I am constructing a form in Angularjs. Based on the value of a radio button in the form, I want to change the number of options in another set of radio buttons. This is very easy using direct DOM manipulation, but I cannot see how to do it in angular. 

I imagine that the solution lies in making the second set of radio buttons a directive, but I don't see how to communicate the state of the first set of radio buttons to the directive.