using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var countryOrder =new List<string> { "UK", "KE", "AU", "USA"};

        var data = new List<ExampleDataClass> {

            new ExampleDataClass {

                Name = "Alice",

                Country = "UK",

                Age = 30,

            },

            new ExampleDataClass {

                Name = "Bob",

                Country = "KE",

                Age = 20,

            },

            new ExampleDataClass {

                Name = "Charlie",

                Country = "UK",

                Age = 30,

            },

            new ExampleDataClass {

                Name = "Alice",

                Country = "KE",

                Age = 40,

            },

            new ExampleDataClass {

                Name = "Bob",

                Country = "AU",

                Age = 50,

            },

            new ExampleDataClass {

                Name = "David",

                Country = "USA",

                Age = 25,

            }

        };

        var reducedData = data.GroupBy(x => x.Name)

                             .Select(g => g.OrderBy(item => countryOrder.IndexOf(item.Country)).First())

                             .ToList();

        foreach (ExampleDataClass item in reducedData) 

        {

            Console.WriteLine(string.Format("Name: \"{0}\", Country: \"{1}\", Age: {2}", item.Name, item.Country, item.Age));

        }

    }

}

​

class ExampleDataClass

{

    public string Name { get; set; }

    public string Country { get; set; }

    public int Age { get; set; }

}