title: How to find the set difference between two Pandas DataFrames
body: <p>I'd like to check the difference between two DataFrame columns. I tried using the command:</p>
  
  <pre><code>np.setdiff1d(train.columns, train_1.columns)
  </code></pre>
  
  <p>which results in an empty array:</p>
  
  <pre><code>array([], dtype=object)
  </code></pre>
  
  <p>However, the number of columns in the dataframes are different:</p>
  
  <pre><code>len(train.columns), len(train_1.columns) = (51, 56)
  </code></pre>
  
  <p>which means that the two DataFrame are obviously different. </p>
  
  <p>What is wrong here?</p>