title: Remove elements from a list in pandas dataframe
body: <p>I'd like to remove a particular value from within a list in the pandas dataframe column. How do I go about this?</p>
  
  <pre><code>df = pd.DataFrame({'A': ['a1', 'a2', 'a3'],
                 'B': [['b1', 'b2'], ['b1', 'b1'], ['b2']],
                 'C': [['c1', 'b1'], ['b3'], ['b2', 'b2']],
                 'D': ['d1', 'd2', 'd3']})
  </code></pre>
  
  <p>I want to remove the string 'b1' in lists from the column 'B' in the dataframe.</p>