solr/solrj/src/java/org/apache/solr/client/solrj/io/eval/HistogramEvaluator.java

/*
 * 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.solr.client.solrj.io.eval;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Locale;

import org.apache.commons.math3.random.EmpiricalDistribution;
import org.apache.commons.math3.stat.descriptive.SummaryStatistics;
import org.apache.solr.client.solrj.io.Tuple;
import org.apache.solr.client.solrj.io.stream.expr.StreamExpression;
import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;

public class HistogramEvaluator extends RecursiveNumericEvaluator implements ManyValueWorker {
  protected static final long serialVersionUID = 1L;
  
  public HistogramEvaluator(StreamExpression expression, StreamFactory factory) throws IOException{
    super(expression, factory);
    
    if(containedEvaluators.size() < 1){
      throw new IOException(String.format(Locale.ROOT,"Invalid expression %s - expecting at least one value but found %d",expression,containedEvaluators.size()));
    }
  }

  @Override
  public Object doWork(Object... values) throws IOException {
    if(Arrays.stream(values).anyMatch(item -> null == item)){
      return null;
    }
    
    List<?> sourceValues;
    Integer bins = 10;
    
    if(values.length >= 1){
      sourceValues = values[0] instanceof List<?> ? (List<?>)values[0] : Arrays.asList(values[0]); 
            
      if(values.length >= 2){
        if(values[1] instanceof Number){
          bins = ((Number)values[1]).intValue();
        }
        else{
          throw new IOException(String.format(Locale.ROOT,"Invalid expression %s - if second parameter is provided then it must be a valid number but found %s instead",toExpression(constructingFactory), values[1].getClass().getSimpleName()));
        }        
      }      
    }
    else{
      throw new IOException(String.format(Locale.ROOT,"Invalid expression %s - expecting at least one value but found %d",toExpression(constructingFactory),containedEvaluators.size()));
    }

    EmpiricalDistribution distribution = new EmpiricalDistribution(bins);
    distribution.load(((List<?>)sourceValues).stream().mapToDouble(value -> ((Number)value).doubleValue()).toArray());;

    List<Tuple> histogramBins = new ArrayList<>();
    for(SummaryStatistics binSummary : distribution.getBinStats()) {
      Tuple tuple = new Tuple();
      tuple.put("max", binSummary.getMax());
      tuple.put("mean", binSummary.getMean());
      tuple.put("min", binSummary.getMin());
      tuple.put("stdev", binSummary.getStandardDeviation());
      tuple.put("sum", binSummary.getSum());
      tuple.put("N", binSummary.getN());
      tuple.put("var", binSummary.getVariance());
      tuple.put("cumProb", distribution.cumulativeProbability(binSummary.getMean()));
      tuple.put("prob", distribution.probability(binSummary.getMin(), binSummary.getMax()));
      histogramBins.add(tuple);
    }
    
    return histogramBins;
  }
    
}