title: Converting python dataframe(pandas) with a timestamp column to R dataframe using rpy2
body: <p>I have a pandas dataframe(df) with data as follows</p>
  
  <pre><code>                        time      id  locality_id  supply_hours
  0  2016-08-31 18:30:00+00:00     NaN          NaN           NaN
  1  2016-08-31 19:30:00+00:00     NaN          NaN           NaN
  2  2016-08-31 20:30:00+00:00     NaN          NaN           NaN
  3  2016-08-31 21:30:00+00:00  453604            1      0.095328
  4  2016-08-31 22:30:00+00:00     NaN          NaN           NaN
  </code></pre>
  
  <p>I neet to convert it to R dataframe. According to docs, all I need is </p>
  
  <pre><code>from rpy2.robjects import pandas2ri
  pandas2ri.activate()
  rdf=rpy2.robjects.DataFrame(df)
  </code></pre>
  
  <p>But I get the following error when I try it</p>
  
  <pre><code>    NotImplementedError: Conversion 'py2ri' not defined for 
  objects of type '&lt;class 'pandas.tslib.Timestamp'&gt;'
  </code></pre>
  
  <p>The following succeeds </p>
  
  <pre><code>rdf2=rpy2.robjects.DataFrame(df[['locality_id','supply_hours']])
  </code></pre>
  
  <p>So clearly it has some issues with converting time column in the dataframe. How to get this working? I am on rpy2==2.8.3 and pandas== 0.16.2.</p>