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));
    }
   
}

}

You didn't say you wanted a running average but just next 7 values, right? — WJS, Jun 18 '21 at 15:55

GURU Shreyansh · Accepted Answer · 2021-06-18T15:53:28.540

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.

@samabcde Very sorry, missed checking the return type. It's working fine now. — GURU Shreyansh, Jun 18 '21 at 15:50
Missing result value: The average of the first 7 numbers is **10**. — Andreas, Jun 18 '21 at 16:04

WJS · Answer 2 · 2021-06-18T16:08:14.073

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

This guarantees that you have sufficient entries. Then it simply averages the appropriate sublist, printing them out as calculated.

List<Integer> list = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
        11, 12, 13, 14);
if (list.size() < 14) {
    System.out.println("Insufficient values provided");
} else {
    int count = 1;
    double sum = 0;
    for (int val : list.subList(7, 14)) {
        sum += val;
        System.out.printf("%d  running average = %.2f%n", val,
                sum / count++);
    }
}

For this particular data, prints

8  running average = 8.00
9  running average = 8.50
10  running average = 9.00
11  running average = 9.50
12  running average = 10.00
13  running average = 10.50
14  running average = 11.00

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

2 Answers2