LINQ 学习路程 -- 查询操作 Distinct Except Intersect Union-优快云博客

Set Operators	Usage
Distinct	去掉集合的重复项
Except	返回两个集合的不同，第一个集合的元素不能出现在第二个集合中
Intersect	返回两个集合的交集，即元素同时出现在两个集合中
Union	Returns unique elements from two sequences, which means unique elements that appear in either of the two sequences.

IList<string> strList = new List<string>(){ "One", "Two", "Three", "Two", "Three" };

IList<int> intList = new List<int>(){ 1, 2, 3, 2, 4, 4, 3, 5 };

var distinctList1 = strList.Distinct();

foreach(var str in distinctList1)
    Console.WriteLine(str);

var distinctList2 = intList.Distinct();

foreach(var i in distinctList2)
    Console.WriteLine(i);

如果要去掉复杂类型的重复项，需要实现IEqualityComparer接口

public class Student 
{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
}

class StudentComparer : IEqualityComparer<Student>
{
    public bool Equals(Student x, Student y)
    {
        if (x.StudentID == y.StudentID 
                && x.StudentName.ToLower() == y.StudentName.ToLower())
            return true;

        return false;
    }

    public int GetHashCode(Student obj)
    {
        return obj.StudentID.GetHashCode();
    }
}

IList<Student> studentList = new List<Student>() { 
        new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
        new Student() { StudentID = 2, StudentName = "Steve",  Age = 15 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 } 
    };


var distinctStudents = studentList.Distinct(new StudentComparer()); 

foreach(Student std in distinctStudents)

Except

第一个集合的元素不在第二个集合中出现，返回新的集合

IList<string> strList1 = new List<string>(){"One", "Two", "Three", "Four", "Five" };
IList<string> strList2 = new List<string>(){"Four", "Five", "Six", "Seven", "Eight"};

var result = strList1.Except(strList2);

foreach(string str in result)
        Console.WriteLine(str);

public class Student 
{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
}

class StudentComparer : IEqualityComparer<Student>
{
    public bool Equals(Student x, Student y)
    {
        if (x.StudentID == y.StudentID && x.StudentName.ToLower() == y.StudentName.ToLower())
            return true;

        return false;
    }

    public int GetHashCode(Student obj)
    {
        return obj.StudentID.GetHashCode();
    }
}

public class Student 
{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
}

class StudentComparer : IEqualityComparer<Student>
{
    public bool Equals(Student x, Student y)
    {
        if (x.StudentID == y.StudentID && x.StudentName.ToLower() == y.StudentName.ToLower())
            return true;

        return false;
    }

    public int GetHashCode(Student obj)
    {
        return obj.StudentID.GetHashCode();
    }
}

Intersect

返回两个集合的交集

IList<string> strList1 = new List<string>() { "One", "Two", "Three", "Four", "Five" };
IList<string> strList2 = new List<string>() { "Four", "Five", "Six", "Seven", "Eight"};

var result = strList1.Intersect(strList2);

foreach(string str in result)
        Console.WriteLine(str);

复杂类型的交集需要实现IEqualityComparer<T>接口

public class Student 
{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
}

class StudentComparer : IEqualityComparer<Student>
{
    public bool Equals(Student x, Student y)
    {
        if (x.StudentID == y.StudentID && 
                        x.StudentName.ToLower() == y.StudentName.ToLower())
            return true;

        return false;
    }

    public int GetHashCode(Student obj)
    {
        return obj.StudentID.GetHashCode();
    }
}

IList<Student> studentList1 = new List<Student>() { 
        new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
        new Student() { StudentID = 2, StudentName = "Steve",  Age = 15 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 } 
    };

IList<Student> studentList2 = new List<Student>() { 
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 } 
    };

var resultedCol = studentList1.Intersect(studentList2, new StudentComparer()); 

foreach(Student std in resultedCol)
    Console.WriteLine(std.StudentName);

Union

两个集合的并集

IList<string> strList1 = new List<string>() { "One", "Two", "three", "Four" };
IList<string> strList2 = new List<string>() { "Two", "THREE", "Four", "Five" };

var result = strList1.Union(strList2);

foreach(string str in result)
        Console.WriteLine(str);

复杂类型的并集需要实现IEqualityComparer<T>接口

public class Student 
{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
}

class StudentComparer : IEqualityComparer<Student>
{
    public bool Equals(Student x, Student y)
    {
        if (x.StudentID == y.StudentID && x.StudentName.ToLower() == y.StudentName.ToLower())
            return true;

        return false;
    }

    public int GetHashCode(Student obj)
    {
        return obj.StudentID.GetHashCode();
    }
}

IList<Student> studentList1 = new List<Student>() { 
        new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
        new Student() { StudentID = 2, StudentName = "Steve",  Age = 15 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 } 
    };

IList<Student> studentList2 = new List<Student>() { 
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 } 
    };

var resultedCol = studentList1.Union(studentList2, new StudentComparer()); 

foreach(Student std in resultedCol)
    Console.WriteLine(std.StudentName);