SummaryArchive.java

package storm.applications.util.math;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * Author: Thilina
 * Date: 11/1/14
 */
public class SummaryArchive {
    private List<Double> archive = new ArrayList<Double>();
    private Long sliceLength;

    public SummaryArchive(Long sliceLength) {
        this.sliceLength = sliceLength;
    }

    public void archive(Double value){
        archive.add(value);
    }

    public double getMedian(){
        int currentIndex = archive.size() - 1;
        int k = 1;
        int numberOfSlices = (int) (24 * 60 * 60 / sliceLength);
        int prev = (currentIndex +2) - numberOfSlices * k;
        List<Double> values = new ArrayList<Double>();
        while (prev > 0){
            values.add(archive.get(prev));
            k++;
            prev = (currentIndex+2) - numberOfSlices * k;
        }
        return (values.size() > 0) ? getMedian(values) : 0.0;
    }

    private double getMedian(List<Double> values){
        Collections.sort(values);
        int length = values.size();
        if (length % 2 == 0){
            return (values.get(length/2) + values.get(length/2 + 1))/2;
        } else {
            return values.get(length/2 + 1);
        }
    }
}