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checking if variable is defined [message #24625]

Wed, 11 April 2001 08:47

Dominik[1]
Messages: 46
Registered: April 2001

Member

Helle there,

I would like to plot a variable, but only if it is existing. When the
Variable is undefined, nothing should happen. So I am searching for an
expression for the if statement. Does anybody know an expression like:
if ( vaiable_name existing) then...

Thanks

Dominik

--
_____________________________
Dominik Paul
dpaul@ukl.uni-freiburg.de
Universit�tsklinikum Freiburg
Abt. PET/Nuklearmedizin

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Re: checking if variable is defined [message #24759 is a reply to message #24625]

Thu, 12 April 2001 05:19

Bernard Puc
Messages: 65
Registered: January 1998

Member

Dominik wrote:
>
> Helle there,
>
> I would like to plot a variable, but only if it is existing. When the
> Variable is undefined, nothing should happen. So I am searching for an
> expression for the if statement. Does anybody know an expression like:
> if ( vaiable_name existing) then...

One way to do this is with the N_ELEMENTS() function:

if (n_elements( variable ) GT 0) then print,'Variable exists'

--
Bernard Puc AETC, INC.
bpuc@va.aetc.com 1225 Jefferson Davis Highway #800
(703) 413-0500 Arlington, VA 22202

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Re: checking if variable is defined [message #24774 is a reply to message #24625]

Wed, 11 April 2001 09:59

davidf
Messages: 2866
Registered: September 1996

Senior Member

Dominik (dpaul@ukl.uni-freiburg.de) writes:

> I would like to plot a variable, but only if it is existing. When the
> Variable is undefined, nothing should happen. So I am searching for an
> expression for the if statement. Does anybody know an expression like:
> if ( vaiable_name existing) then...

IF N_Elements(variable_name) NE 0 THEN doSomething

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@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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