title: Inconsistency when setting figure size using pandas plot method
body: <p>I'm trying to use the convenience of the plot method of a pandas dataframe while adjusting the size of the figure produced.  (I'm saving the figures to file as well as displaying them inline in a Jupyter notebook).  I found the method below successful most of the time, except when I plot two lines on the same chart - then the figure goes back to the default size.</p>
  
  <p>I suspect this might be due to the differences between plot on a series and plot on a dataframe.</p>
  
  <p>Setup example code:</p>
  
  <pre><code>data = {
      'A': 90 + np.random.randn(366),
      'B': 85 + np.random.randn(366)
  }
  
  date_range = pd.date_range('2016-01-01', '2016-12-31')
  
  index = pd.Index(date_range, name='Date')
  
  df = pd.DataFrame(data=data, index=index)
  </code></pre>
  
  <p>Control - this code produces the expected result (a wide plot):</p>
  
  <pre><code>fig = plt.figure(figsize=(10,4))
  
  df['A'].plot()
  plt.savefig("plot1.png")
  plt.show()
  </code></pre>
  
  <p>Result:</p>
  
  <p><a href="https://i.stack.imgur.com/ZtLZ9.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ZtLZ9.png" alt="plot1.png"></a></p>
  
  <p>Plotting two lines - figure size is not (10,4)</p>
  
  <pre><code>fig = plt.figure(figsize=(10,4))
  
  df[['A', 'B']].plot()
  plt.savefig("plot2.png")
  plt.show()
  </code></pre>
  
  <p>Result:</p>
  
  <p><a href="https://i.stack.imgur.com/xrNmh.png" rel="noreferrer"><img src="https://i.stack.imgur.com/xrNmh.png" alt="plot2.png"></a></p>
  
  <p>What's the right way to do this so that the figure size is consistency set regardless of number of series selected?</p>