I am trying to solve an exercise problem from the Practice-It! website.

I am not a student but I have purchased the book(Building Java Programs) from Amazon. I am trying to teach myself how to code. It is not my intention to violate any EE terms of restriction.

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:
standard deviation

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. You may assume that the array passed is non-null and contains at least two values, because the standard deviation is undefined otherwise.

I have written some code but keep that I thought should work but keep failing test cases.
Please review my code an help guide me to a solution.

public static double stdev(int a[]){ double mean = 0; int sum = 0; //1. Work out the Mean (the simple average of the numbers) for (int i = 0; i < a.length; i++) { sum += a[i]; if(i == a.length -1){ mean = sum/a.length; } } //2. Then for each number: subtract the Mean and square the result //GET DIFFERENCE double variance = 0; double [] b = new double [a.length]; for (int i = 0; i < a.length; i++) { //b[i] = Math.sqrt(Math.abs(a[i] - mean)); double diff = Math.abs(a[i] - mean); b[i] = diff * diff; } //3. Then work out the mean of those squared differences. for (int i = 0; i < b.length; i++) { variance += b[i]/b.length; } //4. Take the square root of that and you are done! double standardDeviation = Math.sqrt(Math.ceil(variance)); return standardDeviation; }

I'm no Java expert, but I do have some practice - we can make this a learning exercise for the both of us. I thought I would toss this first post up as I work through your code.

So, step by step, the first problem I see is your mean result. You set the mean type to a double (good), but you're finding the result by dividing an int by an int. That means your result will discard anything after the decimal. You get a value plus a ".0" in this case, your mean is "2.0". I always like to toss in a print statement as I code to check that my result is what I expect.

System.out.println("Average = " + mean); //to see value of mean

You're off on the wrong foot. The calculation of the mean is wrong. I haven't looked beyond that.
a. Don't do the division until the loop is finished
b. (and more importantly) 'sum' should be a double. Why?

Okay, I have changed sum to a double and cast my divisor to a double.

0

For Any Use & On Any Platform

Contextual Guidance at the moment of need helps your employees/users adopt software o& achieve even the most complex tasks instantly. Boost knowledge retention, software adoption & employee engagement with easy solution.

In your step 2 code, I would take out the "Math.abs" function. I get the same result either way, and this may be my rudimentary understanding of standard deviation, but I don't think there's any reference to absolute value in there.

Lastly, and most importantly, there are two ways to calculate standard deviation (WTF!?!?!). I'm guessing your result is ~10.66, but you're "supposed" to be getting 11.237. This is because one way is figuring for a "sample" population, while the other figures for the entire data set.

Java functions are among the best things for programmers to work with as Java sites can be very easy to read and prepare. Java especially simplifies many processes in the coding industry as it helps integrate many forms of technology and different dâ€¦

Whether youâ€™re a college noob or a soon-to-be pro, these tips are sure to help you in your journey to becoming a programming ninja and stand out from the crowd.

This tutorial will introduce the viewer to VisualVM for the Java platform application. This video explains an example program and covers the Overview, Monitor, and Heap Dump tabs.

This tutorial explains how to use the VisualVM tool for the Java platform application. This video goes into detail on the Threads, Sampler, and Profiler tabs.