compare two list and return not matching items using linq

Question

i have a two list  List lt Sent gt  SentList  List lt Messages gt  MsgList    both have the same property called MsgID   MsgList            SentList    MsgID Content      MsgID Content Stauts 1       aaa        1       aaa     0 2       bbb        3       ccc     0 3       ccc         4       ddd 5       eee   i want to compare the MsgID in Msglist with the sentlist and need items which are not in the sent list using linq  Result   MsgID Content 2       bbb 4       ddd 5       eee

User · Answer

You can do like this this is the quickest process  Var result   MsgList Except MsgList Where o   gt  SentList Select s   gt  s MsgID  ToList   Contains o MsgID    ToList      This will give you expected output

User · Answer

List lt Car gt  cars   new List lt Car gt       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 lt Factory gt  factories   new List lt Factory gt          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   gt   factories Any f   gt  f Name    c Name          lblDebug Text    car Name

User · Answer

You could do something like   HashSet lt int gt  sentIDs   new HashSet lt int gt  SentList Select s   gt  s MsgID     var results   MsgList Where m   gt   sentIDs Contains m MsgID      This will return all messages in MsgList which don t have a matching ID in SentList

User · Answer

You can do something like  var notSent   MsgSent Except MsgList  MsgIdEqualityComparer     You will need to provide a custom equality comparer as outlined on MSDN  http   msdn microsoft com en-us library bb336390 aspx  Simply have that equality comparer base equality only on MsgID property of each respective type   Since the equality comparer compares two instances of the same type  you would need to define an interface or common base type that both Sent and Messages implement that has a MsgID property

User · Answer

The naive approach   MsgList Where x   gt   SentList Any y   gt  y MsgID    x MsgID     Be aware this will take up to m n operations as it compares every MsgID in SentList to each in MsgList   up to  because it will short-circuit when it does happen to match

User · Answer

As an extension method  public static IEnumerable lt TSource gt  AreNotEqual lt TSource  TKey  TTarget gt  this IEnumerable lt TSource gt  source  Func lt TSource  TKey gt  sourceKeySelector  IEnumerable lt TTarget gt  target  Func lt TTarget  TKey gt  targetKeySelector         var targetValues   new HashSet lt TKey gt  target Select targetKeySelector         return source Where sourceValue   gt  targetValues Contains sourceKeySelector sourceValue      false       eg   public class Customer       public int CustomerId   get  set       public class OtherCustomer       public int Id   get  set        var customers   new List lt Customer gt          new Customer     CustomerId   1        new Customer     CustomerId   2       var others   new List lt OtherCustomer gt          new OtherCustomer     Id   2        new OtherCustomer     Id   3       var result   customers AreNotEqual customer   gt  customer CustomerId  others  other   gt  other Id  ToList     Debug Assert result Count    1   Debug Assert result 0  CustomerId    1

User · Answer

List lt Person gt  persons1   new List lt Person gt                                   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 lt Person gt  persons2   new List lt Person gt                                   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      Person class  public class Person               public int Id   get  set                public string Name   get  set

User · Answer

Try     public class Sent       public int MsgID      public string Content      public int Status      public class Messages       public int MsgID      public string Content       List lt Sent gt  SentList   new List lt Sent gt      new Sent     MsgID   1  Content    aaa   Status   0    new Sent     MsgID   3  Content    ccc   Status   0                  List lt Messages gt  MsgList   new List lt Messages gt      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   gt  v MsgID  ToArray                List lt Messages gt  result1   MsgList Where o   gt   sentMsgIDs Contains o MsgID   ToList lt Messages gt       Hope it should help

User · Answer

If u wanna Select items of List from 2nd list  MainList Where p   gt  2ndlist Contains p columns from MainList    ToList

User · Answer

Well  you already have good answers  but they re most Lambda  A more LINQ approach would be like  var NotSentMessages                   from msg in MsgList                 where  SentList Any x   gt  x MsgID    msg MsgID                  select msg

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