title: Subtract Col A - Col B in pandas dataframe
body: <p>I have two string columns in a dataframe and I'm looking to subtract common words in B from A.</p>
  
  <pre><code>A -&gt;  Stack Overlflow is great            
  
  
  B -&gt; stack great
  
  
  A-B -&gt; overflow is
  </code></pre>
  
  <p>I have tried the following code. But it only works if the column B has one word.</p>
  
  <pre><code>df['A-B'] = [' '.join(set(a.split())-set(b.split())) for a, b in zip(df['A'], df['B'])]
  </code></pre>
  
  <p>Is there any change I can make so that it works when B has multiple words?</p>