Why can't I replace each object's property in a list within loop?

Question

Why can't I replace each object's property in an IEnumerble list within loop?

 foreach(var group in groupedClassOptions){

            var gradeNo = group.GroupName.Split(' ')[1];

            if (gradeNo != grade0_name)
            {
                var groupTotal = temp.Where(t => t.grade.ToString().Equals(gradeNo)).First().total;
                group.GroupName += " (" + groupTotal + " students)";
            }
            else
            {

                var prepGroupTotal = temp.Where(t => t.grade.ToString().Equals("0")).First().total;
                group.GroupName += " (" + prepGroupTotal + " students)";
            }
        }

after i exit this loop the property GroupName of each group element was expected to change but it didn't.

Example data - groupedClassOptions

[GroupName: Grade Prep,

Options : [Prep A (23 students), Prep B (21 students)],

GroupName: Grade 1,

Options : [1 A (23 students), 1 B (21 students)],

GroupName: Grade 2,

Options : [2 A (23 students), 2 B (21 students)],

]

This is just so you can get the idea, pls ignore any syntax errors. Now i want to replace GroupName: Grade 1 with GroupName: Grade 1 (x students)

Implementation of groupedClassOptions

var groupedClassOptions = dataClass.GroupBy(x => x.grade).Select(x => new OptionGroupVM()
        {
            GroupName = "Grade " + (x.Key == 0 ? grade0_name : x.Key.ToString()) /*+ " (" + (groupTotal.Where(t => t.grade.ToString().Equals(x.Key)).First().total) + " students)"*/,
            Options = x.Select(y => new OptionVM()
            {
                Value = y.classID.ToString(),
                Text = x.Key == 0 ? grade0_name + y.classname.Substring(1) + " (" + y.total + " students)" : y.classname + " (" + y.total + " students)"
            })
        });

I strongly suspect in your if condition. Check value of gradeNo and grade0_name and make sure, it would execute if-inside code — Akash KC, Oct 16 '17 at 02:54
it is executing i have debugged when inside loop works as expected but when exits nothing has been replaced. I am sharing the full code — Samra, Oct 16 '17 at 03:05
It's possible `group` is a copy of original object, and modifying it doesn't change original one. Could you share the implementation of `groupedClassOptions`? — qxg, Oct 16 '17 at 03:14

score 2 · Accepted Answer · answered Oct 16 '17 at 03:20

You need to convert groupedClassOptions to list using ToList() method which makes your object inside list to be updatable.

var groupedClassOptions = dataClass.GroupBy(x => x.grade).Select(x => new OptionGroupVM()
        {
            GroupName = "Grade " + (x.Key == 0 ? grade0_name : x.Key.ToString()) /*+ " (" + (groupTotal.Where(t => t.grade.ToString().Equals(x.Key)).First().total) + " students)"*/,
            Options = x.Select(y => new OptionVM()
            {
                Value = y.classID.ToString(),
                Text = x.Key == 0 ? grade0_name + y.classname.Substring(1) + " (" + y.total + " students)" : y.classname + " (" + y.total + " students)"
            })
        }).ToList();

Now, update object inside above list.

The reason behind not updating object inside IEnumerable is posted in following answer:

IEnumerables do not guarantee that updated values will persist across enumerations. For instance, a List will return the same set of objects on every iteration, so if you update a property, it will be saved across iterations. However, many other implementations of IEnumerables return a new set of objects each time, so any changes made will not persist.

Why can't I replace each object's property in a list within loop?

Example data - groupedClassOptions

1 Answers1