Have List.groupByNel return a SortedMap as well

typelevel · Oct 12, 2017 · 2f0a165 · 2f0a165
1 parent cace36c
commit 2f0a165
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Showing 2 changed files with 6 additions and 4 deletions.
diff --git a/core/src/main/scala/cats/NonEmptyTraverse.scala b/core/src/main/scala/cats/NonEmptyTraverse.scala
@@ -53,9 +53,8 @@ import simulacrum.typeclass
     * {{{
     * scala> import cats.implicits._
     * scala> import cats.data.NonEmptyList
-    * scala> def countWords(words: List[String]): Map[String, Int] = words.groupBy(identity).mapValues(_.length)
     * scala> val x = NonEmptyList.of(List("How", "do", "you", "fly"), List("What", "do", "you", "do"))
-    * scala> x.nonEmptyFlatTraverse(_.groupByNel(identity))
+    * scala> x.nonEmptyFlatTraverse(_.groupByNel(identity) : Map[String, NonEmptyList[String]])
     * res0: Map[String,cats.data.NonEmptyList[String]] = Map(do -> NonEmptyList(do, do, do), you -> NonEmptyList(you, you))
     * }}}
     */

diff --git a/core/src/main/scala/cats/syntax/list.scala b/core/src/main/scala/cats/syntax/list.scala
@@ -1,6 +1,7 @@
 package cats
 package syntax
 
+import scala.collection.immutable.SortedMap
 import cats.data.NonEmptyList
 
 trait ListSyntax {
@@ -27,6 +28,8 @@ final class ListOps[A](val la: List[A]) extends AnyVal {
     * }}}
     */
   def toNel: Option[NonEmptyList[A]] = NonEmptyList.fromList(la)
-  def groupByNel[B : Order](f: A => B): Map[B, NonEmptyList[A]] =
-    toNel.fold(Map.empty[B, NonEmptyList[A]])(_.groupBy(f))
+  def groupByNel[B](f: A => B)(implicit B: Order[B]): SortedMap[B, NonEmptyList[A]] = {
+    implicit val ordering = B.toOrdering
+    toNel.fold(SortedMap.empty[B, NonEmptyList[A]])(_.groupBy(f))
+  }
 }