Freely convert between List T and IEnumerable T

Question

How can I convert a List lt MyObject gt  to an IEnumerable lt MyObject gt  and then back again   I want to do this in order to run a series of LINQ statements on the List  e  g  Sort

User · Answer

A List lt T gt  is an IEnumerable lt T gt   so actually  there s no need to  convert  a List lt T gt  to an IEnumerable lt T gt   Since a List lt T gt  is an IEnumerable lt T gt   you can simply assign a List lt T gt  to a variable of type IEnumerable lt T gt    The other way around  not every IEnumerable lt T gt  is a List lt T gt  offcourse  so then you ll have to call the ToList   member method of the IEnumerable lt T gt

User · Answer

List lt string gt  myList   new List lt string gt     IEnumerable lt string gt  myEnumerable   myList  List lt string gt  listAgain   myEnumerable ToList

User · Answer

A List lt T gt  is an IEnumerable lt T gt   so actually  there s no need to  convert  a List lt T gt  to an IEnumerable lt T gt   Since a List lt T gt  is an IEnumerable lt T gt   you can simply assign a List lt T gt  to a variable of type IEnumerable lt T gt    The other way around  not every IEnumerable lt T gt  is a List lt T gt  offcourse  so then you ll have to call the ToList   member method of the IEnumerable lt T gt

User · Answer

Aside  Note that the standard LINQ operators  as per the earlier example  don t change the existing list - list OrderBy      ToList   will create a new list based on the re-ordered sequence  It is pretty easy  however  to create an extension method that allows you to use lambdas with List lt T gt  Sort   static void Sort lt TSource  TValue gt  this List lt TSource gt  list      Func lt TSource  TValue gt  selector        var comparer   Comparer lt TValue gt  Default      list Sort  x y    gt  comparer Compare selector x   selector y        static void SortDescending lt TSource  TValue gt  this List lt TSource gt  list      Func lt TSource  TValue gt  selector        var comparer   Comparer lt TValue gt  Default      list Sort  x y    gt  comparer Compare selector y   selector x         Then you can use   list Sort x  gt x SomeProp      etc   This updates the existing list in the same way that List lt T gt  Sort usually does

User · Answer

Aside  Note that the standard LINQ operators  as per the earlier example  don t change the existing list - list OrderBy      ToList   will create a new list based on the re-ordered sequence  It is pretty easy  however  to create an extension method that allows you to use lambdas with List lt T gt  Sort   static void Sort lt TSource  TValue gt  this List lt TSource gt  list      Func lt TSource  TValue gt  selector        var comparer   Comparer lt TValue gt  Default      list Sort  x y    gt  comparer Compare selector x   selector y        static void SortDescending lt TSource  TValue gt  this List lt TSource gt  list      Func lt TSource  TValue gt  selector        var comparer   Comparer lt TValue gt  Default      list Sort  x y    gt  comparer Compare selector y   selector x         Then you can use   list Sort x  gt x SomeProp      etc   This updates the existing list in the same way that List lt T gt  Sort usually does

User · Answer

Converting List lt T gt  to IEnumerable lt T gt   List lt T gt  implements IEnumerable lt T gt   and many other such as IList lt T gt   ICollection lt T gt   therefore there is no need to convert a List back to IEnumerable since it already a IEnumerable lt T gt    Example   public class Person       public int Id   get  set        public string Name   get  set       Person person1   new Person     Id   1  Name    Person 1     Person person2   new Person     Id   2  Name    Person 2     Person person3   new Person     Id   3  Name    Person 3      List lt Person gt  people   new List lt Person gt      person1  person2  person3       Converting to an IEnumerable IEnumerable lt Person gt  IEnumerableList   people    You can also use Enumerable AsEnumerable   method  IEnumerable lt Person gt  iPersonList   people AsEnumerable        Converting IEnumerable lt T gt  to List lt T gt   IEnumerable lt Person gt  OriginallyIEnumerable   new List lt Person gt      person1  person2    List lt Person gt  convertToList   OriginallyIEnumerable ToList      This is useful in Entity Framework

User · Answer

Aside  Note that the standard LINQ operators  as per the earlier example  don t change the existing list - list OrderBy      ToList   will create a new list based on the re-ordered sequence  It is pretty easy  however  to create an extension method that allows you to use lambdas with List lt T gt  Sort   static void Sort lt TSource  TValue gt  this List lt TSource gt  list      Func lt TSource  TValue gt  selector        var comparer   Comparer lt TValue gt  Default      list Sort  x y    gt  comparer Compare selector x   selector y        static void SortDescending lt TSource  TValue gt  this List lt TSource gt  list      Func lt TSource  TValue gt  selector        var comparer   Comparer lt TValue gt  Default      list Sort  x y    gt  comparer Compare selector y   selector x         Then you can use   list Sort x  gt x SomeProp      etc   This updates the existing list in the same way that List lt T gt  Sort usually does

User · Answer

A List lt T gt  is an IEnumerable lt T gt   so actually  there s no need to  convert  a List lt T gt  to an IEnumerable lt T gt   Since a List lt T gt  is an IEnumerable lt T gt   you can simply assign a List lt T gt  to a variable of type IEnumerable lt T gt    The other way around  not every IEnumerable lt T gt  is a List lt T gt  offcourse  so then you ll have to call the ToList   member method of the IEnumerable lt T gt

User · Answer

To prevent duplication in memory  resharper is suggesting this   List lt string gt  myList   new List lt string gt     IEnumerable lt string gt  myEnumerable   myList  List lt string gt  listAgain   myList as List lt string gt       myEnumerable ToList       ToList   returns a new immutable list   So changes to listAgain does not effect myList in  Tamas Czinege answer   This is correct in most instances for least two reasons   This helps prevent changes in one area effecting the other area  loose coupling   and it is very readable  since we shouldn t be designing code with compiler concerns   But there are certain instances  like being in a tight loop or working on an embedded or low memory system  where compiler considerations should be taken into consideration

User · Answer

List lt string gt  myList   new List lt string gt     IEnumerable lt string gt  myEnumerable   myList  List lt string gt  listAgain   myEnumerable ToList

User · Answer

Converting List lt T gt  to IEnumerable lt T gt   List lt T gt  implements IEnumerable lt T gt   and many other such as IList lt T gt   ICollection lt T gt   therefore there is no need to convert a List back to IEnumerable since it already a IEnumerable lt T gt    Example   public class Person       public int Id   get  set        public string Name   get  set       Person person1   new Person     Id   1  Name    Person 1     Person person2   new Person     Id   2  Name    Person 2     Person person3   new Person     Id   3  Name    Person 3      List lt Person gt  people   new List lt Person gt      person1  person2  person3       Converting to an IEnumerable IEnumerable lt Person gt  IEnumerableList   people    You can also use Enumerable AsEnumerable   method  IEnumerable lt Person gt  iPersonList   people AsEnumerable        Converting IEnumerable lt T gt  to List lt T gt   IEnumerable lt Person gt  OriginallyIEnumerable   new List lt Person gt      person1  person2    List lt Person gt  convertToList   OriginallyIEnumerable ToList      This is useful in Entity Framework

User · Answer

List lt string gt  myList   new List lt string gt     IEnumerable lt string gt  myEnumerable   myList  List lt string gt  listAgain   myEnumerable ToList

User · Answer

A List lt T gt  is already an IEnumerable lt T gt   so you can run LINQ statements directly on your List lt T gt  variable   If you don t see the LINQ extension methods like OrderBy   I m guessing it s because you don t have a using System Linq directive in your source file   You do need to convert the LINQ expression result back to a List lt T gt  explicitly  though   List lt Customer gt  list       list   list OrderBy customer   gt  customer Name  ToList

User · Answer

A List lt T gt  is an IEnumerable lt T gt   so actually  there s no need to  convert  a List lt T gt  to an IEnumerable lt T gt   Since a List lt T gt  is an IEnumerable lt T gt   you can simply assign a List lt T gt  to a variable of type IEnumerable lt T gt    The other way around  not every IEnumerable lt T gt  is a List lt T gt  offcourse  so then you ll have to call the ToList   member method of the IEnumerable lt T gt

User · Answer

To prevent duplication in memory  resharper is suggesting this   List lt string gt  myList   new List lt string gt     IEnumerable lt string gt  myEnumerable   myList  List lt string gt  listAgain   myList as List lt string gt       myEnumerable ToList       ToList   returns a new immutable list   So changes to listAgain does not effect myList in  Tamas Czinege answer   This is correct in most instances for least two reasons   This helps prevent changes in one area effecting the other area  loose coupling   and it is very readable  since we shouldn t be designing code with compiler concerns   But there are certain instances  like being in a tight loop or working on an embedded or low memory system  where compiler considerations should be taken into consideration

User · Answer

A List lt T gt  is already an IEnumerable lt T gt   so you can run LINQ statements directly on your List lt T gt  variable   If you don t see the LINQ extension methods like OrderBy   I m guessing it s because you don t have a using System Linq directive in your source file   You do need to convert the LINQ expression result back to a List lt T gt  explicitly  though   List lt Customer gt  list       list   list OrderBy customer   gt  customer Name  ToList

User · Answer

Aside  Note that the standard LINQ operators  as per the earlier example  don t change the existing list - list OrderBy      ToList   will create a new list based on the re-ordered sequence  It is pretty easy  however  to create an extension method that allows you to use lambdas with List lt T gt  Sort   static void Sort lt TSource  TValue gt  this List lt TSource gt  list      Func lt TSource  TValue gt  selector        var comparer   Comparer lt TValue gt  Default      list Sort  x y    gt  comparer Compare selector x   selector y        static void SortDescending lt TSource  TValue gt  this List lt TSource gt  list      Func lt TSource  TValue gt  selector        var comparer   Comparer lt TValue gt  Default      list Sort  x y    gt  comparer Compare selector y   selector x         Then you can use   list Sort x  gt x SomeProp      etc   This updates the existing list in the same way that List lt T gt  Sort usually does

User · Answer

List lt string gt  myList   new List lt string gt     IEnumerable lt string gt  myEnumerable   myList  List lt string gt  listAgain   myEnumerable ToList

[c#] Freely convert between List<T> and IEnumerable<T>

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