z-Scores(standard deviation and mean) in PHP

问题:

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 suggestions on how to do this in PHP?

I am trying to do this in the smallest number of steps.

回答1:

to calculate the mean you can do:

$mean = array_sum($array)/count($array)

standard deviation is like so:

// 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) );
}

right off this page

回答2:

How about using the built in statistics package like stats_standard_deviation and stats_harmonic_mean. I can't find a function for standard means, but if you know anything about statistics, I'm sure you can figure something out using the built-in functions.

回答3:

   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);
}