Change some value inside the List T

Question

I have some list  where T is a custom class  and class has some properties   I would like to know how to change one or more values inside of it by using Lambda Expressions  so the result will be the same as the foreach loop bellow   NOTE  list contains multiple items inside  multiple rows           foreach  MyClass mc in list                          if  mc Name     height                   mc Value   30              And this the the linq query  using Lambda expressions   but its not the same as the upper foreach loop  it only returns 1 item  one row  from the list   What I want is  that it returns all the items  all rows  and ONLY changes the appropriate one  the items specified in the WHERE extension method s    list   list Where w   gt  w Name     height   Select s   gt    s Value   30  return s     ToList      NOTE  these 2 example are not the same  I repeat  the linq only returns 1 item  one row   and this is something I don t want  I need all items from the list as well  like foreach loop  it only do changes  but it does not remove any item

User · Answer

This is the way I would do it   saying that  list  is a   lt List lt t gt  gt  where t is a class with a Name and a Value field  but of course you can do it with any other class type       list   list Where c  gt c Name     height            Select  new t   Name   c Name  Value   30            Union list Where c  gt  c Name     height             ToList      This works perfectly   It s a simple linq expression without any loop logic   The only thing you should be aware is that the order of the lines in the result dataset will be different from the order you had in the source dataset  So if sorting is important to you  just reproduce the same order by clauses in the final linq query

User · Answer

How about list Find x   gt  x Name     height   Value   20  This works fine  I know its an old post  but just wondered why hasn t anyone suggested this  Is there a drawback in this code

User · Answer

You could use a projection with a statement lambda  but the original foreach loop is more readable and is editing the list in place rather than creating a new list   var result   list Select i   gt               if  i Name     height   i Value   30        return i         ToList      Extension Method  public static IEnumerable lt MyClass gt  SetHeights      this IEnumerable lt MyClass gt  source  int value        foreach  var item in source               if  item Name     height                       item Value   value                   yield return item            var result   list SetHeights 30  ToList

User · Answer

You could use ForEach  but you have to convert the IEnumerable lt T gt  to a List lt T gt  first   list Where w   gt  w Name     height   ToList   ForEach s   gt  s Value   30

User · Answer

I d probably go with this  I know its not pure linq   keep a reference to the original list if you want to retain all items  and you should find the updated values are in there    foreach  var mc in list Where x   gt  x Name     height           mc Value   30

User · Answer

You can do something like this   var newList   list Where w   gt  w Name     height                  Select s   gt  new  s Name  s Value  30    ToList      But I would rather choose to use foreach because LINQ is for querying while you  want to edit the data

User · Answer

I know this is an old post but  I ve always used an updater extension method        public static void Update lt TSource gt  this IEnumerable lt TSource gt  outer  Action lt TSource gt  updator                        foreach  var item in outer                                updator item                            list Where w   gt  w Name     quot height quot   ToList   Update u   gt  u height   30

[c#] Change some value inside the List<T>

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