title: Plotting frequency distribution through time (stacked)
body: <p>I am trying to plot how many people there were in a shop by date. 
  To do this, first I grouped by date people's names:</p>
  
  <pre><code>df.groupby(['Date', 'Name']).size()
  </code></pre>
  
  <p>The result is shown below</p>
  
  <pre><code>    Date        Name  
  
  
  2020-01-25  John       1
  2020-01-26  John       1
  2020-01-27  John       1
  2020-01-28  Luca       1
              John       1
                   ..
  2020-03-30  John       1
  2020-03-31  Martyn     2
              Christine  1
              Mary       1
              John       1
  </code></pre>
  
  <p>Now, I would like to see how many people there were each day (<code>1</code> on <code>25/01</code>, <code>1</code> on <code>26/01</code>, <code>1</code> on <code>27/01</code>, <code>3</code> on <code>28/01</code>, and so on), and who. 
  So I would need a histogram (bar plot) that can help me to visualise these results. In order to see the frequency of same people on the same day (like Martyn, that went twice), I would need to consider a stacked plot (I think). 
  Since the number of names is around 1000, could you please tell me if it would be possible to have a legend/labels that can be readable? </p>
  
  <p>Could you please show me how to do this? Plots are my weakness (unfortunately). </p>