stats_standard_deviation

(PECL stats >= 1.0.0)

stats_standard_deviation — Returns the standard deviation

Beschreibung

float stats_standard_deviation ( array $a [, bool $sample = false ] )

Warnung

Diese Funktion ist bis jetzt nicht dokumentiert. Es steht nur die Liste der Argumente zur Verfügung.

Parameter-Liste

a
sample

Rückgabewerte

add a note User Contributed Notes stats_standard_deviation

Pascal Woerde 06-Sep-2010 06:04


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 15-Apr-2010 08:40


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) );

}



 ?>

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