title: Return Standard Deviation of column values with other column value condition LINQ
body: <p>I have a table, <code>db.Men</code>, that has three columns</p>
  
  <ul>
  <li>nvarchar "Name"</li>
  <li>int "Age"</li>
  <li>nvarchar "Status"</li>
  </ul>
  
  <p>The <code>Status</code> column has three values only: "Happy", "Normal", and "Bad".</p>
  
  <p>I need to count the average and standard deviation of the ages of "Happy" or "Normal":</p>
  
  <pre><code>using System.Linq 
  
  var ctx     = new DataClasses1DataContext();
  
  double? avg = (from n in ctx.men
                 where n.status == "Happy"
                 select n.age).Average();
  
  int? sum    = (from n in ctx.men
                 where n.status == "Happy"
                 select n.age).Sum();
  </code></pre>
  
  <p>I computed the average and the sum. How can I compute the standard deviation in this conditional status?</p>