title: isset with variable array key count
body: <p>The array is multi-dimensional and has a variable number of sub-keys, like</p>
  
  <p><code>$arr[$a][$b][$c] = 'X';</code></p>
  
  <p>3 in this case. I want to create a function that takes a string like <code>a.b.c</code> as argument and checks if the array has that key in it, then unset it: unset($arr[$a][$b][$c]).</p>
  
  <p>if I give it <code>a.b</code> then it should unset($arr[$a][$b])</p>
  
  <p>I'd appreciate any help...</p>