orderby通过Lambda表达式按项数降序排列

Question

我有MyClass类型:

 MyClass
{
 public string Name { get;set; }
 public string LastName { get;set; }
}

我也得到了我的收藏:

List<MyClass> _Lst = new List<MyClass>();

我添加了一些条目，像这样:
乌利希期刊指南:

_Lst.Add(new MyClass{Name = "Petya" , LastName = "sergeevi4"};
_Lst.Add(new MyClass{Name = "Vasya" , LastName = "petrovi4"};
_Lst.Add(new MyClass{Name = "Igori" , LastName = "alibertovi4"};
_Lst.Add(new MyClass{Name = "Vasya" , LastName = "iakubovi4"};
_Lst.Add(new MyClass{Name = "Vasya" , LastName = "ianukovi4"};

那么我如何排序(降序)我的集合通过Lambda表达式得到这样的东西:

_Lst[0] = Name = "Vasya" , LastName = "iakubovi4"; //Where [n] - just index of mylist;
_Lst[1] = Name = "Vasya" , LastName = "petrovi4";
_Lst[2] = Name = "Vasya" , LastName = "ianukovi4";
_Lst[3] = Name = "Petya" , LastName = "sergeevi4";
_Lst[4] = Name = "Igori" , LastName = "alibertovi4";  

目前我正在做这样的事情:

var NewList = _Lst.OrderByDescending(x => x.Name.Count());  

Answer 1

GroupBy方法完全符合您的要求。组是一个带有键(在本例中是一个名称)的集合。您可以命令分组，然后使用SelectMany:

平铺您的集合

var newList = _Lst.GroupBy(m => m.Name)
    .OrderByDescending(g => g.Count())
    .SelectMany(g => g)
    .ToList();

一个建议:最好使用ToArray()而不是ToList()，因为产生的集合是不可变的，并且不能在事后修改，这会在代码的其他地方引起棘手的错误。

奖金:

按名字匹配顺序排序后，您可能希望按姓氏的字母顺序排序。同样，这很容易，因为每个组都是一个集合。你可以在你的链上添加一个Select来实现这个目标:

var newList = _Lst.GroupBy(m => m.Name)
    .OrderByDescending(g => g.Count())
    .Select(g => g.OrderBy(m => m.LastName))
    .SelectMany(g => g)
    .ToList();

Answer 2

 List<MyClass> _Lst = new List<MyClass>();
 _Lst.Add(new MyClass { Name = "Vasya", LastName = "iakubovi4" });
 _Lst.Add(new MyClass { Name = "Vasya", LastName = "petrovi4" });
 _Lst.Add(new MyClass { Name = "Vasya", LastName = "ianukovi4" });
 _Lst.Add(new MyClass { Name = "Petya", LastName = "sergeevi4" });
 _Lst.Add(new MyClass { Name = "Igori", LastName = "alibertovi4" });
 var result = _Lst.GroupBy(m => m.Name).OrderByDescending(x => x.Count()).SelectMany(x => x).ToList();

Answer 3

把你的代码改成，

var NewList = _Lst.OrderByDescending(x => x.Name);