Get the Max Value of a property for each user

I have an event that fires each time a user visits my page that indicates their progress on a specific set of tasks (ie have they completed 1 task, 2 tasks, etc). This has created some problems for me since I am dealing with a duplicate data issue.

I want to create a bar chart where the x axis would be the number of tasks completed, and y axis the number of users who completed that number of tasks, but I would like each user to only appear once, whatever their max number of tasks is (as this is actually the number of tasks the user has completed). Is this something I can do with the formula option?