onCollectValues

fires after datatable has collected options

void onCollectValues(string id,object data){ ... };

id	string	the id of the column
data	object	the object that contains options

datatable.attachEvent("onCollectValues", function(id, data){
    if (data.values[0].value == "")
    data.values[0].value = "Select something";
});

If you have not checked yet, be sure to visit site of our main product Webix javascript ui components library and page of datatable html product.