making sure a generated array key is unique

Question

I have this array

$array = array(
    "one" => "bar",
    "two"    => "21",
    "three"    => "22",
    "four"    => "25",
    "five" => array(
         "xxxxxxxxxxxxxxxxxx" => array(
             "ar1" => "food",
             "ar2" => "dr",
             "ar3" => "ch",
             "ar4" => "ju"
         ),
        "yyyyyyyyyyyyyyyyyyyy" => array(
             "ar1" => "food",
             "ar2" => "dr",
             "ar3" => "ch",
             "ar4" => "ju"
         )),
    "six" => "et",
    "seven" => "op",
    "eight" => "hjs",
    "nine" => array(
         "1" => array(
             "ar5" => "food",
             "ar87" => "dr",
             "ar21" => "ch",
             "ar443" => "ju"
         ),
         "2" => array(
             "73" => "food",
             "82" => "dr",
             "90" => "ch",
             "2123" => "ju"
         )),
    "ten" => "bar",
    "eleven" => "bar",
    "twelve" => "bar"
);

and i want to make sure that every new array added must have a unique array key.To do that,i first get all the keys of the others i.e $array['nine'] in my case then run a function until a unique key is found.

To add a new array to $array['nine'] and to get all the keys in nine

$keyedd = array_keys($array['nine']);

$appendThis[''.unique_array_key($keyedd).''] = array(
             "73" => "nitrous",
             "82" => "oxide",
             "90" => "laughing",
             "2123" => "gas"
             );

$array['nine'] =  $array['nine'] + $appendThis;

This is the function

function unique_array_key($the_array){
$r = rand();
if (array_key_exists("$r", $the_array)) {
    unique_array_key($the_array);
}
else if(!array_key_exists("$r", $the_array)) {
    echo $r;
}
}

Once i run this

[nine] => Array
        (
            [1] => Array
                (
                    [ar5] => food
                    [ar87] => dr
                    [ar21] => ch
                    [ar443] => ju
                )

            [2] => Array
                (
                    [73] => food
                    [82] => dr
                    [90] => ch
                    [2123] => ju
                )

            [] => Array
                (
                    [73] => nitrous
                    [82] => oxide
                    [90] => laughing
                    [2123] => gas
                )

        )

the newly added array do not have an array key.However,unique_array_key($keyedd); on its own seems to work fine.Why is the function not adding a unique key?.

Answer 1

I would prefer internal PHP functionality for unique key generation:

$appendThis[uniqid()] = array(
    "73"   => "nitrous",
    "82"   => "oxide",
    "90"   => "laughing",
    "2123" => "gas"
);

No needs to reinvent wheel. Check documentation for uniqid() function.

Update
If you have web-cluster running your application simultaneously on several hosts with shared data storage, and more than 10000 ID generations in one second just use:

uniqid(php_uname('n'), true)

for ID generation. Your solution with rand() ID generation have only mt_getrandmax() variations. Usually it is 2147483647. With 10000 ID generations in sec you'll get exceed available ID's limit in 2.4 days, and your code will run in infinite loop because every key check in array will have true result and recursively call new ID generation again and again.

Also, your solution make the application performance dependent on data amount. Than more data you'll have, than higher chance of additional loops for ID generation because of duplicates. For example, if you'll have N already stored arrays with unique ID's, there is a chance next ID will be generated for N+1 cycles.

If your project not highload, will be enough uniqid() or uniqid('', true) if you need additional entropy.

Answer 2

Replace echo $r; with return $r;:

function unique_array_key($the_array){
   $r = rand();
   if (array_key_exists("$r", $the_array)) {
     return unique_array_key($the_array);
   } else {
     return $r;
   }
}

}