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Re: Randomize array order [message #55023 is a reply to message #55022]

Thu, 26 July 2007 05:50

mattf
Messages: 13
Registered: January 2007

Junior Member

On Jul 25, 3:17 pm, Conor <cmanc...@gmail.com> wrote:
> Hi everyone!
>
> Anyone know an efficient way to randomize an array (I have a
> sorted array that I want unsorted). Initially, I tried something like
> this:
>
> array = findgen(1000000)
> unsort = array[sort(randomu(seed,1000000))]
>
> It works, but sorting on a million elements is rather slow. Anyone
> know a faster way?

I think this is one of those vectorization cases where you have a
trade-off between processor time and memory-- the one 'obvious' faster
way that occurs to me is to pre-compute a sequence of a few billion
random integers-- and then just select sub-sequences as needed. It's
possible that there's some intermediate strategy that's not quite so
extravagantly wasteful of memory.

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[Message index]

		Re: Randomize array order By: Michael Galloy on Fri, 27 July 2007 15:35
		Re: Randomize array order By: James Kuyper on Fri, 27 July 2007 14:29
		Re: Randomize array order By: Conor on Fri, 27 July 2007 11:09
		Re: Randomize array order By: David Streutker on Fri, 27 July 2007 10:54
		Re: Randomize array order By: Conor on Fri, 27 July 2007 09:44
		Re: Randomize array order By: James Kuyper on Fri, 27 July 2007 09:29
		Re: Randomize array order By: James Kuyper on Fri, 27 July 2007 09:05
		Re: Randomize array order By: David Streutker on Fri, 27 July 2007 07:54
		Re: Randomize array order By: Paolo Grigis on Fri, 27 July 2007 06:59
		Re: Randomize array order By: Allan Whiteford on Fri, 27 July 2007 05:03
		Re: Randomize array order By: Allan Whiteford on Fri, 27 July 2007 02:33
		Re: Randomize array order By: David Streutker on Thu, 26 July 2007 14:27
		Re: Randomize array order By: Vince Hradil on Thu, 26 July 2007 13:32
		Re: Randomize array order By: David Streutker on Thu, 26 July 2007 09:57
		Re: Randomize array order By: Conor on Thu, 26 July 2007 09:22
		Re: Randomize array order By: Allan Whiteford on Thu, 26 July 2007 08:49
		Re: Randomize array order By: Vince Hradil on Thu, 26 July 2007 08:13
		Re: Randomize array order By: Vince Hradil on Thu, 26 July 2007 07:58
		Re: Randomize array order By: Conor on Thu, 26 July 2007 06:40
		Re: Randomize array order By: Allan Whiteford on Thu, 26 July 2007 06:30
		Re: Randomize array order By: Brian Larsen on Thu, 26 July 2007 06:06
		Re: Randomize array order By: Brian Larsen on Thu, 26 July 2007 06:04
		Re: Randomize array order By: mattf on Thu, 26 July 2007 05:50
		Re: Randomize array order By: Conor on Thu, 26 July 2007 05:28
		Re: Randomize array order By: Conor on Thu, 26 July 2007 05:24
		Re: Randomize array order By: Vince Hradil on Wed, 25 July 2007 12:59

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