结合 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

Question

当我需要比较 2 个列表并生成包含所有唯一项目的第三个列表时，我似乎总是遇到问题。我需要经常执行此操作。

尝试用一个点头的例子来重现这个问题。

我错过了什么吗？ 感谢您的任何建议

想要的结果

   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}", 

客户名称， 客户姓氏， 客户.类别）； } Console.Read();

  }
}

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

Answer 1

您不能使用Concat 和Distinct LINQ 方法来做到这一点吗？

List<Customer> listOne;
List<Customer> listTwo;

List<Customer> uniqueList = listOne.Concat(listTwo).Distinct().ToList(); 

如有必要，您可以使用采用 IEqualityComparer 的 Distinct() 重载来创建自定义相等比较

Answer 2

问题的症结在于 Customer 对象没有 .Equals() 实现。如果您覆盖 .Equals (and .GetHashCode) 则 .Distinct 将使用它来消除重复项。但是，如果您不拥有 Customer 实现，则添加 .Equals 可能不是一种选择。

另一种方法是将custom IEqualityComparer 传递给.Distinct()。这使您可以根据传入的比较器以不同的方式比较对象。

另一个替代方法是 GroupBy 重要的字段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。

例如

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

得到你想要的结果。

Answer 3

我有一个类似的问题，我有两个非常大的随机字符串列表。

我做了一个递归函数，它返回一个带有唯一字符串的新列表。我比较了两个包含 100k 随机字符串的列表（它可能存在也可能不存在重复），每个列表都有 6 个字符 abcdefghijklmnopqrstuvwxyz1234567890，它在大约 230 毫秒内完成。我只测量了给定的函数。

我希望这会给某人带来价值。

Image of test run

makeCodesUnique(List<string> existing, List<string> newL)
{
    // Get all duplicate between two lists
    List<string> duplicatesBetween = newL.Intersect(existing).ToList();

    // Get all duplicates within list
    List<string> duplicatesWithin = newL.GroupBy(x => x)
    .Where(group => group.Count() > 1)
    .Select(group => group.Key).ToList();

    if (duplicatesBetween.Count == 0 && duplicatesWithin.Count == 0)
    {
        // Return list if there are no duplicates
        return newL; 
    }
    else
    {
        if (duplicatesBetween.Count != 0)
        {
            foreach (string duplicateCode in duplicatesBetween)
            {
                newL.Remove(duplicateCode);
            }

            // Generate new codes to substitute the removed ones
            List<string> newCodes = generateSomeMore(duplicatesBetween.Count);
            newL.AddRange(newCodes);
            makeCodesUnique(existing, newL);
        }
        else if (duplicatesWithin.Count != 0)
        {
            foreach (string duplicateCode in duplicatesWithin)
            {
                newL.Remove(duplicateCode);
            }
            List<string> newCodes = generateSomeMore(duplicatesWithin.Count);
            new.AddRange(newCodes);
            makeCodesUnique(existing, newL);
        }
    }
    return newL;
}

Answer 4

最好的选择是实现接口 IEqualityComparer 并在我在本文末尾写的 Union 或 Distinct 方法中使用它 http://blog.santiagoporras.com/combinar-listas-sin-duplicados-linq/

• IEqualityComparer的实现

  公共类 SaintComparer : IEqualityComparer { public bool Equals(Saint item1, Saint item2) { 返回 item1.Name == item2.Name; }

  public int GetHashCode(Saint item)
  {
      int hCode = item.Name.Length;
      return hCode.GetHashCode();
  }
  

  }

• 比较器的使用

  var unionList = list1.Union(list2, new SaintComparer());