trog's haus

My brother needed to figure out how to do a “moving average” in some code he was writing a while ago. I’d never done this before and couldn’t find any really simple code examples so ended up on Wikipedia where I found it’s actually called a cumulative moving average.

Super simple code example follows:

<?php
$numbers = array(1,2,3,4);

// A simple function to calculate averages
function average($array)
{
	return (array_sum($array) / count($array));
}

/*
 * Simple function to calculate moving average with the following parameters
 * $datapoint - the most recently acquired new datapoint
 * $average - the current average
 * $count - the total number of items we're dealing with
 */
function cumulativeAverage($datapoint, $average, $count)
{
	return $average + (($datapoint - $average) /  $count);
}

// First let's print the average calculated normally so we can compare to the final result
print "Normal average:\t\t".average($numbers)."\n";

// $lastav stores the most recently calculated average
$lastav = 0;

// Loop through all the numbers in the array and calculate the cumulative average each time
for ($i = 0; $i<sizeof($numbers);$i++)
{
	$lastav = cumulativeAverage($numbers[$i], $lastav, $i+1);
}

print "Cumulative Average:\t".$lastav."\n";

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