<?php
    $arr = array(
        23 => array(
            'foo' => 'bar',
            'baz' => 'xyz'
        ),
        55 => array(
            'foo' => 'bar',
            'baz' => 'xyz'
        ),
    );

    print_r($arr);

    $serialized = json_encode($arr);
    print_r($serialized);

    $stdclass = json_decode($serialized);
    print_r($stdclass);

    $new_arr = (array) $stdclass;
    print_r($new_arr);

    print_r($new_arr['23']);//error
    print_r($new_arr[23]);//error
?>