title: ValueError: Grouper for <something> not 1-dimensional
body: <p>I'm have the following code which creates a table and a barplot via seaborn.</p>
  
  <pre><code>#Building a dataframe grouped by the # of Engagement Types
  sales_type = sales.groupby('# of Engagement Types').sum()
  
  #Calculating the % of people who bought the course by # engagement types
  sales_type['% Sales per Participants'] =  round(100*(sales_type['Sales'] / sales_type['Had an Engagement']), 2)
  
  #Calculating the # of people who didn't have any engagements
  sales_type.set_value(index=0, col='Had an Engagement', value=sales[sales['Had an Engagement']==0].count()['Sales'])
  
  #Calculating the % of sales for those who didn't have any engagements
  sales_type.set_value(index=0, col='% Sales per Participants',
                       value=round(100 * (sales_type.ix[0, 'Sales'] / 
                                          sales[sales['Had an Engagement']==0].count()['Sales']),2))
  
  #Setting the graph image
  fig, (ax1) = plt.subplots(nrows=1, ncols=1, figsize=(12,4))
  sns.set_style("whitegrid")
  
  # Ploting the histagram for the % of total prospects
  ax1 = sns.barplot(x=sales_type.index,y='% Sales per Participants', data=sales_type ,ax=ax1)
  ax1.set(ylabel = '%')
  ax1.set_title('% Sales per Participants By # of Engagement Types') 
  
  #present the table
  sales_type.xs(['Had an Engagement', 'Sales','% Sales per Participants'],axis=1).transpose()
  #sales_type
  </code></pre>
  
  <p>I'm using the same code concept for other parameters I have with no issue. However, for one parameter I get an error: "ValueError: Grouper for '' not 1-dimensional" for the line code:</p>
  
  <pre><code>ax1 = sns.barplot(x=sales_type.index,y='% Sales per Participants', data=sales_type ,ax=ax1)
  </code></pre>
  
  <p>This error occurs although the dataframe doesn't have more than one dimension.</p>
  
  <p>This is the head of the table:</p>
  
  <pre><code>                       Sales  Pre-Ordered / Ordered Book  \
  # of Engagement Types                                      
  0                        1.0                         0.0   
  1                       20.0                       496.0   
  2                       51.0                       434.0   
  3                       82.0                       248.0   
  4                       71.0                       153.0   
  5                       49.0                        97.0   
  6                        5.0                        24.0   
  
                         Opted In For / Clicked to Kindle  Viewed PLC  \
  # of Engagement Types                                                 
  0                                                   0.0           0   
  1                                               27034.0        5920   
  2                                                6953.0        6022   
  3                                                1990.0        1958   
  4                                                 714.0         746   
  5                                                 196.0         204   
  6                                                  24.0          24   
  
                         # of PLC Engagement  Viewed Webinar  \
  # of Engagement Types                                        
  0                                      0.0               0   
  1                                   6434.0            1484   
  2                                   7469.0            1521   
  3                                   2940.0            1450   
  4                                   1381.0             724   
  5                                    463.0             198   
  6                                     54.0              24   
  
                         # of Webinars (Live/Replay)  \
  # of Engagement Types                                
  0                                              0.0   
  1                                           1613.0   
  2                                           1730.0   
  3                                           1768.0   
  4                                           1018.0   
  5                                            355.0   
  6                                             45.0   
  
                         OCCC Facebook Group Member  Engaged in Cart-Open  \
  # of Engagement Types                                                     
  0                                             0.0                     0   
  1                                           148.0                   160   
  2                                           498.0                  1206   
  3                                           443.0                   967   
  4                                           356.0                   511   
  5                                           168.0                   177   
  6                                            24.0                    24   
  
                         # of Engagement at Cart Open  Had an Engagement  \
  # of Engagement Types                                                    
  0                                               0.0               3387   
  1                                             189.0              35242   
  2                                            1398.0               8317   
  3                                            1192.0               2352   
  4                                             735.0                801   
  5                                             269.0                208   
  6                                              40.0                 24   
  
                         Total # of Engagements  % Sales per Participants  
  # of Engagement Types                                                    
  0                                         0.0                      0.03  
  1                                     35914.0                      0.06  
  2                                     18482.0                      0.61  
  3                                      8581.0                      3.49  
  4                                      4357.0                      8.86  
  5                                      1548.0                     23.56  
  6                                       211.0                     20.83  
  </code></pre>
  
  <p>This is the full error:</p>
  
  <pre><code>---------------------------------------------------------------------------
  ValueError                                Traceback (most recent call last)
  &lt;ipython-input-211-f0185fe64c1a&gt; in &lt;module&gt;()
       12 sns.set_style("whitegrid")
       13 # Ploting the histagram for the % of total prospects
  ---&gt; 14 ax1 = sns.barplot(x=sales_type.index,y='% Sales per Participants', data=sales_type ,ax=ax1)
       15 ax1.set(ylabel = '%')
       16 ax1.set_title('% Sales per Participants By # of Engagement Types')
  
  ValueError: Grouper for '&lt;class 'pandas.core.frame.DataFrame'&gt;' not 1-dimensional
  </code></pre>
  
  <p>I've tried to search the internet and Stack Overflow for this error, but got no results. Does anyone has an idea what's going on?</p>