title: Python pandas, how to only plot a DataFrame that actually have the datapoint and leave the gap out
body: <p>I have a DataFrame with intraday data indexed with DatetimeIndex</p>
  
  <pre><code>df1 =pd.DataFrame(np.random.randn(6,4),index=pd.date_range('1/1/2000',periods=6, freq='1h'))
  df2 =pd.DataFrame(np.random.randn(6,4),index=pd.date_range('1/2/2000',periods=6, freq='1h'))
  df3 = df1.append(df2)
  </code></pre>
  
  <p>so as can be seen there is a big gap between within the two days in <code>df3</code></p>
  
  <p>df3.plot()</p>
  
  <p>will plot every single hour from <code>2000-01-01 00:00:00</code> to <code>2000-01-02 05:00:00</code>, while actually from <code>2000-01-01 06:00:00</code> to <code>2000-01-02 00:00:00</code> there are actually no datapoint.</p>
  
  <p>How to leave those data point in the plot so that from <code>2000-01-01 06:00:00</code> to <code>2000-01-02 00:00:00</code> is not plotted?</p>