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Re: Ordered index array [message #45444 is a reply to message #45443]

Wed, 07 September 2005 10:01

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Emmanuel Christophe writes:

> I would like to change the values on an array according to the order
> they appear. Following this example:
>
> starting with the array
> [3,6,2,1,2,8,1,1]
> I would like to get
> [1,2,3,4,3,5,4,4]
>
> 3 being the first value seen it is affected to 1
> 6 being the second, affected to 2
> ...
>
> I guess this process is similar to lookup tables, or color tables. As I
> would like to process quite big arrays (>60000 long elements), i'm
> looking for an efficient function. I don't really know what to look for
> in IDL help to find something which could help.

How about this:

PRO TEST
a = [3,6,2,1,2,7,1,1]
h = Histogram(a, Reverse_Indices=ri, Min=0)
b = Indgen(N_Elements(h)) + 1
c = Intarr(N_Elements(h))
FOR j=0,N_Elements(h)-1 DO BEGIN
IF ri[j+1] NE ri[j] THEN $
c[ri[ri[j]:ri[j+1]-1]] = Min(b[ri[ri[j]:ri[j+1]-1]])
ENDFOR
Print, c
END

1 2 3 4 3 6 4 4

Note that your original example is wrong. :-)

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		Re: Ordered index array By: Emmanuel Christophe on Thu, 08 September 2005 07:51
		Re: Ordered index array By: David Fanning on Thu, 08 September 2005 06:55
		Re: Ordered index array By: Paolo Grigis on Thu, 08 September 2005 06:51
		Re: Ordered index array By: David Fanning on Thu, 08 September 2005 06:08
		Re: Ordered index array By: David Fanning on Thu, 08 September 2005 06:02
		Re: Ordered index array By: Paolo Grigis on Thu, 08 September 2005 05:30
		Re: Ordered index array By: Paolo Grigis on Thu, 08 September 2005 03:03
		Re: Ordered index array By: Emmanuel Christophe on Thu, 08 September 2005 01:58
		Re: Ordered index array By: Emmanuel Christophe on Thu, 08 September 2005 01:48
		Re: Ordered index array By: Paolo Grigis on Thu, 08 September 2005 01:22
		Re: Ordered index array By: David Fanning on Wed, 07 September 2005 10:17
		Re: Ordered index array By: David Fanning on Wed, 07 September 2005 10:01

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