/***********************************************************************************************************************
*
* Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
*
* Licensed 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 eu.stratosphere.api.java.operators;
import eu.stratosphere.api.common.InvalidProgramException;
import eu.stratosphere.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 Grouping#reduce(ReduceFunction)},</li>
* <li>{@link Grouping#reduceGroup(GroupReduceFunction)}, and</li>
* <li>{@link Grouping#aggregate(Aggregations, int)}.</li>
* </ul>
*
* @param <T> The type of the elements of the grouped DataSet.
*
* @see DataSet
*/
public abstract class Grouping<T> {
protected final DataSet<T> dataSet;
protected final Keys<T> keys;
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.dataSet = set;
this.keys = keys;
}
protected DataSet<T> getDataSet() {
return this.dataSet;
}
protected Keys<T> getKeys() {
return this.keys;
}
}