felixcheung commented on a change in pull request #23746: [SPARK-26761][SQL][R] 
Vectorized R gapply() implementation
URL: https://github.com/apache/spark/pull/23746#discussion_r255845030
 
 

 ##########
 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/objects.scala
 ##########
 @@ -437,6 +440,71 @@ case class FlatMapGroupsInRExec(
   }
 }
 
+/**
+ * Similar with [[FlatMapGroupsInRExec]] but serializes and deserializes 
input/output in
+ * Arrow format.
+ * This is also somewhat similar with
+ * [[org.apache.spark.sql.execution.python.FlatMapGroupsInPandasExec]].
+ */
+case class FlatMapGroupsInRWithArrowExec(
+    func: Array[Byte],
+    packageNames: Array[Byte],
+    broadcastVars: Array[Broadcast[Object]],
+    inputSchema: StructType,
+    output: Seq[Attribute],
+    keyDeserializer: Expression,
+    groupingAttributes: Seq[Attribute],
+    child: SparkPlan) extends UnaryExecNode {
+  override def outputPartitioning: Partitioning = child.outputPartitioning
+
+  override def producedAttributes: AttributeSet = AttributeSet(output)
+
+  override def requiredChildDistribution: Seq[Distribution] =
+    if (groupingAttributes.isEmpty) {
+      AllTuples :: Nil
+    } else {
+      ClusteredDistribution(groupingAttributes) :: Nil
+    }
+
+  override def requiredChildOrdering: Seq[Seq[SortOrder]] =
+    Seq(groupingAttributes.map(SortOrder(_, Ascending)))
+
+  override protected def doExecute(): RDD[InternalRow] = {
+    child.execute().mapPartitionsInternal { iter =>
+      val grouped = GroupedIterator(iter, groupingAttributes, child.output)
+      val getKey = ObjectOperator.deserializeRowToObject(keyDeserializer, 
groupingAttributes)
+      val runner = new ArrowRRunner(
+        func, packageNames, broadcastVars, inputSchema, 
SQLConf.get.sessionLocalTimeZone)
+
+      val groupedByRKey = grouped.map { case (key, rowIter) =>
+        val newKey = rowToRBytes(getKey(key).asInstanceOf[Row])
+        (newKey, rowIter)
+      }
+
+      // The communication mechanism is as follows:
+      //
+      //    JVM side                           R side
+      //
+      // 1. Group internal rows
+      // 2. Grouped internal rows    --------> Arrow record natches
 
 Review comment:
   natches?

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