[xsl] duplicate occurances within strings

[Christopher Hansen <chansen1@xxxxxxxxx>]

If i have a variable $thestring   containing the following string:
"Hello, Hello, Hello, test, dog, cat, cat"

Is there a way to use the string-compare function to parse it and
check for duplicates within the string, and then possibly remove those
extra occurrances...resulting in the string "Hello, test, dog, cat"

Thanks
Chris