How can I return in a ObsevableCollection<T> using C# Linq, all items if no one is selected or just selected items if at least one is selected?

Question

I'm trying to get items in C# in an ObservableCollection<MyClassSelectable> using Linq and Lambda in the following cases :

• Returns All items if no one is selected

Or

• Returns just selected items if at least one is selected.

MyClassSelectable has a property named Selected of bool type.

Is it possible to do it, in only one Linq query line ?

Thank you.

Answer 1

You can first group by the Selected property. This will get you 2 groups if there are selected and not-selected items OR 1 group if all items are either selected or not-selected. Then, order the groups by the selected property. This will put the group with selected items in the first place if there are 2 groups. Then, return the first group.

ObservableCollection<MyClassSelectable> myClassesSelectable;

List<MyClassSelectable> result = myClassesSelectable
    // group by the Selected property
    .GroupBy(mcs => mcs.Selected)
    // order (=> true first, false second)
    .OrderByDescending(g => g.Key)
    // return the first
    .FirstOrDefault()
    ?.ToList();