Remove an item from an IEnumerable T collection

Question

I have a popuplated IEnumerable lt User gt  collection   I want to remove an item from it  how can I do this   foreach var u in users      if u userId   1123             remove          I know your not suppose to remove while looping  so I don t mind either creating a new collection or removing it after   But I don t know how to remove an item  kind of lost for some reason on this   Alternately which I am confused on also  how can I create a new collection like   IEnumerable lt User gt  modifiedUsers   new List lt User gt      foreach var u in users       if u userId    1233               modifiedUsers add                 How can I add to the collection

User · Answer

You can not remove an item from an IEnumerable  it can only be enumerated  as described here  http   msdn microsoft com en-us library system collections ienumerable aspx  You have to use an ICollection if you want to add and remove items  Maybe you can try and casting your IEnumerable  this will off course only work if the underlying object implements ICollection    See here for more on ICollection  http   msdn microsoft com en-us library 92t2ye13 aspx  You can  of course  just create a new list from your IEnumerable  as pointed out by lante  but this might be  sub optimal   depending on your actual use case  of course     ICollection is probably the way to go

User · Answer

Try turning the IEnumerable into a List  From this point on you will be able to use List s Remove method to remove items   To pass it as a param to the Remove method using Linq you can get the item by the following methods    users Single x   gt  x userId    1123   users First x   gt  x userId    1123    The code is as follows   users   users ToList       Get IEnumerable as List  users Remove users First x   gt  x userId    1123       Remove item     Finished

User · Answer

users toList   RemoveAll user   gt   lt your condition gt

User · Answer

You can do something like this   users   users Where x   gt  x userId    userIdToRemove

User · Answer

The IEnumerable interface is just that  enumerable - it doesn t provide any methods to Add or Remove or modify the list at all   The interface just provides a way to iterate over some items - most implementations that require enumeration will implement IEnumerable such as List lt T gt   Why don t you just use your code without the implicit cast to IEnumerable     Treat this like a list  not an enumerable List lt User gt  modifiedUsers   new List lt User gt      foreach var u in users       if u userId    1233                  Use List lt T gt  Add         modifiedUsers Add u

User · Answer

There is now an extension method to convert the IEnumerable lt  gt  to a Dictionary lt   gt  which then has a Remove method   public readonly IEnumerable lt User gt  Users   new User       or however this would be initialized     To take an item out of the collection Users ToDictionary u   gt  u Id  Remove 1123       To take add an item to the collection Users ToList   Add newuser

User · Answer

You can t  IEnumerable lt T gt  can only be iterated   In your second example  you can remove from original collection by iterating over a copy of it  foreach var u in users ToArray       ToArray creates a copy      if u userId    1233               users Remove u

User · Answer

Not removing but creating a new List without that element with LINQ      remove users   users Where u   gt  u userId    123  ToList        new list var modified   users Where u   gt  u userId    123  ToList

User · Answer

You can t remove IEnumerable lt T gt  elements  but you can use the Enumerable Skip Method

[c#] Remove an item from an IEnumerable<T> collection

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