Let me make sure I'm interpreting exactly what you're asking - Based upon the CustomerID, you want to be able to generate a number for the frequency of that user? Are you trying to have something along the lines of Customer X and how many times they purchased, Customer Y and how many times they purchased, etc.?
Thanks for replay.
I don't have a dimensions called purchaser frequency at customer level.
What I am trying to do is to see wherther we can use raw data to do this kind of analysis in Tableau.
another reason I don't want to pre-calcuate the purchaser frequency at customer level is because this frequency can be any period. it's very hard to calculate all periods combination.
If the purchaser frequency is the issue, you can calculate fields based upon Distinct numbers such as customer ID, thus giving you multiple data values on the Tableau side based upon 1 distinct field. As such, yes, I would say what you are trying to accomplish is possible in tableau provided you are willing to uses extracts and table calculations.
I recently authored a topic which I believe, while not your specific problem, may give you some idea of whether or not you can accomplish/how to accomplish what you are asking. If you are interested, there is a workbook and screenshot attached as a sample. See the article at: http://community.tableau.com/thread/117077.