Python sort list to set

Question

*edit

I make

word=['I','love','hello','world','love','I']

when I convert to set, It change the order to

print(set(word))
output: {'world', 'I', 'hello', 'love'}

How to sort the set again to be

{'I', 'love', 'hello', 'world'}

Sets are unordered. If you want order, convert back to a list. E.g. `print(sorted(set(word)))` — khelwood, Oct 07 '19 at 10:43
If you want an "ordered set", you could also use a `dict` in Python 3 and ignore the values. — tobias_k, Oct 07 '19 at 10:49
Possible duplicate of [Sorting a set of values](https://stackoverflow.com/questions/17457793/sorting-a-set-of-values) — Mykola Zotko, Oct 07 '19 at 10:51

khelwood · Accepted Answer · 2019-10-07T11:09:52.090

4

Sets are unordered. If you want order, convert back to a list.

E.g.

print(sorted(set(word)))

sorted will sort your items and return a list.

However, if you want to retain the order of your elements rather than sort them, you can use a set for deduplication and a list for ordering, something like this:

def unique(items):
    seen = set()
    result = []
    for item in items:
        if item not in seen:
            seen.add(item)
            result.append(item)
    return result

and use it as:

>>> word = ['I','love','hello','world','love','I']
>>> print(unique(word))
['I', 'love', 'hello', 'world']

edited Oct 07 '19 at 11:09

answered Oct 07 '19 at 10:45

khelwood

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... provided that OP wants the items in sorted order and not in their original order. – tobias_k Oct 07 '19 at 10:50

score 2 · Answer 2 · answered Oct 07 '19 at 10:57

If you just want an ordered collection of unique values, you can create a dict from the list, either with a dict comprehension or dict.fromkeys. In Python 3, dictionaries will retain insertion order; for older versions, use collections.OrderedDict. The dict will have values besides the keys, but you can just ignore those.

>>> word = ['a','b','c','c','b','e']
>>> {k: None for k in word}
{'a': None, 'b': None, 'c': None, 'e': None}
>>> dict.fromkeys(word)
{'a': None, 'b': None, 'c': None, 'e': None}

Other than sorted, this also works if the original order is different than the sorted order.

>>> word = ['f','a','b','c','c','b','e']
>>> dict.fromkeys(word)
{'f': None, 'a': None, 'b': None, 'c': None, 'e': None}

You can then either convert the result to list or keep it a dict and add more values, but if you make it a set, the order will be lost again. Like a set, the dict also allows fast O(1) lookup, but no set operations like intersection or union.

Python sort list to set

2 Answers2