note 109234 added to function.stats-standard-deviation

// 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($array)) ); } works better if you don't add +1 to the count standard deviation of a constant must be 0 ( http://en.wikipedia.org/wiki/Standard_deviation ) different way : class Tmath{ public static function variance($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) ; } } ---- Server IP: 69.147.83.197 Probable Submitter: 78.125.26.52 ---- Manual Page -- http://www.php.net/manual/en/function.stats-standard-deviation.php Edit -- https://master.php.net/note/edit/109234 Del: integrated -- https://master.php.net/note/delete/109234/integrated Del: useless -- https://master.php.net/note/delete/109234/useless Del: bad code -- https://master.php.net/note/delete/109234/bad+code Del: spam -- https://master.php.net/note/delete/109234/spam Del: non-english -- https://master.php.net/note/delete/109234/non-english Del: in docs -- https://master.php.net/note/delete/109234/in+docs Del: other reasons-- https://master.php.net/note/delete/109234 Reject -- https://master.php.net/note/reject/109234 Search -- https://master.php.net/manage/user-notes.php