calc Jaccard Index in PHP

jaccard.php

<?php
/**
 * Return the degree of similarity (Jaccard Index) for each product
 *
 * @param  array   $mat        user-item matrix $mat[product_id][user_id] 1|null
 * @param  integer $product_id
 * @author Hideaki Kanehara
 * @return array   key: product_id value: degree of similarity
 */
function jaccard($mat,$product_id)
{
    $items = [];
    foreach ($mat as $pid => $row) {
        $numerator = count(array_intersect_assoc($mat[$product_id],$row));
        $denominator = count(array_merge(
            array_intersect_assoc($mat[$product_id],$row),
            array_diff_assoc($mat[$product_id],$row),
            array_diff_assoc($row,$mat[$product_id]
        )));
        $items[$pid] = $numerator / $denominator;
    }
    arsort($items);
    // for recommendation system
    // $num_slice = 5;
    // unset($items[$id]);
    // $items = array_slice($items, 0, $num_slice, True);
    return $items;
}