How to get count of events based on unique visitor in piwik


Piwik tracks data based on visits. can i also get count based on unique visitors. like visitor clicking on a button in two different visits , i want the count as 1 because it is based on unique visitor level.
2. where to change the definition of visitor and visit in piwik,



I would also like to know if there is such a feature or how to generate such reports.