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I am trying to write a recursive lambda expression for going through this following structure. 

NodeID ParentNodeID IsChecked
  1        null        false
  2         1          false
  3         1          false
  4         1          false
  5         1          false
  6         2          false
  7         2          false
  8         2          false
  9         2          false
 10         6          false
 11         6          false
 12         6          false
 13         3          false
 14         3          false
 15         13         false
 16         13         false

//Now i have a List<Int32> checkedNodes Which has 2,3 in it.
List<Int32> checkedNodes = new List<Int32>({2,3});
//I can write a lambda expression which will set these nodes checked value to true.
myList.Where(x => checkedNodes.Contains(x.NodeID)).ToList().ForEach(x => x.Checked = true);

I want to write my lambda expression to set checked for all children and sub children. please Help.

I am open to alternative solution as well if this is not possible.

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6
  • Are you sure you want to use LINQ? You cannot do a recursive LINQ without a recursive function. Commented Jul 3, 2015 at 5:25
  • @YeldarKurmangaliyev I am open for all suggestions. Commented Jul 3, 2015 at 5:27
  • With he way the Linq is designed, probably you can not. I think your best option would be to write it using a normal loop. I guess that would be more readable and easier to write Commented Jul 3, 2015 at 5:28
  • What is Rights in your second query ? is it IsChecked ? Commented Jul 3, 2015 at 5:29
  • @SpiderCode you are right Commented Jul 3, 2015 at 5:46

4 Answers 4

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3

You cannot build a recursive process with LINQ only.
You will need a recursive function.

That's, in my opinion, is an appropriate and elegant solution:

private static void Traverse(Node node)
{
    node.Checked = true; 
    _nodes.Where(x => x.ParentId == node.Id).ToList().ForEach(Traverse);
}

public static void Check(params int[] values)
{
    values.Select(item => _nodes.Single(x => x.Id == item)).ToList().ForEach(Traverse);
}

Traverse is a recursive function which checks the node and calls itself for all its child nodes.
Check is just a function which calls Traverse for every node by given IDs list.

For example, you can wrap it in a public static helper class and it will be convenient to use it:

public static class NodeRecursiveChecker
{
    private static List<Node> _nodes;
    private static void Traverse(Node node)
    {
        node.Checked = true; 
        _nodes.Where(x => x.ParentId == node.Id).ToList().ForEach(Traverse);
    }

    public static void CheckNodes(this List<Node> nodes, params int[] values)
    {
        _nodes = nodes;
        values.Select(item => _nodes.Single(x => x.Id == item)).ToList().ForEach(Traverse);
    }
}

Then, you can use it this way: 

list.CheckNodes(6, 13); // Mark 6, 13 and their children
list.CheckNodes(1); // Mark everything (as 1 is a root in your case)

Here is the DotNetFiddle Demo.

P.S. Note, that I am using LINQ Single function which will throw an exception if there will be no such element in a collection. For example, if you call nodes.CheckNodes(11) and there will be no Node with Id = 11 - it will throw exception. Of course, you can add a check for existence in CheckNodes but it is redundant if you are sure that you will pass only existing Ids. That's why I haven't used it.

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Comments

2

Maybe this is what you're looking for:

Func<Node, bool> predicate = null;
predicate = x => checkedNodes.Contains(x.NodeId) || (x.Parent != null && predicate(x.Parent));

myList.Where(predicate).ToList().ForEach(x => x.IsChecked = true);

Sorry I don't know the declaration of your type containing NodeId, Parent and IsChecked. So I was guessing a little bit.

Maybe you can add an extension method for IEnumerable<T> to have ForEach and remove the ToList call that creates a copy of your collection.

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Comments

1

You can write where clause something like this: 

nodes.Where(node => 
        checkedNodes.Contains(node.Id) || 
        (node.ParentId != null && checkedNodes.Contains((int)node.ParentId))
        ).ToList().ForEach(each => { each.IsChecked = true; });

Have a look at complete demo example Here

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4 Comments

This code is incorrect and works only for depths up to 2. For example, if we have a structure like 1-2-3-4-5-6-7-8-9 and pass "1" - it should check all nodes while your algorithm checks only 1 and 2. Here is the example based on your demo: dotnetfiddle.net/s8LGnk.
@YeldarKurmangaliyev: you mean in this case 2 should also be considered as a parent node ?
In the code sample which I have provided, 1 is a parent of 2; 2 is a parent of 3; 3 is a parent of 4; 4 is a parent of 5 etc. It is like a chain. So, if you check the first element, absolutely all elements should become checked :)
@YeldarKurmangaliyev: Aaah ok. Now I understood exact requirement. Thanks for the clarification :)
1

This is not Linq , but one way of doing this. With the way LInq is designed, your question should be impossible

List<int>  bag = new List<int>();
checkedNodes.ForEach(x=> bag.Add(x));

data.OrderBy(x=>x.ParentNodeId).ToList().ForEach(item=>{
    if(bag.Contains(item.ParentNodeId)){
        bag.Add(item.NodeId);
        item.IsChecked = true;
    }
});

This solution uses a bag to keep list of all parents that are already checked. It is not very efficient, but will work for small collections.

Note that I am sorting based on parent node id first, to reach parents before children. Also note that I am adding newly found parents to the bag.

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4 Comments

@noob this will only get the direct children for current checked nodes, not the sub children.
It isn't impossible. Linq requests a predicate for Where. This predicate could be recursive and it could be a lambda - and of course a recursive lambda.
@VinayPratapSingh , please note I add any newly detected item to my bag. so it will find all nodes. I updated answer to explain this
@Verarind , I understand our solution, and I think that will also work. The efficiency might still not be very good

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