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Re: Testing for NODATA presence in a dataset [message #33388 is a reply to message #33386]

Sat, 21 December 2002 14:20

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Jonathan Greenberg (greenberg@ucdavis.edu) writes:

> I'm having a problem testing for whether an entry in an array is NAN --
> doing something like:
>
> If (value EQ !VALUES.F_NAN) then begin
> print,'Not a number'
> Endif else begin
> print,'Is a number!'
> Endelse
>
> Will always return 'Is a number', even if I set:
> value = !VALUES.F_NAN
>
> What's going wrong with this?

The problem is that NAN is ... well, not a number.
Thus, you can't use it in expressions that
require a number. (Think of it as a mathematical
Catch-22, if you like.)

The proper way to write this code is like this:

If Finite(value) EQ 0 then begin
print,'Not a number'
Endif else begin
print,'Is a number!'
Endelse

Cheers,

David

--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Re: Testing for NODATA presence in a dataset By: thompson on Thu, 26 December 2002 12:58
		Re: Testing for NODATA presence in a dataset By: David Fanning on Thu, 26 December 2002 08:25
		Re: Testing for NODATA presence in a dataset By: thompson on Tue, 24 December 2002 07:11
		Re: Testing for NODATA presence in a dataset By: Kenneth P. Bowman on Mon, 23 December 2002 06:42
		Re: Testing for NODATA presence in a dataset By: tam on Sun, 22 December 2002 18:33
		Re: Testing for NODATA presence in a dataset By: David Fanning on Sat, 21 December 2002 14:20
		Re: Testing for NODATA presence in a dataset By: tam on Mon, 30 December 2002 06:52

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