通过没有外部依赖的指令对AngularJS组进行分组

I'm new to Angular and would like to learn the best way to handle a problem. My goal is to have a reusable means to create group by headers. I created a solution which works, but I think this should be a directive instead of a scope function within my controller, but I'm not sure how to accomplish this, or if a directive is even the right way to go. Any inputs would be greatly appreciated.I'm new to Angular and would like to learn the