Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/1746#discussion_r54547448
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/runtime/aggregate/AggregateReduceGroupFunction.scala
---
@@ -0,0 +1,160 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.flink.api.table.runtime.aggregate
+
+import java.lang.Iterable
+
+import com.google.common.base.Preconditions
+import org.apache.flink.api.common.functions.{CombineFunction,
RichGroupReduceFunction, RichMapPartitionFunction}
+import org.apache.flink.api.table.Row
+import org.apache.flink.configuration.Configuration
+import org.apache.flink.util.Collector
+
+import scala.collection.JavaConversions._
+
+/**
+ * It wraps the aggregate logic inside of
+ * [[org.apache.flink.api.java.operators.GroupReduceOperator]].
+ *
+ * @param aggregates The aggregate functions.
+ * @param groupKeysMapping The index mapping of group keys between
intermediate aggregate Row
+ * and output Row.
+ * @param aggregateMapping The index mapping between aggregate function
list and aggregated value
+ * index in output Row.
+ */
+class AggregateReduceGroupFunction(
+ private val aggregates: Array[Aggregate[_ <: Any]],
+ private val groupKeysMapping: Array[(Int, Int)],
+ private val aggregateMapping: Array[(Int, Int)])
+ extends RichGroupReduceFunction[Row, Row] {
+
+ private final val finalRowLength: Int = groupKeysMapping.length +
aggregateMapping.length
+
+ override def open(config: Configuration) {
+ Preconditions.checkNotNull(aggregates)
+ Preconditions.checkNotNull(groupKeysMapping)
+ }
+
+ /**
+ * For grouped intermediate aggregate Rows, merge all of them into
aggregate buffer,
+ * calculate aggregated values output by aggregate buffer, and set them
into output
+ * Row based on the mapping relation between intermediate aggregate data
and output data.
+ *
+ * @param records Grouped intermediate aggregate Rows iterator.
+ * @param out The collector to hand results to.
+ *
+ */
+ override def reduce(records: Iterable[Row], out: Collector[Row]): Unit =
{
+
+ val inputItr = records.iterator
+ val buffer = inputItr.next
+ while (inputItr.hasNext) {
+ val next = inputItr.next
+ aggregates.foreach(_.merge(next, buffer))
+ }
+
+ val output: Row = new Row(finalRowLength)
--- End diff --
We can reuse the `output` object across `reduce()` calls
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