How to allow duplicate keys in php array [duplicate]

Answer 1

As porneL says, the whole point of arrays is that keys are unique.

If you want to reference multiple entries in an array then you need to search the array values.

  $arr=array(
     0=>array('date'=>time(), 'ip'=>'127.0.0.1', url='index.php'),
     1=>array('date'=>time(), 'ip'=>'192.168.1.2', url='index.php'),
     2=>array('date'=>time(), 'ip'=>'127.0.0.1', url='other.php'));
  $matches=retrieve_keys_matching_subkey($arr, 'ip', '127.0.0.1');
  foreach ($matches as $i) {
     print implode(' ', $arr[$i]) . "\n";
  }

  function retrieve_keys_matching_subkey($arr, $subkey, $value)
  {
     $out=array();
     foreach ($arr as $key=>$sub) {
         if ($sub[$subkey]===$value) {
             $out=$key;
         }
     }
     return $out;
  }

This is obviously going to be more efficient if you maintain indexes. The code for this is not trivial.

If you're working with large datasets then I'd strongly recommend using a DBMS to manage the data. If that is not practical, then use a linked list.

Answer 2

You could have a single key that has a value of an array(aka a multi-dimensional array), which would contain all the elements with that given key. An example might be

$countries = array(
  "United States" => array("California", "Texas"),
  "Canada" => array("Ontario", "Quebec")
);

Answer 3

$array[$key][] = $value;

You then access it via:

echo $array[$key][0];
echo $array[$key][1];

Etc.

Note you are creating an array of arrays using this method.