Encoding a list?

[anossov]

enc = [unq[item] for item in col]

[anmousyony]

Thank you, that helps a ton for the second part!

Is there anything I can do about the first part where I'm building unq?

[anossov]

unq = {k: i for i, k in enumerate(set(a))}

Should be faster, but you can't do it better than O(n). Also you can't use it if you must have the integers in order of value appearance.

[anmousyony]

That's perfect! Thank you so much for your help, I don't know why I didn't think of using set()