+doc #19429 initial merge of docs-dev and docs

akka-docs/rst/scala/code/docs/stream/cookbook/RecipeFlattenSeq.scala

@@ -0,0 +1,28 @@
+package docs.stream.cookbook
+
+import akka.stream.scaladsl.{ Sink, Source }
+
+import scala.collection.immutable
+import scala.concurrent.Await
+import scala.concurrent.duration._
+
+class RecipeFlattenSeq extends RecipeSpec {
+
+  "Recipe for flatteing a stream of seqs" must {
+
+    "work" in {
+
+      val someDataSource = Source(List(List("1"), List("2"), List("3", "4", "5"), List("6", "7")))
+
+      //#flattening-seqs
+      val myData: Source[List[Message], Unit] = someDataSource
+      val flattened: Source[Message, Unit] = myData.mapConcat(identity)
+      //#flattening-seqs
+
+      Await.result(flattened.grouped(8).runWith(Sink.head), 3.seconds) should be(List("1", "2", "3", "4", "5", "6", "7"))
+
+    }
+
+  }
+
+}