这个lambda表达式可以变得更简单吗？

Question

var MaleCount = students.Where(Std => Std.Gender.ToUpper() == "M").Count(); 
var FemaleCount = students.Where(Std => Std.Gender.ToUpper() == "F").Count(); 

//List for storing top students records   
List<StudentEntity> TopStudents = new List<StudentEntity>(); 

//Adding records to List 
if (MaleCount > 0) 
{ 
    var maxMarksM = students.Where(o => o.Gender.ToUpper() == "M").Max(o => o.Marks); 
    TopStudents = students.Where(o => o.Gender.ToUpper() == "M" && o.Marks == maxMarksM).ToList(); 
} 
if (FemaleCount > 0) 
{ 
    var maxMarksF = students.Where(o => o.Gender.ToUpper() == "F").Max(o => o.Marks); 
    TopStudents.AddRange(students.Where(o => o.Gender.ToUpper() == "F" && o.Marks == maxMarksF).ToList()); 
} 

return TopStudents; 

Answer 1

免责声明：我在Groovy编程，但是这不应该在这种情况下的差异。

如果你不想这样，也许使用链式.GroupBy().Where()...解决方案：

拆分students到maleStudents和femaleStudents（使用Where()）。

这应该消除了围绕男性和女性学生的if-wrappers和Count()的需要。

所以我的另类应该是这样的：

var MaleStudents = students.Where(Std => Std.Gender.ToUpper() == "M"); 
var FemaleStudents = students.Where(Std => Std.Gender.ToUpper() == "F"); 

//List for storing top students records   
List<StudentEntity> TopStudents = new List<StudentEntity>(); 

//Adding records to List 
var maxMarksM = MaleStudents.Max(o => o.Marks); 
TopStudents = MaleStudents.Where(o => o.Marks == maxMarksM).ToList(); 

var maxMarksF = FemaleStudents.Max(o => o.Marks); 
TopStudents.AddRange(FemaleStudents.Where(o => o.Marks == maxMarksF).ToList()); 

return TopStudents; 

Answer 2

var topStudents = allStudents 
       .GroupBy(s => s.Gender.ToUpper()) // Dividing the students to groups by gender 
       .Where(g => g.Key == "M" || g.Key == "F") // Including only the Male and Female genders 
       .Select(g => g.Where(s => s.Marks == g.Max(i => i.Marks))) // From each group, finding the highest mark and selecting from that groups all the student with that mark 
       .SelectMany(s => s) // selecting all the students from all the inner groups 
       .ToList(); 

编辑：

@Alexey Subbota建议，栽培大豆可能会叫的次数太多，事实上，它会被调用一次组内每一个学生，这是不必要的，只有我们需要为每个组计算一次最大值。 如果这是一个问题，你可以这样做：

var topStudents = allStudents 
       .GroupBy(s => s.Gender.ToUpper()) // Dividing the students to groups by gender 
       .Where(g => g.Key == "M" || g.Key == "F") // Including only the Male and Female genders 
       .Select(g => new KeyValuePair<int, IEnumerable<Student>>(g.Max(s => s.Marks), g)) // Storing the group together with it's highest score value 
       .Select(g => g.Value.Where(s => s.Marks == g.Key)) // From each group, selecting the student that have the highest score 
       .SelectMany(s => s) // selecting all the students from all the inner groups 
       .ToList();