<?php

     function group_by_key ($array) {
       $result = array();
       foreach ($array as $sub) {
         foreach ($sub as $k => $v) {
           $result[$k][] = $v;
         }
       }
       return $result;
     }

     $array = array (
       0 => array (
         'WS' => array (
           'id' => 2,
           'name' => 'hello'
         )
       ), 
       1 => array (
         'SS' => array(
           'id' => 1,
           'name' => 'hello2'
         )
       ),
       2 => array (
         'WS' => array (
           'id' => 5,
           'name' => 'helloAGAIN'
         )
       )
     );

     print_r(group_by_key($array));

Array
(
    [WS] => Array
        (
            [0] => Array
                (
                    [id] => 2
                    [name] => hello
                )

            [1] => Array
                (
                    [id] => 5
                    [name] => helloAGAIN
                )

        )

    [SS] => Array
        (
            [0] => Array
                (
                    [id] => 1
                    [name] => hello2
                )

        )

)