Merge identical Labels in Pie chart

Hey everyone,
Once again I stubled upon a problem, that I am not able to solve myself.
As you can see in the example file attached, I am trying to make a Piechart. However as you see in the example it doesn't work out the way I want it to. I want the Piechart to show me the combined total of the several retailers. So instead of having the following labels:

AA with value 10
AA with value 12
AA with value 11
BB with value 10
BB with value 13

I want,

AA with value 33
BB with value 23

So i want the piechart to merge the identical labels.

I am wondering if this is possible, and if so, how i can do it