Examples for the sliding operator #25468

akka-docs/src/main/paradox/stream/operators/Source-or-Flow/sliding.md

@@ -4,13 +4,9 @@ Provide a sliding window over the incoming stream and pass the windows as groups
 
 @ref[Simple operators](../index.md#simple-operators)
 
-@@@div { .group-scala }
-
 ## Signature
 
-@@signature [Flow.scala](/akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala) { #sliding }
-
-@@@
+@apidoc[Flow.sliding](Flow) { scala="#sliding(n:Int,step:Int):FlowOps.this.Repr[scala.collection.immutable.Seq[Out]]" java="#sliding(int,int)" } 
 
 ## Description
 
@@ -18,6 +14,37 @@ Provide a sliding window over the incoming stream and pass the windows as groups
 
 Note: the last window might be smaller than the requested size due to end of stream.
 
+## Examples
+
+In this first sample we just see the behavior of the operator itself, first with a window of 2 elements and @scala[the default
+`step` which is 1]@java[a step value of 1].
+
+Scala
+:   @@snip [Sliding.scala](/akka-docs/src/test/scala/docs/stream/operators/sourceorflow/Sliding.scala) { #sliding-1 }
+
+Java
+:   @@snip [Sliding.java](/akka-docs/src/test/java/jdocs/stream/operators/sourceorflow/Sliding.java) { #sliding-1 }
+
+If the stream stops without having seen enough elements to fill a window, the last window will have as many elements
+was emitted before the stream ended. Here we also provide a step to move two elements forward for each window:   
+
+Scala
+:   @@snip [Sliding.scala](/akka-docs/src/test/scala/docs/stream/operators/sourceorflow/Sliding.scala) { #sliding-2 }
+
+Java
+:   @@snip [Sliding.java](/akka-docs/src/test/java/jdocs/stream/operators/sourceorflow/Sliding.java) { #sliding-2 }
+
+One use case for sliding is to implement a moving average, here we do that with a "period" of `5`:
+
+Scala
+:   @@snip [Sliding.scala](/akka-docs/src/test/scala/docs/stream/operators/sourceorflow/Sliding.scala) { #moving-average }
+
+Java
+:   @@snip [Sliding.java](/akka-docs/src/test/java/jdocs/stream/operators/sourceorflow/Sliding.java) { #moving-average }
+
+Sliding can also be used to do simple windowing, see @ref[splitAfter](splitAfter.md).
+
+
 ## Reactive Streams semantics
 
 @@@div { .callout }

akka-docs/src/test/java/jdocs/stream/operators/sourceorflow/Sliding.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2009-2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package jdocs.stream.operators.sourceorflow;
+
+import akka.NotUsed;
+import akka.actor.typed.ActorSystem;
+import akka.stream.javadsl.Source;
+
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
+public class Sliding {
+
+  private final ActorSystem<Void> system = null;
+
+  public void slidingExample1() {
+    // #sliding-1
+    Source<Integer, NotUsed> source = Source.range(1, 4);
+    source.sliding(2, 1).runForeach(n -> System.out.println(n), system);
+    // prints:
+    // [1, 2]
+    // [2, 3]
+    // [3, 4]
+    // #sliding-1
+  }
+
+  public void slidingExample2() {
+    // #sliding-2
+    Source<Integer, NotUsed> source = Source.range(1, 4);
+    source.sliding(3, 2).runForeach(n -> System.out.println(n), system);
+    // prints:
+    // Vector(1, 2, 3)
+    // [1, 2, 3]
+    // [3, 4] - shorter because stream ended before we got 3 elements
+    // #sliding-2
+  }
+
+  public void slidingExample3() {
+    // #moving-average
+    Source<Integer, NotUsed> numbers = Source.from(Arrays.asList(1, 3, 10, 2, 3, 4, 2, 10, 11));
+    Source<Float, NotUsed> movingAverage =
+        numbers
+            .sliding(5, 1)
+            .map(window -> ((float) window.stream().mapToInt(i -> i).sum()) / window.size());
+    movingAverage.runForeach(n -> System.out.println(n), system);
+    // prints
+    // 3.8 = average of 1, 3, 10, 2, 3
+    // 4.4 = average of 3, 10, 2, 3, 4
+    // 4.2 = average of 10, 2, 3, 4, 2
+    // 4.2 = average of 2, 3, 4, 2, 10
+    // 6.0 = average of 3, 4, 2, 10, 11
+    // #moving-average
+  }
+}

akka-docs/src/test/scala/docs/stream/operators/sourceorflow/Sliding.scala

@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2019-2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.sourceorflow
+
+import akka.stream.scaladsl.Source
+import akka.actor.ActorSystem
+
+object Sliding {
+  implicit val system: ActorSystem = ???
+
+  def slidingExample1(): Unit = {
+    //#sliding-1
+    val source = Source(1 to 4)
+    source.sliding(2).runForeach(println)
+    // prints:
+    // Vector(1, 2)
+    // Vector(2, 3)
+    // Vector(3, 4)
+    //#sliding-1
+  }
+
+  def slidingExample2(): Unit = {
+    //#sliding-2
+    val source = Source(1 to 4)
+    source.sliding(n = 3, step = 2).runForeach(println)
+    // prints:
+    // Vector(1, 2, 3)
+    // Vector(3, 4) - shorter because stream ended before we got 3 elements
+    //#sliding-2
+  }
+
+  def slidingExample3(): Unit = {
+    //#moving-average
+    val numbers = Source(1 :: 3 :: 10 :: 2 :: 3 :: 4 :: 2 :: 10 :: 11 :: Nil)
+    val movingAverage = numbers.sliding(5).map(window => window.sum.toFloat / window.size)
+    movingAverage.runForeach(println)
+    // prints
+    // 3.8 = average of 1, 3, 10, 2, 3
+    // 4.4 = average of 3, 10, 2, 3, 4
+    // 4.2 = average of 10, 2, 3, 4, 2
+    // 4.2 = average of 2, 3, 4, 2, 10
+    // 6.0 = average of 3, 4, 2, 10, 11
+    //#moving-average
+  }
+
+}