LINQ query to find if items in a list are contained in another list

Question

I have the following code   List lt string gt  test1   new List lt string gt      bob com     tom com     List lt string gt  test2   new List lt string gt     joe bob com    test sam com       I need to remove anyone in test2 that has  bob com or  tom com   What I have tried is this   bool bContained1   test1 Contains test2   bool bContained2   test2 Contains test1     bContained1   false but bContained2   true  I would prefer not to loop through each list but instead use a Linq query to retrieve the data  bContained1 is the same condition for the Linq query that I have created below   List lt string gt  test3   test1 Where w   gt   test2 Contains w   ToList      The query above works on an exact match but not partial matches   I have looked at other queries but I can find a close comparison to this with Linq  Any ideas or anywhere you can point me to would be a great help

User · Answer

var output   emails Where e   gt  domains All d   gt   e EndsWith d       Or if you prefer   var output   emails Where e   gt   domains Any d   gt  e EndsWith d

User · Answer

bool doesL1ContainsL2   l1 Intersect l2  Count      l2 Count    L1 and L2 are both List lt T gt

User · Answer

Try the following   List lt string gt  test1   new List lt string gt      bob com     tom com     List lt string gt  test2   new List lt string gt     joe bob com    test sam com     var output   from goodEmails in test2             where   from email in test2                 from domain in test1                 where email EndsWith domain                  select email  Contains goodEmails              select goodEmails    This works with the test set provided  and looks correct

User · Answer

List lt string gt  l   new List lt string gt      bob com     tom com     List lt string gt  l2   new List lt string gt     joe bob com    test bob com     List lt string gt  myboblist   l2 Where  i  gt i Contains  bob    ToList lt string gt      foreach  var bob in myboblist      Console WriteLine bob ToString

User · Answer

No need to use Linq like this here  because there already exists an extension method to do this for you   Enumerable Except lt TSource gt   http   msdn microsoft com en-us library bb336390 aspx  You just need to create your own comparer to compare as needed

User · Answer

List lt string gt  test1   new List lt string gt      bob com     tom com     List lt string gt  test2   new List lt string gt     joe bob com    test sam com    bets tom com      var result    from t2 in test2               where test1 Any t   gt  t2 Contains t      false               select t2     If query form is what you want to use  this is legible and more or less as  performant  as this could be   What i mean is that what you are trying to do is an O N M  algorithm  that is  you have to traverse N items and compare them against M values  What you want is to traverse the first list only once  and compare against the other list just as many times as needed  worst case is when the email is valid since it has to compare against every black listed domain    from t2 in test we loop the email list once   test1 Any t   gt  t2 Contains t      false we compare with the blacklist and when we found one match return  hence not comparing against the whole list if is not needed   select t2 keep the ones that are clean   So this is what I would use

User · Answer

something like this   List lt string gt  test1   new List lt string gt      bob com     tom com     List lt string gt  test2   new List lt string gt     joe bob com    test sam com      var res   test2 Where f   gt  test1 Count z   gt  f Contains z      0    Live example  here

User · Answer

I think this would be easiest one   test1 ForEach str   gt  test2 RemoveAll x  gt x Contains str

User · Answer

var test2NotInTest1   test2 Where t2   gt  test1 Count t1   gt  t2 Contains t1    0     Faster version as per Tim s suggestion   var test2NotInTest1   test2 Where t2   gt   test1 Any t1   gt  t2 Contains t1

[c#] LINQ query to find if items in a list are contained in another list

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