Remove duplicates in python list but remember the index

Question

How can I remove duplicates in a list, keep the original order of the items and remember the first index of any item in the list?

For example, removing the duplicates from [1, 1, 2, 3] yields [1, 2, 3] but I need to remember the indices [0, 2, 3].

I am using Python 2.7.

Answer 1

I'd tackle this a little differently and use an OrderedDict and the fact that a lists index method will return the lowest index of an item.

>>> from collections import OrderedDict
>>> lst = [1, 1, 2, 3]
>>> d = OrderedDict((x, lst.index(x)) for x in lst)
>>> d
OrderedDict([(1, 0), (2, 2), (3, 3)]

If you need the list (with its duplicates removed) and the indices separately, you can simply issue:

>>> d.keys()
[1, 2, 3]
>>> d.values()
[0, 2, 3]