Question

I have the following array (example, real one is larger)

Array
(
    [0] => Array
        (
            [984ab6aebd2777ff914e3e0170699c11] => Array
                (
                  [id] => 984ab6aebd2777ff914e3e0170699c11
                  [message] => Test1

        )

    [1] => Array
        (
            [ca403872d513404291e914f0cad140de] => Array
                (
                  [id] => ca403872d513404291e914f0cad140de
                  [message] => Test2
                )

        )

    [2] => Array
        (
            [ca403872d513404291e914f0cad140de] => Array
                (
                  [id] => ca403872d513404291e914f0cad140de
                  [message] => Test3

        )

    [3] => Array
        (
            [ca403872d513404291e914f0cad140de] => Array
                (
                  [id] => ca403872d513404291e914f0cad140de
                  [message] => Test4
                )

        )
)

Now I want to somehow “access” the subarray with a given id, e.g. access the subarray with ID 984ab6aebd2777ff914e3e0170699c11 and then proceed to use this array in a foreach like this..

foreach ($array_with_specific_id as $event) {
    echo $event['message'];
}

Is this possible?

Edit:

DB code to produce array in my model:

  public function get_event_timeline($id)
   {
     $data = array();
      foreach ($id as $result) {
          $query = $this->db->query("SELECT * FROM event_timeline WHERE id = ?", array($result['id']));
          foreach ($query->result_array() as $row)
          {
               array_push($data, array($row['id'] => $row));
          }
      }

      return $data;
   }

Answer 1

When populating your array from the database you can cerate an additional $index array like the following scheme:

$index = array (
    '984ab6aebd2777ff914e3e0170699c11' => ReferenceToElementInData,
    'ca403872d513404291e914f0cad140de' => ReferenceToElementInData,
    // ...
)

This can give you quick access to the elements via their id without an additional foreach loop. Of course it will need additional memory, but this should be ok as you will only save refrences to the original data. However, test it.

Here comes an example:

public function get_event_timeline($id)
{
  $data = array();

  // create an additional index array
  $index = array();

  // counter 
  $c=0;

  foreach ($id as $result) {
      $query = $this->db->query("SELECT * FROM event_timeline WHERE id = ?", array($result['id']));

      // every entry in the index is an array with references to entries in $data
      $index[$result['id']] = array();

      foreach ($query->result_array() as $row)
      {
           array_push($data, array($row['id'] => $row));
           // create an entry in the current index
           $index[$row['id']][] = &$data[$c];
           $c++;
      }
  }

  return array (
      'data' => $data,
      'index' => $index
  );
}

Now you can access the elements via the index array without an additional foreach loop:

$entry = $index['984ab6aebd2777ff914e3e0170699c11'][0];

If there are multiple results per $id (as you mentioned in the comments you can access them using index greater then zero:

$entry = $index['984ab6aebd2777ff914e3e0170699c11'][1];
$entry = $index['984ab6aebd2777ff914e3e0170699c11'][2];

You can get the count of items per $id by calling

$number = count($index['984ab6aebd2777ff914e3e0170699c11']);

That’s much the same like indexes that where used in databases to speed up queries.