title: summing the number of occurrences per day pandas
body: <p>I have a data set like so in a pandas dataframe:</p>
  
  <pre><code>                                  score
  timestamp                                 
  2013-06-29 00:52:28+00:00        -0.420070
  2013-06-29 00:51:53+00:00        -0.445720
  2013-06-28 16:40:43+00:00         0.508161
  2013-06-28 15:10:30+00:00         0.921474
  2013-06-28 15:10:17+00:00         0.876710
  </code></pre>
  
  <p>I need to get counts for the number of measurements, that occur so I am looking for something like this:</p>
  
  <pre><code>                                    count
     timestamp
     2013-06-29                       2
     2013-06-28                       3
  </code></pre>
  
  <p>I do not care about the sentiment column I want the count of the occurrences per day. </p>