title: Chopping a string into a vector of fixed width character elements
body: <p>I have an object containing a text string:</p>
  
  <pre><code>x &lt;- "xxyyxyxy"
  </code></pre>
  
  <p>and I want to split that into a vector with each element containing two letters:</p>
  
  <pre><code>[1] "xx" "yy" "xy" "xy"
  </code></pre>
  
  <p>It seems like the <code>strsplit</code> should be my ticket, but since I have no regular expression foo, I can't figure out how to make this function chop the string up into chunks the way I want it. How should I do this?</p>