title: python pandas sum by hour of day
body: <p>I'm working with the following dataset with hourly counts (df):
  The datframe has 8784 rows (for the year 2016, hourly).</p>
  
  <p><a href="https://i.stack.imgur.com/4wvBM.png" rel="noreferrer"><img src="https://i.stack.imgur.com/4wvBM.png" alt="dataframe (df)"></a></p>
  
  <p>I'd like to see if there are daily trends (e.g if there is an increase in the morning hours. For this i'd like to create a plot that has the hour of the day (from 0 to 24) on the x-axis and number of cyclists on the y axis (something like in the picture below from <a href="http://ofdataandscience.blogspot.co.uk/2013/03/capital-bikeshare-time-series-clustering.html" rel="noreferrer">http://ofdataandscience.blogspot.co.uk/2013/03/capital-bikeshare-time-series-clustering.html</a>). </p>
  
  <p><a href="https://i.stack.imgur.com/vo2Qo.png" rel="noreferrer"><img src="https://i.stack.imgur.com/vo2Qo.png" alt="enter image description here"></a></p>
  
  <p>I experimented with differet ways of <code>pivot</code>, <code>resample</code> and <code>set_index</code> and plotting it with matplotlib, without success. In other words, i couldn't find a way to sum up every observation at a certain hour and then plot those for each weekday</p>
  
  <p>Any ideas how to do this? Thanks in advance!</p>