using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var list = new List<KeyValuePair<string, List<string>>>(){

            new KeyValuePair<string,List<string>>("User 1", new List<string>(){ "trigger1" ,"trigger2", "trigger3" }),

            new KeyValuePair<string,List<string>>("User 2", new List<string>(){ "trigger1" ,"trigger2" }),

            new KeyValuePair<string,List<string>>("User 3", new List<string>(){ "trigger2" ,"trigger3", "trigger4" }),

            new KeyValuePair<string,List<string>>("User 1", new List<string>(){ "trigger0" ,"trigger4" }),

        };

        // Group the collections by user and then select the keys based on those users

        var dictionary = list.GroupBy(l => l.Key)

                             .ToDictionary(

                                x => x.Key, 

                                x => x.SelectMany(l => l.Value)

                                      .Distinct()

                                      .ToList()

                         );

        foreach(var key in dictionary.Keys)

        {

            Console.WriteLine("Key: " + key + ", Values: " + String.Join(",",dictionary[key].ToArray()));

        }

    }

}