/*
* 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.java.operators;
import org.apache.flink.annotation.Internal;
import org.apache.flink.annotation.Public;
import org.apache.flink.api.common.InvalidProgramException;
import org.apache.flink.api.common.functions.Partitioner;
import org.apache.flink.api.common.operators.Keys;
import org.apache.flink.api.java.DataSet;
/**
* Grouping is an intermediate step for a transformation on a grouped DataSet.<br>
* The following transformation can be applied on Grouping:
* <ul>
* <li>{@link UnsortedGrouping#reduce(org.apache.flink.api.common.functions.ReduceFunction)},</li>
* <li>{@link UnsortedGrouping#reduceGroup(org.apache.flink.api.common.functions.GroupReduceFunction)}, and</li>
* <li>{@link UnsortedGrouping#aggregate(org.apache.flink.api.java.aggregation.Aggregations, int)}.</li>
* </ul>
*
* @param <T> The type of the elements of the grouped DataSet.
*
* @see DataSet
*/
@Public
public abstract class Grouping<T> {
protected final DataSet<T> inputDataSet;
protected final Keys<T> keys;
protected Partitioner<?> customPartitioner;
public Grouping(DataSet<T> set, Keys<T> keys) {
if (set == null || keys == null) {
throw new NullPointerException();
}
if (keys.isEmpty()) {
throw new InvalidProgramException("The grouping keys must not be empty.");
}
this.inputDataSet = set;
this.keys = keys;
}
/**
* Returns the input DataSet of a grouping operation, that is the one before the grouping. This means that
* if it is applied directly to the result of a grouping operation, it will cancel its effect. As an example, in the
* following snippet:
* <pre><code>
* DataSet<X> notGrouped = input.groupBy().getDataSet();
* DataSet<Y> allReduced = notGrouped.reduce()
* </pre></code>
* the <code>groupBy()</code> is as if it never happened, as the <code>notGrouped</code> DataSet corresponds
* to the input of the <code>groupBy()</code> (because of the <code>getDataset()</code>).
* */
@Internal
public DataSet<T> getInputDataSet() {
return this.inputDataSet;
}
@Internal
public Keys<T> getKeys() {
return this.keys;
}
/**
* Gets the custom partitioner to be used for this grouping, or {@code null}, if
* none was defined.
*
* @return The custom partitioner to be used for this grouping.
*/
@Internal
public Partitioner<?> getCustomPartitioner() {
return this.customPartitioner;
}
}