How do I calculate the moving average of the 7 most recent values after the first Seven values in java?

Question

My question is how do I calculate the moving average of the 7 most recent values using ArrayList after the first seven values?

This is my code for the first seven values, what I fail to understand is how I would get the average of the 7 most recent values after the first seven values, I would really appreciate it if anyone could help me with this.

import java.util.ArrayList;

import java.io.*;

import java.util.Scanner;

public class MovingAverage{

public static void main(String[]args) throws FileNotFoundException{
    int sum = 0;
    Scanner s = new Scanner(new File("values.txt"));

    ArrayList<Integer> values = new ArrayList<>();
    ArrayList<Integer> averages = new ArrayList<>();
    
    System.out.println("\tValue"+"\t\tRolling Average");
    System.out.println();
    while(s.hasNext())
    {
        values.add(s.nextInt());
    }
     
    for(int i = 0; i<7;i++)
    {
        sum = sum + values.get(i);
        averages.add(sum/(i+1));

        System.out.println("\t"+values.get(i)+"\t\t"+averages.get(i));
    }
   
}

}

Answer 1

Let say you have N (>=K) numbers, and want to calculate the rolling average, then below is an easy procedure:

import java.util.*;
class Main
{
    public static void rollingAverage(ArrayList<Integer> list, int K)
    {
        int sum = 0;
        int avg = 0;
        int N = list.size();
        // This part calculates the average of first (i+1) values
        for (int i=0; i<K; i++)
        {
            sum += list.get(i);
            avg = sum / (i+1);
        }
        // This part calculates the rolling average (average of `K` recent values)
        for (int i=K; i<N; i++)
        {
            sum -= list.get(i-K);   // Subtracting `i-k`th value
            sum += list.get(i);     // Adding current number
            avg = sum / K;
            System.out.println( avg );
        }
    }
    public static void main (String [] arg)
    {
        ArrayList<Integer> list = new ArrayList<>
        (Arrays.asList(10,10,10,10,10,10,10,80,150,220));
        rollingAverage( list , 7 ); // O/P : 20 40 70
    }
}

You can implement your rolling average program using the above approach easily. Feel free to ask any doubt.