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| Re: IDL function randperm? [message #36156 is a reply to message #36154] |
Wed, 20 August 2003 07:43  |
robert.dimeo
Messages: 42
Registered: November 2001
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Member |
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Oops...mistake in the syntax of my last posting...
Try this:
function randperm,n
return,sort(randomn(s,n))
end
Amara.Graps@ifsi.rm.cnr.it (Amara Graps) wrote in message news:<Amara.Graps-2008031259130001@amaramac.ifsi.rm.cnr.it>...
> 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
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| Re: IDL function randperm? [message #36157 is a reply to message #36156] |
Wed, 20 August 2003 07:40 |
robert.dimeo
Messages: 42
Registered: November 2001
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Member |
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Hi,
How about...
function randperm,n
return, array = sort(randomn(s,n))
end
Amara.Graps@ifsi.rm.cnr.it (Amara Graps) wrote in message news:<Amara.Graps-2008031259130001@amaramac.ifsi.rm.cnr.it>...
> 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
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| Re: IDL function randperm? [message #36158 is a reply to message #36157] |
Wed, 20 August 2003 06:52 |
rigby
Messages: 16
Registered: September 1995
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Junior Member |
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This is what I use to randomly reorder an array, stripped down to its
essentials.I stole the idea from the old RSI newsletter many years
ago.
FUNCTION Randomize, list, seed
; LIST is the array to be randomized
; SEED is the random number generator seed
n = n_elements(list)
return, list[sort(randomu(seed,n))]
end ;; Randomize
IDL> seed = 1
IDL> print, Randomize( indgen(5), seed)
1 0 3 2 4
Note that randomu(), and thus Randomize(), returns SEED as a
36-element long array, tho' you can initialize it with a scalar.
--Wayne
Amara.Graps@ifsi.rm.cnr.it (Amara Graps) wrote in message news:<Amara.Graps-2008031259130001@amaramac.ifsi.rm.cnr.it>...
> 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?
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| Re: IDL function randperm? [message #36159 is a reply to message #36158] |
Wed, 20 August 2003 06:50 |
Amara.Graps
Messages: 11
Registered: November 1998
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Junior Member |
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> If I understand your question, you can just generate n uniform random
> variables and then sort the result.
>> [...]
> Ken Bowman
Dear Ken,
Great! That's exactly what I wanted. Thanks alot.
Amara
--
************************************************************ *******
Amara Graps, PhD |Istituto di Fisica dello Spazio Interplanetario
| INAF, Roma, Italia
| tel +39-06-4993-4384 fax +39-06-4993-4383
http://www.mpi-hd.mpg.de/dustgroup/~graps
************************************************************ ******
"We came whirling out of Nothingness scattering stars like dust."
- Rumi
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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
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Senior Member |
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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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