using System;

using System.Data;

using System.Xml;

using System.Collections.Generic;

using System.Linq;

using System.Data.DataSetExtensions;

​

 public static class Extensions

    {

        public static void Convert<T>(this DataColumn column, Func<object, T> conversion)

        {

            foreach (DataRow row in column.Table.Rows)

            {

                row[column] = conversion(row[column]);

            }

        }

    }

    public class Program

    {

        public static void Main()

        {

                    //Dummy data for demo purpose

                    DataTable table = new DataTable();

                    table.Columns.Add("DateColumn", typeof(object));

                    table.Rows.Add(DateTime.Now.AddDays(1));

                    table.Rows.Add(DateTime.Now.AddDays(2));

                    table.Rows.Add(DateTime.Now.AddDays(3));

                    //Call the Extension method like given below

                    table.Columns["DateColumn"].Convert(val => DateTime.Parse(val.ToString()).ToString(" MMMM dd, yyyy"));

                    foreach(DataRow row in table.Rows)

                    {

                        Console.WriteLine(row["DateColumn"]);

                    }

        }           

    }