title: How to find duplicate record using Linq from DataTable
body: <p>Here is if my DataTable</p>
  
  <pre><code>DataTable dt = new DataTable();
  dt.Rows.Add(2,Test1,Sample1);
  dt.Rows.Add(2,Test2,Sample2);
  dt.Rows.Add(4,Test3,Sample3);
  dt.Rows.Add(4,Test4,Sample4);
  dt.Rows.Add(2,Test5,Sample5);
  </code></pre>
  
  <p>I want to display message Duplicate record exist for class 4
  it is possbile by using two loops by comparing, but i want an optimized code that will return me the duplicate record and i will display a message. The code may be using Linq if any body know please share..?</p>