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]

Posted 2023-04-12

【中文标题】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]

【英文标题】：C# LINQ group collection by attribute then sort each group by explicit order defined by a list [duplicate]

【发布时间】：2021-11-15 18:52:23

【问题描述】：

我有一组我想要的 C# 对象

给定属性的分组 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。 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***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

【问题讨论】：

data是一个JSON数组是否正确？

将其作为 C# 对象的集合处理

data.GroupBy(g => g.name).Select(g => new group = g.Key, items = g.OrderBy(g => g.country)); - 类似这样，但您需要考虑 OrderBy 上的国家/地区收集

您应该尝试解决手头的问题，而不仅仅是告诉我们您想要得到什么。

@Flater 我已经输入了代码尝试和预期的输出

【参考方案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