Get reference of a specific item via sequence from a multi-dimension array.

array_item.php

<?php

/**
* Sample Array
*/
$arr = array(
  'key_1' => array(
    'key_1_1'  => array(
      'key_1_1_1'  => array(
        'key_1_1_1_1'  => array(
          'data'
        )
      )
    )
  ),
  'key_2' => array(
    'key_2_1'  => array(
      'key_2_1_1'  => array(
        'key_2_1_1_1'  => array(
          'data'
        )
      )
    )
  )
);

// A small recursion function to get that reference
function &getRef( &$master, $seg, $index)
{
  if( $index == count($seg) ) {
    return $master;
  }
  if( !isset($master[ $seg[$index]]) )
    return false;
  return getRef( $master[ $seg[$index]], $seg, $index+1);
}

$item = &getRef( $arr, array('key_1','key_1_1', 'key_1_1_1'), 0);
$item2 = &getRef( $arr, array( 'key_2', 'key_2_1'), 0);

// Now u can add item
$item['new_key'] = 'Hooooray !!';
$item2['another_new_key'] = 'YUP';

print_r( $arr);