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Re: IDL function randperm? [message #36160 is a reply to message #36159]

Wed, 20 August 2003 06:00

K. Bowman
Messages: 330
Registered: May 2000

Senior Member

In article <Amara.Graps-2008031259130001@amaramac.ifsi.rm.cnr.it>,
Amara.Graps@ifsi.rm.cnr.it (Amara Graps) wrote:

> Greetings!
>
> I wonder if any of you have an IDL function that gives a
> random permutation of an array index, or know of a
> straightforward way to compute it?
>
> In Matlab such a function is called "randperm(n)"
> where n is the length of the array.
>
> For example, if one gives the integer 8, then it returns
> a length 8 integer array with values 0 to 7, randomly permutated.
>
> It is not as simple as it sounds, since the indices are unique.
> I tried variations of randomly SHIFT'g indices from INDGEN()
> with a random number generator, and the values were not
> 'jumbled' satisfactorily.
>
> Thanks in advance for any answer!
> Amara

If I understand your question, you can just generate n uniform random
variables and then sort the result.

IDL> x = LINDGEN(10)
IDL> y = RANDOMU(dseed, 10)
IDL> print, x
0 1 2 3 4 5
6 7
8 9
IDL> print, y
0.138249 0.0700486 0.310873 0.610514 0.332400
0.135694 0.975024
0.370555 0.763737 0.0268037
IDL> z = x[SORT(y)]
IDL> print, z
9 1 5 0 2 4
7 3
8 6

Ken Bowman

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[Message index]

		Re: IDL function randperm? By: meron on Wed, 20 August 2003 21:00
		Re: IDL function randperm? By: robert.dimeo on Wed, 20 August 2003 07:43
		Re: IDL function randperm? By: robert.dimeo on Wed, 20 August 2003 07:40
		Re: IDL function randperm? By: rigby on Wed, 20 August 2003 06:52
		Re: IDL function randperm? By: Amara.Graps on Wed, 20 August 2003 06:50
		Re: IDL function randperm? By: K. Bowman on Wed, 20 August 2003 06:00

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