graphing derived data

[jeffminder]

Have table containing items and the number purchased for each line item as shown below. Would like to have a graph showing all unique items and a total count.

Do I need to create a slice to build a derived table and then graph as normal, or is there another/better way to go about this?  Considered a stacked graph, but actually need the summary data for another purpose as well. 

Existing Table with line items & associated usage count
a,3
b,2
a,6
b,2

Summary Data: Desired view with frequency count for each item (derived)
A: 9
B: 4

[Marc_Dillon]

Create an "Items" table. Give it a virtual column to sum up the line items. Chart that new table & VC.