Github user aokolnychyi commented on a diff in the pull request: https://github.com/apache/spark/pull/16329#discussion_r97589440 --- Diff: examples/src/main/java/org/apache/spark/examples/sql/JavaUserDefinedTypedAggregation.java --- @@ -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.spark.examples.sql; + +// $example on:typed_custom_aggregation$ +import java.io.Serializable; + +import org.apache.spark.sql.Dataset; +import org.apache.spark.sql.Encoder; +import org.apache.spark.sql.Encoders; +import org.apache.spark.sql.SparkSession; +import org.apache.spark.sql.TypedColumn; +import org.apache.spark.sql.expressions.Aggregator; +// $example off:typed_custom_aggregation$ + +public class JavaUserDefinedTypedAggregation { + + // $example on:typed_custom_aggregation$ + public static class Employee implements Serializable { + private String name; + private long salary; + + // Constructors, getters, setters... + // $example off:typed_custom_aggregation$ + public String getName() { + return name; + } + + public void setName(String name) { + this.name = name; + } + + public long getSalary() { + return salary; + } + + public void setSalary(long salary) { + this.salary = salary; + } + // $example on:typed_custom_aggregation$ + } + + public static class Average implements Serializable { + private long sum; + private long count; + + // Constructors, getters, setters... + // $example off:typed_custom_aggregation$ + public Average() { + } + + public Average(long sum, long count) { + this.sum = sum; + this.count = count; + } + + public long getSum() { + return sum; + } + + public void setSum(long sum) { + this.sum = sum; + } + + public long getCount() { + return count; + } + + public void setCount(long count) { + this.count = count; + } + // $example on:typed_custom_aggregation$ + } + + public static class MyAverage extends Aggregator<Employee, Average, Double> { + // A zero value for this aggregation. Should satisfy the property that any b + zero = b + public Average zero() { --- End diff -- @srowen `Average` is a Java bean that holds current sum and count. It is defined earlier. Here it represents a zero value. `MyAverage`, in turn, is the actual aggregator that accepts instances of the `Employee` class, stores intermediate results using an instance of`Average`, and produces `Double` as a result. I can rename `MyAverage` to `MyAverageAggregator` if this makes things clearer.
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