Week 10 - Array Example

Array Example - Statistics for a list

ManageStats.java

import java.io.*;

// ManageStats:  This class manages a list of integers.  It calculates
//               various types of statistics for this list.
public class ManageStats {

	public static void main (String[] args) throws IOException {
		BufferedReader in = new BufferedReader(new InputStreamReader
				(System.in));

		// Read the size of the list, 'N'.
		System.out.print ("Number of values? ");
		int N = Integer.parseInt(in.readLine());
	
		// Declare and instantiate an array 'list' to hold 'N' integers.
		int[] list = new int[N];
	
		// Read contents of 'list' from input.
		for (int i = 0; i < N; i++) {
			System.out.print ("Enter a value: ");
			list[i] = Integer.parseInt(in.readLine());
		}

		// Call the method to print out various statistics
 		System.out.println ("\nList Statistics:");
 		System.out.println ("median = " + median(list));
 		System.out.println ("mean   = " + mean(list));
 		System.out.println ("min    = " + min(list));
 		System.out.println ("max    = " + max(list));
 		System.out.println ("mode   = " + mode(list));
	}

	// median: return the value of the element that is
	// the median in 'list'.  Note: This doesn't work if
	// the list contains duplicate values.
	public static int median (int[] list) {
		for (int i = 0; i < list.length; i++) {
			if (countSmaller(list[i],list) == list.length/2) {	
		 		 return list[i];
			}
		}
		return -999;  // somehow indicate failure if list size is 0.
	}
	
	// countSmaller: return the number of entries in 'list' 
	// that are smaller than 'refVal'.
	private static int countSmaller(int refVal, int[] list){
		int count = 0;
		for (int i = 0; i < list.length; i++) {
			if (list[i] < refVal) {
				count++;
			}
		}
	 	return count;
	}

	// mean: return the average of the elements in 'list'.
	public static double mean (int[] list) {
		if (list.length <= 0) {
			return -999;	// somehow indicate failure
		}

		int sum = 0;
		for (int i = 0; i < list.length; i++) {
			sum += list[i];
		}
		return (double)sum/list.length;
	}

	// min: return the smallest value in 'list'.
	private static int min (int[] list){
		if (list.length <= 0) {
			return -999;	// somehow indicate failure
		}

		int min = list[0];
		for (int i = 1; i < list.length; i++) {
			if (list[i] < min) {
				min = list[i];
			}
		}
 		return min;
	}

	// max: return the largest value in 'list'.
	private static int max (int[] list){
		if (list.length <= 0) {
			return -999;	// somehow indicate failure
		}

		int max = list[0];
		for (int i = 1; i < list.length; i++) {
			if (list[i] > max) {
				max = list[i];
			}
		}
 		return max;
	}

	// mode: return the most frequently occurring value
	// in 'list'.  If there is more than one value that
	// is the mode, just return the first mode in 'list'.
	private static int mode (int[] list){
		if (list.length <= 0) {
			return -999;	// somehow indicate failure
		}

		int highCount = countSame (list[0], list);
		int mode = list[0];
		for (int i = 1; i < list.length; i++) {
			int count = countSame (list[i], list);
			if (count > highCount) {
				highCount = count;
				mode = list[i];
			}
		}

		return mode;
	}

	// countSame: return the number of entries in 'list' 
	// that are same as 'refVal'.
	private static int countSame(int refVal, int[] list){
		int count = 0;
		for (int i = 0; i < list.length; i++) {
			if (list[i] == refVal) {
				count++;
			}
		}
	 	return count;
	}
}

Output for ManageStats.java

Number of values? 9
Enter a value: 6
Enter a value: 8
Enter a value: 6
Enter a value: 5
Enter a value: 4
Enter a value: 6
Enter a value: 3
Enter a value: 8
Enter a value: 3

List Statistics:
median = 6
mean   = 5.444444444444445
min    = 3
max    = 8
mode   = 6