title: Regex to split a string only by the last whitespace character
body: <p>hopefully this should be a quick and simple one, using PHP I'm trying to split a string into an array but by only the last instance of whitespace. So far I have...</p>
  
  <pre><code>$str="hello this is     a    space";
  $arr=preg_split("/\s+/",$str);
  print_r($arr);
  
  Array ( [0] =&gt; hello [1] =&gt; this [2] =&gt; is [3] =&gt; a [4] =&gt; space ) 
  </code></pre>
  
  <p>...which splits by all instances of whitespace.</p>
  
  <p>How can I expand this regular expression to split by only the last instance of whitespace? To become...</p>
  
  <pre><code>Array ( [0] =&gt; hello this is     a [1] =&gt; space ) 
  </code></pre>
  
  <p>Thank you in advance of your help!</p>