How to remove from the list the items that have parents in the same list

Question

I have a List<Item> .

How can I remove items that have parents in the same list using LINQ?

If it is possible I prefer method chain expression.

Item definition:

public class Item {
        public int Id { get; set; }
        public int ParentId { get; set; }
    }

Answer 1

This may help

List<Item> items = new List<Item>();
items.Add(new Item() { Id = 1, ParentId = 2 });
items.Add(new Item() { Id = 2, ParentId = 0 });
items.Add(new Item() { Id = 3, ParentId = 0 });
items.Add(new Item() { Id = 4, ParentId = 1 });
items.Add(new Item() { Id = 5, ParentId = 1 });
items.Add(new Item() { Id = 6, ParentId = 4 });
items.Add(new Item() { Id = 7, ParentId = 4 });
items.Add(new Item() { Id = 8, ParentId = 4 });
items.Add(new Item() { Id = 9, ParentId = 4 });
items.Add(new Item() { Id = 10, ParentId = 4 });
items.Add(new Item() { Id = 11, ParentId = 4 });

var shouldBeRemove =
    (from i in items
     where items.Any(input => input.Id == i.ParentId)
     select i).ToList();

items.RemoveAll(input => shouldBeRemove.Contains(input));

//Those who remain
//item with Id = 2
//item with Id = 3

Answer 2

var Children = List.Where(child => List.Any(parent => parent.Id == child.ParentID)).ToList();
List.RemoveAll(child => Children.Contains(child));