Sort Python Dictionary Objects in a List

Question

I am trying to sort the List using dictionary keys in ascending order.

You can assume just one key per dictionary level.

Input:

res = [{'hi': {'abc': 5}}, {'bye': {'def': 5}}, {'hi': {'cba': 5}}]

My Code:

def getitem (item):
    return (item.keys())

print (sorted(res, key = getitem))

Required Output:

[{'bye': {'def': 5}}, {'hi': {'abc': 5}}, {'hi': {'cba': 5}}]

Do you dictionaries always have one key? In which case, why ese a dictionary at all? The comparison operators for dict.keys objects are for subset relationship — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Jun 21, 2019 at 18:05
Apologies for the confusion, I have updated the examples, there can be just one key in the dict, but there can be more than 1 objects with the same key and if the object key is same ("hi" in the above case), then I would like to sort it by it's nested key ("abc" before "cba"). — Inherited Geek
– Inherited Geek, Commented Jun 21, 2019 at 18:15
You should just be using tuples probably, why a nested dictionary? The tuples would sort naturally how you want them to, and be much more memory efficient — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Jun 21, 2019 at 18:17
I am receiving these dictionary objects one by one from a streaming data source. — Inherited Geek
– Inherited Geek, Commented Jun 21, 2019 at 18:22
... so is there something preventing you from transforming them into a more sane/useful data structure? — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Jun 21, 2019 at 18:25

ggorlen · Accepted Answer · 2019-06-21 18:27:12Z

2

You're close--just pass the dict into iter() to create an iterator, then ask for the next() item in the iterator. This sorts on the first key in the dict if multiple exist (Python 3.6+ dicts are ordered by insertion time). The comparator can return a tuple of relative priority, enabling sorting on the inner key if the outer keys are equal.

res = [{'hi': {'abc': 5}}, {'bye': {'def': 5}}, {'hi': {'cba': 5}}]

def compare(d):
    outer = next(iter(d))
    return outer, next(iter(d[outer]))

print(sorted(res, key=compare))

edited Jun 21, 2019 at 18:27

answered Jun 21, 2019 at 18:05

ggorlen

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3 Comments

chepner Over a year ago

next(iter(x)) would be sufficient; no need to call the keys method.

ggorlen Over a year ago

Good call--thanks. I guess it'll ignore the nested dict?

chepner Over a year ago

It will; Python's sorting methods are stable, so if the two top-level keys are equal, the relative order of the dicts in the input list is preserved.

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