I have a sheet of data dumped from a SQL query that is used to populate a
report.

Lets say that the data looks like this

A|B|C
1| x |y| Joe
2| r | k| John
3| y| x| Joe

I need a function that can look at the report, and where b1 = a3 and a1=b3,
then c1 is changed from joe to duplicate.

This way, Joe is only counted once, since for my purposes, rows 1 and 3 are
duplicate entries.

Thanks