title: Grouping records that haven't groups values
body: <p>Please consider this records:</p>
  
  <pre><code>Id        Week         Value
  -----------------------------
  1          1           1000
  2          1           1200
  3          2           800
  4          3           1800
  5          3           1100
  6          3           1000
  </code></pre>
  
  <p>I want to group records for 4 weeks but we haven't record for week 4.For Example:</p>
  
  <pre><code>Week         Count
  ---------------------
  1              2
  2              1
  3              3
  4              0
  </code></pre>
  
  <p>How I can do this with linq?</p>
  
  <p>Thanks</p>