ANSWER:

@Jeff, you my want something like this:

var $products_backup = $('#products_backup');
$('form').on('click', '.category', function() 
    var $category = $(this);
    if (!$category.is(":checked")) 
        return;
    
    var escaped_category = $category.val().replace(/([ #;&,.+*~':"!^$[]()=>|/@])/g, '\$1');
    var $options = $products_backup.find("optgroup[label='" + escaped_category + "']").find("option");
    //$('#products').empty().append('Select an item').append($options.clone()).val("");
    $category.closest('fieldset').find('.products').empty().append('Select an item').append($options.clone()).val("");
});

See :

• DEMO (original)
• DEMO (update)

As you will see I guessed that the .category elements might be radio buttons. If they are not, then the code will need to be adjusted to a greater or lesser extent.

by Beetroot-Beetroot from http://stackoverflow.com/questions/10565773