title: How to convert datetime64 array to int?
body: <p>With this </p>
  
  <pre><code>pd.Timestamp("31.12.1999 23:59:12").value
  &gt;&gt;946684752000000000
  </code></pre>
  
  <p>I can get the integer value of a datetime elementary value.</p>
  
  <p>How can I get this done for an array of datetime values?</p>
  
  <pre><code>df = pd.DataFrame({"a": ["31.12.1999 23:59:12", "31.12.1999 23:59:13", "31.12.1999 23:59:14"], "b": [4, 5, 6]})
  df.insert(0, 'date', df.a.apply(lambda x: datetime.datetime.strptime(x, "%d.%m.%Y %H:%M:%S")))
  </code></pre>
  
  <p>Apparently, this does not work:</p>
  
  <pre><code>df.date.values.value
  &gt;&gt;AttributeError: 'numpy.ndarray' object has no attribute 'value'
  </code></pre>