Custom Report - unique

Custom Report - unique

I have a custom log coming into EventLog analyzer which as the following:
Timestamp - Username - Success/Failure - AppName

I can create a custom report that tells me the total count of Successful logins but what i really want is a report that shows me the count of unique user Successful logins. I need unique username because the same user could log into tan app multiple times making the success count be much higher than actual unique users.

If this possible with Custom Reports? If so how?