title: Pandas "Can only compare identically-labeled DataFrame objects" error
body: <p>I'm using Pandas to compare the outputs of two files loaded into two data frames (uat, prod):
  ...</p>
  
  <pre><code>uat = uat[['Customer Number','Product']]
  prod = prod[['Customer Number','Product']]
  print uat['Customer Number'] == prod['Customer Number']
  print uat['Product'] == prod['Product']
  print uat == prod
  
  The first two match exactly:
  74357    True
  74356    True
  Name: Customer Number, dtype: bool
  74357    True
  74356    True
  Name: Product, dtype: bool
  </code></pre>
  
  <p>For the third print, I get an error:
  Can only compare identically-labeled DataFrame objects. If the first two compared fine, what's wrong with the 3rd?</p>
  
  <p>Thanks</p>