/*
* Copyright [2013-2015] PayPal Software Foundation
*
* 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 ml.shifu.shifu.core.posttrain;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapreduce.Reducer;
/**
* {@link FeatureImportanceReducer} is to aggregate feature importance statistics and compute the top important
* variables.
*
* @author Zhang David (pengzhang@paypal.com)
*/
public class FeatureImportanceReducer extends Reducer<IntWritable, DoubleWritable, IntWritable, DoubleWritable> {
private Map<Integer, Double> variableStatsMap = new HashMap<Integer, Double>();
public static class FeatureScore {
public FeatureScore(int columnNum, double binAvgScore) {
this.columnNum = columnNum;
this.binAvgScore = binAvgScore;
}
private int columnNum;
private double binAvgScore;
}
@Override
protected void reduce(IntWritable key, Iterable<DoubleWritable> values, Context context) throws IOException,
InterruptedException {
double sum = 0d;
for(DoubleWritable dw: values) {
sum += dw.get();
}
this.variableStatsMap.put(key.get(), sum);
}
@Override
protected void cleanup(Context context) throws IOException, InterruptedException {
List<FeatureScore> featureScores = new ArrayList<FeatureImportanceReducer.FeatureScore>();
for(Entry<Integer, Double> entry: variableStatsMap.entrySet()) {
featureScores.add(new FeatureScore(entry.getKey(), entry.getValue()));
}
Collections.sort(featureScores, new Comparator<FeatureScore>() {
@Override
public int compare(FeatureScore fs1, FeatureScore fs2) {
if(fs1.binAvgScore < fs2.binAvgScore) {
return 1;
}
if(fs1.binAvgScore > fs2.binAvgScore) {
return -1;
}
return 0;
}
});
for(FeatureScore featureScore: featureScores) {
context.write(new IntWritable(featureScore.columnNum), new DoubleWritable(featureScore.binAvgScore));
}
}
}