(a == b)
+  }
+}
+
+FromPairs.main(Array())
+
+// scala> :load solution2.2.6.1_flatMap.scala
+// :load solution2.2.6.1_flatMap.scala
+// result: List(a, b, c, <nothing>)
+// a: List(1, 2, 3, 4)
+// // defined object FromPairs
+

From efc740dd35385bd875d354439851020e70d9d63e Mon Sep 17 00:00:00 2001
From: Andreas Roehler <andreas.roehler@online.de>
Date: Mon, 18 Mar 2024 10:22:06 +0100
Subject: [PATCH 2/3] avoid toList

Signed-off-by: Andreas Roehler <andreas.roehler@online.de>
---
 chapter02/worksheets/solution2.2.6.1_flatMap.scala | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/chapter02/worksheets/solution2.2.6.1_flatMap.scala b/chapter02/worksheets/solution2.2.6.1_flatMap.scala
index 2ca8a9b..c65bec4 100644
--- a/chapter02/worksheets/solution2.2.6.1_flatMap.scala
+++ b/chapter02/worksheets/solution2.2.6.1_flatMap.scala
@@ -19,7 +19,10 @@
 
 object FromPairs {
   def fromPairs[A](xs: Seq[(A, A)]): Seq[A] = {
-    xs.flatMap { x => x.toList }
+    
+    xs.flatMap{ case (x1, x2) => List(x1, x2) }
+
+    
   }
   def main(args: Array[String]) = {
     val result: Seq[String] = fromPairs(List(("a","b"), ("c","<nothing>")))

From 99eba42a942fb4ddf45b7d0d823b13d012ec566c Mon Sep 17 00:00:00 2001
From: Andreas Roehler <andreas.roehler@online.de>
Date: Mon, 18 Mar 2024 10:24:05 +0100
Subject: [PATCH 3/3] formatting

Signed-off-by: Andreas Roehler <andreas.roehler@online.de>
---
 chapter02/worksheets/solution2.2.6.1_flatMap.scala | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/chapter02/worksheets/solution2.2.6.1_flatMap.scala b/chapter02/worksheets/solution2.2.6.1_flatMap.scala
index c65bec4..6fa23a5 100644
--- a/chapter02/worksheets/solution2.2.6.1_flatMap.scala
+++ b/chapter02/worksheets/solution2.2.6.1_flatMap.scala
@@ -19,10 +19,7 @@
 
 object FromPairs {
   def fromPairs[A](xs: Seq[(A, A)]): Seq[A] = {
-    
     xs.flatMap{ case (x1, x2) => List(x1, x2) }
-
-    
   }
   def main(args: Array[String]) = {
     val result: Seq[String] = fromPairs(List(("a","b"), ("c","<nothing>")))