title: Select the first rows from a datatable by LINQ
body: <p>I have a datatable like the following</p>
  
  <pre><code>A  |  B
  -------
  1  |  b1
  1  |  b2
  1  |  b3
  2  |  b4
  2  |  b5
  3  |  b6
  3  |  b7
  3  |  b8
  3  |  b9
  </code></pre>
  
  <p>How can I write a LINQ command to select the first row on each distinct value on column A:</p>
  
  <pre><code>A  |  B
  ---------
  1  |  b1
  2  |  b4
  3  |  b6
  </code></pre>