z-Scores(standard deviation and mean) in PHP

Question

I am trying to calculate Z-scores using PHP. Essentially, I am looking for the most efficient way to calculate the mean and standard deviation of a data set (PHP array). Any

Answer 1

   function standard_deviation($aValues)
{
    $fMean = array_sum($aValues) / count($aValues);
    //print_r($fMean);
    $fVariance = 0.0;
    foreach ($aValues as $i)
    {
        $fVariance += pow($i - $fMean, 2);

    }       
    $size = count($aValues) - 1;
    return (float) sqrt($fVariance)/sqrt($size);
}