Phpml\Math\Statistic\Correlation::pearson()

Complexity

Conditions	3
Paths	3

Size

Total Lines	26
Code Lines	17

Duplication

Lines	0
Ratio	0 %

Importance

Changes	2
Bugs	0	Features	0

<?php
    public static function pearson(array $x, array $y)
    {
        if (count($x) !== count($y)) {
            throw InvalidArgumentException::arraySizeNotMatch();
        }

        $count = count($x);
        $meanX = Mean::arithmetic($x);
        $meanY = Mean::arithmetic($y);

        $axb = 0;
        $a2 = 0;
        $b2 = 0;

        for ($i = 0;$i < $count;++$i) {
            $a = $x[$i] - $meanX;
            $b = $y[$i] - $meanY;
            $axb = $axb + ($a * $b);
            $a2 = $a2 + pow($a, 2);
            $b2 = $b2 + pow($b, 2);
        }

        $corr = $axb / sqrt($a2 * $b2);

        return $corr;
    }
}