[Tutor] Cheating?No, not me:-)

[Israel Evans]

I just ran across something like this that used list comprehensions to do
this...

As far as I can remember it went like this:


>>> occ = {"hello":3, "name":23, "bob":15, "jane":10}

	# switch the keys for the values
>>> pairs = [(v, k) for (k, v) in occ.items()]  

>>> pairs
[(10, 'jane'), (15, 'bob'), (3, 'hello'), (23, 'name')]

>>> pairs.sort()

	# reverse list so that most occurrences are at the front.
>>> pairs.reverse()

	# switch back the keys and values.
>>> pairs = [(k, v) for (v, k) in pairs]

>>> pairs
[('name', 23), ('bob', 15), ('jane', 10), ('hello', 3)]



~Israel~


-----Original Message-----
From: Sean 'Shaleh' Perry [mailto:shalehperry@attbi.com] 
Sent: 17 April 2002 12:43 PM
To: Nicole Seitz
Cc: tutor@python.org
Subject: Re: [Tutor] Cheating?No, not me:-)

> 
> Thanks!
> My program now runs almost perfectly. And I solved the problem how to
print 
> the K most common words. Maybe there's an easier way to determine the most

> common words, I don't know.
> Here's the little function that deals with the most common words.What do
you 
> think of it?
> 
> Note: occ is the dictionary where I store the words and their
occurences,e.g.
> occ = { "hello":3,"you":123,"fool":23}

try this:

$ python
>>> def value_sort(a,b):
...     if a[1] == b[1]: return 0
...     elif a[1] < b[1]: return -1
...     else: return 1
... 
>>> occ = {"hello":3, "name":23, "bob":15, "jane":10}
>>> values = zip(occ.keys(), occ.values())
>>> values
[('hello', 3), ('name', 23), ('bob', 15), ('jane', 10)]
>>> values.sort(value_sort)
>>> values
[('hello', 3), ('jane', 10), ('bob', 15), ('name', 23)]

Getting the first K items in that list should be easy enough.

zip() takes two lists and makes a list of tuples.  the sort method of a list
takes an optional function which defines how to sort.  This function returns
-1
when the first is less than the second, 0 when they are equal and 1 when the
first is greater than the second.




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