title: Remove element from list in pandas dataframe based on value in column
body: <p>Let's say I have following dataframe:</p>
  
  <pre><code>a = [[1,2,3,4,5,6],[23,23,212,223,1,12]]
  b = [1,1]
  
  
  df = pd.DataFrame(zip(a,b), columns = ['a', 'b'])
  </code></pre>
  
  <p>And my goal is to remove the elements in the lists in series A that are in series B.  My attempt at doing so is below:</p>
  
  <pre><code>df['a'] = [i.remove(j) for i,j in zip(df.a, df.b)]
  </code></pre>
  
  <p>The logic seems sounds to me however I'm ending up with df['a'] being a series of nulls.  What is going on here?</p>