/**
* 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.hadoop.contrib.utils.join;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.contrib.utils.join.DataJoinReducerBase;
import org.apache.hadoop.contrib.utils.join.TaggedMapOutput;
/**
* This is a subclass of DataJoinReducerBase that is used to
* demonstrate the functionality of INNER JOIN between 2 data
* sources (TAB separated text files) based on the first column.
*/
public class SampleDataJoinReducer extends DataJoinReducerBase {
/**
*
* @param tags
* a list of source tags
* @param values
* a value per source
* @return combined value derived from values of the sources
*/
protected TaggedMapOutput combine(Object[] tags, Object[] values) {
// eliminate rows which didnot match in one of the two tables (for INNER JOIN)
if (tags.length < 2)
return null;
String joinedStr = "";
for (int i=0; i<tags.length; i++) {
if (i > 0)
joinedStr += "\t";
// strip first column as it is the key on which we joined
String line = ((Text) (((TaggedMapOutput) values[i]).getData())).toString();
String[] tokens = line.split("\\t", 2);
joinedStr += tokens[1];
}
TaggedMapOutput retv = new SampleTaggedMapOutput(new Text(joinedStr));
retv.setTag((Text) tags[0]);
return retv;
}
}