/**
* Calculate the kth q-quantile of a set of numbers in an array.
* As per http://en.wikipedia.org/wiki/Quantile#Quantiles_of_a_population
* Ex: Median is 1st 2-quantile
* Ex: Upper quartile is 3rd 4-quantile
*
* @param array $array set of values.
* @param number $k index of quantile.
* @param number $q number of quantiles.
* @return number kth q-quantile of values.
*/
public static function quantile($array, $k, $q)
{
if ($k == 0) {
return Basic::min($array);
}
if ($k == $q) {
return Basic::max($array);
}
sort($array);
$index = count($array) * $k / $q;
if (fmod($index, 1) == 0) {
return 0.5 * $array[$index - 1] + 0.5 * $array[$index];
}
return $array[floor($index)];
}
