title: How to get first record in each group using Linq
body: <p>Considering the following records:</p>
  
  <pre><code>   Id          F1            F2             F3 
   -------------------------------------------------
     1           Nima          1990           10
     2           Nima          1990           11
     3           Nima          2000           12
     4           John          2001           1
     5           John          2002           2 
     6           Sara          2010           4
  </code></pre>
  
  <p>I want to group by based on the <code>F1</code> field and sort by <code>Id</code> and get all fields from the first record of group similar to these records:</p>
  
  <pre><code>   Id          F1            F2             F3 
   -------------------------------------------------
     1           Nima          1990           10
     4           John          2001           1
     6           Sara          2010           4
  </code></pre>
  
  <p>How can I do this using linq?</p>