title: subtracting array values from another unequal array
body: <p>I have the following which works just fine when the arrays are of an equal length:</p>
  
  <p>(example)</p>
  
  <pre><code>$highNums = array(10,20,30,40,50,60);
  $lowNums = array(0,1,2,3,4,5);
  
  $result = array();
  for($i=0;$i&lt;count($highNums);$i++)
  {
      $result[$i] = $highNums[$i]-$lowNums[$i];
  }
  </code></pre>
  
  <p>The problem lies in that the array keys are dates (months) pulled from the database and where there is, say, 'january' and a value in the $lowNums array there won't always be a 'january' record in the $highNums. </p>
  
  <p>Is there any way to detect any missing values in each array and fill them with 0?
                                  }</p>