Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/4585#discussion_r140167679
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/functions/aggfunctions/CollectAggFunction.scala
---
@@ -0,0 +1,121 @@
+/*
+ * 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.table.functions.aggfunctions
+
+import java.lang.{Iterable => JIterable}
+import java.util
+import java.util.function.BiFunction
+
+import org.apache.flink.api.common.typeinfo.TypeInformation
+import org.apache.flink.api.java.tuple.{Tuple1 => JTuple1}
+import org.apache.flink.api.java.typeutils.{GenericTypeInfo, TupleTypeInfo}
+import org.apache.flink.table.functions.AggregateFunction
+
+import scala.collection.JavaConverters._
+
+/** The initial accumulator for Collect aggregate function */
+class CollectAccumulator[E] extends JTuple1[util.Map[E, Integer]]
+
+abstract class CollectAggFunction[E]
+ extends AggregateFunction[util.Map[E, Integer], CollectAccumulator[E]] {
+
+ @transient
+ private lazy val addFunction = new BiFunction[Integer, Integer, Integer]
{
+ override def apply(t: Integer, u: Integer): Integer = t + u
+ }
+
+ override def createAccumulator(): CollectAccumulator[E] = {
+ val acc = new CollectAccumulator[E]()
+ acc.f0 = new util.HashMap[E, Integer]()
+ acc
+ }
+
+ def accumulate(accumulator: CollectAccumulator[E], value: E): Unit = {
+ if (value != null) {
+ if (accumulator.f0.containsKey(value)) {
+ val add = (x: Integer, y: Integer) => x + y
+ accumulator.f0.merge(value, 1, addFunction)
+ } else {
+ accumulator.f0.put(value, 1)
+ }
+ }
+ }
+
+ override def getValue(accumulator: CollectAccumulator[E]): util.Map[E,
Integer] = {
+ if (accumulator.f0.size() > 0) {
+ new util.HashMap(accumulator.f0)
+ } else {
+ null.asInstanceOf[util.Map[E, Integer]]
+ }
+ }
+
+ def resetAccumulator(acc: CollectAccumulator[E]): Unit = {
+ acc.f0.clear()
+ }
+
+ override def getAccumulatorType: TypeInformation[CollectAccumulator[E]]
= {
+ new TupleTypeInfo(
+ classOf[CollectAccumulator[E]],
+ new GenericTypeInfo[util.Map[E, Integer]](classOf[util.Map[E,
Integer]]))
--- End diff --
We could have an abstract method `getElementTypeInfo()` that returns the
type info for the elements. The basic types can be properly handled and for
`Object` we fall back to `GenericType`.
---
