Change data type by dragging in Data / Recommendations panel

Today, one can change "classification" of an attribute by dragging it from one part of the data panel to another. It's a bit unclear what this means - i.e. if I decide I want customer age to be treated as a category, I can drag it to the Categories section, but nothing really happens as a result except that it appears in a different area in the data panel. I might expect that it will now be treated in graphs as a string, same with things like zip code, I might want it to behave as a category. I think there are implied data types within the categories, and we could support changing them through drag and drop rather than picking from a list in the dialog (or in addition to this method)