using System;

using System.Data;

using System.Xml;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        DataTable table1 = new DataTable();

        table1.Columns.Add("ID", typeof (int));

        table1.Columns.Add("Weight", typeof (int));

        table1.Columns.Add("Name", typeof (string));

        table1.Columns.Add("Breed", typeof (string));

        table1.Rows.Add(23, 57, "Koko", string.Empty);

        table1.Rows.Add(44, 130, "Fido", null);

        table1.Rows.Add(54, 130, "Jack", null);

        table1.Rows.Add(44, 130, "Thad", null);

        table1.Rows.Add(64, 130, "John", null);

        table1.Rows.Add(23, 130, "Brian", null);

        table1.Rows.Add(445, 130, "James", null);

        table1.Rows.Add(64, 134, "Adam", null);

        Dictionary<int, string> dict = new Dictionary<int, string>();

        for (int i = 0; i < table1.Rows.Count; i++)

        {

            int id = Convert.ToInt32(table1.Rows[i][0]);

            if (dict.ContainsKey(id))

            {

                //comma separate the Names

                dict[id] += ", " + table1.Rows[i][2].ToString();

                // change the Name value in the table

                table1.Rows[i][2] = dict[id];

            //Console.WriteLine(dict[id]);

            }

            else

            {

                dict.Add(id, table1.Rows[i][2].ToString());

            }

        //Console.WriteLine()

        }

​

        foreach (DataRow eaRow in table1.Rows)

        {

            Console.WriteLine("ID=" + eaRow[0] + "  Name=" + eaRow[2]);

        }

​

        Console.WriteLine("\n\n");

        //dictionary is correct

        foreach (var item in dict)

        {

            Console.WriteLine("ID=" + item.Key + " Name=" + item.Value);

        }

    }

}