title: Convert a list into a string
body: <p>I would like to convert value stored as a <code>list</code> into a single string.</p>
  
  <p>For example:</p>
  
  <pre><code>l &lt;- list(1,2,3,4)
  </code></pre>
  
  <p>would give:</p>
  
  <pre><code>"1234"
  </code></pre>
  
  <p>and not as using the output of <code>unlist()</code>:</p>
  
  <pre><code>unlist(l)
  #[1] "1" "2" "3" "4"
  </code></pre>