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Re: Converting a set into list

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Daniel Kluev wrote:

>> Both solutions seem to be equivalent in that concerns the number of
>> needed loop runs, but this two-step operation might require one less loop
>> over list1. The set&set solution, in contrary, might require one loop
>> while transforming to a set and another one for the & operation.
> 
> python -m timeit -s "l1 = range(1, 10000); l2 = range(5000, 15000)"
> "l3 = list(set(l1) & set(l2))"
> 100 loops, best of 3: 2.19 msec per loop
> 
> python -m timeit -s "l1 = range(1, 10000); l2 = range(5000, 15000)"
> "s=set(l2); l3 = [i for i in l1 if i in s]"
> 100 loops, best of 3: 2.45 msec per loop
> 
> python -m timeit -s "l1 = range(1, 100000); l2 = range(50000, 150000)"
> "l3 = list(set(l1) & set(l2))"
> 10 loops, best of 3: 28 msec per loop
> 
> python -m timeit -s "l1 = range(1, 100000); l2 = range(50000, 150000)"
> "s=set(l2); l3 = [i for i in l1 if i in s]"
> 10 loops, best of 3: 28.1 msec per loop
> 
> So even with conversion back into list set&set is still marginally faster.

If you are looking for speed, consider

s = set(l1)
s.intersection_update(l2)
l3 = list(s) 

$ python -m timeit -s "l1 = range(1, 10000); l2 = range(5000, 15000)" 
"list(set(l1) & set(l2))"
100 loops, best of 3: 4 msec per loop

$ python -m timeit -s "l1 = range(1, 10000); l2 = range(5000, 15000)" "s = 
set(l1); s.intersection_update(l2); list(s)"
100 loops, best of 3: 1.99 msec per loop

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Converting a set into list TheSaint <nobody@nowhere.net.no> - 2011-05-14 17:02 +0800
  Re: Converting a set into list Peter Otten <__peter__@web.de> - 2011-05-14 11:33 +0200
    Re: Converting a set into list TheSaint <nobody@nowhere.net.no> - 2011-05-14 22:14 +0800
      Re: Converting a set into list Chris Angelico <rosuav@gmail.com> - 2011-05-15 04:22 +1000
  Re: Converting a set into list Ben Finney <ben+python@benfinney.id.au> - 2011-05-15 00:12 +1000
    Re: Converting a set into list TheSaint <nobody@nowhere.net.no> - 2011-05-14 22:51 +0800
      Re: Converting a set into list Ben Finney <ben+python@benfinney.id.au> - 2011-05-15 09:21 +1000
        Re: Converting a set into list Chris Torek <nospam@torek.net> - 2011-05-15 02:11 +0000
          Re: Converting a set into list SigmundV <sigmundv@gmail.com> - 2011-05-15 04:18 -0700
            Re: Converting a set into list SigmundV <sigmundv@gmail.com> - 2011-05-15 04:23 -0700
            Re: Converting a set into list TheSaint <nobody@nowhere.net.no> - 2011-05-15 23:56 +0800
              Re: Converting a set into list Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-05-15 22:27 +0200
                Re: Converting a set into list Daniel Kluev <dan.kluev@gmail.com> - 2011-05-16 13:37 +1100
                Re: Converting a set into list Peter Otten <__peter__@web.de> - 2011-05-16 08:34 +0200
                Re: Converting a set into list TheSaint <nobody@nowhere.net.no> - 2011-05-16 22:23 +0800
                Re: Converting a set into list Ben Finney <ben+python@benfinney.id.au> - 2011-05-17 10:33 +1000
            Re: Converting a set into list Roy Smith <roy@panix.com> - 2011-05-15 13:07 -0400
          Re: Converting a set into list TheSaint <nobody@nowhere.net.no> - 2011-05-16 00:05 +0800
            Re: Converting a set into list Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-15 16:28 +0000
              Re: Converting a set into list TheSaint <nobody@nowhere.net.no> - 2011-05-16 00:35 +0800
          Re: Converting a set into list Duncan Booth <duncan.booth@invalid.invalid> - 2011-05-16 10:24 +0000
            Re: Converting a set into list Chris Torek <nospam@torek.net> - 2011-05-17 01:07 +0000

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