How to check if a value exist in a 2d matrix array PHP

Question

I recently started experimenting with multidimensional arrays in PHP and I was wondering what is the most effective way to check if a value exists in a 2D matrix array.

Example: I want to find if user_id = 7 exists in the 2d matrix array. How can I achieved that ?

$matrix = array();
$query = "SELECT 
            CAST(AVG(r.rating_value) AS DECIMAL(10,1)) as 'rating', 
            u.user_id, 
            s.store_id
        FROM odr o 
            INNER JOIN rating r ON o.rating_id = r.rating_id 
            INNER JOIN store s ON o.store_id = s.store_id 
            INNER JOIN user u ON o.user_id = u.user_id 
        GROUP BY s.store_id, u.user_id 
        ORDER BY rating_value;";
        
$result = $mysqli->query($query);
$rowcount = mysqli_num_rows($result);
if ($rowcount > 1) {
    while ($row = $result->fetch_array()) {
        $matrix[$row['user_id']][$row['store_id']] = $row['rating'];
    }
}
var_dump($matrix);

//output: 
//array(2) { [41]=> array(1) { [35]=> string(3) "5.0" } [37]=> array(2) { 
//[37]=> string(3) "5.0" [35]=> string(3) "5.0" } }