z-Scores(standard deviation and mean) in PHP

php mean standard-deviation
Spencer picture Spencer · Mar 25, 2011 · Viewed 14.3k times · Source

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.

Answer

Naftali aka Neal picture Naftali aka Neal · Mar 25, 2011

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

Related questions

How do I check if a string contains a specific word?

Consider: $a = 'How are you?'; if ($a contains 'are') echo 'true'; Suppose I have the code above, what is the correct way to write the statement if ($a contains 'are')?

Read More
Get the full URL in PHP

I use this code to get the full URL: $actual_link = 'http://'.$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF']; The problem is that I use some masks in my .htaccess, so what we see in the URL is not always …

Read More
How do I get PHP errors to display?

I have checked my PHP ini file (php.ini) and display_errors is set and also error reporting is E_ALL. I have restarted my Apache webserver. I have even put these lines at the top of my script, and …

Read More