Sorting distionary by value

[Steven Majewski]

On Thu, 28 Mar 2002, phil hunt wrote:

> On Wed, 27 Mar 2002 23:02:20 -0500, Peter Hansen <peter at engcorp.com> wrote:
> >Jim Dennis wrote:
> >>
> >>  The core loop is something like:
> >>
> >>         freq = {}
> >>         for line in file:
> >>                 for word in line.split():
> >>                         if word in freq:        freq[word] += 1
> >>                         else:                           freq[word] = 1
> >>
> >>  (assuming Python2.2 for file interation and dictionary membership
> >>  support using "in."  I *really* like those 2.2 features!  They make
> >>  my psuedo-code so executable!)
> >
> >Something like   freq[word] = freq.get(word, 0) + 1
> >
> >would probably be faster, and it's a little simpler I think,
> >although I could see an argument that it's less readable.
> >Also doesn't depend on 2.2.
>
> IIRC in Awk you can just say:   freq[word] ++ and it works
> correctly even when there is no pre-existing index of word in freq.
>
> IMO it's a pity Python isn't like that.
>

However, with 2.2 you can do something like this to give key
access a default value:


Python 2.2.1c1 (#1, Mar 19 2002, 02:06:22)
[GCC 2.95.2 19991024 (release)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> class Dcounter(dict):
...     default = 0
...     def __getitem__( self, key ):
...             return self.get( key, self.default )
...
>>>
>>> count = Dcounter( {'ten':10, 'nine':9 } )
>>> count['ten']
10
>>> count['one'] += 1
>>> count['one']
1
>>> count['two'] += 1
>>> count['two'] += 1
>>> count['two']
2
>>> count
{'nine': 9, 'two': 2, 'ten': 10, 'one': 1}
>>> count['zero']
0



-- Steve Majewski