Want to create a pie chart using expression totals from straight table

[#1]

In the attached file, I used expressions to flag whether clients have been clients for the past 3yrs/2/1. I'm wondering if it's possible to:

a) create a field and map the flag (3/2/1) to the customers

b) create a pie chart using the flag as a dimension and the aggregated sales of 3, then 2, then 1 as the expression.

Thank you in advance.