title: error met in plot two curves in one Figure (python-pandas-matplotlib)
body: <p>I tried to plot two <code>DataFrame</code> curves in one figure using <code>pandas</code> and <code>matplotlib</code> in <code>Python</code>. Here is my code:</p>
  
  <pre><code>import numpy as np
  import pandas as pd
  from pandas import DataFrame
  from matplotlib import pyplot as plt
  plt.figure()
  plt.hold()
  df['open'].plot(color="green", linewidth=1.0, linestyle="-",label='open')
  do = DataFrame(df[df['jiangjz']==True]['open'])
  do.plot(marker='o',linestyle=".") 
  axes = plt.gca()
  axes.set_xticklabels(df.index)
  plt.show()
  </code></pre>
  
  <p>The simple data structure of <code>df['open']</code> and <code>do</code> is:</p>
  
  <pre><code>df:              open       do(one data):        open
       index                         index   
       2014-10-18   11               2014-12-10    12
       2014-12-10   12
       2015-12-10   12
  </code></pre>
  
  <p>the <code>df</code> plotted is a curve and <code>do</code> is a point. If I removed the <code>hold()</code> line and the <code>axes</code> two line, it produces one figure, but the <code>x-lim</code> starts with day <code>2014-12-10</code> rather than <code>2014-10-18</code>. I reset the <code>x-lim</code> of the <code>do</code> to meet the <code>df</code>, but the result becomes two figure. <code>hold()</code> line does not seems to work.</p>