lambda to Sort Dictionary.items() by Value
aleax at aleax.it
Mon Feb 18 09:33:23 CET 2002
Jim Dennis wrote:
> I'm playing with text and I decided to write a simple histogram
> function (calculating letter occurence frequencies, in this case).
> In the course of that I found two simple uses for lambda one of
> which seems like it would be a very common idiom in Python.
Fortunately not, because decorate-sort-undecorate (DSU) is faster
and more general.
> i = h.items()
> i.sort(lambda (k1,v1),(k2,v2): cmp(v2,v1) ) # sort by value, not by
> i=string.join(map(lambda (x,y):x, i),"") # extract letters from each
> return (h,i)
Try instead (Python 2.2, but it's similar in older Pythons, 2.0 & later):
temp = [ (h[key], key) for key in h ]
return h, ''.join([ key for value, key in temp ])
> It seems like one might need to sort dictionary items by value
> pretty often.
Depends on your application field, but DSU and list comprehensions
help when you do have such needs.
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