org.apache.crunch.CombineFn Maven / Gradle / Ivy
/**
* 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.crunch;
import java.io.Serializable;
import java.math.BigInteger;
import java.util.LinkedList;
import java.util.List;
import java.util.SortedSet;
import org.apache.crunch.fn.Aggregators;
import org.apache.crunch.util.Tuples;
import org.apache.hadoop.conf.Configuration;
import com.google.common.base.Joiner;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;
/**
* A special {@link DoFn} implementation that converts an {@link Iterable} of
* values into a single value. If a {@code CombineFn} instance is used on a
* {@link PGroupedTable}, the function will be applied to the output of the map
* stage before the data is passed to the reducer, which can improve the runtime
* of certain classes of jobs.
*
* Note that the incoming {@code Iterable} can only be used to create an
* {@code Iterator} once. Calling {@link Iterable#iterator()} method a second
* time will throw an {@link IllegalStateException}.
*/
public abstract class CombineFn extends DoFn>, Pair> {
}