ZipfGenerator.java

package EE5903;

import java.util.Random;

//credit: https://diveintodata.org/2009/09/13/zipf-distribution-generator-in-java/ [Online; December 2017]

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)+1;
   friquency = (1.0d / Math.pow(rank, this.skew)) / this.bottom;
   dice = rnd.nextDouble();

   while(!(dice < friquency)) {
     rank = rnd.nextInt(size)+1;
     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 <= 10; i++) {
     System.out.println(i+" "+zipf.getProbability(i));
   }
   //use size = 10 and skew = 2 for testing below
   int hist [] = new int [12];
   for(int i=0;i<12;i++) {
       hist[i] = 0;
   }
   System.out.println("Testing the probability distribution:");
   int sum = 0;
    for(int i= 1;i <= 1000000; i++) {
        hist[zipf.next()]++; 
   }
   for(int i=0;i<12;i++)
     System.out.println(i+" "+hist[i]/1000000.0);
    }

}