Are you using v9, or have access to v9?
I ask because LOD calculations (which are only available from v9) may help
Your question, reminded me of Number 10 >> Top 15 LOD Expressions | Tableau Software
It will require some changing, but may give you what you need.
If not, or your still stuck, some (fake) sample data to show your situation would be helpful
I have v9, but I think my question is a little bit different from the case
in the article though..
I have attached mock up data, consisting of just customer id and date of
Thus the result I am looking would in this case be 66,7% in 2011 and 50 %
Mock up.xlsx 8.2 KB
Thanks for the sample data, I see what you mean now.
I will take a look for you, I'm sure its possible.