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Posted by Erwin Moller on 10/05/06 15:20
Jeff Gardner wrote:
> Does anyone have more details on stats_standard_deviation than the
> manual provides?
Hi Jeff,
The describtion is very bad indeed.
Why use an undocumented (bad documented) function for such a simple thing?
I would write my own implementation in such case.
Calculation the SD is very straightforward.
On the same page on www.php.net you can also find a contribution with a
working example.
[Source]
http://nl2.php.net/manual/en/function.stats-standard-deviation.php
function average($array){
$sum = array_sum($array);
$count = count($array);
return $sum/$count;
}
//The average function can be use independantly but the deviation function
uses the average function.
function deviation ($array){
$avg = average($array);
foreach ($array as $value) {
$variance[] = pow($value-$avg, 2);
}
$deviation = sqrt(average($variance));
return $deviation;
}
Regards,
Erwin Moller
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