title: Counting number of entries generated every 30 seconds in R from a csv file
body: <p>I have the following data in a csv file which I read into my R script.</p>
  
  <pre><code>create_date
  2016-03-16 11:25:56
  2016-03-16 11:25:23
  2016-03-16 11:25:12
  2016-03-15 17:25:15
  </code></pre>
  
  <p>I want to count the number of entries generated every 30 seconds. e.g. the number of entries generated in <code>2016-03-16 11:25:01</code> and <code>2016-03-16 11:25:30</code> is <code>2</code>. Between <code>2016-03-16 11:25:31</code> and <code>2016-03-16 11:26:00</code> is <code>1</code> and so on. </p>
  
  <p>How can I do this in R?</p>