Fórum ➡ Filling in a DataTable from a list of KVP's ♦, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

#define DISPLAY_THE_TABLE_ROWS
    
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using System.Data;

// aljodav
// http://rextester.com/users/376

// in reply to the MSDN thread
// http://bit.ly/2eZsGWN

namespace Rextester
{
    using Data=KeyValuePair<int,string>;
    class Program
    {
        static DataTable GetTable(out string col0,out string col1,out string col2){
            /*▶out◀*/col0="Id";col1="Value1";col2="Value2";
            
            string[] titles={col0,col1,col2};
            Type[] types={typeof(int),typeof(string),typeof(string)};
            
            DataTable d=new DataTable();
            d.Columns.AddRange(titles.Zip(types,(title,type)=>new DataColumn(title,type)).ToArray());
            return d;
        }
        static List<Data> GetList(){
            return new List<Data>{
                new Data(1,"100"),
                new Data(1,"200"),
                new Data(2,"56789"),
                new Data(3,"30"),
                new Data(3,"10"),
                new Data(4,"210"),
                //new Data(1,"300"), // raises exception due to excessive # of fields with same Id.
            };
        }
        public static void Main(string[] args)
        {
            string col0,col1,col2;
            DataTable table=GetTable(out col0,out col1,out col2);
            
            GetList()
                .GroupBy(kvp=>kvp.Key,kvp=>kvp.Value,(key,values)=>{
                    if(values.Count()>2)throw new Exception("‼✖ Excessive # of fields with same Id. ✖‼");
                    var array=values.ToArray();
                    DataRow row=table.NewRow();
                    row[col0]=key;
                    row[col1]=array[0];
                    row[col2]=array.Length==2?array[1]:null as string;
                    return row;
                })
                .ToList()
                .ForEach(table.Rows.Add)
                ;
            
            
#if DISPLAY_THE_TABLE_ROWS
    
            string fmt;
            Console.WriteLine((fmt="\t{0,3}  {1,10}  {2,10}"),col0,col1,col2);
            foreach(DataRow row in table.Rows)Console.WriteLine(fmt,row[col0],row[col1],row[col2]);
    
#endif
        
    
            Console.WriteLine("\n\nHello, world!");
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,17 sec, absolute running time: 0,2 sec, cpu time: 0,2 sec, average memory usage: 19 Mb, average nr of threads: 4