Mootools filtering

Question

How can I filter (replace empty() function) in my div container using mootools? Question here: How can I replace my code below to:

1. Remove from container(<div id="fc_contacts" class="fc_contacts">) blocks with id="fc_ID" which not exist in JSON string
2. Add new block to container(<div id="fc_contacts" class="fc_contacts">) if if doesn't exist in container
3. If friend_id is in container and in the JSON - do nothing.

Check in the code please.

My code below:

{"users": [{"friend_id":"62","name":"admin","username":"admin"},{"friend_id":"66","name":"other","username":"other"}],"total": "1","total_online":"1"}

    onSuccess: function(f){ /*Periodical function*/                                 
        for(var i=0; i< f.users.length;i++){
            if(f.users[i].friend_id){                                                           
                friends.push(chat.render('add_contact',f.users[i]));
            } 
        }

        /*  Question here: How can I replace my code below to:
            1. Remove from container(<div id="fc_contacts" class="fc_contacts">) blocks with id="fc_ID" which not exist in JSON string
            2. Add new block to container(<div id="fc_contacts" class="fc_contacts">) if if doesn't exist in container 
            3. If friend_id is in container and in the JSON - do nothing.       
        */

        $('fc_contacts').empty(); /*Replace this*/
        $('fc_contacts').addContacts(friends.join(''), 'bottom');   /*ELSE - ADD NEW*/ //el.empty();

    }


    Element.implement({
        addContacts: function(html,where){
            return this.grab(new Element('<div>', {
                'html': html,
                'class': 'fc_contacts_container'
            }),where);          
        }
    });


    <div id="fc_contacts" class="fc_contacts">
        <div class="fc_contacts_container">
            <div class="fc_contact clear_fix" id="fc_62">
                <!--OTHER HTML!->
            </div>
        </div>
        <div class="fc_contacts_container">
            <div class="fc_contact clear_fix" id="fc_66">
                <!--OTHER HTML!->
            </div>
        </div>
    </div>

Thanks!

P.S

It works with JQUERY (But I need it to be compatible with Mootools):

var ids = [];   
for(var i=0; i<f.users.length;i++){                             
ids.push('fc-' + f.users[i].friend_id);
}
jQuery('#fc_contacts').append(friends.join('')).children().filter(function(i) {
    return ids.indexOf(this.id) === -1;
}).remove();

Answer 1

user889349, here is how i would do it :

$('fc_contacts').getElements("div.fc_contact").each(function(c) {
    var id = c.get("id");
    if(!f.users.some(function(u){return id == 'fc_'+u.friend_id;}))
        c.destroy();
});
f.users.each(function(u) {
    if(!$('fc_'+u.friend_id))
        $('fc_contacts').addContacts(chat.render('add_contact',u), 'bottom');
});

in two steps…