Question
The standard deviation of a list of numbers is a measure of how much
the numbers deviate from the average. If the standard deviation is
small, the numbers are clustered close to the average. If the
standard deviation is large, the numbers are scattered far from the
average. The standard deviation of a list of numbers
,
,
,
and so forth is defined as the square root of the average of the
following numbers:
,
,
,
and so forth.
The number a is the average of the numbers
,
,
,
and so forth.
Define a static method that takes a partially filled array of numbers as its argument and returns the standard deviation of the numbers in the partially filled array. Because a partially filled array requires two arguments, the method should actually have two formal parameters, an array parameter and a formal parameter of type int that gives the number of array positions used. The numbers in the array should be of type double. Write a suitable test program
for your method.
Answer
Program:
import java.util.*;
import java.math.RoundingMode;
import java.text.DecimalFormat;
public class Main
{
public static void main(String args[])
{
int sizeArray = 6;
double[] nums = new double[10];
DecimalFormat df=new DecimalFormat("#.##");
nums[0] = 12.5;
nums[1] = 53.0;
nums[2] = 75.3;
nums[3] = 89.12;
nums[4] = 65.5;
nums[5] = 80.0;
System.out.println("The average standard deviation of a list of numbers is "
+df.format(standardDevList(nums, sizeArray)));
}
public static double standardDevList(double[] n1, int n2)
{
double avg = 0;
double avgStdDev = 0;
for(int index = 0; index < n2; index++)
{
avg += n1[index];
}
avg /= n2;
for(int index2 = 0; index2 < n2; index2++)
{
avgStdDev += (n1[index2] - avg) *
(n1[index2] - avg);
}
avgStdDev = Math.sqrt(avgStdDev / n2);
return avgStdDev;
}
}
Output of the program:
The average standard deviation of a list of numbers is 25.09