from the desk of stinkpot

find the key for the minimum (or maximum) value in a python dictionary

October 11th, 2006 by Lawrence David

assume you’ve got a python dictionary a and you’d like to find the key associated with the minimum (or maximum) value in the dictionary:

>>> a = dict()
>>> a['me'] = 5
>>> a['you'] = 5
>>> a['her'] = 6
>>> a['him'] = 245
>>> print a
{‘me’: 5, ‘you’: 5, ‘him’: 245, ‘her’: 6}

to find the key associated w/ the smallest value, simply invert the python dictionary; now, all the old values will be the keys.  then, simply find the smallest key.  note, however, that if two original values have the same key, only one of the original keys will be printed:

>>> b = dict(map(lambda item: (item[1],item[0]),a.items()))
>>> min_key = b[min(b.keys())]
>>> print min_key
you

Posted in Python | 22 Comments »

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22 Responses to “find the key for the minimum (or maximum) value in a python dictionary”

1. on 24 Oct 2006 at 7:35 pm   lawrence

   i like this better:

   >>> d = {‘bob’:4, ‘krishna’:9, ‘hikari’:5}
   >>> e = d.keys()
   >>> e.sort(cmp=lambda a,b: cmp(d[a],d[b]))
   >>> e
   ['bob', 'hikari', 'krishna']

2. on 24 Oct 2006 at 7:44 pm   Lawrence David

   that was sick lawrence. (i wish i was a python gangsta like you.)

3. on 14 Dec 2007 at 10:29 am   Ryan

   Yet another way, which I prefer, requires python 2.4+.

   >>> a = {‘b’ : 1, ‘a’ : 2, ‘c’ : 5, ‘d’:4}
   >>> b = a.keys()
   >>> b.sort( key = a.__getitem__ )
   >>> b
   ['b', 'a', 'd', 'c']

4. on 26 Feb 2008 at 10:53 am   Jochen

   with python 2.5+ you can just do directly
   max(d,key = lambda a: d.get(a))
   which avoids the sorting

5. on 26 Feb 2008 at 11:06 am   Jochen

   hmm, this also works for earlier pythons
   max([ (d[x],x) for x in d])[1]

6. on 26 Feb 2008 at 11:23 am   Lawrence David

   oh, of course, you’re totally right jochen! thanks for making me a little more knowledgeable about python today!

7. on 29 Jun 2008 at 12:30 pm   Joe

   Jochen: What are d and a in your example?

8. on 28 May 2009 at 1:05 am   Kirk James Gaughan

   Found this page via Google, so I’m sure others are probably still reading it too… although it’s very old by now…

   Anyways, here’s the answer to Joe’s question:

   ‘d’ is the name of your dictionary variable, ‘a’ is just a temporary variable used in the lambda expression

9. on 17 Aug 2009 at 6:44 am   Libell

   alchemy vs metallurgy

   please find a little profiling on this methods
   and the good old classic manual one

   import datetime

   a = {‘b’ : 1, ‘a’ : 2, ‘c’ : 5, ‘d’:4 }

   t = datetime.datetime.now()
   for i in range (1,1000000) :
   ll = max([ (a[x],x) for x in a])[1]
   b = datetime.datetime.now()
   print b – t , ll

   t = datetime.datetime.now()
   for i in range (1,1000000) :
   nn = max(a ,key = lambda x: a.get(x))
   b = datetime.datetime.now()
   print b – t ,nn

   t = datetime.datetime.now()
   for i in range (1,1000000) :
   b = a.keys()
   b.sort( key = a.__getitem__ )
   mm = b[-1]
   print datetime.datetime.now() – t ,mm

   t = datetime.datetime.now()
   for i in range (1,1000000) :
   mmm = -99999999
   qui = None
   for k, x in a.iteritems():
   if x > mmm :
   mmm = x
   qui = k

   print datetime.datetime.now() – t , qui

   ”’
   0:00:03.750000 c
   0:00:03.719000 c
   0:00:03.422000 c
   0:00:02.859000 c
   ”’

10. on 08 Mar 2010 at 10:43 pm   ignacio

    The 4th is probably just faster because you don’t have to lookup the element each time (hash). You can combine that with the above:

    max(a.iteritems(),key=lambda x:x[1])

11. on 23 Mar 2010 at 7:50 am   Mario Orne Diaz Anadon

    I think I am going to win the competition!

    The shortest solution is to write:

    a = dict(((1,3),(0,-1),(3,3)))
    m = max(a, key=a.get)

12. on 19 Feb 2011 at 8:48 pm   Jawaiah Hunter

    Wow Mario that is truly elegant and Pythonic. Rock on bro.

13. on 07 Mar 2011 at 7:30 am   Mikko

    Thanks guys this was very helpful!

14. on 12 Apr 2011 at 11:56 am   Forcasa

    Mario wins this thread.

15. on 02 Feb 2012 at 1:28 pm   THe üBER p12

    Acually the shortest way to write is:

    a=dict(((1,3),(0,-1),(3,3))); m=max(a,key=a.get)

    This is much shorter… 8-|

    But it’s ok. I have tolerance for newbies.

16. on 18 Jan 2013 at 5:56 pm   Layne

    Gents:

    What if you wanted to find out it the two highest Keys had the same value? – Basically I’m looking for the highest value and reporting the Key – but I also need to identify if the 2 top Keys have the same value – i.e. co-dominant.

17. on 29 Jun 2021 at 12:24 pm   read article

    read article

    find the key for the minimum (or maximum) value in a python dictionary » from the desk of stinkpot

18. on 06 Oct 2021 at 8:29 pm   سیستم مدیریت انبار داری

    
    این پیام مشاوره و پیشنهاد مناسب از باب کسانی است که می خواهند دوروبر محتویات هماننده به این مطلب مطالعه بیشتری داشته باشند

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