Add NonEmptyList#toNem (issue #2346) (#2541)

typelevel · Oct 8, 2018 · e2af59a · e2af59a
1 parent ee2b5ee
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diff --git a/core/src/main/scala/cats/data/NonEmptyList.scala b/core/src/main/scala/cats/data/NonEmptyList.scala
@@ -406,6 +406,21 @@ final case class NonEmptyList[+A](head: A, tail: List[A]) {
     */
   def groupByNem[B](f: A => B)(implicit B: Order[B]): NonEmptyMap[B, NonEmptyList[A]] =
     NonEmptyMap.fromMapUnsafe(groupBy(f))
+
+
+  /**
+    * Creates new `NonEmptyMap`, similarly to List#toMap from scala standard library.
+    *{{{
+    * scala> import cats.data._
+    * scala> import cats.instances.int._
+    * scala> val nel = NonEmptyList((0, "a"), List((1, "b"),(0, "c"), (2, "d")))
+    * scala> nel.toNem
+    * res0: NonEmptyMap[Int,String] = Map(0 -> c, 1 -> b, 2 -> d)
+    *}}}
+    *
+    */
+  def toNem[T, U](implicit ev: A <:< (T, U), order: Order[T]): NonEmptyMap[T, U] =
+    NonEmptyMap.fromMapUnsafe(SortedMap(toList.map(ev): _*)(order.toOrdering))
 }
 
 object NonEmptyList extends NonEmptyListInstances {

diff --git a/tests/src/test/scala/cats/tests/NonEmptyListSuite.scala b/tests/src/test/scala/cats/tests/NonEmptyListSuite.scala
@@ -3,10 +3,11 @@ package tests
 
 import cats.kernel.laws.discipline.{SemigroupTests, OrderTests, PartialOrderTests, EqTests}
 
-import cats.data.{NonEmptyList, NonEmptyVector}
+import cats.data.{NonEmptyList, NonEmptyVector, NonEmptyMap}
 import cats.data.NonEmptyList.ZipNonEmptyList
 import cats.laws.discipline.arbitrary._
 import cats.laws.discipline.{CommutativeApplyTests, BimonadTests, NonEmptyTraverseTests, ReducibleTests, SemigroupKTests, SerializableTests}
+import scala.collection.immutable.SortedMap
 
 class NonEmptyListSuite extends CatsSuite {
   // Lots of collections here.. telling ScalaCheck to calm down a bit
@@ -315,6 +316,12 @@ class NonEmptyListSuite extends CatsSuite {
       ior.right.map(xs => xs.sorted should === (xs))
     }
   }
+
+  test("NonEmptyList#toNem is consistent with List#toMap and creating NonEmptyMap from it") {
+    forAll { nel: NonEmptyList[(Int, String)] =>
+      nel.toNem should ===(NonEmptyMap.fromMapUnsafe(SortedMap.empty[Int, String] ++ nel.toList.toMap))
+    }
+  }
 }
 
 @deprecated("to be able to test deprecated methods", since = "1.0.0-RC1")