How to remove item from list in C

Question

I have a list stored in resultlist as follows   var resultlist   results ToList      It looks something like this   ID FirstName  LastName -- ---------  -------- 1  Bill       Smith 2  John       Wilson 3  Doug       Berg   How do I remove ID 2 from the list

User · Answer

You don t specify what kind of list  but the generic List can use either the RemoveAt index  method  or the Remove obj  method      Remove obj  var item   resultList Single x   gt  x Id    2   resultList Remove item       RemoveAt index  resultList RemoveAt 1

User · Answer

Short answer  Remove  from list results  results RemoveAll r   gt  r ID    2   will remove the item with ID 2 in results  in place   Filter  without removing from original list results   var filtered   result Where f   gt  f ID    2   returns all items except the one with ID 2 Detailed answer  I think  RemoveAll   is very flexible  because you can have a list of item IDs which you want to remove - please regard the following example  If you have  class myClass       public int ID  public string FirstName  public string LastName     and assigned some values to results as follows  var results   new List lt myClass gt        new myClass   ID 1  FirstName  quot Bill quot   LastName  quot Smith quot          results 0      new myClass   ID 2  FirstName  quot John quot   LastName  quot Wilson quot         results 1      new myClass   ID 3  FirstName  quot Doug quot   LastName  quot Berg quot           results 2      new myClass   ID 4  FirstName  quot Bill quot   LastName  quot Wilson quot         results 3      Then you can define a list of IDs to remove  var removeList   new List lt int gt      2  3     And simply use this to remove them  results RemoveAll r   gt  removeList Any a   gt  a  r ID     It will remove the items 2 and 3 and keep the items 1 and 4 - as specified by the removeList  Note that this happens in place  so there is no additional assigment required  Of course  you can also use it on single items like  results RemoveAll r   gt  r ID  4    where it will remove Bill with ID 4 in our example  A last thing to mention is that lists have an indexer  that is  they can also be accessed like a dynamic array  i e  results 3  will give you the 4th element in the results list  because the first element has the index 0  the 2nd has index 1 etc   So if you want to remove all entries where the first name is the same as in the 4th element of the results list  you can simply do it this way  results RemoveAll r   gt  results 3  FirstName    r FirstName    Note that afterwards  only John and Doug will remain in the list  Bill is removed  the first and last element in the example   Important is that the list will shrink automatically  so it has only 2 elements left - and hence the largest allowed index after executing RemoveAll in this example is 1  which is results Count   - 1   Some Trivia  You can use this knowledge and create a local function void myRemove      var last   results Count   - 1                      results RemoveAll r   gt  results last  FirstName    r FirstName      What do you think will happen  if you call this function twice  Like myRemove    myRemove      The first call will remove Bill at the first and last position  the second call will remove Doug and only John Wilson remains in the list   DotNetFiddle  Run the demo Note  Since C  Version 8  you can as well write results  1  instead of var last   results Count   - 1  and  results last   void myRemove     results RemoveAll r   gt  results  1  FirstName    r FirstName      So you would not need the local variable last anymore  see indices and ranges  For a list of all the new features in C   look here

User · Answer

resultList   results Where x  gt x Id    2  ToList      There s a little Linq helper I like that s easy to implement and can make queries with  where not  conditions a little easier to read   public static IEnumerable lt T gt  ExceptWhere lt T gt  this IEnumerable lt T gt  source  Predicate lt T gt  predicate        return source Where x  gt  predicate x         usage in above situation resultList   results ExceptWhere x  gt x Id    2  ToList

User · Answer

More simplified   resultList Remove resultList Single x   gt  x Id    2      there is no needing to create a new var object

User · Answer

There is another approach  It uses List FindIndex and List RemoveAt   While  I would probably use the solution presented by KeithS  just the simple Where ToList  this approach differs in that it mutates the original list object  This can be a good  or a bad   feature  depending upon expectations   In any case  the FindIndex  coupled with a guard  ensures the RemoveAt will be correct if there are gaps in the IDs or the ordering is wrong  etc  and using RemoveAt  vs Remove  avoids a second O n  search through the list   Here is a LINQPad snippet   var list   new List lt int gt    1  3  2    var index   list FindIndex i   gt  i    2      like Where Single if  index  gt   0         ensure item found     list RemoveAt index     list Dump              results - gt  1  3   Happy coding

User · Answer

or just resultlist RemoveAt 1  if you know exactly the index

User · Answer

class Program               public static List lt Product gt  list          static void Main string   args                         list   new List lt Product gt      new Product     ProductId 1  Name  Nike 12N0  Brand  Nike  Price 12000 Quantity 50                    new Product     ProductId  2  Name    Puma 560K   Brand    Puma   Price   120000  Quantity   55                     new Product     ProductId 3  Name  WoodLand V2  Brand  WoodLand  Price 21020 Quantity 25                    new Product     ProductId 4  Name  Adidas S52  Brand  Adidas  Price 20000 Quantity 35                    new Product     ProductId 5  Name  Rebook SPEED2O  Brand  Rebook  Price 1200 Quantity 15                  Console WriteLine  Enter ProductID to remove                int uno   Convert ToInt32 Console ReadLine                 var itemToRemove   list Find r   gt  r ProductId    uno               if  itemToRemove    null                  list Remove itemToRemove               Console WriteLine    itemToRemove ProductId  itemToRemove Name  itemToRemove Brand  itemToRemove Price   itemToRemove Quantity                 Console WriteLine  ------------sucessfully Removed---------------                 var query2   from x in list select x              foreach  var item in query2                                  Console WriteLine item ProductId     item Name     item Brand     item Price     item Quantity                      Console WriteLine    item ProductId  item Name  item Brand  item Price   item Quantity

User · Answer

List lt T gt  has two methods you can use    RemoveAt int index  can be used if you know the index of the item  For example   resultlist RemoveAt 1     Or you can use Remove T item    var itemToRemove   resultlist Single r   gt  r Id    2   resultList Remove itemToRemove     When you are not sure the item really exists you can use SingleOrDefault  SingleOrDefault will return null if there is no item  Single will throw an exception when it can t find the item   Both will throw when there is a duplicate value  two items with the same id    var itemToRemove   resultlist SingleOrDefault r   gt  r Id    2   if  itemToRemove    null      resultList Remove itemToRemove

[c#] How to remove item from list in C#?

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