java: Find integer's frequency in an array

问题

I need to develop a java program that asks the user to enter some integers and find the largest, and smallest number, and the average of those numbers. Then, divides the set of array into a number of sub-intervals that the user specifies, then it generates a boundary points each has a length of sub-interval width..

The problem is that I need to create a frequency:

ex: Interval:

14.5-16.5

Frequency: 1 (here it should shows how many integers belong to this boundaries)

Interval:

16.5-18.5

Frequency: 4 and so on.

Here is the code I have so far, almost done except finding the frequency of each boundary..

import java.util.Scanner;
public class Sta
{
    public static void main(final String args[])
    {
        final Scanner input = new Scanner(System.in);

        int num=0;
        int range=0;
        int subnum;
        int subwid;

        System.out.print("How many numbers do you want to enter: ");
        num=input.nextInt();

        final int array[]=new int[num];

        System.out.print("Enter the numbers now: ");
        for(int i=0; i<array.length; i++)
        {
            array[i]=input.nextInt();
        }

        System.out.print("These are the numbers you entered:\n");
        printArray(array);

        int smallest=array[0];
        int largest=array[0];

        for (final int element : array) {
            if(element>largest) {
                largest=element;
            } else if(element<smallest) {
                smallest=element;
            }
            range=largest-smallest;
        }
        System.out.printf("Largest is %d\n",largest);
        System.out.printf("Smallest is %d\n",smallest);
        System.out.printf("Range is %d\n",range);

        System.out.print("Enter the number of subinterval: ");
        subnum=input.nextInt();

        subwid=range/subnum;
        System.out.printf("The width of subinterval is %d\n", subwid);

        /* this part should find the boundaries and find the elements that fall between
           the each two boundaries */
        for(double boundary=smallest-.5; boundary <=largest+.5; boundary +=subwid)
        {
        System.out.printf("Boundaries are %.1f\n",boundary);

        for(int element=0; element<array.length; element++)
          {
            if(element>=boundary)
              {
            System.out.printf("f=%d\n",element);
              }
          }
         }
    }

    public static void printArray(final int arr[])
    {

        for (final int element : arr) {
            System.out.print(element + "\n");
        }
    }

}

The question is how do I find the frequencies as in the above table example ??

回答1:

Here are some options:

Nested Loops: For each range, count the number of numbers that fall in that range.
'new int[subnum]'. In one pass, count the number of items in each range. Consider using division and truncation.
Sort the numbers. Count how many occur before each boundary.

来源：https://stackoverflow.com/questions/7824795/java-find-integers-frequency-in-an-array

标签

java

frequency