How can I create a random, circular partner assignment?

Question

I'm allowing users to register on my site for a 'game'; as is normal, they all receive unique IDs. At a given point in time, registration will cease. At that time, I would like to run code to assign partners, but not pairs.

So, if I had the following:

+--------+-------+
| user_id | partner |
+--------+-------+
| 1 | |
| 3 | |
| 7 | |
| 11 | |
| 12 | |
| 18 | |
+--------+-------+

what would I do to end up with something like this:

+--------+--------+
| user_id | partnr |
+--------+--------+
| 1 | 7 |
| 3 | 12 |
| 7 | 18 |
| 11 | 1 |
| 12 | 11 |
| 18 | 3 |
+--------+--------+

1,7,18,3,12,11;1,7,18,3,12,11

$query = "SELECT users FROM tabl";
$result = mysql_query ($query)
    or die ("Query '$query' failed with error message: \"" . mysql_error () . '"');

while ($row = mysql_fetch_array($result)) {
    $users[] = $row[0];
}

$current = end($users);
$partners = array();
foreach ($users as $user)
{
        $partners[$user] = $current;
        $current = $user;
}
print_r($partners);

This seems to work, thanks to Sjoerd, but I need to write it back to the partner column.

Answer 1

• Retrieve the list of users.
• Shuffle this list (optional).
• Assign each user the next one in the list as partner, where the last user gets the first user as partner.

Code to loop through the array and assign partners:

$users = array('john', 'jack', 'jones', 'joelle', 'jesica');

$current = end($users);
$partners = array();
foreach ($users as $user)
{
        $partners[$user] = $current;
        $current = $user;
}
print_r($partners);

Answer 2

Sorry if there are mistakes ... I havn't been coding PHP for a long time ...

$i = rand(1, length($players) - 1)
for ($p = 0; $p < length($players); $p++)
{
    $partners[$p] = $players[$i];
    if (++$i > length($players))
    {
        $i = 0;
    }
}

Answer 3

• Select out the ids in a random order
• Have two copies of the resulting array
• Pop one element of the end of one array and push it on the top (ie offset the entire array by one)

• Update the table as user_id,partner_id pairs

  $results = mysql_query("SELECT user_ids FROM -tablename- ORDER BY RAND()");
  
  
  $user_ids = array();
  $partner_ids = array();
  
  
  while($row = mysql_fetch_array($results))
  {
      $user_ids[] = $row['user_id'];
      $partner_ids[] = $rowp['user_id'];
  }
  
  
  $lastPartnerId = array_pop($partner_ids);
  array_unshift($partner_ids,$lastPartnerId);
  
  
  for($i=0;$i<count($user_ids);$i++)
  {
      mysql_query("UPDATE -tablename- SET partner_id = {$partner_ids[$i]} WHERE user_id = {$user_ids[$i]}");
  }