Treatment bucketing using consistent hashing

gistfile1.txt

package com.jes.experiment;

import org.apache.commons.math3.stat.descriptive.moment.StandardDeviation;
import org.apache.commons.math3.stat.descriptive.moment.Variance;

import java.nio.ByteBuffer;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import java.util.stream.IntStream;

/**
 * @author Tyler J on 5/26/17.
 */
public class BucketUtil {

    static Object bucket(Object key, String salt, Object ... buckets) throws NoSuchAlgorithmException {
        MessageDigest digest = MessageDigest.getInstance("MD5");
        byte[] hash = digest.digest((key.toString() + salt).getBytes());
        return buckets[Math.abs(hash.hashCode()) % buckets.length];
    }

    public static void main(String[] argv) throws Exception {
        Map<Object, Integer> counts = new HashMap<>();
        String salt = "12345lslkjdsa;jsd;ja";
        int buckets = 3;
        int samples = 5000;

        //Same key and salt is always the same bucket

        ArrayList<String> treatments = new ArrayList<>();
        for(int i = 0; i < buckets; i++) {
            treatments.add("t" + i);
        }

        for(int i = 0; i < samples; i++) {
            Object bucket = bucket(i, salt, treatments.toArray());


            Integer count = counts.get(bucket);
            if(count != null) {
                counts.put(bucket, count + 1);
            } else {
                counts.put(bucket, 1 );
            }
        }

        StandardDeviation std = new StandardDeviation();
        Variance variance = new Variance();
        double[] vals = counts.values().stream().mapToDouble(o -> o.doubleValue()).toArray();
        double stdDev = std.evaluate(vals);
        double var = variance.evaluate(vals);
        double diffFromExpected = (stdDev / (samples / buckets)) * 100;


        for(Map.Entry<Object, Integer> entry : counts.entrySet()) {
            System.out.println(entry.getKey() + " " + entry.getValue().toString());
        }
        System.out.println("StdDev " + stdDev);
        System.out.println("% diff from expected " + diffFromExpected);
    }
}