title: Aggregate function on multiple columns in DataTable
body: <p>I have data as following in DataTable</p>
  
  <pre><code>Date   Date1           Visits     M      F
  1Jan   2015-01-01      0          0      0
  1Jan   2015-01-01      0          0      0
  1Jan   2015-01-01      10         7      3
  2Jan   2015-01-02      2          2      0
  2Jan   2015-01-02      15         10     5
  3Jan   2015-01-03      20         17     3
  </code></pre>
  
  <p>I want to apply aggregate SUM function on <code>Visits</code>, <code>M</code>, <code>F</code> and GROUP BY Date and Date1. So that results would be-</p>
  
  <pre><code>Date    Date1        Visits     M      F
  1Jan    2015-01-01   10         7      3
  2Jan    2015-01-02   17         12     5
  3Jan    2015-01-03   20         17     3
  </code></pre>
  
  <p>How could this be achieved using DataTables in C#</p>