title: Aggregating hourly count in dplyr
body: <p>I have following dataframe in R</p>
  
  <pre><code>Date                      ID      
  01-01-2017 12:39:00       CDF
  01-01-2017 01:39:00       WED
  01-01-2017 02:39:00       QWE
  01-01-2017 05:39:00       TYU
  01-01-2017 17:39:00       ERT
  02-01-2017 02:30:34       DEF   
  </code></pre>
  
  <p>I want to calculate hourly count of ID. My desired dataframe would be</p>
  
  <pre><code>Date           hours               Count
  01-01-2017     00:00 - 01:00       1
  01-01-2017     01:00 - 02:00       1
  01-01-2017     02:00 - 03:00       1
  01-01-2017     03:00 - 04:00       0
  01-01-2017     04:00 - 05:00       0
  01-01-2017     05:00 - 06:00       1
  .
  01-01-2017     23:00 - 00:00       0 
  .
  02-01-2017     12:00 - 01:00       0 
  02-01-2017     01:00 - 02:00       0
  02-01-2017     02:00 - 03:00       1
  </code></pre>
  
  <p>Where there is no id exists,I want hourly bucket to be zero. Every date will contain 24 hours movement. </p>
  
  <p>How can I achieve this in R?</p>