title: PerformanceWarning: Adding/subtracting array of DateOffsets to Series not vectorized "Series not vectorized", PerformanceWarning)
body: <p>I have a table having following data:</p>
  
  <pre><code>    StudentID   LO_0    LO_1
  0   student001  2017-02-07T16:37:57 2017-01-21T15:32:46
  11  student015  2017-02-07T15:32:09 2017-01-03T21:15:33
  56  student072  2017-02-07T19:59:46 2017-02-06T14:03:57
  63  student079  2017-02-04T16:52:43 2017-01-23T10:00:27
  </code></pre>
  
  <p>When I issue below command from jupyter "notebook" then I get expected result</p>
  
  <pre><code>df_test['Delta_t']= abs((df_test.loc[:,item1] - df_test.loc[:,item2]).astype('timedelta64[h]').astype('int'))
  
      Delta_t
      409
      834
      29
      294
  </code></pre>
  
  <p>But when I run this same command from a python script, I get following performance warning and error for the same command:</p>
  
  <pre><code>anaconda/lib/python3.5/site-packages/pandas/core/ops.py:477: PerformanceWarning: Adding/subtracting array of DateOffsets to Series not vectorized "Series not vectorized", PerformanceWarning)
  </code></pre>
  
  <p>error</p>
  
  <pre><code>TypeError: ufunc subtract cannot use operands with types dtype('&lt;M8[ns]') and dtype('O')
  </code></pre>