Python: sorting dictionary of dictionaries

Question

I have a dict (which is also a key of a larger dict) of dicts that looks like

wd[wc][dist][True]={'course': {'#': 1, 'Fisher': 4.0},
 'i': {'#': 1, 'Fisher': -0.2222222222222222},
 'of': {'#': 1, 'Fisher': 2.0},
 'will': {'#': 1, 'Fisher': 3.5}}

I want to sort the key words (at the highest level) by their corresponding 'Fisher' value... so that the output looks like

wd[wc][dist][True]={'course': {'Fisher': 4.0, '#': 1}, 'will': {'Fisher': 3.5, '#': 1}, 'of': {'Fisher': 2.0, '#': 1}, 'i': {'Fisher': -0.2222222222222222, '#': 1}}

I've tried working with items() and sorted() but can't work it out... Please help me out :(

Unfortunately you can't sort a dictionary, it's unordered. Read this great post for pointers on how to do it: http://stackoverflow.com/questions/613183/python-sort-a-dictionary-by-value — Henrik Andersson, May 07 '13 at 06:30
2021: for Python >=3.7 the language specifies that dictionaries are order-preserving, and CPython implements this. — DisappointedByUnaccountableMod, Jun 11 '21 at 13:22
See https://stackoverflow.com/questions/613183/how-do-i-sort-a-dictionary-by-value — DisappointedByUnaccountableMod, Jun 11 '21 at 13:27

Ashwini Chaudhary · Accepted Answer · 2015-09-13T02:10:06.523

40

You can't sort a dict, but can get a sorted list of keys, values or (key,values) pairs.

>>> dic = {'i': {'Fisher': -0.2222222222222222, '#': 1}, 'of': {'Fisher': 2.0, '#': 1}, 'will': {'Fisher': 3.5, '#': 1}, 'course': {'Fisher': 4.0, '#': 1}}

>>> sorted(dic.items(), key=lambda x: x[1]['Fisher'], reverse=True)
[('course', {'Fisher': 4.0, '#': 1}),
 ('will', {'Fisher': 3.5, '#': 1}),
 ('of', {'Fisher': 2.0, '#': 1}),
 ('i', {'Fisher': -0.2222222222222222, '#': 1})
]

Or create an collections.OrderedDict(introduced in Python 2.7) after getting the sorted (key,value) pairs:

>>> from collections import OrderedDict
>>> od = OrderedDict(sorted(dic.items(), key=lambda x: x[1]['Fisher'], reverse=True))
>>> od
OrderedDict([
('course', {'Fisher': 4.0, '#': 1}),
('will', {'Fisher': 3.5, '#': 1}),
('of', {'Fisher': 2.0, '#': 1}),
('i', {'Fisher': -0.2222222222222222, '#': 1})
])

For your dictionary, try this:

>>> from collections import OrderedDict
>>> dic = wd[wc][dist][True]
>>> wd[wc][dist][True]= OrderedDict(sorted(dic.items(), key=lambda x: x[1]['Fisher'], reverse=True))

edited Sep 13 '15 at 02:10

answered May 07 '13 at 06:31

Ashwini Chaudhary

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Note that [`OrderedDict`](http://docs.python.org/2/library/collections.html?highlight=ordereddict#ordereddict-examples-and-recipes) is only for Python versions 2.7 and above. – Burhan Khalid May 07 '13 at 06:36
using items() results in KeyError... why could that be? – ytrewq May 07 '13 at 06:38
@CosmicRabbitMediaInc One of your dictionaries may not have the `Fisher` key, is that correct? Try `all('Fisher' in d[k] for k in d)` and post output – jamylak May 07 '13 at 06:42
@jamylak Ive tried print dic.items() but it alone results in key error... is it still related to fisher key? btw my dic itself is also a key of a larger dic.. – ytrewq May 07 '13 at 06:44
@CosmicRabbitMediaInc This answer works fine, your data structure is not a dictionary – jamylak May 07 '13 at 06:45
@jamylak sorry I have a very clumsy understanding of dict and list... How could the answer be modified to fit my case? – ytrewq May 07 '13 at 06:46
1

@CosmicRabbitMediaInc Then try `larger_dict[key].items()`, or post the larger `dict` in question body. – Ashwini Chaudhary May 07 '13 at 06:46
@AshwiniChaudhary sorry for the confusion. I modified the question. Your new suggestion still results in key error... – ytrewq May 07 '13 at 06:48
@AshwiniChaudhary that worked magically. Thank you so much for saving me :) – ytrewq May 07 '13 at 06:59

score 5 · Answer 2 · answered May 07 '13 at 07:09

5

If you just need the keys in order, you can get a list like this

dic = {'i': {'Fisher': -0.2222222222222222, '#': 1}, 'of': {'Fisher': 2.0, '#': 1}, 'will': {'Fisher': 3.5, '#': 1}, 'course': {'Fisher': 4.0, '#': 1}}
sorted(dic, key=lambda k: dic[k]['Fisher'])

if 'Fisher' might be missing, you can use this to move those entries last

sorted(dic, key=lambda x:dic[x].get('Fisher', float('inf')))

or '-inf' to place them at the beginning

answered May 07 '13 at 07:09

John La Rooy

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How would you remove the entries completely if they don't have 'Fisher'? – Professor Dragon Dec 27 '19 at 20:41

Python: sorting dictionary of dictionaries

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