Data aggregation for chart

Content

Hello,

I have a Business object with Task's name and Hours.
I try to make a simple pie chart where I want to see the Task name and Total hours. 
I can't find any aggregation functions to make it on the fly based on BO data.
Also, I can't make another BO with a special aggregation field because I want to make a dynamic filter for data from the original BO and the system provides only a constant filter.
I have already made JS function to aggregate data in the object with a needed structure but the chart doesn't want to work with it.