Authors:
Stuart Reges, Marty Stepp
Chapter:
Arrays
Exercise:
Exercises
Question:6 | ISBN:9780136091813 | Edition: 2
Question
Write a method called stdev that returns the standard deviation of an array of integers. Standard deviation is computed by taking the square root of the sum of the squares of the differences between each element and the mean, divided by one less than the number of elements. (It’s just that simple!) More concisely and mathematically, the standard deviation of an array a is written as follows:
For example, if the array passed contains the values {1, –2, 4, -4, 9, -6, 16, -8, 25, -10}, your method should return approximately 11.237 .
Answer
Implementation of stdev method:
public static double stdev(int[] a)
{
if(a.length == 0)
return 0;
double total = 0;
for(int i = 0; i < a.length; i++)
{
total += a[i];
}
double average = total / a.length;
total = 0;
for(int i = 0; i < a.length; i++)
{
total += Math.pow((a[i] - average), 2.0);
}
double sdv = Math.sqrt(total / (a.length - 1));
return sdv;
}