title: How to Plot a Dash plotly graph with categories count on a particular date
body: <p>How to plot a stacked bar graph of the count of the number of "Major /Minor" issues at any point of time?</p>
  
  <p>I have data in csv file as follows:</p>
  
  <pre><code>Issue_Date   Severity
  
  20.2.2020    Major 
  20.2.2020    Minor
  31.3.2020    Major 
  31.3.2020    Major 
  31.3.2020    Minor
  01.4.2020    Major
  </code></pre>
  
  <p>I am reading the above CSV using pandas data frame and I tried to count the occurrence of particular Severity on a given date using group by method</p>
  
  <pre><code>data = df.groupby(["Issue_Date", "Severity"]).size()
  </code></pre>
  
  <p>Here "data" is a Series
  Output:</p>
  
  <pre><code>Issue_Date     Severity
  20.2.2020       Major     1
                  Minor     1
  31.3.2020       Major     2
                  Minor     1
  01.4.2020       Major     1
  </code></pre>
  
  <p>On xaxis display Issue_date and on yaxis display counts and plot stacked categories on the basis of severity.</p>
  
  <p>How can I achieve it using dash plotly?</p>