stojg\recommend\strategy\Paerson::run()

Complexity

Conditions	5
Paths	9

Size

Total Lines	39
Code Lines	25

Duplication

Lines	0
Ratio	0 %

Importance

Changes	3
Bugs	1	Features	0

<?php
    public function run($ratings1, $ratings2)
    {
        $numCoRatedItems = 0;
        $dotProduct = 0;
        $rating1Sum = 0;
        $rating1SumSqr = 0;
        $rating2Sum = 0;
        $rating2SumSqr = 0;
        foreach ($ratings1 as $item => $rating1) {
            if (!isset($ratings2[$item])) {
                continue;
            }
            $numCoRatedItems += 1;
            $dotProduct += $rating1 * $ratings2[$item];
            $rating1Sum += $rating1;
            $rating1SumSqr += pow($rating1, 2);
            $rating2Sum += $ratings2[$item];
            $rating2SumSqr += pow($ratings2[$item], 2);
        }

        // There is no correlation at all
        if ($numCoRatedItems == 0) {
            return false;
        }

        $denominator = sqrt(
            ($rating1SumSqr - (pow($rating1Sum, 2) / $numCoRatedItems)) *
            ($rating2SumSqr - (pow($rating2Sum, 2) / $numCoRatedItems))
        );

        if ($denominator == 0) {
            return false;
        }

        // the closer abs(paerson) is to 1 to better correlation is it
        $paerson = ($dotProduct - ($rating1Sum * $rating2Sum / $numCoRatedItems)) / $denominator;

        return 1 - abs($paerson);
    }
}