Re: User selectable lower array bound?

[Paul van Delst <paul.vandelst(at)noaa.gov>]

Jeff Guerber wrote:
> 
> On Thu, 2 Aug 2001, Paul van Delst wrote:
> 
> > Is is just me, or would anyone else find useful the ability to define
> > arrays in IDL such that the lower bound is *not* always zero? Sorta
> > like:
> >
> >   x = FINDGEN( 11, LOWER = -5 )
> > or
> >   y = DBLARR( 100, LOWER = 1 )
> >
> > so that accessing elements such as x[ -4 ] or y[ 100 ] are o.k.?  [...]
> 
>    Here, here!!  This was #1 on my (13-item) contribution to last summer's
> "Top 10 IDL Requests" discussion.  As I pointed out then, Fortran's had
> this capability for decades.  (And IDL is expressly a data-analysis
> language, like Fortran, not a systems-programming language like C.)  The
> biggest problem I see is that certain IDL intrinsics, like WHERE(), return
> -1 to indicate an invalid index.  Perhaps WHERE could return
> (lowerbound-1) instead, on the presumption that existing programs would be
> using 0-based arrays?  Of course it's much better to check the COUNT=
> keyword anyway.  (This would also be a good application for some sort of
> "undefined value" type.)

Well, maybe WHERE could work as it does now, but for cases where the start index is not
zero, a function like the Fortran 90 intrinsic LBOUND() could be used.

BTW, I never check the WHERE result either, always the COUNT value.

paulv

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