Select unique rows from a DataTable

1. Logic:
   
       /// <summary>
   

       /// Selects the distinct from data table.
   
       /// </summary>
   
       /// <param name="TableName">Name of the table.</param>
   
       /// <param name="SourceTable">The source table.</param>
   
       /// <param name="FieldName">Name of the field.</param>
   
       /// <returns></returns>
   
       public static DataTable DistinctDataFromDataTable(string TableName, DataTable SourceTable, string FieldName)
   
       {
   
           DataTable dt = new DataTable(TableName);
   
           dt.Columns.Add(FieldName, SourceTable.Columns[FieldName].DataType);
   
   
   
           object LastValue = null;
   
           foreach (DataRow dr in SourceTable.Select("", FieldName))
   
           {
   
               if (LastValue == null || !(ColumnEqual(LastValue, dr[FieldName])))
   
               {
   
                   LastValue = dr[FieldName];
   
                   dt.Rows.Add(new object[] { LastValue });
   
               }
   
           }
   
           return dt;
   
       }
   
   
   
       /// <summary>
   
       /// Columns the equal.
   
       /// </summary>
   
       /// <param name="A">The A.</param>
   
       /// <param name="B">The B.</param>
   
       /// <returns></returns>
   
       private static bool ColumnEqual(object A, object B)
   
       {
   
   
   
           // Compares two values to see if they are equal. Also compares DBNULL.Value.
   
           // Note: If your DataTable contains object fields, then you must extend this
   
           // function to handle them in a meaningful way if you intend to group on them.
   
   
   
           if (A == DBNull.Value && B == DBNull.Value) //  both are DBNull.Value
   
               return true;
   
           if (A == DBNull.Value || B == DBNull.Value) //  only one is DBNull.Value
   
               return false;
   
           return (A.Equals(B));  // value type standard comparison
   
       }

   
   Example:
   
   public static void GetUserNames()  
2.         {  
3.             DataTable dt = new DataTable();  
4.             dt.Columns.Add("UserId", typeof(int));  
5.             dt.Columns.Add("UserName", typeof(string));  
6.             dt.Rows.Add(1, "Joe Smith");  
7.             dt.Rows.Add(2, "John Doe");  
8.             dt.Rows.Add(3, "Joe Smith");  
9.             dt.Rows.Add(4, "Jane Smith");  
10.             dt.Rows.Add(5, "Jane Doe");  
11.   
12.             DataTable filterTable = GetUniqueEntries(dt);  
13.   
14.         }  
15.   
16.   
17.         /// <summary>  
18.         /// Gets the unique entries.  
19.         /// </summary>  
20.         /// <param name="dt">DataTable</param>  
21.         /// <returns></returns>  
22.         private static DataTable GetUniqueEntries(DataTable dt)  
23.         {  
24.             var query = (  
25.             from row in dt.AsEnumerable()  
26.             select row.Field<string>("UserName")).Distinct();  
27.   
28.             DataTable dtDistinctNames = new DataTable();  
29.             dtDistinctNames.Columns.Add("UserName", typeof(string));  
30.   
31.             //have to return a datatable, thus loop through entries  
32.             foreach (string item in query)  
33.             {  
34.                 DataRow newRow = dtDistinctNames.NewRow();  
35.                 newRow["UserName"] = item;  
36.                 dtDistinctNames.Rows.Add(newRow);  
37.             }  
38.   
39.             return dtDistinctNames;  
40.         } 
    This code snippet will return you a list of users where 'username' are unique. There eliminating duplicate names from the list. There are alternative ways to do this type of functionality