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);

        foreach(DataRow row in table1.Rows)

        {

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

        }

        //var groupedList = from r in table1.Rows

        //      group r by r.ID into rows

        //      select new {

        //          ID = rows.First().ID,

        //          Name = string.Join(",", (from n in rows select n.Name).ToArray()) 

        //      };

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

        {

            Console.WriteLine("ID="+table1.Rows[i][0] + "  Name=" + table1.Rows[i][2]);

        }

        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))

            {

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

            }

            else

            {

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

            }

        }

        foreach(var item in dict)

        {

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

        }

    }

}