使用列表类型的 class 的属性以外的值创建一个新列表

Question

我有一个Customers具有Id和Name属性的客户。 创建Customers列表后，我想要一个没有重复名称的新customer列表，即 Customers.Name 必须是唯一的。 我现在的output：

Gustavo
Gabriel
Mariza
Sandro
Gustavo
Gabriel
Lilian
Sandro

预计 Output：

Gustavo
Gabriel
Mariza
Sandro
Lilian

我试试这个，但我一直在犯与类型转换相关的错误：

using System;
using System.Collections.Generic;
using System.Linq;

namespace SelectDistinct
{
    public class Program
    {
        static void Main(string[] args)
        {
            List<Customers> customers = new List<Customers>();
            customers.Add(new Customers(0, "Gustavo"));
            customers.Add(new Customers(0, "Gabriel"));
            customers.Add(new Customers(0, "Mariza"));
            customers.Add(new Customers(0, "Sandro"));
            customers.Add(new Customers(0, "Gustavo"));
            customers.Add(new Customers(0, "Gabriel"));
            customers.Add(new Customers(0, "Lilian"));
            customers.Add(new Customers(0, "Sandro"));

            customers = customers.Select(x => x.Name.Distinct());

            customers.ToList().ForEach(x =>
            {
                Console.WriteLine(x.ToString());
            });
        }

        public class Customers
        {
            public int Id { get; set; }
            public string Name { get; set; }

            public Customers(int id, string name)
            {
                Id = id;
                Name = name;
            }
        }
    }
}

谁能帮忙？

Answer 1

使用GroupBy给你一个预期的结果

var result = customers
    .GroupBy(c => c.Name)
    .Select(g => g.First())
    .ToList();
result.ForEach(c => Console.WriteLine(c.Name));

Output 将是以下

Gustavo
Gabriel
Mariza
Sandro
Lilian

Answer 2

您发布的代码中有很多错误。

我注意到的第一件事是.Distinct()的错误放置。 您已将它放在 select 内和Name变量之后，这是不合逻辑的。

第二件事是，您正在尝试将类型为IEnumerable<char>的customers.Select(x => x.Name.Distinct())分配给类型为List<Customers>的customers变量。

现在，要实现您要查找的内容，您必须正确使用Distinct扩展并将结果分配给正确的变量。

这是您的完整工作代码：

static void Main(string[] args)
{
    List<Customers> customers = new List<Customers>();
    customers.Add(new Customers(0, "Gustavo"));
    customers.Add(new Customers(0, "Gabriel"));
    customers.Add(new Customers(0, "Mariza"));
    customers.Add(new Customers(0, "Sandro"));
    customers.Add(new Customers(0, "Gustavo"));
    customers.Add(new Customers(0, "Gabriel"));
    customers.Add(new Customers(0, "Lilian"));
    customers.Add(new Customers(0, "Sandro"));

    IEnumerable<string> distinctNames = customers.Select(x=>x.Name).Distinct();

    distinctNames.ToList().ForEach(x =>
    {
        Console.WriteLine(x.ToString());
    });

    Console.ReadKey();
}

public class Customers
{
    public int Id { get; set; }
    public string Name { get; set; }

    public Customers(int id, string name)
    {
        Id = id;
        Name = name;
    }
}

这是 output：

Answer 3

Distinct方法使用默认的相等比较器。
您需要重载Equals和GetHashCode方法才能正常工作。

public class Customers
{
    // your code here

    public override string ToString() => Id + " " + Name;

    public override bool Equals(object obj)
    {
        return obj is Customers customers &&
                Id == customers.Id &&
                Name == customers.Name;
    }

    public override int GetHashCode()
    {
        int hashCode = -1919740922;
        hashCode = hashCode * -1521134295 + Id.GetHashCode();
        hashCode = hashCode * -1521134295 + EqualityComparer<string>.Default.GetHashCode(Name);
        return hashCode;
    }
}