CODEWITHSUNDEEP
pythonsortingdictionary
Shane Reustle
Shane Reustle

Reputation: 8952

How to sort a Python dict's keys by value

I have a dict that looks like this

{ "keyword1":3 , "keyword2":1 , "keyword3":5 , "keyword4":2 }

And I would like to convert it DESC and create a list of just the keywords. Eg, this would return

["keyword3" , "keyword1" , "keyword4" , "keyword2"]

All examples I found use lambda and I'm not very strong with that. Is there a way I could loop through this, and sort them as I go? Thanks for any suggestions.

PS: I could create the initial dict differently if it would help.

Upvotes: 25

Views: 36419

Answers (5)

Sagar Pise
Sagar Pise

Reputation: 887

It is not possible to sort a dict, only to get a representation of a dict that is sorted. Dicts are inherently order less, but other types, such as lists and tuples, are not. So you need a sorted representation, which will be a list—probably a list of tuples. For instance,

'''
Sort the dictionary by score. if the score is same then sort them by name 
{ 
 'Rahul'  : {score : 75} 
 'Suhas' : {score : 95} 
 'Vanita' : {score : 56} 
 'Dinesh' : {score : 78} 
 'Anil'  : {score : 69} 
 'Anup'  : {score : 95} 
} 
'''
import operator

x={'Rahul' : {'score' : 75},'Suhas' : {'score' : 95},'Vanita' : {'score' : 56}, 
   'Dinesh' : {'score' : 78},'Anil' : {'score' : 69},'Anup' : {'score' : 95} 
  }
sorted_x = sorted(x.iteritems(), key=operator.itemgetter(1))
print sorted_x

output:

[('Vanita', {'score': 56}), ('Anil', {'score': 69}), ('Rahul', {'score': 75}), ('Dinesh', {'score': 78}), ('Anup', {'score': 95}), ('Suhas', {'score': 95})]

Upvotes: 1

John La Rooy
John La Rooy

Reputation: 304127

>>> d={ "keyword1":3 , "keyword2":1 , "keyword3":5 , "keyword4":2 }
>>> sorted(d, key=d.get, reverse=True)
['keyword3', 'keyword1', 'keyword4', 'keyword2']

Upvotes: 19

Messa
Messa

Reputation: 25181

I would come up with something like this:

[k for v, k in sorted(((v, k) for k, v in theDict.items()), reverse=True)]

But KennyTM's solution is much nicer :)

Upvotes: 2

JiminyCricket
JiminyCricket

Reputation: 7410

i always did it this way....are there advantages to using the sorted method?

keys = dict.keys()
keys.sort( lambda x,y: cmp(dict[x], dict[y]) )

whoops didnt read the part about not using lambda =(

Upvotes: 2

kennytm
kennytm

Reputation: 523174

You could use

res = list(sorted(theDict, key=theDict.__getitem__, reverse=True))

(You don't need the list in Python 2.x)

The theDict.__getitem__ is actually equivalent to lambda x: theDict[x].

(A lambda is just an anonymous function. For example

>>> g = lambda x: x + 5
>>> g(123)
128

This is equivalent to

>>> def h(x):
...   return x + 5
>>> h(123)
128

)

Upvotes: 45

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