title: data points connected in wrong order in line graph
body: <p>I'm reading a pandas dataframe, and trying to generate a plot from it. In the plot, the data points seem to be getting connected in an order determined by ascending y value, resulting in a weird zig-zagging plot like this:</p>
  
  <p><img src="https://i.stack.imgur.com/KNHRi.jpg" alt="enter image description here"></p>
  
  <p>The code goes something like this:</p>
  
  <pre><code>from pandas import DataFrame as df
  import matplotlib as mpl
  mpl.use('Agg')
  import matplotlib.pyplot as plt
  
  data = df.from_csv(...)
  
  plt.plot(data['COL1'], data['COL2'])
  </code></pre>
  
  <p>Any suggestions on how to fix the order in which the dots are connected (i.e. connect them in the sequence in which they appear going from left to right on the plot)? Thanks.</p>