Fastest way to get sorted unique list in python?

Question

What is the fasted way to get a sorted, unique list in python? (I have a list of hashable things, and want to have something I can iterate over - doesn\'t matter whether the lis

Answer 1

Maybe this is not the answer you are searching for, but anyway, you should take this into your consideration.

Basically, you have 2 operations on a list:

unique_list = set(your_list)       # O(n) complexity
sorted_list = sorted(unique_list)  # O(nlogn) complexity

Now, you say "it seems to me that first checking for uniqueness and then sorting is wasteful", and you are right. But, how bad really is that redundant step? Take n = 1000000:

# sorted(set(a_list))
O(n) => 1000000
o(nlogn) => 1000000 * 20 = 20000000
Total => 21000000

# Your fastest way
O(nlogn) => 20000000
Total: 20000000

Speed gain: (1 - 20000000/21000000) * 100 = 4.76 %

For n = 5000000, speed gain: ~1.6 %

Now, is that optimization worth it?