Help with recursion on one array algorithm in PHP

Although this sounds like a math/CS question, I am sure someone out there will be able to help me out with this.

I have two tables, similarityTable and items. The items table contains the following data:

itemID   itemName
------   -----
    1    A
    2    B
    3    C
    4    D
    5    E

and the similarityTable:

item1  item2
-----  -----
   1   2
   1   3
   2   1
   2  开发者_如何学编程 3
   3   1
   3   4
   4   1
   4   2

From the above, it is seen that item1 of ID=1 is similar to item2 of ID 2,3. Item1 of ID=2 is similar to item2 of ID 1,3. That makes Item1 also similar to 3. Now, item1 of ID=3 is similar to 4. This means that item1 of ID1 is similar to 1,2,3,4 but not to 5.

I have attempted to do an algorithm on this idea. Full code posted below. It does not work. Anybody has enough grey matter to solve this?

<?php
$server = 'localhost:3306';
$username = 'root';
$password = '';
$databasename = "test";
mysql_connect($server, $username, $password) or die('Error connecting to MySQL');
mysql_select_db($databasename);
function getSimilarities ($inddex, $prepared_stack1)  //this function returns the array of item2 given Item1
{
    $link = mysqli_connect('localhost', 'root', '', 'test');
    /* check connection */
    if (! $link) {
        printf("Connect failed: %s\n", mysqli_connect_error());
        exit();
    }
    $stmt = mysqli_prepare($link, 
    "SELECT
                items.itemName
        FROM similarityTable
        INNER JOIN items ON similarityTable.item2 = items.itemID
        WHERE item1 = ?");
    mysqli_stmt_bind_param($stmt, 'i', $inddex);
    mysqli_stmt_execute($stmt);
    $rows = array();
    $row = new stdClass();
    mysqli_stmt_bind_result($stmt, $row);
    while (mysqli_stmt_fetch($stmt)) {
        $rows[] = $row; //contains array of what we want
    }
    printArray($rows);
    return X($rows, $prepared_stack1);
}
function X ($stack, $prepared_stack1) //This is my recursive function
{
    if (empty($stack)) {}else{

        $i = $stack[0];
        echo $i;
        $a = array_pop($stack);
        if (in_array($i, $prepared_stack1)) {
                    echo "smthg";       
        } else {
            array_push($prepared_stack1, $i);
            X(getSimilarities($i), $prepared_stack1);
        }
    }
    return $prepared_stack1;
}

function printArray($array){
    foreach ($array as $value) {
    $new1[] = $value;
}
$query = "(" . implode(",", $new1) . ")";
echo "<b>" . $query . "</b>";
}

/////////////////////////////
$prepared_stack = array();
$myArray = getSimilarities(1, $prepared_stack);

mysql_close();
?>

With the following data:

$data = array(
   array(1, 2), // item1 = 1, item2 = 2
   array(1, 3), // item1 = 1, item2 = 3
   array(2, 1), // etc.
   array(2, 3),
   array(3, 1),
   array(3, 4),
   array(4, 1),
   array(4, 2),
);

If you want to check what items each item is similar to, no need for recursion, simply do:

$similarity = array();
foreach ($data as $item) {
    $id = $item[0];
    if (isset($similarity[$id])) continue;

    $array = array();
    foreach ($data as $sim) {
        list($item1, $item2) = $sim;
        if ($item1 == $id) $current = $item2;
        else if ($item2 == $id) $current = $item1;
        else continue;
        if (!in_array($current, $array)) $array[] = $current;
    }
    $similarity[$id] = $array;
}

This will give you an array with each key being an item ID, with an array:

Array
(
    // item 1 is similar to 2,3,4
    [1] => Array
        (
            [0] => 2
            [1] => 3
            [2] => 4
        )

    // item 2 is similar to 1,3,4
    [2] => Array
        (
            [0] => 1
            [1] => 3
            [2] => 4
        )

    // and so on...
    [3] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 4
        )

    // etc.
    [4] => Array
        (
            [0] => 3
            [1] => 1
            [2] => 2
        )
)