How to sort a Python dict (dictionary) by keys or values

Date: Sept. 13, 2007 | Modified: Sept. 7, 2008 | Tags: datastructures, python | 10 Comments

How to sort a dict by keys (Python 2.4 or greater):

mydict = {'carl':40,
          'alan':2,
          'bob':1,
          'danny':3}

for key in sorted(mydict.iterkeys()):
    print "%s: %s" % (key, mydict[key])

Results:

alan: 2
bob: 1
carl: 40
danny: 3

Taken from the Python FAQ: http://www.python.org/doc/faq/general/#why-doesn-t-list-sort-return-the-sorted-list. To sort the keys in reverse, add reverse=True as a keyword argument to the sorted function.

How to sort a dict by keys (Python older than 2.4):

keylist = mydict.keys()
keylist.sort()
for key in keylist:
    print "%s: %s" % (key, mydict[key])

The results are the same as the above.

How to sort a dict by value (Python 2.4 or greater):

for key, value in sorted(mydict.iteritems(), key=lambda (k,v): (v,k)):
    print "%s: %s" % (key, value)

Results:

bob: 1
alan: 2
danny: 3
carl: 40

Taken from Nick Galbreath's Digital Sanitation Engineering blog article

10 Comments — Comments feed for this post

#1 Marius commented on 2007-11-30:

Thank you.

#2 Sven Siegmund commented on 2008-05-07:

Thanks a lot. Exactly what I was looking for.

#3 Mike commented on 2008-09-11:

Thanks, "How to sort a dict by value" was helpful. :)

#4 Gregg Lind commented on 2008-09-12:

Thanks for the link to my article. If you need faster dictionary sorting than the ones you describe, it has some tips, as Nick's updated blog also shows.

#5 Eliot commented on 2008-09-12:

Gregg, Good work-- your article shows that you have obviously explored this topic much more thoroughly than I have. I will definitely try your method the next chance I get.

#6 Rama krishna commented on 2011-02-11:

tnx

#7 gcd0318 commented on 2011-02-15:

are you sure this works? please see my result (I did in python shell):

>>> d={80: '0101', 75: '1011', 85: '0001', 70: '1111'}
>>> d
{80: '0101', 75: '1011', 85: '0001', 70: '1111'}
>>> kl=list(d.keys())
>>> kl
[80, 75, 85, 70]
>>> new_kl = kl + []
>>> new_kl
[80, 75, 85, 70]
>>> new_kl.sort()
>>> new_kl
[70, 75, 80, 85]
>>> new_d = {}
>>> for k in new_kl:
    new_d[k] = d[k]
    print(new_d)

{70: '1111'}
{75: '1011', 70: '1111'}
{80: '0101', 75: '1011', 70: '1111'}
{80: '0101', 75: '1011', 85: '0001', 70: '1111'}
>>> new_d
{80: '0101', 75: '1011', 85: '0001', 70: '1111'}
>>>

#8 Eliot commented on 2011-03-28:

gcd0318:
The items in a dict are stored in an undefined order. Printing the dict only confirms this fact.

If you need to operate on items in a dict in a sorted order, you can operate on each item within the for loop.

Or you can use a data structure that preserves order such as a list or the new OrderedDict data structure in the collections module added in Python 2.7. See http://docs.python.org/library/collections.html#collections.OrderedDict

#9 ovi commented on 2011-08-04:

Can someone explain the following behavior:

DICT = {'C':'C','G':'G','S':'S','E':'E','GE':'GE','fRrc':'GE','fAct':'FO'}

print DICT {'C': 'C', 'E': 'E', 'G': 'G', 'S': 'S', 'fRrc': 'GE', 'GE': 'GE', 'fAct': 'FO'}

Why is the order of the elements in the dictionary changed?

In fact, from what I've understood, there is no defined order about how the elements are stored.

So, the question is ... there is such a structure in python? (I don't want the dictionary to be sorted, I just want to preserve the order how they were initially added).

Thanks

#10 Joe commented on 2012-01-31:

Sweet, thanks for the simple solution!


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