Question

IN JAVA

your software company has been requested to provide a prototype program performing the simple statistical evaluations. You will need to implement a main program that reads the values into the array (or you could write another method to read them in), then call each of the various methods that you will convert from your previous programming project. The following methods comprise the StatPackage.

The function specifications are as follows:

Your StatPackage will accept up to 500 values as input.

Numerical values will be printed with two significant digits to the right of the decimal point.

The program will contain the following functions:

static double calcMean (int scores [], count) calculates the mean value for the values stored in the array scores mean is essentially the same as the average.

static double calcMedian (int scores [], count) calculates the median value for the values stored in the array scores median is the is middle value of the stored values.

static double calcVariance (int scores [], count) calculates the variance value for the values stored in the array scores Variance is determined by the formula:

            the sum of the square of the values / count
                                - square of the sum of the values / square of the count
                    

static double calcStdDev (double variance) calculates the standard deviation value for the values stored in the array scores. Standard deviation is the square root of the variance.

Answer 1

import java.io.*;
import java.util.Arrays;

public class StatPackage {

   public static double calcMean(int[] scores, int count) {
       return sum(scores) / (double) count;
   }

   public static double calcMedian(int[] scores, int count) {
       int[] sorted = sort(Arrays.copyOf(scores, count));
       int n = count/2;
       if(count % 2 == 1) {
           //length is odd
           return (double) sorted[n];
       }
       //else we average the two middle values
       return (sorted[n-1]+sorted[n])/ (double) 2;
   }

   public static double calcVariance(int[] scores, int count) {
       int a = 0;
       int b = 0;
       for(int i = 0; i < count; i++) {
           a += scores[i] * scores[i];
       }
       int sum = sum(scores);
       b = sum*sum;
       return ((double)a)/count - ((double) b)/(count * count);
   }

   public static double calcStdDev(int[] scores, int count) {
       return Math.sqrt(calcVariance(scores, count));
   }

   public static void main(String[] args) throws IOException {
       BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
       String line;
       int[] arr = new int[500];
       int i = 0;
       while((line = stdin.readLine()) != null && i < arr.length) {
           arr[i] = Integer.parseInt(line);
           i++;
       }
       if(i != arr.length) {
           arr = Arrays.copyOf(arr, i);
       }
       System.out.printf("Mean: %.02f%n", calcMean(arr, arr.length));
       System.out.printf("Median: %.02f%n", calcMedian(arr, arr.length));
       System.out.printf("Variance: %.02f%n", calcVariance(arr, arr.length));
       System.out.printf("Standard Deviation: %.02f%n", calcStdDev(arr, arr.length));
   }

   //
   //Utilities
   //

   //Merge-sort that doesn't mutate the original
   //As it copies twice every recursion, it is not very time/space efficient
   //First wrote something like this for AP CS
   private static int[] sort(int[] arr) {
       int[] res = Arrays.copyOf(arr, arr.length);
       if(res.length == 0) {
           return new int[0];
       }
       if(res.length == 1) {
           return res;
       }
       if(res.length == 2) {
           if(res[0] > res[1]) {
               swap(res, 0, 1);
               return res;
           }
           return res;
       }
       int n = arr.length / 2;
       int[] left = sort(Arrays.copyOfRange(res, 0, n));
       int[] right = sort(Arrays.copyOfRange(res, n, res.length));
       int i = 0, j = 0;
       while(i < left.length && j < right.length) {
           if(left[i] < right[j]) {
               res[i+j] = left[i];
               i++;
           } else {
               res[i+j] = right[j];
               j++;
           }
       }
       if(i+j != res.length) {
           if(i == left.length) {
               for(; j < right.length; j++) {
                   res[i+j] = right[j];
               }
           } else if(j == right.length) {
               for(; i < left.length; i++) {
                   res[i+j] = left[i];
               }
           }
       }
       return res;
   }

   //Swaps two values in-place
   private static void swap(int[] arr, int a, int b) {
       int temp = arr[a];
       arr[a] = arr[b];
       arr[b] = temp;
   }

   private static String toString(int[] arr) {
       String str = "";
       for(int i : arr) {
           str += i + " ";
       }
       return str;
   }

   //Sum doesn't even need a count variable because the array will init to 0;
   private static int sum(int[] arr) {
       int sum = 0;
       for(int i : arr) {
           sum += i;
       }
       return sum;
   }

   private static String toString(double[] arr) {
       String str = "";
       for(double d : arr) {
           str += String.format("%.02f ", d);
       }
       return str;
   }
}