Retrieve subarray of array by key value

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;
   }

it requires two forach using main array, and for that example yes you can. — user1646111
– user1646111, Commented Feb 5, 2013 at 16:35

hek2mgl · Accepted Answer · 2013-02-05 17:27:25Z

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.

edited Feb 5, 2013 at 17:27

answered Feb 5, 2013 at 16:44

hek2mgl

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4 Comments

edwardmp Over a year ago

This seems to work thanks.. I have got a little other issue though. The Query could produce multiple results per flight_id.. Only one works right now. Any idea how to fix that? I should loop trough the multiple events for each ID

hek2mgl Over a year ago

I'm not sure if understood you correctly.. I such cases you expect that my code : $entry = $index[$flight_id] will return both records, yes?

edwardmp Over a year ago

Yes, exactly! But it could be more than two records

edwardmp Over a year ago

Brilliant! With some minor changes working perfectly now. Thanks so much!

Julio · Accepted Answer · 2013-02-05 16:37:04Z

0

I'd probably just get rid of the containing array as it seems unnecessary. However, you could do something like:

function get_message($specific_id, $arrays) {
    foreach($arrays as $array) {
        if(in_array($specific_id, $array)) {
            return $array['message'];
        }
    }
}

I haven't had a chance to test this, but it should work.

answered Feb 5, 2013 at 16:37

Julio

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1 Comment

edwardmp Over a year ago

What is the best way to get rid of the containing array? Check my post to see the model code

Marcin · Accepted Answer · 2013-02-05 16:44:12Z

0

function doTheJob($inputArray, $lookingFor) {

    foreach ($inputArray as $subArray) {
        foreach ($subArray as $subKey => $innerArray) {
            if ($subKey == $lookingFor) {
                return $innerArray;
            }
        }
    }
    return NULL;
}

Alternatively, you can use array_filter instead of outer foreach.

answered Feb 5, 2013 at 16:44

Marcin

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