Average of a stream of numbers

Difficulty Level : Easy
Last Updated : 26 Mar, 2021

Difficulty Level: Rookie
Given a stream of numbers, print average (or mean) of the stream at every point. For example, let us consider the stream as 10, 20, 30, 40, 50, 60, …

  Average of 1 numbers is 10.00
  Average of 2 numbers is 15.00
  Average of 3 numbers is 20.00
  Average of 4 numbers is 25.00
  Average of 5 numbers is 30.00
  Average of 6 numbers is 35.00
  ..................

To print mean of a stream, we need to find out how to find average when a new number is being added to the stream. To do this, all we need is count of numbers seen so far in the stream, previous average and new number. Let n be the count, prev_avg be the previous average and x be the new number being added. The average after including x number can be written as (prev_avg*n + x)/(n+1).

C++

#include <stdio.h>
 
// Returns the new average after including x
float getAvg(float prev_avg, int x, int n)
{
    return (prev_avg * n + x) / (n + 1);
}
 
// Prints average of a stream of numbers
void streamAvg(float arr[], int n)
{
    float avg = 0;
    for (int i = 0; i < n; i++) {
        avg = getAvg(avg, arr[i], i);
        printf("Average of %d numbers is %f \n", i + 1, avg);
    }
    return;
}
 
// Driver program to test above functions
int main()
{
    float arr[] = { 10, 20, 30, 40, 50, 60 };
    int n = sizeof(arr) / sizeof(arr[0]);
    streamAvg(arr, n);
 
    return 0;
}

Java

// Java program to find average
// of a stream of numbers
class GFG {
 
    // Returns the new average after including x
    static float getAvg(float prev_avg, float x, int n)
    {
        return (prev_avg * n + x) / (n + 1);
    }
 
    // Prints average of a stream of numbers
    static void streamAvg(float arr[], int n)
    {
        float avg = 0;
        for (int i = 0; i < n; i++)
        {
            avg = getAvg(avg, arr[i], i);
            System.out.printf("Average of %d numbers is %f \n",
                                                   i + 1, avg);
        }
        return;
    }
 
    // Driver program to test above functions
    public static void main(String[] args)
    {
        float arr[] = { 10, 20, 30, 40, 50, 60 };
        int n = arr.length;
        streamAvg(arr, n);
    }
}
 
// This code is contributed by Smitha Dinesh Semwal

Python3

# Returns the new average
# after including x
def getAvg(prev_avg, x, n):
    return ((prev_avg *
             n + x) /
            (n + 1));
 
# Prints average of
# a stream of numbers
def streamAvg(arr, n):
    avg = 0;
    for i in range(n):
        avg = getAvg(avg, arr[i], i);
        print("Average of ", i + 1,
              " numbers is ", avg);
 
# Driver Code
arr = [10, 20, 30,
       40, 50, 60];
n = len(arr);
streamAvg(arr, n);
 
# This code is contributed
# by mits

C#

// C# program to find average
// of a stream of numbers
using System;
 
class GFG
{
 
    // Returns the new average
    // after including x
    static float getAvg(float prev_avg,
                        float x, int n)
    {
        return (prev_avg * n + x) / (n + 1);
    }
 
    // Prints average of
    // a stream of numbers
    static void streamAvg(float[] arr,
                          int n)
    {
        float avg = 0;
        for (int i = 0; i < n; i++)
        {
            avg = getAvg(avg, arr[i], i);
            Console.WriteLine("Average of {0} " +
                                "numbers is {1}",
                                     i + 1, avg);
        }
        return;
    }
 
    // Driver Code
    public static void Main(String[] args)
    {
        float[] arr = {10, 20, 30,
                       40, 50, 60};
        int n = arr.Length;
        streamAvg(arr, n);
    }
}
 
// This code is contributed by mits

PHP

<?php
// PHP program for Average of
// a stream of numbers
 
// Returns the new average
// after including x
function getAvg($prev_avg, $x, $n)
{
    return ($prev_avg * $n + $x) /
                        ($n + 1);
}
 
// Prints average of a
// stream of numbers
function streamAvg($arr, $n)
{
    $avg = 0;
    for ($i = 0; $i < $n; $i++)
    {
        $avg = getAvg($avg, $arr[$i], $i);
        echo "Average of ",$i + 1, "numbers is "
                                    ,$avg,"\n";
    }
    return;
}
 
    // Driver Code
    $arr = array(10, 20, 30, 40, 50, 60);
    $n = sizeof($arr);
    streamAvg($arr, $n);
 
// This code is contributed by aj_36
?>

Javascript

<script>
// javascript program to find average
// of a stream of numbers
 
// Returns the new average after including x
function getAvg( prev_avg,  x,  n)
{
    return (prev_avg * n + x) / (n + 1);
}
 
// Prints average of a stream of numbers
function streamAvg( arr,  n)
{
    let avg = 0;
    for (let i = 0; i < n; i++) {
        avg = getAvg(avg, arr[i], i);
       document.write("Average of "+(i + 1) +" numbers is "+  avg.toFixed(6) + "<br/>");
    }
    return;
}
 
// Driver program to test above functions
    let arr = [10, 20, 30, 40, 50, 60 ];
    let n = arr.length;
    streamAvg(arr, n);
    
// This code is contributed by todaysgaurav
 
</script>

Output :

Average of 1 numbers is 10.000000 
Average of 2 numbers is 15.000000 
Average of 3 numbers is 20.000000 
Average of 4 numbers is 25.000000 
Average of 5 numbers is 30.000000 
Average of 6 numbers is 35.000000

The above function getAvg() can be optimized using following changes. We can avoid the use of prev_avg and number of elements by using static variables (Assuming that only this function is called for average of stream). Following is the oprimnized version.

C++

#include <bits/stdc++.h>
using namespace std;
 
// Returns the new average after including x
float getAvg(int x)
{
    static int sum, n;
 
    sum += x;
    return (((float)sum) / ++n);
}
 
// Prints average of a stream of numbers
void streamAvg(float arr[], int n)
{
    float avg = 0;
    for (int i = 0; i < n; i++)
    {
        avg = getAvg(arr[i]);
        cout<<"Average of "<<i+1<<" numbers is "<<fixed<<setprecision(1)<<avg<<endl;
    }
    return;
}
 
// Driver code
int main()
{
    float arr[] = { 10, 20, 30, 40, 50, 60 };
    int n = sizeof(arr) / sizeof(arr[0]);
    streamAvg(arr, n);
 
    return 0;
}
 
// This code is contributed by rathbhupendra

C

#include <stdio.h>
 
// Returns the new average after including x
float getAvg(int x)
{
    static int sum, n;
 
    sum += x;
    return (((float)sum) / ++n);
}
 
// Prints average of a stream of numbers
void streamAvg(float arr[], int n)
{
    float avg = 0;
    for (int i = 0; i < n; i++) {
        avg = getAvg(arr[i]);
        printf("Average of %d numbers is %f \n", i + 1, avg);
    }
    return;
}
 
// Driver program to test above functions
int main()
{
    float arr[] = { 10, 20, 30, 40, 50, 60 };
    int n = sizeof(arr) / sizeof(arr[0]);
    streamAvg(arr, n);
 
    return 0;
}

Java

// Java program to return
// Average of a stream of numbers
class GFG
{
static int sum, n;
     
// Returns the new average
// after including x
static float getAvg(int x)
{
    sum += x;
    return (((float)sum) / ++n);
}
 
// Prints average of a
// stream of numbers
static void streamAvg(float[] arr,
                      int n)
{
    float avg = 0;
    for (int i = 0; i < n; i++)
    {
        avg = getAvg((int)arr[i]);
        System.out.println("Average of "+ (i + 1) +
                           " numbers is " + avg);
    }
    return;
}
 
// Driver Code
public static void main(String[] args)
{
    float[] arr = new float[]{ 10, 20, 30,
                               40, 50, 60 };
    int n = arr.length;
    streamAvg(arr, n);
}
}
 
// This code is contributed by mits

Python3

# Returns the new average
# after including x
def getAvg(x, n, sum):
    sum = sum + x;
    return float(sum) / n;
 
# Prints average of a
# stream of numbers
def streamAvg(arr, n):
    avg = 0;
    sum = 0;
    for i in range(n):
        avg = getAvg(arr[i], i + 1, sum);
        sum = avg * (i + 1);
        print("Average of ", end = "");
        print(i + 1, end = "");
        print(" numbers is ", end = "");
        print(avg);
    return;
 
# Driver Code
arr= [ 10, 20, 30,
       40, 50, 60 ];
n = len(arr);
streamAvg(arr,n);
 
# This code is contributed by mits

C#

using System;
 
class GFG
{
static int sum, n;
     
// Returns the new average
// after including x
static float getAvg(int x)
{
 
    sum += x;
    return (((float)sum) / ++n);
}
 
// Prints average of a
// stream of numbers
static void streamAvg(float[] arr, int n)
{
    float avg = 0;
    for (int i = 0; i < n; i++)
    {
        avg = getAvg((int)arr[i]);
        Console.WriteLine("Average of {0} numbers " +
                             "is {1}", (i + 1), avg);
    }
    return;
}
 
// Driver Code
static int Main()
{
    float[] arr = new float[]{ 10, 20, 30,
                               40, 50, 60 };
    int n = arr.Length;
    streamAvg(arr, n);
 
    return 0;
}
}
 
// This code is contributed by mits

PHP

<?php
// Returns the new average
// after including x
function getAvg($x)
{
    static $sum;
    static $n;
    $sum += $x;
    return (((float)$sum) / ++$n);
}
 
// Prints average of
// a stream of numbers
function streamAvg($arr, $n)
{
    for ($i = 0; $i < $n; $i++)
    {
        $avg = getAvg($arr[$i]);
        echo "Average of " . ($i + 1) .
             " numbers is ".$avg." \n";
    }
    return;
}
 
// Driver Code
$arr = array(10, 20, 30,
             40, 50, 60);
$n = sizeof($arr) / sizeof($arr[0]);
streamAvg($arr, $n);
 
// This code is contributed by mits
?>

Javascript

<script>
// javascript program to return
// Average of a stream of numbers
 
    var sum=0, n=0;
 
    // Returns the new average
    // after including x
    function getAvg(x) {
        sum += x;
        n++;
        return (sum / n);
    }
 
    // Prints average of a
    // stream of numbers
    function streamAvg( arr , m) {
        var avg = 0;
        for (i = 0; i < m; i++) {
            avg = getAvg(parseInt(arr[i]));
            document.write("Average of " + (i + 1) + " numbers is " + avg.toFixed(1)+"<br/>");
        }
        return;
    }
 
    // Driver Code
     
        var arr =  [ 10, 20, 30, 40, 50, 60 ];
        var m = arr.length;
        streamAvg(arr, m);
 
// This code is contributed by todaysgaurav
</script>

Output:

Average of 1 numbers is 10.0
Average of 2 numbers is 15.0
Average of 3 numbers is 20.0
Average of 4 numbers is 25.0
Average of 5 numbers is 30.0
Average of 6 numbers is 35.0

Thanks to Abhijeet Deshpande for suggesting this optimized version.
Related article:
Program for average of an array (Iterative and Recursive)
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready. To complete your preparation from learning a language to DS Algo and many more, please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

My Personal Notes