| /* |
| * 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.common.functions; |
| |
| import java.io.Serializable; |
| |
| import org.apache.flink.annotation.Public; |
| import org.apache.flink.util.Collector; |
| |
| /** |
| * The interface for group reduce functions. GroupReduceFunctions process groups of elements. |
| * They may aggregate them to a single value, or produce multiple result values for each group. |
| * The group may be defined by sharing a common grouping key, or the group may simply be |
| * all elements of a data set. |
| * <p> |
| * For a reduce functions that works incrementally by combining always two elements, see |
| * {@link ReduceFunction}. |
| * <p> |
| * The basic syntax for using a grouped GroupReduceFunction is as follows: |
| * <pre>{@code |
| * DataSet<X> input = ...; |
| * |
| * DataSet<X> result = input.groupBy(<key-definition>).reduceGroup(new MyGroupReduceFunction()); |
| * }</pre> |
| * |
| * Partial computation can significantly improve the performance of a {@link GroupReduceFunction}. |
| * This technique is also known as applying a Combiner. |
| * Implement the {@link GroupCombineFunction<T, T>} interface to enable partial computations, i.e., |
| * a combiner for this {@link GroupReduceFunction}. |
| * |
| * @param <T> Type of the elements that this function processes. |
| * @param <O> The type of the elements returned by the user-defined function. |
| */ |
| @Public |
| public interface GroupReduceFunction<T, O> extends Function, Serializable { |
| |
| /** |
| * The reduce method. The function receives one call per group of elements. |
| * |
| * @param values All records that belong to the given input key. |
| * @param out The collector to hand results to. |
| * |
| * @throws Exception This method may throw exceptions. Throwing an exception will cause the operation |
| * to fail and may trigger recovery. |
| */ |
| void reduce(Iterable<T> values, Collector<O> out) throws Exception; |
| } |