Except

Ravshan Sodiqov

Algebra kursining to’plamlar mavzusidan shunisi ma’lumki, bizga quyidagicha A = {2, 3 , 5, 6, 8} va B={2, 3, 4, 7, 8} to’plamlar berilgan bo’lsa, A\B to’plam A to’plamdan ikki to’plamning kesishmasidagi sonlarning olib tashlanganiga teng bo’ladi, ya’ni A\B = {5, 6}.

LINQ metodlari ichida Except bizga xuddi mana shu imkoniyatni taqdim etadi. Demak, Except() metodi birinchi to’plamdagi ikkinchi to’plamda mavjud bo’lmagan yangi to’plamni qaytaradi.

Method syntax:

using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
    static void Main(string[] args)
    {
        List<int> list1 = new List<int>() { 2, 3, 5, 6, 8 };

        List<int> list2 = new List<int>() { 2, 3, 4, 7, 8 };

        //Method syntax
        var result1 = list1.Except(list2).ToList();

        foreach (var i in result1)
        {
            Console.WriteLine(i);
        }

        //Output: 5  6

    }
}

Query syntax:

using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
    static void Main(string[] args)
    {
        List<int> list1 = new List<int>() { 2, 3, 5, 6, 8 };

        List<int> list2 = new List<int>() { 2, 3, 4, 7, 8 };

        //Query syntax
        var result2 = (from item in list1 select item).Except(list2).ToList();
        foreach (var i in result2)
        {
            Console.WriteLine(i);
        }

        //Output: 5  6
    }
}

Endi esa bir sinfga tegishli bo’lgan ikkita object ni qanday taqqoslash mumkinligi haqida bosh qotirsak. Masalan, bu muammoni “ Car ” sinfiga tegishli bo’lgan ikkita object ustida qanday hal etish mumkin ? Bu sinfga tegishli bo’lgan mashinalarimiz “Id” va “Name” xususiyatlariga ega bo’lsin.

public class Car
{
        public int Id { get; set; }
        public string Name { get; set; }
}

Endigi navbat bu objectlarni taqqoslash uchun asosiy “CarsComparer” sinfini yaratish. Bu sinfga IEqualityComparer<Cars> interfeysini implementatsiya qilamiz va ushbu interfeysga tegishli Equals() va GetHashCode() metodlarini qayta yuklaymiz:

public class CarComparer : IEqualityComparer<Car>
{
    public bool Equals(Car x, Car y)
    {

        //Taqqoslangan objectlar bir xil ma'lumotlarga murojaat qilishini tekshirish.
        if (Object.ReferenceEquals(x, y)) return true;

        //Object larni null qiymatga tekshirish
        if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
            return false;

        //Object larning xususiyatlarini taqqoslash
        return x.Id == y.Id && x.Name == y.Name;
    }

    public int GetHashCode(Car obj)
    {
        //Obyektni null qiymatga tekshirish
        if (Object.ReferenceEquals(obj, null)) return 0;

        //Obyektning Id xususiyati uchun HashCode ni hisoblash
        int hashCarId = obj.Id.GetHashCode();

        //Obyektning Name xususiyati uchun HashCode ni hisoblash
        int hashCarName = obj.Name == null ? 0 : obj.Name.GetHashCode();

        //Obyektning HashCode ni qaytarish 
        return hashCarName ^ hashCarId;
    }

}

Nega aynan bunday yozdik va bu qanday ishlaydi? GetHashCode() orqali Car sinfiga tegishli bo’lgan obyektimizning Id va Name xususiyatlari uchun HashCode ni hisoblab, Obyektimizning HashCode ni qaytardik. Equals() metodi orqali esa taqqoslanadigan obyektlarning bir xil ma’lumotga ega ekanligi, ulardan birortasi null qiymatga teng ekanligini va ularni xususiyatlari bo’yicha taqqoslash imkoniga ega bo’ldik.

Oxirgi bosqich: “Biz kutgan onlar yetib keldi” : So’ngida esa Car sinfiga tegishli obyektlarni o’zida jamlagan ikki massiv yaratib o’zaro farqli elemantlarni taqqoslashni ko’rib chiqamiz

using System;
using System.Linq;
using System.Collections.Generic;
namespace exept
{
    class program
    {

        public static void Main(string[] args)
        {
            //Birinchi to'plam
            Car[] cars1 =
            {
                new Car{ Id= 1, Name="BMW"},
                new Car{ Id = 2, Name="RollsRoys"},
                new Car{ Id = 3, Name="Wolskvagen"}
            };

            //Ikkinchi to'plam
            Car[] cars2 =
            {
                new Car{ Id = 1, Name="Lacetti"},
                new Car{ Id = 2, Name="RollsRoys" }
            };

            //To'plamlarni taqqoslash
            IEnumerable<Car> result = cars1.Except(cars2, new CarComparer());

            foreach (var item in result)
                Console.WriteLine(item.Id + " " + item.Name);

            //Output: 1  BMW
            //        2  Wolksvagen

            Console.ReadKey();
        }
    }


    public class CarComparer : IEqualityComparer<Car>
    {
        public bool Equals(Car x, Car y)
        {

            //Taqqoslangan objectlar bir xil ma'lumotlarga murojaat qilishini tekshirish.
            if (Object.ReferenceEquals(x, y)) return true;

            //Object larni null qiymatga tekshirish
            if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
                return false;

            //Object larning xususiyatlarini taqqoslash
            return x.Id == y.Id && x.Name == y.Name;
        }

        public int GetHashCode(Car obj)
        {
            //Obyektni null qiymatga tekshirish
            if (Object.ReferenceEquals(obj, null)) return 0;

            //Obyektning Id xususiyati uchun HashCode ni hisoblash
            int hashCarId = obj.Id.GetHashCode();

            //Obyektning Name xususiyati uchun HashCode ni hisoblash
            int hashCarName = obj.Name == null ? 0 : obj.Name.GetHashCode();

            //Obyektning HashCode ni qaytarish 
            return hashCarName ^ hashCarId;
        }

    }

    public class Car
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }
}

Natijada esa “cars1” to’plamiga tegishli bo’lgan “RollsRoys” obyekti barcha xususiyatlari bo’yicha “cars2” da ham saqlangani uchun “cars1” dan olib tashlanganini ko’rish mumkin.

“Bizni kutar biz kutgan kodlar” :)