Merge pull request #3265 from kiendang/add-filternot

Add `Stream.filterNot`

Author: mpilquist

core/shared/src/main/scala/fs2/Chunk.scala

@@ -120,6 +120,9 @@ abstract class Chunk[+O] extends Serializable with ChunkPlatform[O] with ChunkRu
     Chunk.array(b.result()).asInstanceOf[Chunk[O]]
   }
 
+  /** Returns a chunk that has only the elements that do not satisfy the supplied predicate. */
+  def filterNot(p: O => Boolean): Chunk[O] = filter(!p(_))
+
   /** Returns the first element for which the predicate returns true or `None` if no elements satisfy the predicate. */
   def find(p: O => Boolean): Option[O] =
     iterator.find(p)

core/shared/src/main/scala/fs2/Stream.scala

@@ -1082,6 +1082,10 @@ final class Stream[+F[_], +O] private[fs2] (private[fs2] val underlying: Pull[F,
     */
   def filter(p: O => Boolean): Stream[F, O] = mapChunks(_.filter(p))
 
+  /** Emits only inputs which do not match the supplied predicate.
+    */
+  def filterNot(p: O => Boolean): Stream[F, O] = mapChunks(_.filterNot(p))
+
   /** Like `filter`, but allows filtering based on an effect.
     *
     * Note: The result Stream will consist of chunks that are empty or 1-element-long.

core/shared/src/test/scala/fs2/StreamCombinatorsSuite.scala

@@ -567,6 +567,40 @@ class StreamCombinatorsSuite extends Fs2Suite {
     }
   }
 
+  group("filterNot") {
+    property("1") {
+      forAll { (s: Stream[Pure, Int], n0: Int) =>
+        val n = (n0 % 20).abs + 1
+        val predicate = (i: Int) => i % n == 0
+        s.filterNot(predicate).assertEmits(s.toList.filterNot(predicate))
+      }
+    }
+
+    property("2") {
+      forAll { (s: Stream[Pure, Double]) =>
+        val predicate = (i: Double) => i - i.floor < 0.5
+        val s2 = s.mapChunks(c => Chunk.array(c.toArray))
+        assertEquals(s2.filterNot(predicate).toList, s2.toList.filterNot(predicate))
+      }
+    }
+
+    property("3") {
+      forAll { (s: Stream[Pure, Byte]) =>
+        val predicate = (b: Byte) => b < 0
+        val s2 = s.mapChunks(c => Chunk.array(c.toArray))
+        s2.filterNot(predicate).assertEmits(s2.toList.filterNot(predicate))
+      }
+    }
+
+    property("4") {
+      forAll { (s: Stream[Pure, Boolean]) =>
+        val predicate = (b: Boolean) => !b
+        val s2 = s.mapChunks(c => Chunk.array(c.toArray))
+        s2.filterNot(predicate).assertEmits(s2.toList.filterNot(predicate))
+      }
+    }
+  }
+
   property("find") {
     forAll { (s: Stream[Pure, Int], i: Int) =>
       val predicate = (item: Int) => item < i