title: How to filter a pandas DatetimeIndex by day of week and hour in the day
body: <p>I have a pandas DatetimeIndex and I would like to filter the index by the criterion that the day of the week and hour of the day matches a list. 
  For example, I have of list of tuples indicating valid (day of week, hour, minute) for each TimeStamp:</p>
  
  <pre><code>[(4, 6), (5, 7)]
  </code></pre>
  
  <p>The final index should only contain date times that are Friday(day_of_week = 4) hour 6 or Saturday(day_of_week = 5) hour 7.</p>
  
  <p>Lets say the input data frame is like:</p>
  
  <pre><code>2016-04-02 06:30:00  1
  2016-04-02 06:45:00  2
  2016-04-02 07:00:00  3
  2016-04-02 07:15:00  4
  2016-04-03 07:30:00  5
  2016-04-03 07:45:00  6
  2016-04-03 08:00:00  7
  </code></pre>
  
  <p>After the filter, it should be like:</p>
  
  <pre><code>2016-04-02 06:30:00  1
  2016-04-02 06:45:00  2
  2016-04-03 07:30:00  5
  </code></pre>
  
  <p>Because I only keep indices whose day of week and hour of the day in the list  <code>[(4, 6), (5, 7)]</code></p>