Assign a number to each unique value in a list

Question

I have a list of strings. I want to assign a unique number to each string (the exact number is not important), and create a list of the same length using these numbers, in o

Answer 1

If you have k different values, this maps them to integers 0 to k-1 in order of first appearance:

>>> names = ['b', 'c', 'd', 'c', 'b', 'a', 'b']
>>> tmp = {}
>>> [tmp.setdefault(name, len(tmp)) for name in names]
[0, 1, 2, 1, 0, 3, 0]