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Re: N_ELEMENTS and WHERE: Scalar or Array ? [message #14181 is a reply to message #14130]

Wed, 03 February 1999 00:00

wmc
Messages: 117
Registered: February 1995

Senior Member

Craig Markwardt <craigmnet@astrog.physics.wisc.edu> wrote:
> wmc@bas.ac.uk writes:
>> ...
>> But since this has come up, & its one of my pet peeves: why cannot where
>> return a null array to indicate no-elements-match. And then array[null] would
>> match to nothing. This would allow one to say
>>
>> array[where(wurble)]='stoat'

> Amen brother! It is sadly unfortunate that where(0) returns a number
> at all. A null array -- if IDL had them! -- would be the best.

> Of course, there is the trade-off between power user and newbie user.
> Consider the following:

> wh_one = where(x GT 1)
> x[wh_ine] = 0 ; NOTE the type

> Because of the typo, the second statement would have the mysterious
> side effect of having no effect at all! (including no error message) I
> would still love to have it, but newbies might go crazy.

No, we're not going completely perl here: there is a distinction between an
undeclared variable (which would still cause an error in your example above)
and a variable initialised with a null value (which is what I would like
"where" to return). So your newbie would be safe.

In fact, would there be a problem with a "null" type, which would perhaps be
variable type #11? Then you don't have to worry about the actual value it
contains.

-W.

--
William M Connolley | wmc@bas.ac.uk | http://www.nbs.ac.uk/public/icd/wmc/
Climate Modeller, British Antarctic Survey | Disclaimer: I speak for myself

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[Message index]

		N_ELEMENTS and WHERE: Scalar or Array ? By: rmlongfield on Fri, 29 January 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: davidf on Wed, 03 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: steinhh on Wed, 03 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: wmc on Wed, 03 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: wmc on Wed, 03 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: Jack Saba on Tue, 02 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: steinhh on Tue, 02 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: Craig Markwardt on Mon, 01 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: wmc on Mon, 01 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: steinhh on Mon, 01 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: wmc on Mon, 01 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: Mark Buckley on Fri, 29 January 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: davidf on Fri, 29 January 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: David Ritscher on Fri, 29 January 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: David Kastrup on Fri, 29 January 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: R.Bauer on Fri, 29 January 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: David Ritscher on Thu, 04 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: Michael Werger on Thu, 04 February 1999 00:00
		Re: N_ELEMENTS and WHERE: Scalar or Array ? By: Annette Schloss on Wed, 03 February 1999 00:00

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