Ex, C# - rextester

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Microsoft (R) Visual C# Compiler version 2.9.0.63208 (958f2354)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {

List<MyRecord> records = new List<MyRecord>()
            {
                new MyRecord() { Company = "CompanyA", Item = "ItemA", Key = "9f94413b-63cb-4ad5-869a-4502988a22c9" },
                new MyRecord() { Company = "CompanyA", Item = "ItemA", Key = "6c6a1b37-84a5-4878-a493-5dad5bf60ee4" },
                new MyRecord() { Company = "CompanyB", Item = "ItemA", Key = "25c5ffca-69a5-45a6-9643-635791dc1bfd" }
            };

List<MyRecord> results = records
                .GroupBy(r => new { r.Company, r.Item })
                .Select(g => new MyRecord() { Company = g.Key.Company, Item = g.Key.Item, Key = g.First().Key })
                .ToList();
            
            foreach (var entry in results)
            {
                Console.WriteLine("Company = {0}, Item = {1}, Key = {2}", entry.Company, entry.Item, entry.Key);
            }            
        }
    }
    
    public class MyRecord
    {
        public string Company {get;set;}
        public string Item {get;set;}
        public string Key {get;set;}
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,34 sec, absolute running time: 0,11 sec, cpu time: 0,11 sec, average memory usage: 19 Mb, average nr of threads: 4, absolute service time: 0,48 sec