[RESOLVED] How to detect repeated names in a string of names?

A typical string will look like this:

"sam,larry,bill,mary,allen,jim,fred,joe,john"

This string is correct in the sense that no names are repeated

However, on occasions, the string could look like this:

"sam,larry,bill,sam,mary,allen,sam,jim,fred,bill,joe,john"

'sam' is repeated two times and 'bill' is repeated one time . I do not know from one time to the next what names will appear in the string so I cannot check on fixed names.

Is there a simple way to detect if any name appears more than once and remove it from the string if it does?