Union扩展方法需要两个集合,并返回一个新集合,其中包含两个集合中不同的元素。看下面的实例。
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);
One Two three THREE Four Five
Union扩展方法不能为复杂类型的集合返回正确的结果。您需要实现IEqualityComparer接口,以便从Union方法中获取正确的结果。
为 Student 类实现IEqualityComparer接口,如下所示:
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(); } }
现在,您可以在Union扩展方法中传递上述StudentComparer类以获得正确的结果:
示例:Uion运算符 - C#
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);
John Steve Bill Ron
C # & VB.Net 查询语法不支持联合运算符。但是,您可以对查询变量使用 Union 方法,或者将整个查询包装到方括号中,然后调用 Union ()。