Python list giving different order

Question

why is the order different in the below.

Edit:

Also what is the correct solution for this,i.e, remove duplicates and preserve order

def rt(s):
  s = list(s)
  print s
  print set(s)

print rt('abc')

Output

['a', 'b', 'c']
set(['a', 'c', 'b'])
None

What sort of solution are you looking for? Do you want to have an ordered set? — Zibi, Aug 20 '15 at 13:16
possible duplicate of [How do you remove duplicates from a list in Python whilst preserving order?](http://stackoverflow.com/questions/480214/how-do-you-remove-duplicates-from-a-list-in-python-whilst-preserving-order) — juanchopanza, Aug 20 '15 at 13:38

score 3 · Answer 1 · answered Aug 20 '15 at 13:13

3

Because set isn't an ordered structures. Internally, a set uses a hash table, and there is no restriction that the hashed function maintain the ordering of its arguments.

answered Aug 20 '15 at 13:13

juanchopanza

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@Rajeev A solution requires a problem. What is the problem? After your edit, the question is quite unclear. – juanchopanza Aug 20 '15 at 13:17
@Rajeev Is the input list always sorted? – juanchopanza Aug 20 '15 at 13:29

hspandher · Answer 2 · 2015-08-20T14:19:32.977

3

You can use OrderedSet, which serves your purpose.

Documentation

pip install orderedset


from orderedset import OrderedSet

def rt(s):
    s = list(s)
    print s
    print OrderedSet(s)

print rt('abc')

edited Aug 20 '15 at 14:19

answered Aug 20 '15 at 13:18

hspandher

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The most correct answer is the most downvoted too :) – Andrea Corbellini Aug 20 '15 at 13:29
Agreed. But the function would be more useful if it returned something. – juanchopanza Aug 20 '15 at 13:37
1

@juanchopanza I wrote the same function user asked the question with, it was just to withdraw analogy – hspandher Aug 20 '15 at 14:06

Peter Wood · Accepted Answer · 2015-08-20T14:06:16.420

1

def unique(sequence):
    seen = set()
    for e in sequence:
        if e not in seen:
            seen.add(e)
            yield e

Usage:

>>> ''.join(unique('aaabbddeffg'))
'abdefg'

See the itertools recipes for a slightly more efficient version, called unique_everseen.

edited Aug 20 '15 at 14:06

answered Aug 20 '15 at 13:29

Peter Wood

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score 0 · Answer 4 · edited May 23 '17 at 12:01

0

If you want to have a set with preserved order, you can look here for various solutions: Why are there no containers sorted by insertion order in Python's standard libraries?

If you want to eliminate the duplicates, and sort it you can use:

s = sorted(set(s))

From most inner call:

set - removes duplicates

sorted - sorts it in ascending order.

Also, you're missing a return statement, thus last print is None

edited May 23 '17 at 12:01

Community

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answered Aug 20 '15 at 13:24

Zibi

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The two calls to `list` are totally unnecessary. BTW, it appears that the OP wants to preserve order, not sort the elements. – Andrea Corbellini Aug 20 '15 at 13:27
Thanks for noticing. Edited in case OP finds it helpful. – Zibi Aug 20 '15 at 13:30

Python list giving different order

4 Answers4