Cascading Dropdowns

Is there a way to do the cascading drop downs without having to have multiple columns?

I know there is away to display different fields on a form, but I only want to restrict the items displayed in a single dropdown based off a response in a different column. For example: If you have a Category dropdown & a SubCategory dropdown, I want the available options in the subcategory dropdown to be limited based off of the selection in the Category dropdown. I don't want to have multiple columns.

Was thinking there might be some kind of formula that could do this?