title: Remove dtype datetime NaT
body: <p>I am preparing a pandas df for output, and would like to remove the NaN and NaT in the table, and leave those table locations blank.  An example would be</p>
  
  <pre><code>mydataframesample 
  
  col1    col2     timestamp
  a       b        2014-08-14
  c       NaN      NaT
  </code></pre>
  
  <p>would become</p>
  
  <pre><code>col1    col2     timestamp
  a       b        2014-08-14
  c       
  </code></pre>
  
  <p>Most of the values are dtypes object, with the timestamp column being datetime64[ns].  In order to fix this, I attempted to use panda's <code>mydataframesample.fillna(' ')</code> to effectively leave a space in the location.  However, this doesn't work with the datetime types.  In order to get around this, I'm trying to convert the timestamp column back to object or string type.</p>
  
  <p>Is it possible to remove the NaN/NaT without doing the type conversion?  If not, how do I do the type conversion (tried str() and astype(str) but difficulty with datetime being the original format)?</p>