Fast sort algorithms for arrays with mostly duplicated elements?

Question

What are efficient ways to sort arrays that have mostly a small set of duplicated elements? That is, a list like:

{ 10, 10, 55, 10, 999, 8851243, 10, 55, 55, 55, 10

Answer 1

IMO Pidgeonhole sort is a good example for such data.

I will clarify a bit: if you know that quantity of the unique elements in the array is reasonable and you know that there are a lot of duplicates I would think of implementing something like counting sort but make list of "buckets" dynamic. After the first pass you will get rid of duplicates, then sort array without duplicates with some good sorting algorithm and then restore sorted array in a way like counting sort does.