合并2个列表并删除重复项.在第三个列表中输出.我的尝试不起作用 [英] Combining 2 lists and and remove duplicates .Output in a third list .My attempts do not work

问题描述

当我需要比较2个列表并生成包含所有唯一项的第3个列表时，我似乎总是遇到问题.我需要经常执行此操作.

I always seem to have a problem when I need to compare 2 list and produce a 3rd list which include all unique items.I need to perform this quite often.

尝试通过举个例子来重现该问题.

Attempt to reproduce the issue with a noddy example.

我错过了什么吗? 谢谢你的建议

Am I missing something? Thanks for any suggestions

所需结果

   Name= Jo1 Surname= Bloggs1 Category= Account
   Name= Jo2 Surname= Bloggs2 Category= Sales
   Name= Jo5 Surname= Bloggs5 Category= Development
   Name= Jo6 Surname= Bloggs6 Category= Management
   Name= Jo8 Surname= Bloggs8 Category= HR
   Name= Jo7 Surname= Bloggs7 Category= Cleaning

class Program
{
    static void Main(string[] args)
    {
          List<Customer> listOne = new List<Customer>();
        List<Customer> listTwo = new List<Customer>();

        listOne.Add(new Customer { Category = "Account", Name = "Jo1", Surname = "Bloggs1" });
        listOne.Add(new Customer { Category = "Sales", Name = "Jo2", Surname = "Bloggs2" });
        listOne.Add(new Customer { Category = "Development", Name = "Jo5", Surname = "Bloggs5" });
        listOne.Add(new Customer { Category = "Management", Name = "Jo6", Surname = "Bloggs6" });



        listTwo.Add(new Customer { Category = "HR", Name = "Jo8", Surname = "Bloggs8" });
        listTwo.Add(new Customer { Category = "Sales", Name = "Jo2", Surname = "Bloggs2" });
        listTwo.Add(new Customer { Category = "Management", Name = "Jo6", Surname = "Bloggs6" });
        listTwo.Add(new Customer { Category = "Development", Name = "Jo5", Surname = "Bloggs5" });
        listTwo.Add(new Customer { Category = "Cleaning", Name = "Jo7", Surname = "Bloggs7" });


    List<Customer> resultList = listOne.Union(listTwo).ToList();//**I get duplicates why????**

        resultList.ForEach(customer => Console.WriteLine("Name= {0} Surname= {1} Category= {2}", customer.Name, customer.Surname, customer.Category));
        Console.Read();

        IEnumerable<Customer> resultList3 = listOne.Except(listTwo);//**Does not work**

        foreach (var customer in resultList3)
        {
            Console.WriteLine("Name= {0} Surname= {1} Category= {2}", customer.Name, customer.Surname, customer.Category);
        }

        **//Does not work**
        var resultList2 = (listOne
                       .Where(n => !(listTwo
                           .Select(o => o.Category))
                           .Contains(n.Category)))
                       .OrderBy(n => n.Category);

        foreach (var customer in resultList2)
        {
            Console.WriteLine("Name= {0} 
                             Surname= {1} 
                             Category= {2}", 

customer.Name， 客户.姓氏， 客户(类别)； } Console.Read();

customer.Name, customer.Surname, customer.Category); } Console.Read();

  }
}

public class Customer
{
    public string Name { get; set; }
    public string Surname { get; set; }
    public string Category { get; set; }
}

推荐答案

问题的症结在于Customer对象没有.Equals()实现.如果您覆盖.Equals(

The crux of the problem is the Customer object doesn't have a .Equals() implementation. If you override .Equals (and .GetHashCode) then .Distinct would use it to eliminate duplicates. If you don't own the Customer implementation, however, adding .Equals may not be an option.

另一种方法是将自定义IEqualityComparer 传递给.Distinct ().这样，您可以根据传入的比较器以不同的方式比较对象.

An alternative is to pass a custom IEqualityComparer to .Distinct(). This lets you compare objects in different ways depending on which comparer you pass in.

另一种替代方法是对重要字段进行分组并从组中获取任何项目(因为在这种情况下，GroupBy充当.Equals).这需要编写最少的代码.

Another alternative is to GroupBy the fields that are important and take any item from the group (since the GroupBy acts as .Equals in this case). This requires the least code to be written.

例如

    var result = listOne.Concat(listTwo)
        .GroupBy(x=>x.Category+"|"+x.Name+"|"+x.Surname)
        .Select(x=>x.First());

这将获得您想要的结果.

which gets your desired result.

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