PHP multidimensional array search by value

If you are using (PHP 5 >= 5.5.0) you don't have to write your own function to do this, just write this line and it's done.

If you want just one result:

$key = array_search(40489, array_column($userdb, 'uid'));

For multiple results

$keys = array_keys(array_column($userdb, 'uid'), 40489);

In case you have an associative array as pointed in the comments you could make it with:

$keys = array_keys(array_combine(array_keys($userdb), array_column($userdb, 'uid')),40489);

If you are using PHP < 5.5.0, you can use this backport, thanks ramsey!

Update: I've been making some simple benchmarks and the multiple results form seems to be the fastest one, even faster than the Jakub custom function!

function searchForId($id, $array) {
   foreach ($array as $key => $val) {
       if ($val['uid'] === $id) {
           return $key;
       }
   }
   return null;
}

This will work. You should call it like this:

$id = searchForId('100', $userdb);

It is important to know that if you are using === operator compared types have to be exactly same, in this example you have to search string or just use == instead ===.

Based on angoru answer. In later versions of PHP (>= 5.5.0) you can use one-liner.

$key = array_search('100', array_column($userdb, 'uid'));

Here is documentation: http://php.net/manual/en/function.array-column.php.

In later versions of PHP (>= 5.5.0) you can use this one-liner:

$key = array_search('100', array_column($userdb, 'uid'));