stats_skew
If you want one function for the population and sample, you can use this function:
<?php
function standard_deviation($aValues, $bSample = false)
{
$fMean = array_sum($aValues) / count($aValues);
$fVariance = 0.0;
foreach ($aValues as $i)
{
$fVariance += pow($i - $fMean, 2);
}
$fVariance /= ( $bSample ? count($aValues) - 1 : count($aValues) );
return (float) sqrt($fVariance);
}
stats_standard_deviation
(PECL stats >= 1.0.0)
stats_standard_deviation — Returns the standard deviation
Description
float stats_standard_deviation
( array
$a
[, bool $sample = false
] )Warning
This function is currently not documented; only its argument list is available.
Parameters
-
a -
-
sample -
Return Values
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User Contributed Notes
stats_standard_deviation - [4 notes]
Pascal Woerde ¶
2 years ago
tripollite at gmail dot com ¶
10 months ago
Function to calculate square of value - mean
<?php
function sd_square($x, $mean) { return pow($x - $mean,2); }
?>
Function to calculate standard deviation (uses sd_square)
<?php
function sd($array) {
// square root of sum of squares devided by N-1
return sqrt(array_sum(array_map("sd_square", $array, array_fill(0,count($array), (array_sum($array) / count($array)) ) ) ) / (count($array)) );
}
?>
works better if you don't add +1 to the count
standard deviation of a constant must be 0 ( http://en.wikipedia.org/wiki/Standard_deviation )
different way :
<?php
class Tmath{
public static function variance($data, $round = 2)
{
if( count($data) == 0 )
return NULL;
$total_ecart = 0;
$moyenne = self::moyenne($data, 10*$round);
if( $moyenne == 0)
return 0;
foreach( $data as $element)
{
$total_ecart += pow($element, 2);
}
return round($total_ecart/count($data) - pow($moyenne,2),$round);
}
public static function ecartType($data, $round = 2)
{
return round(sqrt(self::variance($data,10*$round)),2);
}
public static function moyenne($data, $round = 2)
{
if( count($data) == 0 )
return NULL;
return round(array_sum($data)/count($data),$round) ;
}
}
?>
pmcdougl at gac dot edu ¶
1 year ago
It should be known that this function also casts all of the values of the array to floats. If you pass an array of integers, they will come out as an array of floats.
$data = array(2,3,3,3,3,2,5);
var_dump($data);
$standardDeviation = stats_standard_deviation($data);
var_dump($data);
Prints:
array
0 => int 2
1 => int 3
2 => int 3
3 => int 3
4 => int 3
5 => int 2
6 => int 5
array
0 => float 2
1 => float 3
2 => float 3
3 => float 3
4 => float 3
5 => float 5
6 => float 2
Sharon ¶
3 years ago
If you don't have the stat package you can use these functions:
<?php
// Function to calculate square of value - mean
function sd_square($x, $mean) { return pow($x - $mean,2); }
// Function to calculate standard deviation (uses sd_square)
function sd($array) {
// square root of sum of squares devided by N-1
return sqrt(array_sum(array_map("sd_square", $array, array_fill(0,count($array), (array_sum($array) / count($array)) ) ) ) / (count($array)-1) );
}
?>