LINQ:对结果进行分组(MSDN)
一个例子
帮助程序类和数据源示例
public class StudentClass
{
#region data
public enum GradeLevel { FirstYear = 1, SecondYear, ThirdYear, FourthYear };
public class Student
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int ID { get; set; }
public GradeLevel Year;
public List<int> ExamScores;
}
protected static List<Student> students = new List<Student>
{
new Student {FirstName = "Terry", LastName = "Adams", ID = 120,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 99, 82, 81, 79}},
new Student {FirstName = "Fadi", LastName = "Fakhouri", ID = 116,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 99, 86, 90, 94}},
new Student {FirstName = "Hanying", LastName = "Feng", ID = 117,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 93, 92, 80, 87}},
new Student {FirstName = "Cesar", LastName = "Garcia", ID = 114,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 97, 89, 85, 82}},
new Student {FirstName = "Debra", LastName = "Garcia", ID = 115,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 35, 72, 91, 70}},
new Student {FirstName = "Hugo", LastName = "Garcia", ID = 118,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 92, 90, 83, 78}},
new Student {FirstName = "Sven", LastName = "Mortensen", ID = 113,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 88, 94, 65, 91}},
new Student {FirstName = "Claire", LastName = "O'Donnell", ID = 112,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 75, 84, 91, 39}},
new Student {FirstName = "Svetlana", LastName = "Omelchenko", ID = 111,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 97, 92, 81, 60}},
new Student {FirstName = "Lance", LastName = "Tucker", ID = 119,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 68, 79, 88, 92}},
new Student {FirstName = "Michael", LastName = "Tucker", ID = 122,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 94, 92, 91, 91}},
new Student {FirstName = "Eugene", LastName = "Zabokritski", ID = 121,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 96, 85, 91, 60}}
};
#endregion
//Helper method, used in GroupByRange.
public static int GetPercentile(Student s)
{
double avg = s.ExamScores.Average();
return avg > 0 ? (int)avg / 10 : 0;
}
public static List<Student> GetStudents()
{
return students;
}
public void QueryHighScores(int exam, int score)
{
var highScores = from student in students
where student.ExamScores[exam] > score
select new { Name = student.FirstName, Score = student.ExamScores[exam] };
foreach (var item in highScores)
{
Console.WriteLine($"{item.Name,-15}{item.Score}");
}
}
}
按单个属性分组示例
var students = StudentClass.GetStudents();
#region 按单个属性分组示例
Console.WriteLine("Group by a single property in an object:");
var queryFirstLetters =
from student in students
group student by student.LastName[0];
foreach (var studentGroup in queryFirstLetters)
{
Console.WriteLine($"Key: {studentGroup.Key}");
// Nested foreach is required to access group items.
foreach (var student in studentGroup)
{
Console.WriteLine($"\t{student.LastName}, {student.FirstName}");
}
}
#endregion
queryFirstLetters 关联:
参考:
对查询结果进行分组 https://docs.microsoft.com/zh-cn/dotnet/csharp/linq/group-query-results