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Non-intuitive result with !Null in Where() [message #85610]

Wed, 21 August 2013 09:42

Matthew Argall
Messages: 286
Registered: October 2011

Senior Member

This is not what I expected. If there are no elements, how can "count" be non-zero? I was hoping that Where() would return !Null and "count" would be 0.

IDL> print, n_elements(!Null)
0
IDL> print, where(!Null ne 0, count)
0
IDL> print, count
1
IDL> print, where(!Null ne 0, count, /NULL)
0
IDL> print, count
1
IDL> print, !Null[0]
% Expression must be an array in this context: !NULL.
IDL> print, (!Null)[0]
% Variable is undefined: <UNDEFINED>.

The Where function is telling me I can access !Null at element 0, but I cannot.

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

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[Message index]

		Non-intuitive result with !Null in Where() By: Matthew Argall on Wed, 21 August 2013 09:42
		Re: Non-intuitive result with !Null in Where() By: David Fanning on Wed, 21 August 2013 09:48
		Re: Non-intuitive result with !Null in Where() By: Matthew Argall on Wed, 21 August 2013 10:52
		Re: Non-intuitive result with !Null in Where() By: Heinz Stege on Wed, 21 August 2013 16:51

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