Huffman Coding - Grouping Symbols

Question

I am using a Huffman code found on the Internet to get the frequencies of random integers stored in a 2D array as a matrix.

Link to Huffman code - Java: http://rosettacode.org/wiki/Huffman_coding

Method Q1 asks the user to set the matrix size. The matrix is filled with random integers [0, 255].

public void q1(){
    System.out.println();
    System.out.println("Question 1 - Creating Random Matrix");

    Scanner in = new Scanner(System.in);

    //Matrix number of rows
    System.out.print("Insert size of rows M: ");
    rows = in.nextInt();

    //Matrix number of columns
    System.out.print("Insert size of columns N: ");
    columns = in.nextInt();

    System.out.println();

    matrix = new int[rows][columns];

    //Initialising randomisation
    Random r = new Random();

    //Filling matrix and printing values
    for (int m = 0; m < rows; m++){
        for (int n = 0; n < columns; n++){
            matrix[m][n] = r.nextInt(256);
            System.out.print("[" + matrix[m][n] + "] \t");
        }
        System.out.print("\n");
    }
    System.out.println();
}

Method Q2 needs to re-display all random integers found in the matrix and their frequency.

public void q2() {
    // we will assume that all our characters will have code less than 256, for simplicity
    int[] charFreqs = new int[256];
    StringBuilder sb = new StringBuilder();
    String [] st = new String[5];

    System.out.println();
    System.out.println("Alphabet " + "\t" + "Frequency" + "\t" + "Probability");
    for (int m = 0; m < rows; m++){
        for (int n = 0; n < columns; n++){
            String sentence = String.valueOf(matrix[m][n]);
            System.out.print(matrix[m][n] + "\n");

            //read each character and record the frequencies
            for (int i = 0; i < sentence.length(); i++){
                char c = sb.append(sentence[i]);
            }

            for (char c : sentence.toCharArray()){
                charFreqs[c]++;
            }
        }
    }       

    // build tree
    HuffmanTree tree = buildTree(charFreqs);

    // print out results
    System.out.println("SYMBOL\tWEIGHT\tHUFFMAN CODE");
    printCodes(tree, new StringBuffer());
}

The current program calculates the frequency by splitting the random integers into seperate digits. I need the frequency to be calculated upon each of the random integers.

Any help please?

Thank you

Welcome to StackOverflow. It's not entirely clear what your question is. What is the expected result and how is that different from the result you're getting? — genisage, Feb 10 '15 at 23:04

score 1 · Answer 1 · answered Feb 10 '15 at 23:12

A fairly simple way you can do this using Java 8 streams (if they are available to you):

Map<Integer, Integer> frequencies = Arrays.stream(matrix)
    .flatMap(Arrays::stream)
    .collect(Collectors.groupingBy(Function.identity(), Collectors.counting());

Huffman Coding - Grouping Symbols

1 Answers1