Querying nested collection (parent / children)

Question

I am trying to get all menus and children that satisfy those conditions using linq:

Menus should have either a link or children count > 0 to be displayed at the
website
For the menus that has children : they should have at least one child menu that has a link

This is the Menu class:

public class Menu
{
    public string Name { get; set; }
    public string Link { get; set; }

    public List<Menu> Children { get; set; }

    public  Menu()
    {
        Children = new List<Menu>();
    }
}

Suppose we have this data structure:

        List<Menu> root = new List<Menu>();
        Menu parent_1 = new Menu() { Name = "Parent 1", Link = null };
        Menu parent_2 = new Menu() { Name = "Parent 2", Link = null };


        //children for parent 1
        Menu p1_child_1 = new Menu() { Name = "p1_child_1", Link = null };
        Menu p1_child_2 = new Menu() { Name = "p1_child_2", Link = null };
        //sub children of p1_child_2
        Menu p1_child_1_1 = new Menu() { Name = "p1_child_1_1", Link = "l1-1" };
        Menu p1_child_1_2 = new Menu() { Name = "p1_child_1_2", Link = null };

        p1_child_1.Children.AddRange(new List<Menu> { p1_child_1_1 , p1_child_1_2 });
        parent_1.Children.AddRange(new List<Menu> { p1_child_1, p1_child_2 });


        Menu p2_child_1 = new Menu() { Name = "p2_child_1", Link = null };
        Menu p2_child_2 = new Menu() { Name = "p2_child_2", Link = "l2-2" };

        Menu p2_child_1_1 = new Menu() { Name = "p2_child_1_1", Link = null };
        Menu p2_child_1_2 = new Menu() { Name = "p2_child_1_2", Link = null };

        p2_child_1.Children.AddRange(new List<Menu> { p2_child_1_1, p2_child_1_2 });


        parent_2.Children.AddRange(new List<Menu> { p2_child_1, p2_child_2 });

        root.Add(parent_1);
        root.Add(parent_2);

Result: The filtered list returned based on the conditions requested will be:

parent_1

p1_child_1
- p1_child_1_1

parent_2

p2_child_2

How to achieve that using Linq or alternative approach taking into consideration the menu could have up to many levels?

Trying the solution as proposed in the comments, i added the extension method

 public static IEnumerable<TResult> SelectHierarchy<TResult>(this IEnumerable<TResult> source, Func<TResult, IEnumerable<TResult>> collectionSelector, Func<TResult, bool> predicate)
    {
        if (source == null)
        {
            yield break;
        }
        foreach (var item in source)
        {
            if (predicate(item))
            {
                yield return item;
            }
            var childResults = SelectHierarchy(collectionSelector(item), collectionSelector, predicate);
            foreach (var childItem in childResults)
            {
                yield return childItem;
            }
        }

Then called the method:

var result = root.SelectHierarchy(n => n.Children, n => n.Children.Count > 0 || n.Link != null).ToList();

However this is not what i want, I expect two menus which carry the subMenus that satisfy my condition, but i am getting 6 menus which i guess are flattened.

Although, p2_child_1 was returned since children count > 0, however it shouldn't cause its menus has no links. ( I placed the predicate as above, since i don't have other option.

Linq is not designed for recursive queries. You'd have to create some iterator that iterates recursively then query _that_. If you have something that works Linq isn't going to help a whole lot. — D Stanley, Jan 09 '17 at 20:23
Can you please provide both the sample data and the expected output as valid C# code? So, for example, if you wanted to add two numbers together you might provide us with: `int x = 3; int y = 5;` and I want the result `int z = 8`. We can then be sure that when we provide the code `x + y` we know we're going to give you the result you want. — Enigmativity, Jan 09 '17 at 20:27
please have a look at these posts http://stackoverflow.com/questions/5422735/how-do-i-select-recursive-nested-entities-using-linq-to-entity http://stackoverflow.com/questions/19237868/get-all-children-to-one-list-recursive-c-sharp — Chandan Rai, Jan 09 '17 at 20:30
You can check my answer on this post http://stackoverflow.com/questions/40656366/iterate-through-objects-with-lists-of-the-object/40657294#40657294 — Franck, Jan 09 '17 at 20:45
@Enigmativity How the question marked as duplicate (which is for **searching** tree) does solve building a **filtered** tree? — Ivan Stoev, Jan 09 '17 at 20:58
@IvanStoev - The OP asks for "The filtered list" so it seems to me that this is a valid duplicate. D Stanley obviously feels the same. Otherwise it's really very difficult to properly interpret questions that don't provide clear inputs and outputs in valid C# code. A better question might have clarified that better. — Enigmativity, Jan 09 '17 at 21:01
@Enigmativity Looking at the sample data and the desired result, it's obvious (to me) that OP has a list with root nodes and wants to get a new list with modified nodes with some nodes eliminated (like `child 1` and `child 1.1`). Also he's asking for *LINQ **or alternative approach***. But anyway, I guess you know better :) — Ivan Stoev, Jan 09 '17 at 21:09
@IvanStoev - I'm happy to be corrected, but the OP needs to weigh in with his actual requirements. If he pings me I'll reopen if need be. — Enigmativity, Jan 09 '17 at 21:26
@h.salman - Well done for such a good update to your question. — Enigmativity, Jan 09 '17 at 23:43

Enigmativity · Accepted Answer · 2017-01-10T00:26:46.887

2

This works for me:

public static class Ex
{
    public static List<Menu> CloneWhere(this List<Menu> source, Func<Menu, bool> predicate)
    {
        return
            source
                .Where(predicate)
                .Select(x => new Menu()
                {
                    Name = x.Name,
                    Link = x.Link,
                    Children = x.Children.CloneWhere(predicate)
                })
                .Where(predicate)
                .ToList();
    }
}

The sample data looks like this:

...then I can apply this:

var result = root.CloneWhere(m => m.Children.Any() || m.Link != null);

...and I get this result:

edited Jan 10 '17 at 00:26

answered Jan 09 '17 at 23:42

Enigmativity

113,464
11
89
172

Thanks @Enigmativit. That is a nice illustration, however in my case `p2_child_1' should not be returned since its has no link and no children (since its children has already no links and was removed). This was my concern. – Hussein Salman Jan 09 '17 at 23:51
@h.salman - Your sample code has `p2_child_1.Children.AddRange(new List { p2_child_1_1, p2_child_1_2 });` so that menu has children. Is that not right? – Enigmativity Jan 10 '17 at 00:07
@Slai - `p2_child_1` has children in the source data. Is the filtering meant to apply to final result? – Enigmativity Jan 10 '17 at 00:21
@h.salman - I've updated the query to filter post the re-build. – Enigmativity Jan 10 '17 at 00:27
@Enigmativity, Yes as "Slai" has mentioned, it should not be in the result since it has no children and its link is null (in the first case it has children, but the children and itself has no links, so all has to be removed). I have illustrated that in Sample Result. Thanks for your help.. – Hussein Salman Jan 10 '17 at 00:27

Ivan Stoev · Answer 2 · 2017-01-10T15:01:05.873

Assuming the depth is not so big to cause stack overflow, you can use a simple recursive method or recursive lambda as follows:

Func<List<Menu>, List<Menu>> filter = null;
filter = items =>
    (from item in items
     let children = filter(item.Children)
     where item.Link != null || children.Any()
     select new Menu { Name = item.Name, Link = item.Link, Children = children }
    ).ToList();
var filtered = filter(root);

The essential part is to process the children first (post order traversal) before filtering the parent.

Querying nested collection (parent / children)

2 Answers2