How to access others variable inside of array_walk?

    $sample = [
        ['id'=>2, 'name' => 'one'],
        ['id'=>3, 'name' => 'two'],
    ];
    $id = 2;
    function test_alter(&$item1, $key, $prefix)
    {   
    if($item1['id'] == $prefix){
        $item1['name'] =  $item1['name']." modified";
        }            
    }
    array_walk($sample, 'test_alter', $id);
    echo "<pre>";
    print_r($sample);

Output

Array(
    [0] => Array
        (
            [id] => 2
            [name] => one modified
        )
    [1] => Array
        (
            [id] => 3
            [name] => two
        )
)

The scope of a variable is the context within which it is defined. For the most part all PHP variables only have a single scope. This single scope spans included and required files as well.

Using global keyword outside a function is not an error. It can be used if the file is included from inside a function.

$id = 10;
array_walk($profile_items, function(&$a) {
global $id;
    $count = $this->db->where('profile_item_id', $a['id'])->where('cover_type_id', $id)->count_all_results('cover_type_profile_items_link');
    $a['selected'] = $id;
});
echo "<pre>";
print_r($profile_items).exit;

add parameter to use() like this, if you want to modify the $id, trans it by reference with &, otherwise by value.

array_walk($value, function($v, $k) use ($id){});

or

array_walk($value, function($v, $k) use (&$id){});

You can pass $id to your function array_walk using use like :

  $id = 10;
  array_walk($profile_items, function(&$a) use($id){
  $count = $this->db->where('profile_item_id', $a['id'])->where('cover_type_id', $id)->count_all_results('cover_type_profile_items_link');
 $a['selected'] = $id;
});
echo "<pre>";
 print_r($profile_items).exit;