package com.splout.db.hadoop;
/*
* #%L
* Splout SQL Hadoop library
* %%
* Copyright (C) 2012 Datasalt Systems S.L.
* %%
* 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.
* #L%
*/
import java.io.IOException;
import org.apache.hadoop.io.NullWritable;
import com.datasalt.pangool.io.ITuple;
import com.datasalt.pangool.tuplemr.TupleMRException;
import com.datasalt.pangool.tuplemr.TupleReducer;
/**
* Reusable TupleReducer that aggregates the counts of a certain field in the Tuple.
* <p>
* There are nicer implementations of this in the work-in-progress Pangool-flow project of Pangool but I decided not to
* depend on it until it has a first stable version.
*/
@SuppressWarnings("serial")
public class SumReducer extends TupleReducer<ITuple, NullWritable> {
String field;
/**
* Will (int) sum the field "field"
*/
public SumReducer(String field) {
this.field = field;
}
public void reduce(ITuple group, Iterable<ITuple> tuples, TupleMRContext context, Collector collector)
throws IOException, InterruptedException, TupleMRException {
int totalCount = 0;
ITuple outTuple = null;
for(ITuple tuple : tuples) {
totalCount += (Integer) tuple.get(field);
outTuple = tuple;
}
outTuple.set(field, totalCount);
collector.write(outTuple, NullWritable.get());
}
}