LINQ 学习路程 -- 查询操作 Distinct Except Intersect Union

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>(){ , , , , , , ,  };

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 = , StudentName = "John", Age =  } ,
        new Student() { StudentID = , StudentName = "Steve",  Age =  } ,
        new Student() { StudentID = , StudentName = "Bill",  Age =  } ,
        new Student() { StudentID = , StudentName = "Bill",  Age =  } ,
        new Student() { StudentID = , StudentName = "Bill",  Age =  } ,
        new Student() { StudentID = , StudentName = "Bill",  Age =  } ,
        new Student() { StudentID = , StudentName = "Ron" , Age =  }
    };

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 = , StudentName = "John", Age =  } ,
        new Student() { StudentID = , StudentName = "Steve",  Age =  } ,
        new Student() { StudentID = , StudentName = "Bill",  Age =  } ,
        new Student() { StudentID = , StudentName = "Ron" , Age =  }
    };

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

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 = , StudentName = "John", Age =  } ,
        new Student() { StudentID = , StudentName = "Steve",  Age =  } ,
        new Student() { StudentID = , StudentName = "Bill",  Age =  } ,
        new Student() { StudentID = , StudentName = "Ron" , Age =  }
    };

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

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

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