Please can you clarify what you mean by "unique"?


Do you want a count of the names which only appear once:

John
John
Peter
Bob

would give a count of 2, because John appears more than once so the unique names are Peter and Bob.



....or do you want a count of distinct names?

John
John
Peter
Bob

Would give a count of 3, because there are 3 distinct names in the list: John, Peter, Bob.