title: LINQ compound aggregation
body: <p>I have a simple LINQ question:</p>
  
  <p>I have a collection of FooBars. A Foobar has a foo property and a bar property.
  I want to aggregate both foo and bar without running through my collection of foobars more than once.</p>
  
  <p>Ie. I want something equivalent to SQL:</p>
  
  <pre><code>SELECT SUM(Foo), SUM(Bar) From FooBars
  </code></pre>
  
  <p>or</p>
  
  <pre><code>int fooSum, barSum;
  foreach (var foobar in foobars)
  {
     fooSum += foobar.Foo;
     barSum += foobar.Bar;
  }
  </code></pre>
  
  <p>Is there an elegant way to write this with a compound select (or similar) in LINQ?</p>