title: Append two dataframes (Python Pandas)
body: <p>Very basic issue, but I'm having a hard time figuring out what's wrong. As a result of a Logistic Regression model, I have a set of predictions. I turned that numpy array into a dataframe (single column). Now I want to 'attach' the results to my original data, so I can check my predictions. Seems so simple, but I get the following message:</p>
  
  <p>RuntimeWarning: '&lt;' not supported between instances of 'str' and 'int', sort order is undefined for incomparable objects
  result = result.union(other)</p>
  
  <p>Sample Looks like this:</p>
  
  <pre><code>Set
  ColA, ColB, ColC
  1234, AAAA, BBBB
  
  Pred
  0 -- column name
  1 -- values
  
  Desired result:
  ColA, ColB, ColC, 0
  1234, AAAA, BBBB, 1
  
  Actual result:
  ColA, ColB, ColC, NaN
  NaN,  NaN,  NaN,  1
  
  My code seems straightforward:
  
  res = Set.append(Pred)
  res
  </code></pre>
  
  <p>Any help with this issue would be great. As you might see, I am at a beginner level in Pandas...</p>
  
  <p>Regards, M.</p>