Re: how to separate a list into two lists?

Path	csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!feeder.news-service.com!news2.euro.net!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path	<rosuav@gmail.com>
X-Original-To	python-list@python.org
Delivered-To	python-list@mail.python.org
X-Spam-Status	OK 0.016
X-Spam-Evidence	'H': 0.97; 'S': 0.00; 'subject:two': 0.07; '(use': 0.09; 'done?': 0.09; 'tuple': 0.09; 'elements,': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; "that'll": 0.16; 'wrote:': 0.16; 'subject:list': 0.18; 'header:In- Reply-To:1': 0.22; 'dictionary': 0.23; 'loop,': 0.23; 'pm,': 0.24; 'aug': 0.24; 'separate': 0.28; 'handled': 0.28; 'loop': 0.28; 'sat,': 0.28; 'lists': 0.28; 'message-id:@mail.gmail.com': 0.29; 'construct': 0.30; 'efficiently': 0.30; 'tuples': 0.30; 'subject:?': 0.31; 'list': 0.32; 'there': 0.33; 'to:addr:python- list': 0.33; '...': 0.34; 'subject:lists': 0.36; 'another': 0.37; 'but': 0.37; 'two': 0.37; 'think': 0.38; 'received:google.com': 0.38; 'received:209.85': 0.38; 'subject:: ': 0.39; 'under': 0.39; 'to:addr:python.org': 0.39; 'your': 0.61; 'order': 0.62; 'hood.': 0.84; 'technically': 0.93
DKIM-Signature	v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=enxSrnvAJRHl0rrPCFD9jcc2WP0ZWP5Y5BENpFDxwEw=; b=pEbbGN3R16hRBmFsG4OU4I0xUE5evAwkRn2gIqCVfsL3bFsPV8Zi9sdf8ZStXRd69y RxytB13Gw2RhKtL3jJDgEhGLU6GHHo9C3sc/Y31cdOm4+7c/ATWjfBdxBiOTqvfUpM4U gxrO850vVjw/cp7UKW7S5jk8tTmN4lwvfxgFw=
MIME-Version	1.0
In-Reply-To	<CAN1Fwxcdtt0u_TT=civMes1hA2qvfkH2YckES7B7qRE++DXzJQ@mail.gmail.com>
References	<CAN1Fwxcdtt0u_TT=civMes1hA2qvfkH2YckES7B7qRE++DXzJQ@mail.gmail.com>
Date	Sat, 6 Aug 2011 18:14:16 +0100
Subject	Re: how to separate a list into two lists?
From	Chris Angelico <rosuav@gmail.com>
To	python-list@python.org
Content-Type	text/plain; charset=ISO-8859-1
X-BeenThere	python-list@python.org
X-Mailman-Version	2.1.12
Precedence	list
List-Id	General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe	<http://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive	<http://mail.python.org/pipermail/python-list>
List-Post	<mailto:python-list@python.org>
List-Help	<mailto:python-list-request@python.org?subject=help>
List-Subscribe	<http://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups	comp.lang.python
Message-ID	<mailman.1984.1312650859.1164.python-list@python.org> (permalink)
Lines	22
NNTP-Posting-Host	2001:888:2000:d::a6
X-Trace	1312650859 news.xs4all.nl 23926 [2001:888:2000:d::a6]:37260
X-Complaints-To	abuse@xs4all.nl
Xref	x330-a1.tempe.blueboxinc.net comp.lang.python:10977

Show key headers only | View raw

On Sat, Aug 6, 2011 at 6:07 PM, smith jack <thinke365@gmail.com> wrote:
> if a list L is composed with tuple consists of two elements, that is
> L = [(a1, b1), (a2, b2) ... (an, bn)]
>
> is there any simple way to divide this list into two separate lists , such that
> L1 = [a1, a2... an]
> L2=[b1,b2 ... bn]
>
> i do not want to use loop, any methods to make this done?

One easy way is to use list comprehensions. Technically that'll
involve a loop, but the loop is handled efficiently under the hood.

L1 = [x[0] for x in L]
L2 = [x[1] for x in L]

Another way would be to construct a dictionary from your list of
tuples and then use the keys() and values() of that dictionary to form
your lists (use collections.OrderedDict if the order matters). But I
think the list comps are the best way.

ChrisA

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

Thread

Re: how to separate a list into two lists? Chris Angelico <rosuav@gmail.com> - 2011-08-06 18:14 +0100
  Re: how to separate a list into two lists? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-07 10:27 +1000

csiph-web