Task — Average of stream

You are given a stream of numbers, @stream. Write a script to print the average of the stream at every point.

Examples

Input: @N = (10, 20, 30, 40, 50, 60, 70, 80, 90, ...)
Output:      10, 15, 20, 25, 30, 35, 40, 45, 50, ...

Average of first number is 10.
Average of first 2 numbers (10+20)/2 = 15
Average of first 3 numbers (10+20+30)/3 = 20
Average of first 4 numbers (10+20+30+40)/4 = 25 and so on.

Analysis

This is pretty straightforward and probably lends itself to a one-liner. I have chosen, for the sake of clarity to expand it to a few lines in which $j loops over the indices of @stream and at each point accumulates a total.

That total divided by the current $j + 1 gives the average to date.

Try it 

#!/usr/bin/perl

# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge

use v5.26;    # The Weekly Challenge - 2021-07-19
use utf8;     # Week 122 - task 1 - Average of stream
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';
use Encode;

average_of_stream(10, 20, 30, 40, 50, 60, 70, 80, 90);
average_of_stream(-5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5);
average_of_stream(1, 2.5, 3.78, -6.31, 5);

sub average_of_stream {
    
    my (@stream, $total, $j, @average);
    
    # initialise
    @stream = @_;
    $total = 0;
    for $j (0 .. $#stream) {
        $total += $stream[$j];
        $average[$j] = sprintf('%.2f', $total / ($j + 1));
    }
    
    say qq[\nInput:  (] . join(', ', @stream) . ')';
    say qq[Output: (] . join(', ', @average) . ')';
}

last updated 2026-03-06 — 9 lines of code

Output

Input:  (10, 20, 30, 40, 50, 60, 70, 80, 90)
Output: (10.00, 15.00, 20.00, 25.00, 30.00, 35.00, 40.00,
   45.00, 50.00)

Input:  (-5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5)
Output: (-5.00, -4.50, -4.00, -3.50, -3.00, -2.50, -2.00,
   -1.50, -1.00, -0.50, 0.00)

Input:  (1, 2.5, 3.78, -6.31, 5)
Output: (1.00, 1.75, 2.43, 0.24, 1.19)