CODEWITHSUNDEEP
pythonsortingdictionary
norman
norman

Reputation: 5586

Sorting with a python dictionary

I have a dictionary of "documents" in python with document ID numbers as keys and dictionaries (again) as values. These internal dictionaries each have a 'weight' key that holds a floating-point value of interest. In other words:

documents[some_id]['weight'] = ...

What I want to do is obtain a list of my document IDs sorted in descending order of the 'weight' value. I know that dictionaries are inherently unordered (and there seem to be a lot of ways to do things in Python), so what is the most painless way to go? It feels like kind of a messy situation...

Upvotes: 2

Views: 1227

Answers (3)

jbiz
jbiz

Reputation: 424

This seems to work for me. The inspiration for it came from OrderedDict and question #9001509

from collections import OrderedDict

d = {
    14: {'weight': 90},
    12: {'weight': 100},
    13: {'weight': 101},
    15: {'weight': 5}
 }

sorted_dict = OrderedDict(sorted(d.items(), key=lambda rec: rec[1].get('weight')))
print sorted_dict

Upvotes: 0

user764357
user764357

Reputation:

I took the approach that you might want the keys as well as the rest of the object:

# Build a random dictionary
from random import randint
ds = {}                             # A |D|ata |S|tructure
for i in range(20,1,-1):
  ds[i]={'weight':randint(0,100)}

sortedDS = sorted(ds.keys(),key=lambda x:ds[x]['weight'])
for i in sortedDS :
 print i,ds[i]['weight']

sorted() is a python built in that takes a list and returns it sorted (obviously), however it can take a key value that it uses to determine the rank of each object. In the above case it uses the 'weight' value as the key to sort on.

The advantage of this over Ameers answer is that it returns the order of keys rather than the items. Its an extra step, but it means you can refer back into the original data structure

Upvotes: 2

Ameer
Ameer

Reputation: 2638

I would convert the dictionary to a list of tuples and sort it based on weight (in reverse order for descending), then just remove the objects to get a list of the keys

l = documents.items()
l.sort(key=lambda x: x[1]['weight'], reverse=True)
result = [d[0] for d in l]

Upvotes: 2

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