Make a Selection Field Not Show?

Hi guys

Firstly I’ve posted a few questions on here and got swift answers, so massive thanks to all who have been helping me out (if you’re reading this new one :P)

Now I have another:

I’ve made a custom field that is a selection with values 1-9. I’d like an option to make it not visible if it isn’t used. How would I do that?

As far as I can tell, by default the first value is selected and as such the field with the value 1 is displayed on the listings page.

Many thanks