using System;

using System.Collections.Generic;

using System.Linq;

using System.Text.Json;

using System.Text.Json.Serialization;

public class Program

{

    public static void Main()

    {

        var person1 = new Person()

        {

            PersonFacadeId = "1",

            UserProfiles = new List<UserProfile>()

            {

                new UserProfile()

                {

                    Identifier = new List<Identifier>()

                    {

                        new Identifier()

                        {

                            System = "System1",

                            Value = "Value1"

                        }

                    }

                }

            }

        };

        var person2 = new Person()

        {

            PersonFacadeId = "1",

            UserProfiles = new List<UserProfile>()

            {

                new UserProfile()

                {

                    Identifier = new List<Identifier>()

                    {

                        new Identifier()

                        {

                            System = "System2",

                            Value = "Value2"

                        }

                    }

                }

            }

        };

        var person3 = new Person()

        {

            PersonFacadeId = "2",

            UserProfiles = new List<UserProfile>()

            {

                new UserProfile()

                {

                    Identifier = new List<Identifier>()

                    {

                        new Identifier()

                        {

                            System = "System3",

                            Value = "Value3"

                        }

                    }

                }

            }

        };

        var persons = new List<Person>()

        {

            person1,

            person2,

            person3

        };

        var duplicatePersons = persons.GroupBy(x => x.PersonFacadeId, (key, groupByPersons) =>

            {

                var person = groupByPersons.First();

                person.UserProfiles = groupByPersons.SelectMany(x => x.UserProfiles).ToList();

                return person;

            });

​

​

        Console.WriteLine(JsonSerializer.Serialize(duplicatePersons));

    }

    public class Person

    {

        public string PersonFacadeId { get; set; }

        public string PersonResourceId { get; set; }

        public string HstreamId { get; set; }

        public string HealthStreamId { get; set; }

        public string GivenName { get; set; }

        public string FamilyName { get; set; }

        public string EmailAddress { get; set; }

        public bool IsEmailAddressConfirmed { get; set; }

        public string NrpId { get; set; }

        public int? NrpRankId { get; set; }

        public int? NrpStatusId { get; set; }

        public List<Identifier> Identifier { get; set; }

        public List<UserProfile> UserProfiles { get; set; }

    }

    public class UserProfile

    {

        public string UserProfileResourceId { get; set; }

        public List<Identifier> Identifier { get; set; }

    }

    public class Identifier

    {

        public string System { get; set; }

        public string Value { get; set; }

    }

}