Isotope - Sorting whilst IGNORING nth element

I want to do a random sort with Isoptope, whilst ignoring the first item. I have given that item a class (.firstthing).

I found this code on a previous post isotope resort without moving the first element ( excatly what I am looking for ) but unfortunately, it doesn't work with Isotope 2.

Can anyone suggest why ?

getSortData: {
    name: function ($elem) {
        return $elem.data('name');
    },
    myrandom: function ($elem) {
        if($elem.hasClass('menu')) {
             return -1;   
        }
        return Math.random();
    }
}