title: filtering rows in Pandas with specific words (python)
body: <pre><code>mask = df['command'].str.contains('&lt;')   
  df[mask]
  </code></pre>
  
  <p>I am using the command above to filter out the rows in which its <code>command</code> column contains <code>&lt;</code>. This gives me:</p>
  
  <pre><code>ValueError: cannot index with vector containing NA / NaN values
  </code></pre>
  
  <p>Any help?</p>