Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #35793

Re: dict comprehension question.

Show all headers | View raw

On 12/29/12 15:40, Mitya Sirenef wrote:
>>       >>> w = [1,2,3,1,2,4,4,5,6,1]
>>       >>> s = set(w)
>>       >>> s
>>       set([1, 2, 3, 4, 5, 6])
>>       >>> {x:w.count(x) for x in s}
>>       {1: 3, 2: 2, 3: 1, 4: 2, 5: 1, 6: 1}
>
> Indeed, this is much better -- I didn't think of it..

Except that you're still overwhelmed by iterating over every element 
in "w" for every distinct element.  So you've gone from O(N**2) to 
O(k*N).

The cleanest way to write it (IMHO) is MRAB's

  >>> w = [1, 2, 3, 1, 2, 4, 4, 5, 6, 1]
  >>> from collections import Counter
  >>> results = dict(Counter(w))

which should gather all the statistics in one single pass across "w" 
making it O(N), and it's Pythonically readable.

-tkc

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

dict comprehension question. Quint Rankid <qbr567@gmail.com> - 2012-12-29 11:48 -0800
  Re: dict comprehension question. Roy Smith <roy@panix.com> - 2012-12-29 14:58 -0500
  Re: dict comprehension question. Mitya Sirenef <msirenef@lightbird.net> - 2012-12-29 15:01 -0500
  Re: dict comprehension question. Mitya Sirenef <msirenef@lightbird.net> - 2012-12-29 15:09 -0500
  Re: dict comprehension question. Joel Goldstick <joel.goldstick@gmail.com> - 2012-12-29 15:15 -0500
  Re: dict comprehension question. Peter Otten <__peter__@web.de> - 2012-12-29 21:32 +0100
  Re: dict comprehension question. MRAB <python@mrabarnett.plus.com> - 2012-12-29 20:39 +0000
  Re: dict comprehension question. Mitya Sirenef <msirenef@lightbird.net> - 2012-12-29 16:40 -0500
  Re: dict comprehension question. Terry Reedy <tjreedy@udel.edu> - 2012-12-29 18:22 -0500
  Re: dict comprehension question. Terry Reedy <tjreedy@udel.edu> - 2012-12-29 18:56 -0500
    Re: dict comprehension question. Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-01-01 03:10 +0000
      Re: dict comprehension question. 88888 Dihedral <dihedral88888@googlemail.com> - 2013-01-01 00:40 -0800
  Re: dict comprehension question. Tim Chase <python.list@tim.thechases.com> - 2012-12-29 18:26 -0600
  Re: dict comprehension question. Joel Goldstick <joel.goldstick@gmail.com> - 2012-12-29 23:10 -0500

csiph-web