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Groups > comp.lang.python > #47621
| From | Peter Otten <__peter__@web.de> |
|---|---|
| Subject | Re: Split a list into two parts based on a filter? |
| Date | 2013-06-11 02:11 +0200 |
| Organization | None |
| References | <kp5d9e$2hf$1@panix2.panix.com> <CAPTjJmrDNe8ASxD8xsok=-_zoDRrUZjHydYSm3G_SJy8T2a_5A@mail.gmail.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.3000.1370909462.3114.python-list@python.org> (permalink) |
Chris Angelico wrote:
> 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()]
>
> Python doesn't, AFAIK, have a "destructive remove and return"
> operation, and del is a statement rather than an expression/operator,
> but maybe this basic idea could be refined into something more useful.
> It guarantees to call is_new only once per song.
>
> The iterator version strikes my fancy. Maybe this isn't of use to you,
> but I'm going to try my hand at making one anyway.
> >>> def iterpartition(pred,it):
> """Partition an iterable based on a predicate.
>
> Returns two iterables, for those with pred False and those
True."""
> falses,trues=[],[]
> it=iter(it)
> def get_false():
> while True:
> if falses: yield falses.pop(0)
> else:
> while True:
> val=next(it)
> if pred(val): trues.append(val)
> else: break
> yield val
> def get_true():
> while True:
> if trues: yield trues.pop(0)
> else:
> while True:
> val=next(it)
> if not pred(val):
falses.append(val)
> else: break
> yield val
> return get_false(),get_true()
An alternative implementation, based on itertools.tee:
import itertools
def partition(items, predicate=bool):
a, b = itertools.tee((predicate(item), item) for item in items)
return ((item for pred, item in a if not pred),
(item for pred, item in b if pred))
if __name__ == "__main__":
false, true = partition(range(10), lambda item: item % 2)
print(list(false))
print(list(true))
def echo_odd(item):
print("checking", item)
return item % 2
false, true = partition(range(10), echo_odd)
print("FALSE", [next(false) for _ in range(3)])
print("TRUE", next(true))
print("FALSE", list(false))
print("TRUE", list(true))
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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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