LINQ 学习路程 -- 查询操作 Distinct Except Intersect Union
2024-09-27 20:12:30
| 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);
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