using System;

using System.Linq;

using System.Data;

using System.Data.DataSetExtensions;

using System.Collections.Generic;

using System.Xml;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        DataTable dt = new DataTable();

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

            dt.Columns.Add("Address", typeof(string));

            AddRow(dt, "companies", "addresses");

            AddRow(dt, "companies", "bids");

            AddRow(dt, "companies", "commitments");

            AddRow(dt, "companies", "evaluations");

            AddRow(dt, "companies", null);

​

            var result = dt.AsEnumerable().GroupBy(x => x.Field<string>("Name"))

                                          .Select(x => new

                                          {

                                              Name = x.Key,

                                              Address = x.Where(z => z.Field<string>("Address") != null)

                                                         .Select(z => z.Field<string>("Address")).ToList()

                                          });

​

            string jsonResult = JsonConvert.SerializeObject(result);

            Console.WriteLine(jsonResult);

    }

    private static void AddRow(DataTable dt,string name, object add)

        {

            DataRow row1 = dt.NewRow();

            row1["Name"] = name;

            row1["Address"] = add;

            dt.Rows.Add(row1);

        }

}