Parsing and ordering a string of dates

I have a random string of dates formatted as such:
"10/5/2009,10/6/2009,10/5/2009,10/10/2009,10/10/2009,10/10/2009,10/4/2009"
I also have an integer variable called count.  When count is equal to 1, I would like to pull all of the unique dates from the string and order them by date.   So count = 1 would return:
"10/4/2009,10/5/2009,10/6/2009,10/10/2009"


When count is > 1, then I would only like to return the dates that appear in the string "count" number of times.  So:
count = 2 would return ----> "10/5/2009,10/10/2009"
count = 3  ------> "10/10/2009"
count = 4 -------> ""


What's the simplest way to do this?

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