Calculating Average/Max/Min from an array in Java

Question

I have my code that will read in a a list of numbers in a file called "QuizScores.txt". However, in this file, certain numbers contain letters. I have told my program to simply ignore those instances and move onto the next number. My issue now if that my code is only reading one line at a time where I need it to look at the entire file, read it in, calculate the average, the maximum, and the minimum, and finally output that to a file called "QuizStats.txt". Any help with this would be greatly appreciated! Thanks!

QuizScores:

Code:

import java.io.*;

public class ScoreReader {


    public static void main(String[] args) {
        BufferedReader reader = null;

        try {
               String currentLine;

               reader = new BufferedReader(new FileReader("QuizScores.txt"));
               while ((currentLine = reader.readLine()) != null) {

                   int sum = 0;
                   String[] nums = currentLine.split("\\s+");
                   for (int i = 0; i < nums.length; i++) {
                       try{
                           double num = Integer.parseInt(nums[i]);
                           if (num != -1) {
                               sum += num;
                           }
                       } catch( NumberFormatException err )
                       {

                       }
                   }

                   System.out.println(sum);
               }
            } catch (IOException err) {
                err.printStackTrace();
            } 
            catch (NumberFormatException err) {}
            finally {
                try {
                   if (reader != null){
                       reader.close();
                   }
                }
                   catch (IOException err) {
                    err.printStackTrace();
                   }
            }
    }
}

Don't you want double sum and double num = Double.parseDouble(nums[i]);? — Elliott Frisch
– Elliott Frisch, Commented Apr 10, 2014 at 19:21
Could I still calculate the average, max, and min even if the file is read in one line at a time? Because I couldn't get that to work and assumed that was my problem. — Ben
– Ben, Commented Apr 10, 2014 at 19:21
You can. add a counter variable to count the number of values you have, then divide the sum by that counter to get the average. add another two variables for the max and min - as you read in each value, compare it to the current max and min and update the max and min as necessary... — anycard
– anycard, Commented Apr 10, 2014 at 19:23
@ElliottFrisch Yeah, you're right, the code is still a work in progress. Thanks for catching that though. :) — Ben
– Ben, Commented Apr 10, 2014 at 19:24

Jonathan · Accepted Answer · 2014-04-10 19:31:28Z

2

double min = 0.0;
double max  = 0.0;
int count = 0;



sum += num;
count++;
if (num > max) {
    max = num;
}
if (num < min) {
    min = num;
}
double avg = (double) sum/count;

Then the avg, sum, min, and max are all known. I would probably take a different approach from the beginning, but the code above should work with your code. I have not run it though.

answered Apr 10, 2014 at 19:31

Jonathan

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2 Comments

Ben Over a year ago

Will this not still output the entire list of numbers if I try to print the avg/max/min to the command line?

Jonathan Over a year ago

Im a little confused by your question. You could print the average by System.out.println(String.valueOf(avg)); Follow this pattern for the other variables. Is this what you are asking??

CodeCamper · Accepted Answer · 2014-04-10 20:48:33Z

Try this code

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class ScoreReader {

    public static void main(String[] args) {
        BufferedReader reader = null;
        double average = 200.0;
        double min = Double.MAX_VALUE;
        double max = Double.MIN_VALUE;
        int n = 1;
        String currentLine;
        double c;
        try {
            reader = new BufferedReader(new FileReader("QuizScores.txt"));
            System.out.println("--Quiz Scores--");
            while ((currentLine = reader.readLine()) != null) {
                try {
                    c = Double.parseDouble(currentLine);
                } catch (Exception ex) {
                    continue;
                }
                max = max > c ? max : c;
                min = min < c ? min : c;
                average += (c - average) / n;
                n++;
                System.out.println(c);
            }
            System.out.println("--Summary--");
            System.out.println("Average: " + average);
            System.out.println("Minimum: " + min);
            System.out.println("Maximum: " + max);
        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        }
        try {
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output

--Quiz Scores--
45.0
63.0
34.7
75.0
4.0
8.0
15.0
16.0
23.0
42.0
67.0
34.0
67.0
--Summary--
Average: 37.97692307692308
Minimum: 4.0
Maximum: 75.0

Is this what you are looking for?

Ricardo Jl Rufino · Accepted Answer · 2016-05-16 02:05:34Z

 private class Statistics{

    public double min = -1;
    public double max;
    public double avg;
    public long sum;

    Statistics(List<Long> list){

        int count = 0;
        for (Long num : list) {
            sum += num;
            count++;

            if(min == -1) min= num;

            if (num > max) {
                max = num;
            }
            if (num < min) {
                min = num;
            }
        }

        this.avg = sum/(double)count;
    }

}

// USAGE

    Statistics statistics = new Statistics(Arrays.asList(1l, 2l, 3l, 4l));

    System.out.println(statistics.avg);
    System.out.println(statistics.min);
    System.out.println(statistics.max);
    System.out.println(statistics.sum);

user1720205 · Accepted Answer · 2014-04-10 19:22:25Z

0

Read line by line parsing only the numbers and put those into a list, then pass that list to a function such as:

 public static Float getAverage(ArrayList <Float> x)
 {
    Float sum = 0.0f;

    for (Float a : x )
        sum += a;

    return sum / x.size();
 }

answered Apr 10, 2014 at 19:22

user1720205

3 Comments

Elliott Frisch Over a year ago

Why should he do that? Keep the sum as you go, and count the numbers you've parsed....

user1720205 Over a year ago

That's fine too but he also wants to use the same data for other computations so he could hold it in one array, but it is really just a personal preference.

Jonathan Over a year ago

If the data set was small and the manipulation simple, separating the read and data cleaning from the computation would make the code a little more readable. With a data set that is small, such as this, that approach could be justified.

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