title: How to calculate returns from a vector of prices?
body: <p>I have to calculate the return of a vector that gives a historical price series of a stock.  The vector is of a form:</p>
  
  <pre><code>a &lt;- c(10.25, 11.26, 14, 13.56) 
  </code></pre>
  
  <p>I need to calculate daily gain/loss (%) - i.e. what is the gain it has from 10.25 to 11.26 then from 11.26 to 14 etc.  </p>
  
  <p>Is there a function to calculate this automatically?</p>