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Re: IDL-way to use WHERE result as subscripting indices without having to do IF count [message #76184 is a reply to message #76183]

Fri, 20 May 2011 06:19

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Robin Wilson writes:

> I'm sure this has been discussed before, but I can't find the
> discussion. I have a lot of code that looks like the following:
>
> Array[WHERE(Input LT 5)] = 2
> Array[WHERE(Input GT 7 AND OtherArray LT 9) = 6
> etc...
>
> I know I shouldn't be using WHERE like that without checking the count
> of items returned, as it will crash if there are no values in Input less
> than 5. My question is: is there an IDL-way to do this, without putting
> in loads of IF count NE 0 statements above each of the assignemnts?
> That'll make the code a lot longer, a lot messier etc.
>
> Any ideas?

Bite the bullet. You'll be glad you did. :-)

Or, if in IDL 8, set the NULL keyword to the Where
function:

IDL> a=[1,2]
IDL> help, where(a lt 0)
<Expression> LONG = -1
IDL> help, where(a lt 0, /null)
<Expression> UNDEFINED = !NULL
IDL> c=a[where(a lt 0, /NULL)]

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: IDL-way to use WHERE result as subscripting indices without having to do IF count By: Heinz Stege on Fri, 20 May 2011 08:22
		Re: IDL-way to use WHERE result as subscripting indices without having to do IF count By: David Fanning on Fri, 20 May 2011 06:27
		Re: IDL-way to use WHERE result as subscripting indices without having to do IF count By: David Fanning on Fri, 20 May 2011 06:19
		Re: IDL-way to use WHERE result as subscripting indices without having to do IF count By: Robin Wilson on Fri, 20 May 2011 06:18
		Re: IDL-way to use WHERE result as subscripting indices without having to do IF count By: penteado on Fri, 20 May 2011 06:16

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