使用 LINQ 对数据列表进行分组并从每个分组数据中获取最大值

Question

我有一个class，假设如下：

  public class Customer{
      public string Name;
      public int Score;
  }

所以，我有一份客户名单。客户可能具有相同的名称和不同的分数。现在我想在名字相同的情况下获得最高分的客户。

例如：

var customers = new List<Customer>()
{
    new Customer() { Name = "Rahim", Score = 30 },
    new Customer() { Name = "Rahim", Score = 25 },
    new Customer() { Name = "Karim", Score = 49 },
    new Customer() { Name = "Aziz", Score = 24 },
};

输出应该是，

Rahim 30
Karim 49
Aziz 24

Answer 1

使用 linq，我们需要先按名称分组，然后应用 SelectMany 从每个组中检索最高分，如下所示：

    using System;
    using System.Collections;
    using System.Collections.Generic;
    using System.Linq;
    class HelloWorld {
      static void Main() {   
          var customerList = new List<Customer>{
              new Customer {Name = "a", Score =30},
               new Customer {Name = "a", Score =35},
                new Customer {Name = "b", Score =20},
                 new Customer {Name = "c", Score =50},
                  new Customer {Name = "b", Score =60},
                   new Customer {Name = "a", Score =80},
          };

    List<Customer> customers = customerList
    .GroupBy(t => t.Name)
    .SelectMany(a => a.Where(b => b.Score == a.Max(c => c.Score))).ToList();
                
                foreach(var data in customers){
                    Console.WriteLine(data.Name +","+ data.Score);
                }   
                Console.ReadLine();
      }
      
      public class Customer{
          public string Name;
          public int Score;
      }

Answer 2

使用以下查询：

var customers = customerList
    .GroupBy(x => x.Name)
    .Select(g => g.OrderByDescending(x => x.Score).First())
    .ToList();

Answer 3

使用 MaxBy 运算符非常简单：

var customers = new List<Customer>()
{
    new Customer() { Name = "Rahim", Score = 30 },
    new Customer() { Name = "Rahim", Score = 25 },
    new Customer() { Name = "Karim", Score = 49 },
    new Customer() { Name = "Aziz", Score = 24 },
};

使用 .NET 6.0：

List<Customer> output =
    customers
        .GroupBy(c => c.Name)
        .Select(c => c.MaxBy(x => x.Score))
        .ToList();

使用微软的交互框架（System.Interactive）：

List<Customer> output =
    customers
        .GroupBy(c => c.Name)
        .SelectMany(c => c.MaxBy(x => x.Score))
        .ToList();

这给了我：

使用 LINQ 对数据列表进行分组并从每个分组数据中获取最大值

Grouping list of data with LINQ and get maximum from each grouped data

c#

linq