Indexing a list with an unique index

Question

I have a list say l = [10,10,20,15,10,20]. I want to assign each unique value a certain \"index\" to get [1,1,2,3,1,2].

This is my code:

Answer 1

For completness, you can also do it eagerly:

from itertools import count

wordid = dict(zip(set(list_), count(1)))

This uses a set to obtain the unique words in list_, pairs each of those unique words with the next value from count() (which counts upwards), and constructs a dictionary from the results.

Original answer, written by nneonneo.