var data = {

    status: "ok",

    image_size_list: [

    {

        image_size_id: "22",

        ad_class: "N"

    },

    {

        image_size_id: "19",

        ad_class: "C"

    },

    {

        image_size_id: "24",

        ad_class: "N"

    },

    {

        image_size_id: "15",

        ad_class: "C"

    }]

};

data.image_size_list = $.grep(data.image_size_list,function(item){

    return item.ad_class=='N';

});