Zipf Distribution Random Generator in Java

Research

When I carry out some experiments, I usually make synthetic data sets generated by some probability distributions. Especially, Zipf distribution is frequently used for a synthetic data set. Zipf distribution is one of the discrete power law probability distributions. You can get detail information from Zipf’s law in Wikipedia. Anyway, I attached my own java class for zip distribution. Below graphs are generated by my own java code and the gnuplot.

import java.util.Random;

public class ZipfGenerator {
 private Random rnd = new Random(System.currentTimeMillis());
 private int size;
 private double skew;
 private double bottom = 0;

 public ZipfGenerator(int size, double skew) {
  this.size = size;
  this.skew = skew;

  for(int i=1;i < size; i++) {
  this.bottom += (1/Math.pow(i, this.skew));
  }
 }

 // the next() method returns an random rank id.
 // The frequency of returned rank ids are follows Zipf distribution.
 public int next() {
   int rank;
   double friquency = 0;
   double dice;

   rank = rnd.nextInt(size);
   friquency = (1.0d / Math.pow(rank, this.skew)) / this.bottom;
   dice = rnd.nextDouble();

   while(!(dice &lt; friquency)) {
     rank = rnd.nextInt(size);
     friquency = (1.0d / Math.pow(rank, this.skew)) / this.bottom;
     dice = rnd.nextDouble();
   }

   return rank;
 }

 // This method returns a probability that the given rank occurs.
 public double getProbability(int rank) {
   return (1.0d / Math.pow(rank, this.skew)) / this.bottom;
 }

 public static void main(String[] args) {
   if(args.length != 2) {
     System.out.println("usage: ./zipf size skew");
     System.exit(-1);
   }

   ZipfGenerator zipf = new ZipfGenerator(Integer.valueOf(args[0]),
   Double.valueOf(args[1]));
   for(int i=1;i <= 100; i++)
     System.out.println(i+" "+zipf.getProbability(i));
 }
}

#distribution#java#probability#zipf