add last, sortBy and sorted to NonEmptyList (#1578)

* add last, sortBy and sorted to NonEmptyList * update comment for unreachable code and optimise sorted * use pattern match in Nel#last * pass Order instance as parameter for sortBy
typelevel · Mar 31, 2017 · 388acd1 · 388acd1
1 parent 02fb9a1
commit 388acd1
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diff --git a/core/src/main/scala/cats/data/NonEmptyList.scala b/core/src/main/scala/cats/data/NonEmptyList.scala
@@ -20,6 +20,11 @@ final case class NonEmptyList[+A](head: A, tail: List[A]) {
    */
   def toList: List[A] = head :: tail
 
+  def last: A = tail.lastOption match {
+    case None    => head
+    case Some(a) => a
+  }
+
   /**
    *  Applies f to all the elements of the structure
    */
@@ -218,6 +223,40 @@ final case class NonEmptyList[+A](head: A, tail: List[A]) {
     NonEmptyList((head, 0), bldr.result)
   }
 
+  /**
+    * Sorts this `NonEmptyList` according to an `Order` on transformed `B` from `A`
+    *
+    * {{{
+    * scala> import cats.data.NonEmptyList
+    * scala> import cats.instances.int._
+    * scala> val nel = NonEmptyList.of(('a', 4), ('z', 1), ('e', 22))
+    * scala> nel.sortBy(_._2)
+    * res0: cats.data.NonEmptyList[(Char, Int)] = NonEmptyList((z,1), (a,4), (e,22))
+    * }}}
+    */
+  def sortBy[B](f: A => B)(implicit B: Order[B]): NonEmptyList[A] =
+    toList.sortBy(f)(B.toOrdering) match {
+      case x :: xs => NonEmptyList(x, xs)
+      case Nil     => sys.error("unreachable: sorting a NonEmptyList cannot produce an empty List")
+    }
+
+  /**
+    * Sorts this `NonEmptyList` according to an `Order`
+    *
+    * {{{
+    * scala> import cats.data.NonEmptyList
+    * scala> import cats.instances.int._
+    * scala> val nel = NonEmptyList.of(12, 4, 3, 9)
+    * scala> nel.sorted
+    * res0: cats.data.NonEmptyList[Int] = NonEmptyList(3, 4, 9, 12)
+    * }}}
+    */
+  def sorted[AA >: A](implicit AA: Order[AA]): NonEmptyList[AA] =
+    toList.sorted(AA.toOrdering) match {
+      case x :: xs => NonEmptyList(x, xs)
+      case Nil     => sys.error("unreachable: sorting a NonEmptyList cannot produce an empty List")
+    }
+
   /**
     * Groups elements inside of this `NonEmptyList` using a mapping function
     *

diff --git a/tests/src/test/scala/cats/tests/NonEmptyListTests.scala b/tests/src/test/scala/cats/tests/NonEmptyListTests.scala
@@ -232,6 +232,25 @@ class NonEmptyListTests extends CatsSuite {
     }
   }
 
+  test("NonEmptyList#last is consistent with List#last") {
+    forAll { nel: NonEmptyList[Int] =>
+      nel.last should === (nel.toList.last)
+    }
+  }
+
+  test("NonEmptyList#sorted is consistent with List#sorted") {
+    forAll { nel: NonEmptyList[Int] =>
+      nel.sorted.toList should === (nel.toList.sorted)
+    }
+  }
+
+  test("NonEmptyList#sortBy is consistent with List#sortBy") {
+    forAll { (nel: NonEmptyList[Int], f: Int => Int) =>
+      nel.sortBy(f).toList should === (nel.toList.sortBy(f))
+    }
+  }
+
+
   test("NonEmptyList#groupBy is consistent with List#groupBy") {
     forAll { (nel: NonEmptyList[Int], f: Int => Int) =>
       nel.groupBy(f).mapValues(_.toList) should === (nel.toList.groupBy(f))