PHP merging arrays based on specific array key

Question

I have 2 arrays that I want to merge based on a key's value in array 1. In the below example, I want the game_modes put into the games_list based on a key (id) in games_list.

Array 1 which is pulled from a table full of games:

$games_list = array(
  0 => array(
    'id' => 23,
    'name' => 'Call of Duty: Modern Warfare 3'
    ),
  2 => array(
    'id' => 1,
    'name' => 'Call of Duty: Black Ops'
    )
  );

Array 2 which is pulled from a table full of game modes:

$game_modes = array(
  0 => array(
    'id' => 1,
    'game_id' => 1,
    'description' => 'Capture the Flag'
    ),
  1 => array(
    'id' => 2,
    'game_id' => 1,
    'description => 'Domination'
    ),

  2 => array(
    'id' => 3,
    'game_id' => 23,
    'description' => 'Kill Confirmed'
    )
  );

I would like the result to be:

$games_list = array(
  0 => array(
    'id' => 23,
    'name' => 'Call of Duty: Modern Warfare 3'
    'modes' => array(
        array(
          'id' => 3,
          'game_id' => 23,
          'description' => 'Kill Confirmed'
          )
        )
    ),
  2 => array(
    'id' => 1,
    'name' => 'Call of Duty: Black Ops'
    'modes'=> array(
      0 => array(
        'id' => 1,
        'game_id' => 1,
        'description' => 'Capture the Flag'
        ),
      1 => array(
        'id' => 2,
        'game_id' => 1,
        'description => 'Domination'
        )
      )
    )
  );

Additional info, the site I'm working on currently has 71 games in its database and each game could have some arbitrary number of game modes.

Now, I could easily do a bunch of for loops and avoid this question all together. As of right now I don't have ton of game modes entered into the database but I keep adding more all the time. Over time doing exponentially more loops all the time will eventually make the page load speed come to a crawl.

I have taken the time to place this data into memcache to make future calls quicker avoiding the loop.

I've never been good with array_map as I don't quite understand how it works or if its even the right route.

Answer 1

Don't you think query level solution would be better? The lengthy way would be:

// array:  $game_modes;
// array:  $game_lists;

foreach ($game_modes as $gm=>$modes){
   if (isset($modes['game_id'])){
      foreach ($game_lists as $gl=>$lists){
         if ($lists['id'] == $modes['game_id']){
            $game_lists[$gl]['modes'][] = $modes;
            //break;
         }
      }
   }
}

Output Category : Summary

$query = 'SELECT 
                g.id, g.name_name,
                group_concat(gm.description) as descriptions
          FROM games as g
          LEFT JOIN games_modes as gm
               ON g.id = gm.game_id
          GROUP BY g.id';

Result:

  id |  name                     |  descriptions
------------------------------------------------------------
  1  |  Call of Duty: Black Ops  |  Capture the Flag, Domination

Output Category : Detail

$query = 'SELECT 
                g.id, g.name_name,
                gm.id, gm.description
          FROM games as g
          LEFT JOIN games_modes as gm
               ON g.id = gm.game_id
          ORDER BY g.id';

Result:

  id |  name                     |  id   |  description
----- --------------------------- ------- ------------------
  1  |  Call of Duty: Black Ops  |   1   |  Capture the Flag
  1  |  Call of Duty: Black Ops  |   2   |  Domination

Answer 2

Try this to decrease looping

$cachearray = array();
foreach ($game_modes as $gm=>$modes){
  if(array_key_exists($modes['game_id'],$cachearray))
  {
     $cachearray[$modes['game_id']]['modes'][] = $modes;
  }
  else         
     foreach ($games_list as $gl=>$lists){
        if ($lists['id'] == $modes['game_id']){
           $games_list[$gl]['modes'][] = $modes;
           $cachearray[$lists['id']] = &$games_list[$gl];
           break;
        }
     }
}

print_r($games_list);

It will be easier if you have $games_list array like this

$games_list = array(
   23 => array(
     'id' => 23,
     'name' => 'Call of Duty: Modern Warfare 3'
   ),
   1 => array(
     'id' => 1,
     'name' => 'Call of Duty: Black Ops'
   )
);

And will more powerfull by using query

Answer 3

If you want to user array map, this code should be possible:

$ids = array_map(function($game) { return $game['id']; }, $games_list);
$id_mapping = array_flip($ids);    

foreach($game_modes as $mode) {
    if (array_key_exists($mode['game_id'], $id_mapping)) {
        $games_list[$id_mapping[$mode['game_id']]]['modes'][] = $mode;
    }
}

But I do not know whether this is faster than the two for loops.

Answer 4

try this:

$mode_map = array();
foreach($game_modes as $mode)
{
    $game_id = $mode['game_id'];
    if(!isset($mode_map[$game_id]))
    {
        $mode_map[$game_id] = array();
    }

    $mode_map[$game_id][] = $mode;
}

foreach($games_list as &$game)
{
    $game_id = $game['id'];
    if(isset($mode_map[$game_id]))
    {
        $game['modes'] = $mode_map[$game_id];
    }
}

print_r($games_list);

result:

Array
(
    [0] => Array
        (
            [id] => 23
            [name] => Call of Duty: Modern Warfare 3
            [modes] => Array
                (
                    [0] => Array
                        (
                            [id] => 3
                            [game_id] => 23
                            [description] => Kill Confirmed
                        )

                )

        )

    [2] => Array
        (
            [id] => 1
            [name] => Call of Duty: Black Ops
            [modes] => Array
                (
                    [0] => Array
                        (
                            [id] => 1
                            [game_id] => 1
                            [description] => Capture the Flag
                        )

                    [1] => Array
                        (
                            [id] => 2
                            [game_id] => 1
                            [description] => Domination
                        )

                )

        )

)