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Re: list comprehension question

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Dave Angel於 2012年10月17日星期三UTC+8下午10時37分01秒寫道：
> On 10/17/2012 10:06 AM, rusi wrote:
> 
> > On Oct 17, 5:33 pm, Dave Angel <d...@davea.name> wrote:
> 
> >> On 10/17/2012 12:43 AM, Kevin Anthony wrote:> Is it not true that list comprehension is much faster the the for loops?
> 
> >>
> 
> >>> If it is not the correct way of doing this, i appoligize.
> 
> >>> Like i said, I'm learing list comprehension.
> 
> >> list comprehensions CAN be much faster, but not necessarily.  The most
> 
> >> complex a loop, the less likely it'll help much.
> 
> > One-lining the comprehension seems to make a difference of about 10%
> 
> > out here. Maybe Ive missed something? Seems too large�
> 
> >
> 
> > # My original suggestion
> 
> > def dot(p,q): return sum (x*y for x,y in zip(p,q))
> 
> > def transpose(m): return zip(*m)
> 
> > def mm(a,b): return mmt(a, transpose(b))
> 
> > def mmt(a,b): return [[dot(ra, rb) for rb in b] for ra in a]
> 
> >
> 
> > # One-liner (Thanks Hans for reminding me of sum)
> 
> >
> 
> > def mm1(a,b): return [[sum([x*y for x,y in zip(ra,rb)]) for rb in
> 
> > zip(*b)] for ra in a]
> 
> >
> 
> >>>> t1=Timer("res=mm1(m,m)", setup="from __main__ import mm1, m")
> 
> >>>> t1.timeit(1000)
> 
> > 12.276363849639893
> 
> >>>> t0=Timer("res=mm(m,m)", setup="from __main__ import mm, m")
> 
> >>>> t0.timeit(1000)
> 
> > 13.453603029251099
> 
> 
> 
> And I'd wager all the improvement is in the inner loop, the dot() function.
> 
> 
> 
> 
> 
> -- 
> 
> 
> 
> DaveA

Thanks for the tips of matrix operations over some fields or rings 
other than the real field and the complex field.

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Re: list comprehension question Dave Angel <d@davea.name> - 2012-10-17 08:32 -0400
  Re: list comprehension question rusi <rustompmody@gmail.com> - 2012-10-17 07:06 -0700
    Re: list comprehension question rusi <rustompmody@gmail.com> - 2012-10-17 07:33 -0700
    Re: list comprehension question Dave Angel <d@davea.name> - 2012-10-17 10:36 -0400
      Re: list comprehension question 88888 Dihedral <dihedral88888@googlemail.com> - 2012-10-17 07:45 -0700
      Re: list comprehension question 88888 Dihedral <dihedral88888@googlemail.com> - 2012-10-17 07:45 -0700
      Re: list comprehension question rusi <rustompmody@gmail.com> - 2012-10-17 07:50 -0700
        Re: list comprehension question 88888 Dihedral <dihedral88888@googlemail.com> - 2012-10-17 08:06 -0700

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