Empty Array causing an error

I have a large query and part of it depends upon a returned Array.  If there is no data returned by the query, the Array is empty, obviously.  But My code so far has an area that is looking for the the second part of the Array Data:
$a = false;
  $b = false; 
  if($wave[0] <= $wave_max) $a = true; 
   if($wave[1] >= $wave_min) $b = true; 
   	$wavelength = '';
   	if($a && $b) $wavelength = true;

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So if the return is empty, I get an error on this line:  if($wave[1] >= $wave_min) $b = true; , the second part of the array.
The error message is:
A PHP Error was encountered
Severity: Notice
Message: Undefined offset: 1
And refers to that line
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Dave BaldwinFixer of ProblemsCommented:
You can use 'isset' to check to see if the variable exists.

I typically use 'isset' check $_POST variables to see if they exist and set them to a default values if they don't.  Something like below.

if(!isset($wave[1])) $wave[1] ='';

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rgranlundAuthor Commented:
Thanks Dave.  I have been spinning my wheels for a while.
Dave BaldwinFixer of ProblemsCommented:
You're welcome, glad to help.
Ray PaseurCommented:
You may find this function useful, too.
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