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Re: Negative indexing and the WHERE function in IDL 8.0 [message #72165]

Thu, 19 August 2010 06:29

wlandsman
Messages: 743
Registered: June 2000

Senior Member

On Aug 19, 8:09 am, svhhaugan <s.v.h.hau...@gmail.com> wrote:
> On Aug 18, 6:31 pm, Chris Torrence <gorth...@gmail.com> wrote:
>
> How about using "compile_opt strictarrsubs" (which is IDL 7-
> compatible)
> to imply what it always implied in IDL 7 and before: all negative
> array subscripts are illegal, whether scalar or arrays.

That won't work for IDL 8.0 users who want to use the negative scalar
indexing, but still need strictarrsubs to give an error when
subscripting an array with another array with out of bound indices.

IDL> print,!version
{ x86_64 darwin unix Mac OS X 8.0 Jun 17 2010 64 64}

IDL> a = intarr(4)
IDL> a[ [-1,1,2,5] ] = [6,7,8,9]
IDL> print,a
6 7 8 9

--Wayne

P.S. I go back to the very early days (1986) of IDL when WHERE()
didn't have the COUNT parameter, and one had to specifically test
whether the returned index was equal to -1.

index = where(array)
if index[0] NE -1 then ....

but I had never seen before the use of CATCH to make sure WHERE()
returns a valid value. It seems very convoluted to me, but I suppose
it makes sense if one expects WHERE() to normally return a valid
index, and a single CATCH clause can be used for multiple WHERE()
statements to test for errors. But now those errors won't be
caught...

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[Message index]

		Re: Negative indexing and the WHERE function in IDL 8.0 By: wlandsman on Thu, 19 August 2010 06:29
		Re: Negative indexing and the WHERE function in IDL 8.0 By: svhhaugan on Thu, 19 August 2010 05:09
		Re: Negative indexing and the WHERE function in IDL 8.0 By: chris_torrence@NOSPAM on Wed, 18 August 2010 09:31
		Re: Negative indexing and the WHERE function in IDL 8.0 By: svhhaugan on Fri, 20 August 2010 03:36
		Re: Negative indexing and the WHERE function in IDL 8.0 By: Greg Hennessy on Thu, 19 August 2010 18:35
		Re: Negative indexing and the WHERE function in IDL 8.0 By: penteado on Thu, 19 August 2010 11:02

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