/**
* 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.mahout.ga.watchmaker.cd.tool;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Reporter;
import org.apache.mahout.ga.watchmaker.cd.tool.DescriptionUtils.Range;
import org.apache.mahout.common.StringUtils;
import java.io.IOException;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
/**
* Combines attribute description strings into a String.<br>
* <ul>
* <li>For Numerical attributes, the string contains the min and max values
* found.</li>
* <li>For Categorical attributes, the string contains the distinct values
* found.</li>
* </ul>
*
* See Descriptors, for more informations about the job parameter
*/
public class ToolReducer extends MapReduceBase implements
Reducer<LongWritable, Text, LongWritable, Text> {
private Descriptors descriptors;
private final Set<String> distinct = new HashSet<String>();
@Override
public void configure(JobConf job) {
super.configure(job);
String descriptors = job.get(ToolMapper.ATTRIBUTES);
if (descriptors != null)
configure((char[]) StringUtils.fromString(descriptors));
}
void configure(char[] descriptors) {
if (descriptors == null || descriptors.length == 0)
throw new IllegalArgumentException("Descriptors's array not found or is empty");
this.descriptors = new Descriptors(descriptors);
}
@Override
public void reduce(LongWritable key, Iterator<Text> values,
OutputCollector<LongWritable, Text> output, Reporter reporter)
throws IOException {
output.collect(key, new Text(combineDescriptions((int) key.get(), values)));
}
/**
* Combines a given attribute descriptions into a single descriptor.
*
* @param index attribute index
* @param values available descriptions
* @return
* @throws RuntimeException if the attribute should be ignored.
*/
String combineDescriptions(int index, Iterator<Text> values) {
if (descriptors.isNumerical(index))
return numericDescription(values);
else if (descriptors.isNominal(index))
return nominalDescription(values);
else
throw new IllegalArgumentException();
}
static String numericDescription(Iterator<Text> values) {
double min = Double.POSITIVE_INFINITY;
double max = Double.NEGATIVE_INFINITY;
while (values.hasNext()) {
Range range = DescriptionUtils.extractNumericalRange(values.next().toString());
min = Math.min(min, range.min);
max = Math.max(max, range.max);
}
return DescriptionUtils.createNumericalDescription(min, max);
}
String nominalDescription(Iterator<Text> values) {
distinct.clear();
// extract all distinct values
while (values.hasNext()) {
DescriptionUtils.extractNominalValues(values.next().toString(), distinct);
}
// create a new description
return DescriptionUtils.createNominalDescription(distinct);
}
}