title: TypeError: only integer scalar arrays can be converted to a scalar index Pandas Merge
body: <p>I am trying to merge two pandas dataframes. Here are what the dataframes' columns look like:</p>
  
  <p>toi_data:</p>
  
  <pre><code>MultiIndex([(    'Player',),
              (       'Pos',),
              (     'Shift',),
              (        'GP',),
              (    'EV TOI',),
              ('EV CF% Rel',),
              (  'EV GF/60',),
              (  'EV GA/60',),
              (    'PP TOI',),
              ('PP CF% Rel',),
              (  'PP GF/60',),
              (  'PP GA/60',),
              (    'SH TOI',),
              ('SH CF% Rel',),
              (  'SH GF/60',),
              (  'SH GA/60',),
              (      'Year',),
              (      'Team',)],
             )
  </code></pre>
  
  <p>new_df:</p>
  
  <pre><code>Index(['Player', 'Team', 'Year', 'Age', 'Pos', 'Country', 'Ht', 'Wt',
         'Birth Date', 'Draft', 'S/C', 'Salary', 'Summary', 'GP', 'G', 'A',
         'PTS', '+/-', 'PIM', 'EV', 'PP', 'SH', 'GW', 'EV.1', 'PP.1', 'SH.1',
         'S', 'S%', 'TOI', 'ATOI', 'OPS', 'DPS', 'PS', 'BLK', 'HIT', 'FOW',
         'FOL', 'FO%'],
        dtype='object')
  </code></pre>
  
  <p>Here is the code where I am trying to merge the two:</p>
  
  <pre><code>df2 = pd.merge(df1, toi_data, on=['Player', 'Team', 'Year'])
  </code></pre>
  
  <p>The error I am getting is:</p>
  
  <pre><code>TypeError: only integer scalar arrays can be converted to a scalar index
  </code></pre>
  
  <p>So my thought is that the toi_data dataframe is causing the error to be thrown. I've tried using .unstack() and reset_index(inplace=True) to convert the Multi-Index, but neither worked. Any ideas on how I can resolve this error? Thank you in advance!</p>