Bigram.java

package Entropy;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

/*This class creates bigrams and calculates entropy*/
public class Bigram {

 public static void main(String[] args) throws IOException {

  try {
   File f = new File("MidFile.txt");
   FileReader fr = new FileReader(f);
   BufferedReader br = new BufferedReader(fr);

   ArrayList < String > s = new ArrayList();
   ArrayList < String > bigrams = new ArrayList();
   HashMap < String, Integer > map = new HashMap < String, Integer > ();

   String str = null;
   while ((str = br.readLine()) != null) {

    str = str.replaceAll("[^a-zA-Z ]", "");
    str = str.replaceAll("\\[", "").replaceAll("\\]", "");
    s.add(str);
   }
   StringBuilder build = new StringBuilder();
   for (String sb: s) {
    build.append(sb);
   }
   char p;
   int count = 0;

   for (int i = 0; i < build.length() - 1; i++) {

    //if the previous or next character isnt space
    if (build.charAt(i) != 32 && build.charAt(i + 1) != 32) {

     String gram = Character.toString(build.charAt(i)) + Character.toString(build.charAt(i + 1));
     bigrams.add(gram);
    }
   }
   System.out.println(bigrams);

   StringBuilder bd = new StringBuilder();
   for (String sb: bigrams) {
    build.append(sb);
   }

   //Store bigrams in map
   for (String word: bigrams) {
    Integer counti = map.get(word);
    map.put(word, (counti == null) ? 1 : counti + 1);
   }

   int sum = 0;
   for (int add: map.values()) {
    sum += add;
   }

   //Iterate over map values and store frequencies in frequency array
   int msize = map.size();
   double fin[] = new double[msize];
   Set entries = map.entrySet();
   Iterator ei = entries.iterator();
   int i = 0;

   while (ei.hasNext()) {

    Map.Entry mapping = (Map.Entry) ei.next();
    fin[i] = (int) mapping.getValue();
    i++;
   }

   //probability array
   double pro[] = new double[msize];

   //entropy array
   double entrop[] = new double[msize];

   //calculate probability for all bigrams
   for (int m = 0; m < fin.length; m++) {
    double prob = fin[m] / sum;
    pro[m] = prob;
   }

   //calculate all entropies
   for (int e = 0; e < pro.length; e++) {

    double ent = (pro[e]) * (-Math.log(pro[e]) / Math.log(2.0));
    entrop[e] = ent;
   }
   double entropy = 0.0;
   for (double l: entrop) {
    entropy += l;
   }
   System.out.println("Entropy for all bigrams is:" + entropy + " bits");

   br.close();
  } catch (IOException e) {

   System.out.println(e.getMessage());
  }
 }
}