Rank within sub group

[rainstorm90]

I have the following table which I need to rank each person by their group. I will need to create a KPI object with the rank for the person selected. For example if Leo is selected, even if his rank is 3, the rank within his group should be 2. 

I have already created a variable to get the current group for the person selected. Can someone show me how can I get the rank within sub group? Thank you!