title: Get count of records in datatable by groupings
body: <p>I have a DataTable with the following data:</p>
  
  <pre><code>Salesman---ClientID
  Bob--------1
  Bob--------2
  Bob--------3
  Tom--------4
  Joe--------5
  Joe--------6
  Tim--------7
  Tim--------8
  </code></pre>
  
  <p>From this, I would like to get a count of how many clients each salesman has.  In this case:</p>
  
  <pre><code>Salesman---CountOfClients
  Bob--------3
  Tom--------1
  Joe--------2
  Tim--------2
  </code></pre>
  
  <p>This program is reading in text files with this data and is not connected to a database, so SQL is not an option.</p>
  
  <p>Using C#, how can I accomplish the desired results?</p>