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Groups > comp.lang.python > #44061
| Date | 2013-04-22 14:03 +0100 |
|---|---|
| From | Blind Anagram <blindanagram@nowhere.org> |
| Newsgroups | comp.lang.python |
| Subject | Re: List Count |
| References | <sridnffI6YhxuOjMnZ2dnUVZ7tSdnZ2d@brightview.co.uk> <mailman.907.1366635127.3114.python-list@python.org> |
| Message-ID | <mailman.910.1366636010.3114.python-list@python.org> (permalink) |
On 22/04/2013 13:51, Dave Angel wrote: > On 04/22/2013 07:58 AM, Blind Anagram wrote: >> I would be grateful for any advice people can offer on the fastest way >> to count items in a sub-sequence of a large list. >> >> I have a list of boolean values that can contain many hundreds of >> millions of elements for which I want to count the number of True values >> in a sub-sequence, one from the start up to some value (say hi). >> >> I am currently using: >> >> sieve[:hi].count(True) >> >> but I believe this may be costly because it copies a possibly large part >> of the sieve. >> >> Ideally I would like to be able to use: >> >> sieve.count(True, hi) >> >> where 'hi' sets the end of the count but this function is, sadly, not >> available for lists. >> >> The use of a bytearray with a memoryview object instead of a list solves >> this particular problem but it is not a solution for me as it creates >> more problems than it solves in other aspects of the program. >> >> Can I assume that one possible solution would be to sub-class list and >> create a C based extension to provide list.count(value, limit)? >> >> Are there any other solutions that will avoid copying a large part of >> the list? >> > > Instead of using the default slice notation, why not use > itertools.islice() ? > > Something like (untested): > > import itertools > > it = itertools.islice(sieve, 0, hi) > sum(itertools.imap(bool, it)) > > I only broke it into two lines for clarity. It could also be: > > sum(itertools.imap(bool, itertools.islice(sieve, 0, hi))) > > If you're using Python 3.x, say so, and I'm sure somebody can simplify > these, since in Python 3, many functions already produce iterators > instead of lists. Thanks, I'll look at these ideas. And, yes, my interest is mainly in Python 3.
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List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 12:58 +0100
Re: List Count Dave Angel <davea@davea.name> - 2013-04-22 08:51 -0400
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 14:03 +0100
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 14:03 +0100
Re: List Count Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-22 13:13 +0000
Re: List Count Skip Montanaro <skip@pobox.com> - 2013-04-22 08:57 -0500
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 15:15 +0100
Re: List Count Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-22 16:14 +0100
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 16:50 +0100
Re: List Count Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-22 17:06 +0100
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 17:38 +0100
Re: List Count Skip Montanaro <skip@pobox.com> - 2013-04-22 12:48 -0500
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 20:22 +0100
Re: List Count Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-22 21:18 +0100
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 22:25 +0100
Re: List Count Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 00:06 +0100
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-23 07:45 +0100
Re: List Count Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-22 23:28 +0000
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-23 08:00 +0100
Re: List Count Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-22 22:03 +0100
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 22:32 +0100
Re: List Count Dave Angel <davea@davea.name> - 2013-04-22 21:47 -0400
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-23 08:02 +0100
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 17:38 +0100
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-22 16:50 +0100
Re: List Count Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-22 23:01 +0000
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-23 08:05 +0100
Re: List Count Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 12:08 +0100
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-23 12:45 +0100
Re: List Count Terry Jan Reedy <tjreedy@udel.edu> - 2013-04-23 15:01 -0400
Re: List Count Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-23 14:49 +0000
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-23 17:57 +0100
Re: List Count Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 18:45 +0100
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-23 19:30 +0100
Re: List Count Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 20:16 +0100
Re: List Count Terry Jan Reedy <tjreedy@udel.edu> - 2013-04-23 16:00 -0400
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-23 21:41 +0100
Re: List Count Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 21:38 +0100
Re: List Count Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-24 01:59 +0000
Re: List Count Blind Anagram <blindanagram@nowhere.org> - 2013-04-24 10:01 +0100
Re: List Count Peter Otten <__peter__@web.de> - 2013-04-22 15:22 +0200
Re: List Count 88888 Dihedral <dihedral88888@googlemail.com> - 2013-04-22 06:36 -0700
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