Combine two arrays on a key?

Question

If I wanted to associate items from one array with another array via identical values, eg. items.group_id -> groups.group_id, is there an array function to do that neatly? =)

I have two arrays:

$items = array(
              [0] => array(
                          'group_id' => 456,
                          'item_id' => 123,
                          // Rest of details
                     );
              [1] => array(
                          'group_id' => 457,
                          'item_id' => 124,
                          // Rest of details
                     );
              [2] => array(
                          'group_id' => 457,
                          'item_id' => 125,
                          // Rest of details
                     );
              [3] => array(
                          'group_id' => 456,
                          'item_id' => 126,
                          // Rest of details
                     );
          );

$groups = array(
                [0] => array(
                          'group_id' => 456,
                          'group_name' => 'General'
                     );
                [1] => array(
                          'group_id' => 457,
                          'group_name' => 'Ungeneral'
                     );
          );

And the result I want is:

$groups = array(
                [0] => array(
                          'group_id' => 456,
                          'group_name' => 'General'
                          [0] => array(
                                     'item_id' => 123,
                                     // Rest of details
                                 );
                          [1] => array(
                                     'item_id' => 126,
                                     // Rest of details
                                 );
                     );
                [1] => array(
                          'group_id' => 457,
                          'group_name' => 'Ungeneral'
                          [0] => array(
                                     'item_id' => 124,
                                     // Rest of details
                                 );
                          [1] => array(
                                     'item_id' => 125,
                                     // Rest of details
                                 );
                     );
          );

It's probably not too complicated, but I was hoping there would be a neat solution already implemented in PHP! Many thanks for any help.

Answer 1

I don't think there's a built-in function to do this, but here's some basic code that should handle it:

<?php
    // First, group the items by their group_id
    $items_by_group = array();
    foreach($items as $item) {
        $items_by_group[$item['group_id']][] = $item;
    }

    // Second, go through the groups and if they have any associated items,
    // add them to that group's array.
    foreach($groups as $key => $value) {
        if(isset($items_by_group[$value['group_id']])) {
            foreach($items_by_group[$value['group_id']] as $ikey => $ivalue) {
                unset($ivalue['group_id']);
                $groups[$key][$ikey] = $ivalue;
            }
        }
    }
?>

Note that the above code safely handles cases where you have items with an invalid group id (one for a group that's not defined - it'll ignore those items).

Answer 2

It would be easier if you keyed your groups array by the id instead of numerical indexes

$newArray = array();
foreach($groups as $group) {
  // add the group, and an items array we can append to later.
  $newArray[$group['group_id']] = $group;
  $newArray[$group['group_id']]['items'] = array();  
}
foreach ($items as $item) {
  $newArray[$item['group_id']]['items'][] = $item;
}

Should result in an array like this:

$newArray = array(
   [456] => array(
     'group_id' => 456,
     'group_name' => 'General'
     'items' => array(
       [0] => array(
         'item_id' => 123,
         // Rest of details
       );
       [1] => array(
         'item_id' => 126,
         // Rest of details
         );
       );
     );

Answer 3

I found a solution that works for me, with some help from your solutions chaps.

$links_by_group = array();
     foreach($links as $link) {
      $linked_groups = $this->return_linked_groups($link['link_id']);
   foreach($linked_groups as $group){
    $links_by_group[$group][$link['link_id']] = $link;
   }
     }

Thanks for the help!