stats_skew
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
stats_standard_deviation
(PECL stats >= 1.0.0)
stats_standard_deviation — Возвращает стандартное отклонение
Описание
float stats_standard_deviation
( array
$a
[, bool $sample = false
] )Внимание
К настоящему времени эта функция еще не была документирована; для ознакомления доступен только список аргументов.
Список параметров
-
a -
-
sample -
Возвращаемые значения
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User Contributed Notes
stats_standard_deviation
pmcdougl at gac dot edu
06-Mar-2012 10:40
Pascal Woerde
07-Sep-2010 12:04
If you want one function for the population and sample, you can use this function:
<?php
function standard_deviation($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);
}
Sharon
16-Apr-2010 02:40
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) );
}
?>