How to list categories and subcategories in JSON format?

Question

I need to integrate this plugin with my WordPress site, and the categories must be in this format:

 "Option 1": {"Suboption":200},
 "Option 2": {"Suboption 2": {"Subsub 1":201, "Subsub 2":202},
                "Suboption 3": {"Subsub 3":203, "Subsub 4":204, "Subsub 5":205}
               }

How can I get that?
I tried the options of the json-api.

And this is the walker:

class MyWalker extends Walker_Category {
    var $tree_type = 'category';

    var $db_fields = array ('parent' => 'parent', 'id' => 'term_id');

    function start_lvl( &$output, $depth, $args = array() ) {
        if ( 'list' != $args['style'] )
            return;

        $indent = str_repeat("\t", $depth);
        $output .= "$indent:{";
    }

    function end_lvl( &$output, $depth, $args = array() ) {
        if ( 'list' != $args['style'] )
            return;

        $indent = str_repeat("\t", $depth);
        $output .= "$indent}\n";
    }

    function start_el($output, $category, $depth , $args = array() ) {
        extract($args);
        $cat_name = esc_attr( $category->name );
        $cat_name = apply_filters( 'list_cats', $cat_name, $category );
        $output .= '"' . $cat_name.'=>'.$depth . '",';
    }

    function end_el($output, $page, $depth = 0, $args = array() ) {
        if ( 'list' != $args['style'] )
            return;

        $output .= "\n";
    }
}

Answer 1

Here is a fast example using get_categories instead of a plugin or the walker class, maybe it will help you in the right direction, it will list all children of a parent category in json format. As brasofilo mentions since you require a specific format you will want to build a custom array.

// let's get the bare minimum going
$args = array(
    'type'                     => 'post',
    'child_of'                 =>  20, //change this, hardcoded as example
    'taxonomy'                 =>  'category'
);

$categories = get_categories( $args );
$json = json_encode($categories);

var_dump($json); //do what you want