Python removing repetitions using list(set(v)) changes array order

Question

I've the following array with multiple repetitions and I want to remove them mantaining the order.

v = ['maier', 'tapa pure', 'embega', 'maier', 'tapa pure', 'embega', 'maier', 'tapa pure', 'embega', 'maier', 'tapa pure', 'embega', 'maier', 'tapa pure', 'embega', 'maier', 'tapa pure', 'embega', 'maier', 'tapa pure', 'embega', 'maier', 'tapa pure', 'embega']

I use list(set(v)) and I get the following output:
['embega', 'maier', 'tapa pure']

What I want to have is to remove the repetition, but maintain the original order:
['maier', 'tapa pure', 'embega']

I cant use v[:3] because the repetitions length is variable.

How can I do it?

Thanks in advance.

score 5 · Answer 1 · answered Feb 28 '14 at 10:42

5

You should be using collections.OrderedDict's fromkeys function, like this

from collections import OrderedDict
print OrderedDict.fromkeys(v).keys()
# ['maier', 'tapa pure', 'embega']

answered Feb 28 '14 at 10:42

thefourtheye

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score 3 · Accepted Answer · answered Feb 28 '14 at 10:42

3

seen_items = set()
w = [] 
for item in v:
    if item not in seen_items:
        w.append(item)
        seen_items.add(item)

answered Feb 28 '14 at 10:42

Jayanth Koushik

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1

the way you do it, the set() is unnecessary. seen_items could be a list too and nothing would change. Actually you could write `if item not in w; w.append(item)` – rantanplan Feb 28 '14 at 10:44
4

Search in a list would be O(n) compared to O(1) for a set. – Jayanth Koushik Feb 28 '14 at 10:45
ok in that you're correct. – rantanplan Feb 28 '14 at 10:46

Python removing repetitions using list(set(v)) changes array order

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