title: pandas: filter rows of DataFrame with operator chaining
body: <p>Most operations in <code>pandas</code> can be accomplished with operator chaining (<code>groupby</code>, <code>aggregate</code>, <code>apply</code>, etc), but the only way I've found to filter rows is via normal bracket indexing</p>
  
  <pre><code>df_filtered = df[df['column'] == value]
  </code></pre>
  
  <p>This is unappealing as it requires I assign <code>df</code> to a variable before being able to filter on its values.  Is there something more like the following?</p>
  
  <pre><code>df_filtered = df.mask(lambda x: x['column'] == value)
  </code></pre>