C # Two collection comparison of the usage of the except of the Difference LINQ

C # Two collections compare difference values for the except of a value type of LINQ

    List<string> strList1 = new List<string>(){"a", "b", "c", "d"};    List<string> strList2 = new List<string>() { "a", "b", "f", "e"};    var strList3 = strList1.Except(strList2).ToList();    for (int i = 0; i < strList3.Count; i++)    {        Console.WriteLine(strList3[i]);    }

The result of the output is C D

var strList3 = strlist1.except (strList2). ToList ();

This means that the strList1 is not in the strList2, and the obtained difference is stored in the StrList3 (ie: strList1, strList2)

var strList3 = strlist2.except (strList1). ToList ();

So the result of the output is F E

Here will strList1 and strList2 position swap, is strList2 in which is not strList1 in StrList3 (ie: strList2, strList1)

Collection comparison difference for reference types

First create the Student class

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

Then create a list of 2

    List<Student> studentList1=new List<Student>()    {        new Student(){Id = 1,Name = "小明"},        new Student(){Id = 2,Name = "小刚"},        new Student(){Id = 3,Name = "小红"},    };    List<Student> studentList2 = new List<Student>()    {        new Student(){Id = 1,Name = "小明"}    };    var studentList3 = studentList1.Except(studentList2).ToList();    for (int i = 0; i < studentList3.Count; i++)    {        Console.WriteLine($"学号: {studentList3[i].Id} 姓名: {studentList3[i].Name}");    }

Result output

学号: 1 姓名: 小明学号: 2 姓名: 小刚学号: 3 姓名: 小红

This is because except generates a difference of two sequences by using the default equality comparer to compare values, and the Equals and GetHashCode methods need to be rewritten

As follows:

1. Method One

    public class Student    {        public int Id { get; set; }        public string Name { get; set; }        public override bool Equals(object obj)        {            if (obj is Student)            {                Student student = obj as Student;                return Id == student.Id && Name == student.Name;            }            return false;        }        public override int GetHashCode()        {            return Id.GetHashCode() ^ Name.GetHashCode();        }    }

1. Method two overrides a class to let it inherit IEqualityComparer

    public class StudentComparer: IEqualityComparer<Student>    {        public bool Equals(Student x, Student y)        {            return x.Id == y.Id && x.Name == y.Name;        }        public int GetHashCode(Student obj)        {            return obj.Id.GetHashCode() ^ obj.Name.GetHashCode();        }    }

Special attention

var studentList3 = studentList1.Except(studentList2,new StudentComparer()).ToList();

We need to add the parameter new Studentcomparer ()

C # Two collection comparison of the usage of the except of the Difference LINQ