How to do grouping for data visualization in OAC

we had a requirement to develop a workbook on Business unit wise Average age of employees. For that i have made a connection with Oracle Analytics and then i have created a dataset by considering two subject areas. i.e., Worker assignment real time for Business units and Person real time for DOB of employees. and i have joined both the data sets with personid column. When i try to visualize the data in workbook, it resulting personwise data but not with BU wise.