Re: Split a list into two parts based on a filter?

References	<kp5d9e$2hf$1@panix2.panix.com> <CAPTjJmrDNe8ASxD8xsok=-_zoDRrUZjHydYSm3G_SJy8T2a_5A@mail.gmail.com> <kp7fmp$es8$2@ger.gmane.org> <CAPTjJmqJftDD8zjW9NZen=61ePD8Tuf1Rsph9K+kmJpNd=ZmEw@mail.gmail.com> <kp7pk1$2i7$1@ger.gmane.org>
Date	2013-06-12 04:27 +1000
Subject	Re: Split a list into two parts based on a filter?
From	Chris Angelico <rosuav@gmail.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.3038.1370975224.3114.python-list@python.org> (permalink)

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On Wed, Jun 12, 2013 at 4:13 AM, Peter Otten <__peter__@web.de> wrote:
> Chris Angelico wrote:
>
>> On Wed, Jun 12, 2013 at 1:28 AM, Serhiy Storchaka <storchaka@gmail.com>
>> wrote:
>>> 11.06.13 01:50, Chris Angelico написав(ла):
>>>
>>>> On Tue, Jun 11, 2013 at 6:34 AM, Roy Smith <roy@panix.com> wrote:
>>>>>
>>>>> new_songs = [s for s in songs if s.is_new()]
>>>>> old_songs = [s for s in songs if not s.is_new()]
>>>>
>>>>
>>>> Hmm. Would this serve?
>>>>
>>>> old_songs = songs[:]
>>>> new_songs = [songs.remove(s) or s for s in songs if s.is_new()]
>
> I think you meant old_songs.remove(s).

Ah, yes, editing fail. I started by mutating the original list, then
thought "Oh, better to work with a copy"... and forgot to complete the
edit.

>>> O(len(songs)**2) complexity.
>>
>> Which isn't significant if len(songs) is low. We weren't told the
>> relative costs - is the is_new call ridiculously expensive? Everything
>> affects algorithmic choice.
>
> But is it correct? In the general case, no:
>
>>>> numbers = [1, 1.0, 2.0, 2]
>>>> ints = numbers[:]
>>>> floats = [ints.remove(n) or n for n in numbers if isinstance(n, float)]
>>>> floats
> [1.0, 2.0]
>>>> ints
> [1.0, 2] # hmm

Sure, but the implication of the original is that they're uniquely
identifiable. Anyway, it wasn't meant to be absolutely perfect, just
another notion getting thrown out there... and then thrown out :)

ChrisA

Thread

Split a list into two parts based on a filter? roy@panix.com (Roy Smith) - 2013-06-10 16:34 -0400
  Re: Split a list into two parts based on a filter? Chris Angelico <rosuav@gmail.com> - 2013-06-11 08:50 +1000
  Re: Split a list into two parts based on a filter? Roel Schroeven <roel@roelschroeven.net> - 2013-06-11 00:50 +0200
    Re: Split a list into two parts based on a filter? Roy Smith <roy@panix.com> - 2013-06-11 00:11 -0400
      Re: Split a list into two parts based on a filter? Serhiy Storchaka <storchaka@gmail.com> - 2013-06-11 18:27 +0300
        Re: Split a list into two parts based on a filter? Roy Smith <roy@panix.com> - 2013-06-11 20:33 -0400
          Re: Split a list into two parts based on a filter? Phil Connell <pconnell@gmail.com> - 2013-06-12 07:32 +0100
            Re: Split a list into two parts based on a filter? Roy Smith <roy@panix.com> - 2013-06-12 07:39 -0400
              Re: Split a list into two parts based on a filter? Fábio Santos <fabiosantosart@gmail.com> - 2013-06-12 12:51 +0100
              Re: Split a list into two parts based on a filter? Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2013-06-12 15:06 +0300
              Re: Split a list into two parts based on a filter? Terry Reedy <tjreedy@udel.edu> - 2013-06-12 14:07 -0400
          Re: Split a list into two parts based on a filter? Serhiy Storchaka <storchaka@gmail.com> - 2013-06-12 19:28 +0300
          Re: Split a list into two parts based on a filter? Fábio Santos <fabiosantosart@gmail.com> - 2013-06-12 17:57 +0100
          Re: Split a list into two parts based on a filter? Terry Reedy <tjreedy@udel.edu> - 2013-06-12 14:47 -0400
          Re: Split a list into two parts based on a filter? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-06-13 10:43 +0100
  Re: Split a list into two parts based on a filter? Chris Rebert <clp2@rebertia.com> - 2013-06-10 16:03 -0700
  Re: Split a list into two parts based on a filter? Tim Chase <python.list@tim.thechases.com> - 2013-06-10 18:10 -0500
  Re: Split a list into two parts based on a filter? Fábio Santos <fabiosantosart@gmail.com> - 2013-06-11 00:08 +0100
    Re: Split a list into two parts based on a filter? alex23 <wuwei23@gmail.com> - 2013-06-11 17:44 -0700
  Re: Split a list into two parts based on a filter? Chris Angelico <rosuav@gmail.com> - 2013-06-11 09:12 +1000
  Re: Split a list into two parts based on a filter? Peter Otten <__peter__@web.de> - 2013-06-11 02:11 +0200
  Re: Split a list into two parts based on a filter? Peter Otten <__peter__@web.de> - 2013-06-11 08:43 +0200
  Re: Split a list into two parts based on a filter? Jonas Geiregat <jonas@geiregat.org> - 2013-06-11 08:47 +0200
  Re: Split a list into two parts based on a filter? Fábio Santos <fabiosantosart@gmail.com> - 2013-06-11 14:48 +0100
    Re: Split a list into two parts based on a filter? rusi <rustompmody@gmail.com> - 2013-06-11 09:37 -0700
      Re: Split a list into two parts based on a filter? Fábio Santos <fabiosantosart@gmail.com> - 2013-06-11 18:05 +0100
        Re: Split a list into two parts based on a filter? rusi <rustompmody@gmail.com> - 2013-06-11 10:23 -0700
          Re: Split a list into two parts based on a filter? Chris Angelico <rosuav@gmail.com> - 2013-06-12 03:37 +1000
            Re: Split a list into two parts based on a filter? rusi <rustompmody@gmail.com> - 2013-06-11 11:13 -0700
          Re: Split a list into two parts based on a filter? Fábio Santos <fabiosantosart@gmail.com> - 2013-06-11 19:05 +0100
  Re: Split a list into two parts based on a filter? Joshua Landau <joshua.landau.ws@gmail.com> - 2013-06-11 15:22 +0100
  Re: Split a list into two parts based on a filter? Serhiy Storchaka <storchaka@gmail.com> - 2013-06-11 18:28 +0300
  Re: Split a list into two parts based on a filter? Chris Angelico <rosuav@gmail.com> - 2013-06-12 03:28 +1000
    Re: Split a list into two parts based on a filter? Roy Smith <roy@panix.com> - 2013-06-11 20:12 -0400
  Re: Split a list into two parts based on a filter? Peter Otten <__peter__@web.de> - 2013-06-11 20:13 +0200
  Re: Split a list into two parts based on a filter? Peter Otten <__peter__@web.de> - 2013-06-11 20:18 +0200
  Re: Split a list into two parts based on a filter? Chris Angelico <rosuav@gmail.com> - 2013-06-12 04:27 +1000
  Re: Split a list into two parts based on a filter? Roel Schroeven <roel@roelschroeven.net> - 2013-06-11 22:22 +0200

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