title: matplotlib.pyplot plot function shows incorrect sequence of points
body: <p>I have just started Python. Esp from core R backgroud, it might be very question.
  Here is my data<a href="https://i.stack.imgur.com/9GqgA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9GqgA.png" alt="enter image description here"></a></p>
  
  <p>i just want date value for every month_year value( simple x-y plot) . I tried these options- 
  1) </p>
  
  <pre><code>plt.plot(grouped_warning_data['month_year'], grouped_warning_data['date'])
  </code></pre>
  
  <p>2)    </p>
  
  <pre><code>plt.figure()
  plt.plot(grouped_warning_data['month_year'], grouped_warning_data['date'])
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/nJx6t.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nJx6t.png" alt="enter image description here"></a></p>
  
  <p>I dont know why sequence( connection to points)  is incorrect. What should i change?</p>