title: Random change the order of rows in a data frame
body: <p>I have a dataframe which have one column like this:</p>
  
  <pre><code>&gt; df$stocks
  1 stock1
  2 stock2
  3 stock3
  4 stock4
  </code></pre>
  
  <p>Is there any function which changes randomly the order of rows when I execute it like the first time I execute it the result of the data frame will be:</p>
  
  <pre><code> &gt; df$stocks
      1 stock2
      2 stock1
      3 stock4
      4 stock3
  </code></pre>
  
  <p>The next time will be something different etc.</p>