title: GroupBy items and count item every hour in Pandas
body: <p>I have the following dataset with a 'datetime' object as index</p>
  
  <pre><code>index                                Item
  
  2016-10-30 09:58:11                 Bread
  2016-10-30 10:05:34          Scandinavian
  2016-10-30 10:05:34          Scandinavian
  2016-10-30 10:07:57         Hot chocolate
  2016-10-30 10:07:57                   Jam
  2016-10-30 10:07:57               Cookies
  2016-10-30 10:19:12                Pastry
  2016-10-30 10:19:12                Coffee
  2016-10-30 10:19:12                   Tea
  2016-10-30 10:20:51                Pastry
  2016-10-30 10:20:51                 Bread
  2016-10-30 10:21:59                 Bread
  2016-10-30 10:21:59                Muffin
  </code></pre>
  
  <p>Being new to Pandas I am a bit lost on how to groupby the dataframe. I need the two things 1) item count for every hour, like total count for 'Bread' every hour</p>
  
  <p>Something like the following</p>
  
  <pre><code>index           item          count
  
   2016-10-30 09:00:00   Bread   3
   2016-10-30 10:00:00  Coffee  10
   2016-10-30 11:00:00   Toast   1
  </code></pre>
  
  <p>Then a total count of items in the 24-hour day span</p>
  
  <pre><code>index          item  count
  
   2016-10-30    Bread  13
   2016-10-30   Coffee  1200
   2016-10-30    Toast  19
  </code></pre>
  
  <p>Probably two separate operations?</p>