using System;

using System.Linq;

using Newtonsoft.Json;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        IEnumerable<MyObject> input = new[] { new MyObject { MyId = 1, MyValue = "abc" }, new MyObject { MyId = 2, MyValue = "xyz" }, new MyObject { MyId = 1, MyValue = "xxx" } };

        var filtered = input.GroupBy(x => x.MyId).Where(x => x.All(y=> y.MyValue != "xxx")).Select(x => x.First());

        Console.WriteLine(JsonConvert.SerializeObject(filtered));

    }

    public class MyObject

    {

        public int MyId { get; set; }

        public string MyValue { get; set; }

    }

}