Foreach，for循环PHP冗余

Question

I have the following code:

<select multiple="multiple">
    <?php $sql = "SELECT book_id, book_name FROM book ORDER BY book_name";
        try {
            $conn = new PDO("...");
            $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

            foreach ($conn->query($sql) as $row) {
                $myId   = $row['book_id'];
                $myName = $row['book_name'];
                for ($i = 0; $i < count($array); $i++) {
                    if ($myId != $array[$i]) {
                        echo("<option value='$myId'>$myName</option>");
                    }
                }
            }
        }
        catch(PDOException $e) {
        ...
        }
        $conn = null;
    ?>
</select>

My purpose is to have a selector <select>, where the not previously associated books with the user appear. In this case, the $array holds the Id of the books that are already link to this user.

I know the problem is the nested loop, because I got the result I want, eg (for a $row = 3 and a $i = 2):

Book1
Book1
Book2
Book2
Book3
Book3

And the desired result would be:

Book1
Book2
Book3

But I can't figured out how to compared the Id's, without nesting the loops.

Answer 1

instead of your for-loop

  for ($i = 0; $i < count($array); $i++) {
                    if ($myId != $array[$i]) {
                        echo("<option value='$myId'>$myName</option>");
                    }
                }

try in_array() instad:

if(!in_array($myId, $array)) {
    echo("<option value='$myId'>$myName</option>");
}

even if $array contains $id multiple times, this will only write once.

edit: forgot the ! to negate. the condition.