title: How to filter dates on multiindex dataframe
body: <p>I'm looking for a way to filter a multiindex dataframe like the following by day of the week and/or selected dates. Let's say I need </p>
  
  <ul>
  <li>a query to <code>select only mondays</code>; </li>
  <li>another query in which I want to <code>select all days except monday and friday</code>;</li>
  <li>a third query to select data present in an input list of dates, like <code>select all dates in ['2015-05-14', '2015-05-21', '2015-05-22']</code>;</li>
  <li>and finally, a query combining selection based on day of week and a list of dates, like <code>select all dates in ['2015-05-14', '2015-05-21', '2015-05-22'] and thursdays</code>.</li>
  </ul>
  
  <p>What's the way to do it?</p>
  
  <pre><code>                Col1        Col2     Col3    Col4
  Date        Two 
  2015-05-14  10   81.370003  6.11282  39.753  44.950001
              11   80.419998  6.03380  39.289  44.750000
              C3   80.879997  6.00746  41.249  44.360001
  2015-05-19   3   80.629997  6.10465  41.047  40.980000
              S9   80.550003  6.14370  41.636  42.790001
  2015-05-21  19   80.480003  6.16096  42.137  43.680000
  2015-05-22  C3   80.540001  6.13916  42.179  43.490002
  </code></pre>