Loop structure for histogram

Question

I'm trying to write a Java program that generates a histogram of asterisks for each occurrence of a value in an array.

If the elements are, respectively, 0,1,2,3,4,5,6,7,8,9 the output should have an asterisk for each occurrence. For example,

0:*
1:*
2:*
3:*
4:*
5:*
6:*
7:*
8:*
9:*

However, my output is

0:**********
1:
2:
3:
4:
5:
6:
7:
8:
9:

The following code below is my own.

public static void drawHistogram(double[] array) {

    String count = "";

    for (int i = 0; i < array.length; i++) {
        if (array[i] >= 0 && array[i] < 1) {
            count += "*";
        } else if (array[i] >= 1 && array[i] < 2) {
            count += "*";
        } else if (array[i] >= 2 && array[i] < 3) {
            count += "*";
        } else if (array[i] >= 3 && array[i] < 4) {
            count += "*";
        } else if (array[i] >= 4 && array[i] < 5) {
            count += "*";
        } else if (array[i] >= 5 && array[i] < 6) {
            count += "*";
        } else if (array[i] >= 6 && array[i] < 7) {
            count += "*";
        } else if (array[i] >= 2 && array[i] < 8) {
            count += "*";
        } else if (array[i] >= 2 && array[i] < 9) {
            count += "*";
        } else if (array[i] >= 9 && array[i] < 10) {
            count += "*";
        } else if (array[i] >= 10 && array[i] < 11) {
            count += "*";
        }
    }
    for (int j = 0; j <= 10; j++) {
        System.out.print(j + count);
        count = "";
        System.out.println();
    }
}

How can I fix this issue?

Answer 1

This solution uses (int) Math.floor(array[i]) to choose the bracket into which to put the double value, thus getting rid of the multiple if-then-else statements. I've also used StringBuilder instead of String to make the repeated concatenation of asterisks a little more efficient.

public static void drawHistogram(double[] array) {

    StringBuilder histoGram[] = new StringBuilder[11];
    for (int i = 0; i < histoGram.length; i++) {
        histoGram[i] = new StringBuilder();
    }

    for (int i = 0; i < array.length; i++) {
        int bracket = (int) Math.floor(array[i]);
        if (bracket >= 0 && bracket < histoGram.length) {
            histoGram[bracket].append("*");
        }
    }
    for (int j = 0; j < 11; j++) {
        System.out.format("%02d: %s\n", j, histoGram[j].toString());
    }
}

Test main method:

public static void main(String args[]) {
    double[] testValues = new double[100];
    for (int i = 0; i < 100; i++) {
        testValues[i] = Math.random() * 11.0;
    }
    drawHistogram(testValues);
}

Sample output:

00: *******
01: ********
02: ***********
03: ************
04: ********
05: **********
06: *******
07: ********
08: **********
09: ************
10: *******