C# LINQ 组按属性集合，然后按列表定义的显式顺序对每个组进行排序[重复]

Question

我有一组我想要的 C# 对象

1. 给定属性的分组
2. 然后按另一个属性对每个组进行排序。 排序顺序由列表明确定义。
3. 然后我只想从每个组中获取最上面的项目

例如，考虑：

data = [
  {​​​​​"name": "Alice", "country": "UK", "age": 30}​​​​​,
  {​​​​​​​"name": "Bob", "country": "KE", "age": 20}​​​​​​​,
  {​​​​​​​"name": "Charlie", "country": "UK", "age": 30}​​​​​​​,
  {​​​​​​​"name": "Alice", "country": "KE", "age": 40}​​​​​​​,
  {​​​​​​​"name": "Bob", "country": "AU", "age": 50}​​​​​​​,
  {​​​​​​​"name": "David", "country": "USA", "age": 25}​​​​​​​,
]

我想按name 分组，然后按country 对每个组进行排序，以遵循另一个集合中指定的明确顺序，例如：

var countryOrder = new List<string> { "UK", "KE", "AU", "USA"};

然后我想根据这个顺序只选择每个组的顶级成员，这样我最终会得到一个名称唯一的对象列表（例如，UK、KE 中的一个Alice， AU 或 USA) 但遵循明确定义的优先顺序。

以下是给定示例的预期输出：

output = [
  {"name": "Alice", "country": "UK", "age": 30},
  {"name": "Bob", "country": "KE", "age": 20},
  {"name": "Charlie", "country": "UK", "age": 30},
  {"name": "David", "country": "USA", "age": 25},
]

我已尝试使用以下代码：

using System;
using System.Collections.Generic;
using System.Linq;
                    
public class Program
{
    public static void Main()
    {
        var countryOrder =new List<string> { "UK", "KE", "AU", "USA"};
        
        var data = new List<ExampleDataClass> {
            new ExampleDataClass { Name = "Alice", Country = "UK", Age = 30 },
            new ExampleDataClass { Name = "Bob", Country = "KE", Age = 20 },
            new ExampleDataClass { Name = "Charlie", Country = "UK", Age = 30 },
            new ExampleDataClass { Name = "Alice", Country = "KE", Age = 40 },
            new ExampleDataClass { Name = "Bob", Country = "AU", Age = 50 },
            new ExampleDataClass { Name = "David", Country = "USA", Age = 25 }
        };
        
        var reducedData = data
            .GroupBy(x => x.Name)
            .Select(g => g.OrderBy(item => countryOrder.IndexOf(item.Country)).Min())
            .ToList();
        
        reducedData.ForEach(item => Console.WriteLine(reducedData));
    }
}

class ExampleDataClass
{
    public string Name { get; set; }
    public string Country { get; set; }
    public int Age { get; set; }
}

.Select(g => g.OrderBy(item => countryOrder.IndexOf(item.Country)).Min()) 给出运行时异常：

Run-time exception (line 50): At least one object must implement IComparable.

Stack Trace:

[System.ArgumentException: At least one object must implement IComparable.]
   at System.Collections.Comparer.Compare(Object a, Object b)
   at System.Collections.Generic.ObjectComparer`1.Compare(T x, T y)
   at System.Linq.Enumerable.Min[TSource](IEnumerable`1 source)
   at Program.<>c__DisplayClassd.<Main>b__9(IGrouping`2 g) :line 50
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Program.Main() :line 49

Answer 1

这是我找到的解决方案：

using System;
using System.Collections.Generic;
using System.Linq;
                    
public class Program
{
    public static void Main()
    {
        var countryOrder =new List<string> { "UK", "KE", "AU", "USA"};
        
        var data = new List<ExampleDataClass> {
            new ExampleDataClass {
                Name = "Alice",
                Country = "UK",
                Age = 30,
            },
            
            new ExampleDataClass {
                Name = "Bob",
                Country = "KE",
                Age = 20,
            },
            
            new ExampleDataClass {
                Name = "Charlie",
                Country = "UK",
                Age = 30,
            },
            
            new ExampleDataClass {
                Name = "Alice",
                Country = "KE",
                Age = 40,
            },
            
            new ExampleDataClass {
                Name = "Bob",
                Country = "AU",
                Age = 50,
            },
            
            new ExampleDataClass {
                Name = "David",
                Country = "USA",
                Age = 25,
            }
        };
        
        var reducedData = data.GroupBy(x => x.Name)
                             .Select(g => g.OrderBy(item => countryOrder.IndexOf(item.Country)).First())
                             .ToList();
        
        foreach (ExampleDataClass item in reducedData) 
        {
            Console.WriteLine(string.Format("Name: \"{0}\", Country: \"{1}\", Age: {2}", item.Name, item.Country, item.Age));
        }
    }
}

class ExampleDataClass
{
    public string Name { get; set; }
    
    public string Country { get; set; }
    
    public int Age { get; set; }
}

输出

Name: "Alice", Country: "UK", Age: 30
Name: "Bob", Country: "KE", Age: 20
Name: "Charlie", Country: "UK", Age: 30
Name: "David", Country: "USA", Age: 25

链接到 dotnetfiddle https://dotnetfiddle.net/6geHtk