title: Python bar and line chart with groups in one graph
body: <p>I have a data like this:  </p>
  
  <pre><code>Group   yq        Value1    Value2
  G       2014Q1     0.07        1.1
  G       2014Q2     0.06        1.09
  G       2014Q3     0.09        1.11
  G       2014Q4     0.04        1.13
  I       2014Q1     0.10        1.2
  I       2014Q2     0.13        1.25
  I       2014Q3     0.15        1.23
  I       2014Q4     0.18        1.4
  </code></pre>
  
  <p>I want to plot line and bar chart in one graph.<br>
  I tried to plot bar first, but it output two graphs (2 groups, G and I):  </p>
  
  <pre><code>import matplotlib.pyplot as plt
  ax = dataset.groupby('Group')[['yq', 'Value1']].plot(x = 'yq', kind='bar')
  </code></pre>
  
  <p>After that, I tried to draw line chart with it.  </p>
  
  <pre><code>fig, ax1 = plt.subplots(figsize=(7, 5))
  ax2 = ax1.twinx()
  dataset[['Value1', 'yq', 'Group']].groupby('Group').plot(x = 'yq', kind='bar', color='y', ax=ax1)
  dataset[['Value2', 'yq', 'Group']].groupby('Group').plot(x = 'yq', kind='line', marker='d', ax=ax2)
  ax1.yaxis.tick_right()
  ax2.yaxis.tick_left()
  </code></pre>
  
  <p>However, the plot is weird. It does not proper show all labels on x-axis. To be concise. it just show year rather than year and quarter.<br>
  Moreover, the plot does not plot bar chart on it either.  </p>
  
  <p>Any suggestion?  </p>
  
  <p>I also tried:  </p>
  
  <pre><code>fig, ax = plt.subplots(figsize=(10, 5))
  dataset[['Value1', 'yq', 'Group']].plot(x = 'yq', kind='bar', stacked=False, title='get_title', color='grey', ax=ax, grid=False)
  ax2 = ax.twinx()
  ax2.plot(ax.get_xticks(), dataset[['Value2']].values, linestyle='-', marker='o', color='k', linewidth=1.0, label='percentage')
  lines, labels = ax.get_legend_handles_labels()
  lines2, labels2 = ax2.get_legend_handles_labels()
  ax.legend(lines + lines2, labels + labels2, loc='best')
  ax.yaxis.set_ticks_position("right")
  ax2.yaxis.set_ticks_position("left")
  fig.autofmt_xdate()
  plt.show()
  </code></pre>
  
  <p>This plot is incorrect but can plot line and bar on same graph.  </p>