When should we use Radix sort?

Question

It seems Radix sort has a very good average case performance, i.e. O(kN): http://en.wikipedia.org/wiki/Radix_sort

Yet it seems like most people are still using

Answer 1

Radix sort takes O(k*n) time. But you have to ask what is K. K is the "number of digits" (a bit simplistic but basically something like that).

So, how many digits do you have? Quite answer, more than log(n) (log using the "digit size" as base) which makes the Radix algorithm O(n log n).

Why is that? If you have less than log(n) digits, then you have less than n possible numbers. Hence you can simply use "count sort" which takes O(n) time (just count how many of each number you have). So I assume you have more than k>log(n) digits...

That's why people don't use Radix sort that much. Although there are cases where it's worthwhile using it, in most cases quick sort is much better.