title: R: Calculate time intervals
body: <p>If I have a vector of dates and hours such as...</p>
  
  <pre><code>c("2016-03-15 13","2016-03-16 23","2016-03-17 06","2016-03-18 15","2016-03-19 08","2016-03-20 21")
  </code></pre>
  
  <p>Can I find the number of hours that pass between each timestamp? I looked into <code>difftime</code> but it requires 2 vectors.</p>