比较两个列表并使用 linq 返回不匹配的项目

Question

我有两个列表

List<Sent> SentList;
List<Messages> MsgList;

两者都具有称为 MsgID 的相同属性；

MsgList            SentList  

MsgID Content      MsgID Content Stauts
1       aaa        1       aaa     0
2       bbb        3       ccc     0
3       ccc        
4       ddd
5       eee

我想将 Msglist 中的 MsgID 与 sentlist 进行比较，并需要使用 linq 不在已发送列表中的项目

Result 

MsgID Content
2       bbb
4       ddd
5       eee

Answer 1

你可以这样做：

HashSet<int> sentIDs = new HashSet<int>(SentList.Select(s => s.MsgID));

var results = MsgList.Where(m => !sentIDs.Contains(m.MsgID));

这将返回MsgList 中没有SentList 中匹配ID 的所有消息。

Answer 2

天真的方法：

MsgList.Where(x => !SentList.Any(y => y.MsgID == x.MsgID))

请注意，这将需要最多 m*n 操作，因为它将 SentList 中的每个 MsgID 与 MsgList 中的每个 MsgList 进行比较（“最多”，因为它会在它发生时短路 em> 恰好匹配）。

Answer 3

嗯，你已经有了很好的答案，但它们大多是 Lambda。更多的 LINQ 方法就像

var NotSentMessages =
                from msg in MsgList
                where !SentList.Any(x => x.MsgID == msg.MsgID)
                select msg;

Answer 4

你可以这样做，这是最快的过程

Var result = MsgList.Except(MsgList.Where(o => SentList.Select(s => s.MsgID).ToList().Contains(o.MsgID))).ToList();

这将为您提供预期的输出。

Answer 5

你可以这样做

var notSent = MsgSent.Except(MsgList, MsgIdEqualityComparer);

您需要提供 MSDN 上概述的自定义相等比较器

http://msdn.microsoft.com/en-us/library/bb336390.aspx

只需让相等比较器基于每个相应类型的 MsgID 属性的相等性。由于相等比较器比较相同类型的两个实例，因此您需要定义 Sent 和 Messages 都实现的具有 MsgID 的接口或公共基类型 属性。

Answer 6

试试，

  public class Sent
{
    public int MsgID;
    public string Content;
    public int Status;

}

public class Messages
{
    public int MsgID;
    public string Content;
}

  List<Sent> SentList = new List<Sent>() { new Sent() { MsgID = 1, Content = "aaa", Status = 0 }, new Sent() { MsgID = 3, Content = "ccc", Status = 0 } };
            List<Messages> MsgList = new List<Messages>() { new Messages() { MsgID = 1, Content = "aaa" }, new Messages() { MsgID = 2, Content = "bbb" }, new Messages() { MsgID = 3, Content = "ccc" }, new Messages() { MsgID = 4, Content = "ddd" }, new Messages() { MsgID = 5, Content = "eee" }};

            int [] sentMsgIDs = SentList.Select(v => v.MsgID).ToArray();
            List<Messages> result1 = MsgList.Where(o => !sentMsgIDs.Contains(o.MsgID)).ToList<Messages>();

希望它会有所帮助。

Answer 7

作为扩展方法

public static IEnumerable<TSource> AreNotEqual<TSource, TKey, TTarget>(this IEnumerable<TSource> source, Func<TSource, TKey> sourceKeySelector, IEnumerable<TTarget> target, Func<TTarget, TKey> targetKeySelector) 
{
    var targetValues = new HashSet<TKey>(target.Select(targetKeySelector));

    return source.Where(sourceValue => targetValues.Contains(sourceKeySelector(sourceValue)) == false);
}

例如。

public class Customer
{
    public int CustomerId { get; set; }
}

public class OtherCustomer
{
    public int Id { get; set; }
}


var customers = new List<Customer>()
{
    new Customer() { CustomerId = 1 },
    new Customer() { CustomerId = 2 }
};

var others = new List<OtherCustomer>()
{
    new OtherCustomer() { Id = 2 },
    new OtherCustomer() { Id = 3 }
};

var result = customers.AreNotEqual(customer => customer.CustomerId, others, other => other.Id).ToList();

Debug.Assert(result.Count == 1);
Debug.Assert(result[0].CustomerId == 1);

Answer 8

List<Person> persons1 = new List<Person>
           {
                    new Person {Id = 1, Name = "Person 1"},
                    new Person {Id = 2, Name = "Person 2"},
                    new Person {Id = 3, Name = "Person 3"},
                    new Person {Id = 4, Name = "Person 4"}
           };


        List<Person> persons2 = new List<Person>
           {
                    new Person {Id = 1, Name = "Person 1"},
                    new Person {Id = 2, Name = "Person 2"},
                    new Person {Id = 3, Name = "Person 3"},
                    new Person {Id = 4, Name = "Person 4"},
                    new Person {Id = 5, Name = "Person 5"},
                    new Person {Id = 6, Name = "Person 6"},
                    new Person {Id = 7, Name = "Person 7"}
           };
        var output = (from ps1 in persons1
                      from ps2 in persons2
                      where ps1.Id == ps2.Id
                      select ps2.Name).ToList();

人物类

public class Person
{        
    public int Id { get; set; }       

    public string Name { get; set; }
}

Answer 9

如果你想从第二个列表中选择列表项：

MainList.Where(p => 2ndlist.Contains(p.columns from MainList )).ToList();

Answer 10

List<Car> cars = new List<Car>() {  new Car() { Name = "Ford", Year = 1892, Website = "www.ford.us" }, 
                                    new Car() { Name = "Jaguar", Year = 1892, Website = "www.jaguar.co.uk" }, 
                                    new Car() { Name = "Honda", Year = 1892, Website = "www.honda.jp"} };

List<Factory> factories = new List<Factory>() {     new Factory() { Name = "Ferrari", Website = "www.ferrari.it" }, 
                                                    new Factory() { Name = "Jaguar", Website = "www.jaguar.co.uk" }, 
                                                    new Factory() { Name = "BMW", Website = "www.bmw.de"} };

foreach (Car car in cars.Where(c => !factories.Any(f => f.Name == c.Name))) {
    lblDebug.Text += car.Name;
}