How to group table list by one to many relationship field

I am trying to to group change_type which is a field in table transfers. An employee can has many transfers, each transfer change_type can be new-join, change-role, exit. I want to list only 1 line for each employee. So I clone employeeResource and modify it query to have child transfers record. I would like to groupw by change_type , so that records of change_type will be listed together. I try to put $table->groups['transfers.change_type]) , it won't work. Please advise how I could achive this. #groups