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• WPF tree data binding model & repository

  - by Am

  Hi, I have a well defined tree repository. Where I can rename items, move them up, down, etc. Add new and delete. The data is stored in a table as follows: Index Parent Label Left Right 1 0 root 1 14 2 1 food 2 7 3 2 cake 3 4 4 2 pie 5 6 5 1 flowers 8 13 6 5 roses 9 10 7 5 violets 11 12 Representing the following tree: (1) root (14) (2) food (7) (8) flowers (13) (3) cake (4) (5) pie (6) (9) roeses (10) (11) violets (12) or root food cake pie flowers roses violets Now, my problem is how to represent this in a bindable way, so that a TreeView can handle all the possible data changes? Renaming is easy, all I need is to make the label an updatble field. But what if a user moves flowers above food? I can make the relevant data changes, but they cause a complete data change to all other items in the tree. And all the examples I found of bindable hierarchies are good for non static trees.. So my current (and bad) solution is to reload the displayed tree after relocation change. Any direction will be good. Thanks

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• C# expression tree for ordinary code

  - by rwallace

  It's possible to create an expression tree, if you declare it as such. But is it possible to get an expression tree for an ordinary chunk of code such as a method or property getter? What I'm trying to do is, let's say for an order processing system, I have a class for order items: class Item : Entity { [Cascade] public Document document { get; set; } public int line { get; set; } public Product product { get; set; } public string description { get; set; } public decimal qty { get; set; } public decimal price { get; set; } public decimal net { get { return qty * price; } } public VatCode vat_code { get; set; } } where the net value equals qty * price, so I'd like to declare it as such, either with a property or method, and then also have the framework introspect that expression so it can generate appropriate SQL for defining a corresponding calculated column in a corresponding database view. The most obvious way to do this would be to get the expression tree for a property getter or a method, but I can't find any indication how to do this, or that it is possible. (I have found a way to get a method body as a byte stream, but that's not what's desired here.) If that isn't possible, I suppose the recommended solution would be to declare something like a static field that is an expression tree, and compile/run it at run time for internal use, and also introspect as normal for SQL generation?

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• How to render all records from a nested set into a real html tree

  - by Christoph Schiessl

  I'm using the awesome_nested_set plugin in my Rails project. I have two models that look like this (simplified): class Customer < ActiveRecord::Base has_many :categories end class Category < ActiveRecord::Base belongs_to :customer # Columns in the categories table: lft, rgt and parent_id acts_as_nested_set :scope => :customer_id validates_presence_of :name # Further validations... end The tree in the database is constructed as expected. All the values of parent_id, lft and rgt are correct. The tree has multiple root nodes (which is of course allowed in awesome_nested_set). Now, I want to render all categories of a given customer in a correctly sorted tree like structure: for example nested <ul> tags. This wouldn't be too difficult but I need it to be efficient (the less sql queries the better). Update: Figured out that it is possible to calculate the number of children for any given Node in the tree without further SQL queries: number_of_children = (node.rgt - node.lft - 1)/2. This doesn't solve the problem but it may prove to be helpful.

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• How to improve Minecraft-esque voxel world performance?

  - by SomeXnaChump

  After playing Minecraft I marveled a bit at its large worlds but at the same time I found them extremely slow to navigate, even with a quad core and meaty graphics card. Now I assume Minecraft is fairly slow because: A) It's written in Java, and as most of the spatial partitioning and memory management activities happen in there, it would naturally be slower than a native C++ version. B) It doesn't partition its world very well. I could be wrong on both assumptions; however it got me thinking about the best way to manage large voxel worlds. As it is a true 3D world, where a block can exist in any part of the world, it is basically a big 3D array [x][y][z], where each block in the world has a type (i.e BlockType.Empty = 0, BlockType.Dirt = 1 etc.) Now, I am assuming to make this sort of world perform well you would need to: A) Use a tree of some variety (oct/kd/bsp) to split all the cubes out; it seems like an oct/kd would be the better option as you can just partition on a per cube level not a per triangle level. B) Use some algorithm to work out which blocks can currently be seen, as blocks closer to the user could obfuscate the blocks behind, making it pointless to render them. C) Keep the block object themselves lightweight, so it is quick to add and remove them from the trees. I guess there is no right answer to this, but I would be interested to see peoples' opinions on the subject. How would you improve performance in a large voxel-based world?

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• What is the best way to manage large 3d worlds (i.e minecraft style)?

  - by SomeXnaChump

  After playing minecraft I was marvelling a bit at their large worlds but at the same time finding it extremely slow to navigate, even with a quad core and meaty graphics card. Now I assume its fairly slow because: A) Its written in Java, and as most of the actual spatial partitioning and other memory management activities happen in there it would be slower than a native C++ version. B) They are not partitioning their world very well I could be wrong on both assumptions, however it got me thinking about the best way to manage large worlds. As it is more of a true 3d world, where a block can exist in any part of the world, it is basically a big 3d array [x][y][z], where each block in the world has a type (i.e BlockType.Empty = 0, BlockType.Dirt = 1 etc). Now I am assuming to make this sort of world performant you would need to: a) Use a tree of some variety (oct/kd/bsp) to split all the cubes out, it seems like an oct/kd would be the better option as you can just partition on a per cube level not a per triangle level. b) Use some algorithm to work out if the blocks within the scene can currently be seen, as blocks closer to the user could obfuscate the blocks behind, making it pointless to render them. c) Keep the block object themselves lightweight, so it is quick to add and remove them from the trees I guess there is no right answer to this, but I would be interested to see peoples opinions on the subject.

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• Disallow an user to go up in the tree with pure-ftpd

  - by Klaus

  Hello, I added an user to pure-ftpd with adduser -h /blah user, using busybox. Unfortunately, he is able to go up in the tree and see the root folder. How can I disallow this ?

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• View an XML file without any carriage returns or other text formatting as a tree

  - by justinhj

  I've opened an XML file in emacs, and it's the output from a web request so it's just in one long line. Can I execute a command to format it into a tree structure?

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• Tree structured troubleshooting survey which gives solution based on answers

  - by japie1001

  Is there some online tool which let me design a tree structured questionaire/survey which suggests a solution to a problem. Example troubleshooting survey for the problem of black monitor screen: Q1: Is the powercable connected to the monitor? 0 Yes 0 NO If answer is no: "The solution to your problem is to connect the power cable" If answer is yes: Contiue with Q2 Q2: Is the computer turned on: 0 yes 0 no etc Is there something like Google Forms where I can achieve this with online?

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• How Spanning Tree Protocol detects Loops

  - by AMIT

  For last few days I've been reading about Spanning Tree Protocol ,L2 protocol and understood how it prevents loop in network ,various steps in STP but one thing i wanted to know how STP actually detects the loops in network so that it can prevent it.Somewhere I read STP uses BPDU as probe and detects loops I mean how it happen is when switch send a BPDU with Destination Address as multicast and receive same BPDU again mean there is loop in network . But is it how STP detects loops in network?

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• Building a directory tree from a list of file paths

  - by Abignale

  I am looking for a time efficient method to parse a list of files into a tree. There can be hundreds of millions of file paths. The brute force solution would be to split each path on occurrence of a directory separator, and traverse the tree adding in directory and file entries by doing string comparisons but this would be exceptionally slow. The input data is usually sorted alphabetically, so the list would be something like: C:\Users\Aaron\AppData\Amarok\Afile C:\Users\Aaron\AppData\Amarok\Afile2 C:\Users\Aaron\AppData\Amarok\Afile3 C:\Users\Aaron\AppData\Blender\alibrary.dll C:\Users\Aaron\AppData\Blender\and_so_on.txt From this ordering my natural reaction is to partition the directory listings into groups... somehow... before doing the slow string comparisons. I'm really not sure. I would appreciate any ideas. Edit: It would be better if this tree were lazy loaded from the top down if possible.

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• Google Closure Library - Adding non-TreeNode children to a TreeNode

  - by Andreas Jansson

  Hi, I'm using the Google Closure Library and goog.ui.tree in particular to build a tree structure GUI component. It works pretty well out of the box, but I'd like to add a few extra controls to each of the leaves (goog.ui.Checkboxes in particular). The problem is that Component.addChild has been overridden in BaseNode so that each added child is treated as a child tree node as opposed to a child component. In effect plenty of errors are thrown if you try to add anything else than an actual tree node as a child, as these children are traversed and BaseNode-specific functions are called on them. I must admit I'm quite a Closure newb, but I reckon there must be some workaround for this, right? Essentially all I want to do is have a bunch of checkboxes appear next to each leaf in my tree. Thanks, Andreas

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• JQuery treeview - add node(s) in middle of tree

  - by Chris

  Hi all, I'm just getting started with JQuery and the treeview plugin so this should be a relatively easy question: The example code for adding branches to the tree: var newnodes = $("<li><span class='folder'>New Sublist</span><ul>" + "<li><span class='file'>Item1</span></li>" + "<li><span class='file'>Item2</span></li></ul></li>").appendTo("#browser"); $("#browser").treeview({ add: branches }); Works fine for me, but adds the new branch at the end of the tree - instead what I want is to be able to select a specific node and add to that branch. I've managed to get the node being added by using the id of the particular node instead of the whole treeview in - appendTo("nodeID") However I can't get the tree to render correctly, either with: $("nodeID").treeview({ add: branches }); or $("browser").treeview({ add: branches }); or calling it on both without arguments. Cheers in advance

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• Setting TreeView.DataContext doesn't refresh the tree

  - by dan gibson

  I have a List that I've bound to a TreeView. Setting TreeView.DataContext works - everything displays correctly. I then change the list (add an item to it) and set TreeView.DataContext again (to the same value) but the tree does not refresh with the new items. How do I get the treeview to refresh? This is basically my code: public class xItemCollection : ObservableCollection<xItem> { } public class xItem : INotifyPropertyChanged { xItemCollection _Items; public xItem() { _Items = new xItemCollection(); } public xItemCollection Items {get{return _Items;}} } ... this.RootItem = new xItem(); treeView.DataContext = this; Adding items to the list works until the tree is rendered for the first time. After it is rendered, adding/removing items does not refresh the tree.

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• Design a GUI browser to view a tree

  - by iamrohitbanga

  I have a large tree. I want to be able to visualize it using a GUI tool. I want the ability to pan and zoom the tree image so that i can focus on part of the tree. Is there an existing tool to achieve this? If not i would like to write a small tool for myself to be able to do this. what is the simplest way of doing this? what computer language should i use? the image should look something like http://upload.wikimedia.org/wikipedia/commons/d/df/Binary_tree.png I should be able to zoom and pan the image.

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• Expression Tree

  - by nettguy

  My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally in LINQ to SQL query the compiler translates it into parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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• How to get a reference to node in DOM tree in Google Chrome debugger console

  - by .yahoo.co.jpaqwsykcj3aulh3h1k0cy6nzs3isj

  In the Google Chrome debugger, I often want to get a reference to a node in the DOM tree. I can click the "magnifying glass" button and then click the desired element in the browser window to select the corresponding node in the DOM tree displayed in the debugger. But how can I get a reference to that node in the console? If the element has an id, document.getElementById works, but if there is no id, is there a better alternative to XPath or manual traversal of the DOM tree using children? In case XPath is the best way, is there a better way than doing something like this: var evaluator = new XPathEvaluator(); var result = evaluator.evaluate("//div", document.documentElement, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null); which is a pain to type out each time.

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• Tree View Control problem with render Control function

  - by vikas

  I am using TreeView Control in Asp.net. I have placed this control inside a panel. The tree control is completely binded (we don’t want populate on demand) with an Xmldatasource during a callback and then I call Panel.renderControl to return the response (HTML) to the client side callback handler. Problem: 1. The tree expand/collapse (on click of plus sign) is causing postback whereas when I normally bind a tree with xml during postback and without using renderControl of container control, the expand/collapse (on click of plus sign) is being handled at client side.

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• Gaining information from nodes of tree

  - by jainp

  I am working with the tree data structure and trying to come up with a way to calculate information I can gain from the nodes of the tree. I am wondering if there are any existing techniques which can assign higher numerical importance to a node which appears less frequently at lower level (Distance from the root of the tree) than the same nodes appearance at higher level and high frequency. To give an example, I want to give more significance to node Book, at level 2 appearing once, then at level 3 appearing thrice. Will appreciate any suggestions/pointers to techniques which achieve something similar. Thanks, Prateek

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• Finding the heaviest length-constrained path in a weighted Binary Tree

  - by Hristo

  UPDATE I worked out an algorithm that I think runs in O(n*k) running time. Below is the pseudo-code: routine heaviestKPath( T, k ) // create 2D matrix with n rows and k columns with each element = -8 // we make it size k+1 because the 0th column must be all 0s for a later // function to work properly and simplicity in our algorithm matrix = new array[ T.getVertexCount() ][ k + 1 ] (-8); // set all elements in the first column of this matrix = 0 matrix[ n ][ 0 ] = 0; // fill our matrix by traversing the tree traverseToFillMatrix( T.root, k ); // consider a path that would arc over a node globalMaxWeight = -8; findArcs( T.root, k ); return globalMaxWeight end routine // node = the current node; k = the path length; node.lc = node’s left child; // node.rc = node’s right child; node.idx = node’s index (row) in the matrix; // node.lc.wt/node.rc.wt = weight of the edge to left/right child; routine traverseToFillMatrix( node, k ) if (node == null) return; traverseToFillMatrix(node.lc, k ); // recurse left traverseToFillMatrix(node.rc, k ); // recurse right // in the case that a left/right child doesn’t exist, or both, // let’s assume the code is smart enough to handle these cases matrix[ node.idx ][ 1 ] = max( node.lc.wt, node.rc.wt ); for i = 2 to k { // max returns the heavier of the 2 paths matrix[node.idx][i] = max( matrix[node.lc.idx][i-1] + node.lc.wt, matrix[node.rc.idx][i-1] + node.rc.wt); } end routine // node = the current node, k = the path length routine findArcs( node, k ) if (node == null) return; nodeMax = matrix[node.idx][k]; longPath = path[node.idx][k]; i = 1; j = k-1; while ( i+j == k AND i < k ) { left = node.lc.wt + matrix[node.lc.idx][i-1]; right = node.rc.wt + matrix[node.rc.idx][j-1]; if ( left + right > nodeMax ) { nodeMax = left + right; } i++; j--; } // if this node’s max weight is larger than the global max weight, update if ( globalMaxWeight < nodeMax ) { globalMaxWeight = nodeMax; } findArcs( node.lc, k ); // recurse left findArcs( node.rc, k ); // recurse right end routine Let me know what you think. Feedback is welcome. I think have come up with two naive algorithms that find the heaviest length-constrained path in a weighted Binary Tree. Firstly, the description of the algorithm is as follows: given an n-vertex Binary Tree with weighted edges and some value k, find the heaviest path of length k. For both algorithms, I'll need a reference to all vertices so I'll just do a simple traversal of the Tree to have a reference to all vertices, with each vertex having a reference to its left, right, and parent nodes in the tree. Algorithm 1 For this algorithm, I'm basically planning on running DFS from each node in the Tree, with consideration to the fixed path length. In addition, since the path I'm looking for has the potential of going from left subtree to root to right subtree, I will have to consider 3 choices at each node. But this will result in a O(n*3^k) algorithm and I don't like that. Algorithm 2 I'm essentially thinking about using a modified version of Dijkstra's Algorithm in order to consider a fixed path length. Since I'm looking for heaviest and Dijkstra's Algorithm finds the lightest, I'm planning on negating all edge weights before starting the traversal. Actually... this doesn't make sense since I'd have to run Dijkstra's on each node and that doesn't seem very efficient much better than the above algorithm. So I guess my main questions are several. Firstly, do the algorithms I've described above solve the problem at hand? I'm not totally certain the Dijkstra's version will work as Dijkstra's is meant for positive edge values. Now, I am sure there exist more clever/efficient algorithms for this... what is a better algorithm? I've read about "Using spine decompositions to efficiently solve the length-constrained heaviest path problem for trees" but that is really complicated and I don't understand it at all. Are there other algorithms that tackle this problem, maybe not as efficiently as spine decomposition but easier to understand? Thanks.

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• Expression Tree : C#

  - by nettguy

  My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally when our LINQ to SQL query compiler translates it to parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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• WPF: Calling a method from a different "branch" of the tree

  - by sofri

  Hey, I'm doing a WPF Application. The tree looks like this: SurfaceWindow --- Startscreen ..........................-------- Page---------- Subpage I'm trying to call a method from the "Subpage" from the "Code Behind" of the Startscreen(Startscreen.xaml.cs). The method from the Subpage looks like this: public void showTheme(ThemeViewModel theme) { ... } If know that I can call it when I'm on the "Page" or the "SurfaceWindow", because it's in the same "branch" of the tree, and I just do something like this: ThemeViewModel theme = (ThemeViewModel)mvm.CurrentItem.ThemeViewModel; katalog.katalogblatt.showTheme(theme); But how do I do it when I'm not on the same branch of the tree and want to call the method?

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• Secondary keys in a B-tree

  - by Phenom

  Let's say that there is a file that contains an unsorted list of student information, which includes a student ID number as well as other information. I want to make a program that retrieves student information based on student ID number. In order to make it efficient, I store the student IDs in a B-tree. So when I enter a student ID number, it searches the B-tree to see if its there or not. It also does one more thing. If it finds the student ID number, then it also returns where in the file that student's information is. This is the secondary key. The program uses this information to locate the rest of the student's information and prints it to screen. Can this be done? Is this how a b-tree works?

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• Tree data structure in php

  - by Piyush

  in my application user starts a new tree or get added under a child-user and keep on adding users in branches in such a way- >there are 10 level of tree type structure. >root node contain 1 user and each node(user) can have max 5 child-user in this way tree will be like level 0 = 1 user , level 1 = 5 user, level 2 = 25 user , level 3 = 125 user and so on. I created one MySQL table having columns like- User_id , level, super_id, child1_id, child2_id, child3_id, child4_id, child5_id my question is How can I get all child-user(child to child also) of a particular user at any level do I need to add some more columns in my table??

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• WPF Logical Tree - bottom up vs. top down

  - by Dor Rotman

  Hello, I've read the MSDN article about the layouts pass, that states: When a node is added or removed from the logical tree, property invalidations are raised on the node's parent and all its children. As a result, a top-down construction pattern should always be followed to avoid the cost of unnecessary invalidations on nodes that have already been validated. Now lets assume I do this. Won't the users see the control tree populate itself and the layout change several times during the control creation process? I want the whole control tree to just appear completely full. Thanks!

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• java - Depth First Search - Perform DFS on a tree

  - by DJDonaL3000

  Im trying to perform DFS on a Minimum Spanning Tree which contains 26 nodes. Nodes are named 'A' to 'Z' and the tree is undirected. I have an empty function called DFS here that I am trying to write, which (i presume) takes in the tree (a 2D array) a startNode (randomly selected node 'M') and the endNode (randomly selected node 'Z'). The weights of connected nodes are identified in the 2D array parameter, but how do I actually get started visiting nodes? All that is required is to print each nodeName in the order of the DFS traversal. Do I need to create a Node_class for each node in the 2d array??

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