title: Pandas 0.13.1 use of groupby( ) with drop_duplicates( ) or dropna ( )
body: <p>I've just updated from a previous version to Pandas 0.13.1 - happily, this has opened up some options to me. Unhappily, it appears to have caused problems for some of my data wrangling code. I hadn't made any changes other than updating the Pandas version from 0.11.0</p>
  
  <p>The code that worked before, and no longer works, is as follows:</p>
  
  <pre><code>g_pres = g_pres.groupby(['follow','Focal','std_epoch']).dropna(0)
  </code></pre>
  
  <p>and/or</p>
  
  <pre><code>g_pres = g_pres.groupby(['follow','Focal','std_epoch']).drop_duplicates(0)
  </code></pre>
  
  <p>Using either results in the following Attribute Error:</p>
  
  <pre><code> ---------------------------------------------------------------------------
   AttributeError                            Traceback (most recent call last)
   &lt;ipython-input-169-5d3c7458da40&gt; in &lt;module&gt;()
   ----&gt; 1 g_pres = g_pres.groupby(['follow','Focal','std_epoch']).dropna(0)
  
   //anaconda/lib/python2.7/site-packages/pandas/core/groupby.pyc in __getattr__(self, attr)
       293 
       294         if hasattr(self.obj, attr) and attr != '_cache':
       --&gt; 295             return self._make_wrapper(attr)
       296 
       297         raise AttributeError("%r object has no attribute %r" %
  
  //anaconda/lib/python2.7/site-packages/pandas/core/groupby.pyc in _make_wrapper(self, name)
      308                    "using the 'apply' method".format(kind, name,
      309                                                      type(self).__name__))
  --&gt; 310             raise AttributeError(msg)
      311 
      312         f = getattr(self.obj, name)
  
  AttributeError: Cannot access callable attribute 'dropna' of 'DataFrameGroupBy' objects,         try using the 'apply' method
  </code></pre>
  
  <p>I have looked at the release notes, searching for groupby, drop_duplicates, and drop_na, but I can't find anything to indicate (at least to me) what might have caused this change. I am a beginner so perhaps I'm overlooking something. </p>
  
  <p>Does the drop_duplicates function no longer work for groupby dataframes? Is there a new syntax? ...Is this a feature or a bug? </p>
  
  <p>I thought perhaps the addition of the inplace method meant I needed to specify something that had been the default previously, but a look at the documentation for the relevant methods didn't yield any progress. </p>
  
  <p>[EDITED TO ADD EXAMPLE DATA]</p>
  
  <p>Example input: </p>
  
  <pre><code>      follow     std_epoch     Focal     0
   0    1          1             53704     51602
   1    1          1             53704     51602
   2    1          2             53704     51602
   3    2          1             53505     51509     
   4    2          2             53505     51509
  </code></pre>
  
  <p>Example output, where I want to group by follow, std_epoch, and Focal -- and drop duplicate values from column '0', group-wise (in this example, that's row 2 in the input).</p>
  
  <pre><code>      follow     std_epoch     Focal     0
   0    1          1             53704     51602
   1    1          2             53704     51602
   2    2          1             53505     51509     
   3    2          2             53505     51509
  </code></pre>