title: I want to get hour ranges of a dataframe
body: <p>I want to demonstrate the hour ranges of a dataframe which has index column as date.</p>
  
  <p>For example, I have as the following data:</p>
  
  <pre><code>Date                   col1 
  2019-10-10 00:00:00    person1
  2019-10-10 01:00:00    person1
  2019-10-10 02:00:00    person1
  2019-10-10 03:00:00    person2
  2019-10-10 04:00:00    person2
  2019-10-10 05:00:00    person2
  2019-10-10 06:00:00    person2
  2019-10-10 07:00:00    person2
  2019-10-10 08:00:00    person3
  2019-10-10 09:00:00    person3
  2019-10-10 10:00:00    person3
  2019-10-10 11:00:00    person3
  2019-10-10 12:00:00    person3
  </code></pre>
  
  <p>I want to this data like this:</p>
  
  <pre><code>Hour               col2
  00:00 - 02:00      person1
  03:00 - 07:00      person2
  08:00 - 12:00      person3
  </code></pre>
  
  <p>How can I do this?</p>