title: Convert float64 column to datetime pandas
body: <p>I have the following <code>pandas DataFrame</code> column <code>dfA['TradeDate']</code>:</p>
  
  <pre><code>0     20100329.0
  1     20100328.0
  2     20100329.0
  ...
  </code></pre>
  
  <p>and I wish to transform it to a datetime.</p>
  
  <p>Based on another tread on SO, I convert it first to a string and then apply the <code>strptime</code> function.</p>
  
  <pre><code>dfA['TradeDate'] = datetime.datetime.strptime( dfA['TradeDate'].astype('int').to_string() ,'%Y%m%d')
  </code></pre>
  
  <p>However this returns the error that my format is incorrect (<code>ValueError</code>).</p>
  
  <p>An issue that I spotted is that the column is not properly to string, but to an object.</p>
  
  <p>When I try:</p>
  
  <pre><code>dfA['TradeDate'] = datetime.datetime.strptime( dfA['TradeDate'].astype(int).astype(str),'%Y%m%d')
  </code></pre>
  
  <p>It returns: must be a Str and not Series.</p>