How to update value in a List using LINQ

Question

I have a list which I want to update using LINQ.

class Student
{
    private string name;
    private int marks;
    public string Name { get; set;}
    pub         


        

Answer 1

LINQ is for querying, not for updating the data. Use LINQ to get the items that you want to modify, and then modify them in a foreach loop:

foreach ( var tom in myList.Where(w => w.Name == "Tom")) {
    tom.Marks = 35;
}

Demo.

Answer 2

Select(), like any other LINQ method, doesn't change a source collection, instead, it return a new collection.

So you should either assign that new collection to myList:

myList = myList.Where(w => w.Name == "Tom").Select(w => { w.Marks = 35; return w}).ToList();

or assign Marks property in a separate foreach loop

myList.Where(w => w.Name == "Tom").ToList().ForEach(w => w.Marks = 35);

Answer 3

This is kind of clunky, but works, and doesn't depend on being passed a reference. It creates a new list based on the old.

var myList=myList.Select(l=>new Student { 
   l.Name,
   Marks=l.Name=="Tom"?35:l.Marks}).ToList();

Or more silly:

var myList=myList.Where(l=>l.Name!="Tom").Union(
  myList.Where(l=>l.Name=="Tom").Select(l=>new Student { 
   l.Name,
   Marks=35})).ToList();

Answer 4

how about old good for loop

for(int i = 0; i < myList.Count; i++)
if (myList[i].Name  == "Tom")
{
    myList[i].Marks = 35;
    break;
}

Answer 5

well @dasblinkenlight code should work but you can also try something like this

 var query = from x in list
             where x.Name = yourcondition
             select new { x };
foreach(var item in query)
   item.x.FieldToUpdate = SetValue;

Answer 6

Try:

myList .Where(w=> w.Name  == "dTomi").ToList().ForEach(i => i.Marks  = 35);