My first question would be, is there a specific reason why you’re storing these as numbers? If not, then I would suggest using the strings as the storage values.
If you do (and there are a couple of reasons why you might), then you have a couple different options. But the short answer is that there’s no direct way to do that with your choices defined that way.
See the full discussion at How to properly validate a form with radio buttons for some ideas. [Edit: You can probably start with post #9 in that thread.]