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• SQL: Recursive Path

  - by Chris

  Is it possible to create a "tree resolver" in SQL? I have a table: ID Name Parent 1 a 2 b 1 3 c 1 4 d 3 Now I want a SQL query that returns: ID PATH 1 /a 2 /a/b 3 /a/c 4 /a/c/d Is this possible with SQL? It would make many things easier for me. Any help would really be appreciated!

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• AST generation for a an application developed both in visual basic and c#

  - by Dev

  Hi, I'm currently understanding one application developed both in visual basic and c#. Running through the code is getting tough as code is around 50KLOC. So i'm planning for generation of AST (abstract syntax tree). Will it be possible to generate for both language together. Atleast a call graph generation will be helpful (but can't find any tool which works for both languages) Please let me know if this question is confusing. Thanks in Advance Dev

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• How to get all objects with their children using django orm?

  - by kender

  Hi, I got very simple hierarchical structure: every object can have 0 or 1 parent. There's no limit on how many children each object can have. So in my application I got such a model: class O(Model): name = CharField(max_length = 20) parent = ForeignKey('O', related_name = 'children') Now I would like to be able to fetch all objects who have a particular one Object1 in their parent-tree (as in their parent or parent of their parents, etc). Should I use mptt or is there a simpler approach?

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• Getting all database entries into organized array

  - by Industrial

  Hi everyone, I have just made the update/add/delete part for the "Closure table" way of organizing query hierarchical data that are shown on page 70 in this slideshare: http://www.slideshare.net/billkarwin/sql-antipatterns-strike-back However, I have a bit of an issue getting the full tree back as an multidimensional array from a single query. Here's what I would like to get back: array ( 'topvalue' = array ( 'Subvalue', 'Subvalue2', 'Subvalue3' = array ('Subvalue 1', 'Subvalue 2', 'Subvalue 3' ) ); );

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• Visualization of object trees in VS

  - by Robin Orheden

  Hi, I am implementing a SPA tree algorithm and is looking for a Visual Studio plugin that let me visualize objects and their relationsships in debug/runtime. Visualization like: [0]-----[1] | \ / [2] \ / | [4] [3] | \ \ | [6] \[5] Any ideas?

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• m-estimate for continuous values

  - by Null

  I'm building a custom regression tree and want to use m-estimate for pruning. Does anyone know how to calculate that. http://www.ailab.si/blaz/predavanja/UISP/slides/uisp07-RegTrees.ppt might help (slide 12, how should Em look like?)

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• Return extra data besides tree data from ExtJS TreeLoader dataUrl?

  - by Chad Johnson

  I asked this question in the Ext JS forums, but I received no responses, so I am asking here. I have a TreePanel (code below) that uses a TreeLoader and an AsyncTreeNode. In my API method specified by the TreeLoader's dataUrl, I return a JSON array to populate the tree. This works great, of course. However, I need to return an additional item--an integer--in addition to the array, and I need to display that value somewhere else in my UI. Is this possible? If not, what else would be a good solution? Here's the code I have currently: tree = new Ext.tree.TreePanel({ enableDD: true, rootVisible: false, useArrows: true, loader: new Ext.tree.TreeLoader({ dataUrl: '/api/method' }), root: new Ext.tree.AsyncTreeNode() });

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• Is it possible to find the KNN for a node that is *IN* the KD-tree?

  - by Stephen

  Hi there, Trying to create a KNN search using a KD-tree. I can form the KD-tree fine (or at least, I believe I can!). My problem is that I am searching to find the closest 2 neighbours to every point in a list of points. So, is there a method to find the K nearest neighbours to a point using a KD tree even if the point is actually IN the tree, or do I need to construct a seperate KD tree for each point, leaving out the point that I wish to search for? My implementation language is C++, but I am more looking for either an algorithm or general help, thanks! Thanks, Stephen

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• How to see if type is instance of a class in Haskell?

  - by Raekye

  I'm probably doing this completely wrong (the unhaskell way); I'm just learning so please let me know if there's a better way to approach this. Context: I'm writing a bunch of tree structures. I want to reuse my prettyprint function for binary trees. Not all trees can use the generic Node/Branch data type though; different trees need different extra data. So to reuse the prettyprint function I thought of creating a class different trees would be instances of: class GenericBinaryTree a where is_leaf :: a -> Bool left :: a -> a node :: a -> b right :: a -> a This way they only have to implement methods to retrieve the left, right, and current node value, and prettyprint doesn't need to know about the internal structure. Then I get down to here: prettyprint_helper :: GenericBinaryTree a => a -> [String] prettyprint_helper tree | is_leaf tree = [] | otherwise = ("{" ++ (show (node tree)) ++ "}") : (prettyprint_subtree (left tree) (right tree)) where prettyprint_subtree left right = ((pad "+- " "| ") (prettyprint_helper right)) ++ ((pad "`- " " ") (prettyprint_helper left)) pad first rest = zipWith (++) (first : repeat rest) And I get the Ambiguous type variable 'a0' in the constraint: (Show a0) arising from a use of 'show' error for (show (node tree)) Here's an example of the most basic tree data type and instance definition (my other trees have other fields but they're irrelevant to the generic prettyprint function) data Tree a = Branch (Tree a) a (Tree a) | Leaf instance GenericBinaryTree (Tree a) where is_leaf Leaf = True is_leaf _ = False left (Branch left node right) = left right (Branch left node right) = right node (Branch left node right) = node I could have defined node :: a -> [String] and deal with the stringification in each instance/type of tree, but this feels neater. In terms of prettyprint, I only need a string representation, but if I add other generic binary tree functions later I may want the actual values. So how can I write this to work whether the node value is an instance of Show or not? Or what other way should I be approaching this problem? In an object oriented language I could easily check whether a class implements something, or if an object has a method. I can't use something like prettyprint :: Show a => a -> String Because it's not the tree that needs to be showable, it's the value inside the tree (returned by function node) that needs to be showable. I also tried changing node to Show b => a -> b without luck (and a bunch of other type class/preconditions/whatever/I don't even know what I'm doing anymore).

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• Patterns for a tree of persistent data with multiple storage options?

  - by Robin Winslow

  I have a real-world problem which I'll try to abstract into an illustrative example. So imagine I have data objects in a tree, where parent objects can access children, and children can access parents: // Interfaces interface IParent<TChild> { List<TChild> Children; } interface IChild<TParent> { TParent Parent; } // Classes class Top : IParent<Middle> {} class Middle : IParent<Bottom>, IChild<Top> {} class Bottom : IChild<Middle> {} // Usage var top = new Top(); var middles = top.Children; // List<Middle> foreach (var middle in middles) { var bottoms = middle.Children; // List<Bottom> foreach (var bottom in bottoms) { var middle = bottom.Parent; // Access the parent var top = middle.Parent; // Access the grandparent } } All three data objects have properties that are persisted in two data stores (e.g. a database and a web service), and they need to reflect and synchronise with the stores. Some objects only request from the web service, some only write to it. Data Mapper My favourite pattern for data access is Data Mapper, because it completely separates the data objects themselves from the communication with the data store: class TopMapper { public Top FetchById(int id) { var top = new Top(DataStore.TopDataById(id)); top.Children = MiddleMapper.FetchForTop(Top); return Top; } } class MiddleMapper { public Middle FetchById(int id) { var middle = new Middle(DataStore.MiddleDataById(id)); middle.Parent = TopMapper.FetchForMiddle(middle); middle.Children = BottomMapper.FetchForMiddle(bottom); return middle; } } This way I can have one mapper per data store, and build the object from the mapper I want, and then save it back using the mapper I want. There is a circular reference here, but I guess that's not a problem because most languages can just store memory references to the objects, so there won't actually be infinite data. The problem with this is that every time I want to construct a new Top, Middle or Bottom, it needs to build the entire object tree within that object's Parent or Children property, with all the data store requests and memory usage that that entails. And in real life my tree is much bigger than the one represented here, so that's a problem. Requests in the object In this the objects request their Parents and Children themselves: class Middle { private List<Bottom> _children = null; // cache public List<Bottom> Children { get { _children = _children ?? BottomMapper.FetchForMiddle(this); return _children; } set { BottomMapper.UpdateForMiddle(this, value); _children = value; } } } I think this is an example of the repository pattern. Is that correct? This solution seems neat - the data only gets requested from the data store when you need it, and thereafter it's stored in the object if you want to request it again, avoiding a further request. However, I have two different data sources. There's a database, but there's also a web service, and I need to be able to create an object from the web service and save it back to the database and then request it again from the database and update the web service. This also makes me uneasy because the data objects themselves are no longer ignorant of the data source. We've introduced a new dependency, not to mention a circular dependency, making it harder to test. And the objects now mask their communication with the database. Other solutions Are there any other solutions which could take care of the multiple stores problem but also mean that I don't need to build / request all the data every time?

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• Coupling an MFC CListCtrl and CTreeCtrl to get a view of the whole tree, not just one node at a time

  - by omatai

  Consider Windows Explorer (or regedit or similar). To the left side, there is a tree view, and to the right, a list view. In all cases I know of, the contents of the right view reflect the attributes of the selected node from the left pane. This is all well and good... but just not what I want. The nodes of the tree I want to display have a very few attributes (2-3) associated with each node - a reasonable amount to display horizontally as a row in a table. Rather than waste all that list view space on a single node with very few properties, I would like to have my list view display a table of the whole tree's properties (as the part of the tree currently expanded). So the nth line in the left view (tree) will correspond directly to the nth line in the right view (list/table), and I will get a decent overview of the properties of my tree. Does anyone know of code that does this? I am guessing that slaving a CListCtrl to a CTreeCtrl would be the way to go, and somehow overriding the vertical scrolling functions so that they are locked together. I'm just not sure that it is possible to lock the scrolls together like this... among other things! All advice gratefully welcomed :-)

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• Reasonably faster way to traverse a directory tree in Python?

  - by Sridhar Ratnakumar

  Assuming that the given directory tree is of reasonable size: say an open source project like Twisted or Python, what is the fastest way to traverse and iterate over the absolute path of all files/directories inside that directory? I want to do this from within Python (subprocess is allowed). os.path.walk is slow. So I tried ls -lR and tree -fi. For a project with about 8337 files (including tmp, pyc, test, .svn files): $ time tree -fi > /dev/null real 0m0.170s user 0m0.044s sys 0m0.123s $ time ls -lR > /dev/null real 0m0.292s user 0m0.138s sys 0m0.152s $ time find . > /dev/null real 0m0.074s user 0m0.017s sys 0m0.056s $ tree appears to be faster than ls -lR (though ls -R is faster than tree, but it does not give full paths). find is the fastest. Can anyone think of a faster and/or better approach? On Windows, I may simply ship a 32-bit binary tree.exe or ls.exe if necessary. Update 1: Added find

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• How do we keep dependent data structures up to date?

  - by Geo

  Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, but how can we manage the complexity of updating the graphs when the parse tree is modified? We know exactly how the tree has been modified, but how can the change be propagated to the other trees in a way that doesn't become difficult to manage? Naturally the dependent graph can be updated by simply reconstructing it from scratch every time the first graph changes, but then there would be no way of knowing the details of the changes in the dependent graph. I currently have four ways to attempt to solve this problem, but each one has difficulties. Nodes of the dependent tree each observe the relevant nodes of the original tree, updating themselves and the observer lists of original tree nodes as necessary. The conceptual complexity of this can become daunting. Each node of the original tree has a list of the dependent tree nodes that specifically depend upon it, and when the node changes it sets a flag on the dependent nodes to mark them as dirty, including the parents of the dependent nodes all the way down to the root. After each change we run an algorithm that is much like the algorithm for constructing the dependent graph from scratch, but it skips over any clean node and reconstructs each dirty node, keeping track of whether the reconstructed node is actually different from the dirty node. This can also get tricky. We can represent the logical connection between the original graph and the dependent graph as a data structure, like a list of constraints, perhaps designed using a declarative language. When the original graph changes we need only scan the list to discover which constraints are violated and how the dependent tree needs to change to correct the violation, all encoded as data. We can reconstruct the dependent graph from scratch as though there were no existing dependent graph, and then compare the existing graph and the new graph to discover how it has changed. I'm sure this is the easiest way because I know there are algorithms available for detecting differences, but they are all quite computationally expensive and in principle it seems unnecessary so I'm deliberately avoiding this option. What is the right way to deal with these sorts of problems? Surely there must be a design pattern that makes this whole thing almost easy. It would be nice to have a good solution for every problem of this general description. Does this class of problem have a name?

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• Dynamically evaluating simple boolean logic in Python

  - by a paid nerd

  I've got some dynamically-generated boolean logic expressions, like: (A or B) and (C or D) A or (A and B) A empty - evaluates to True The placeholders get replaced with booleans. Should I, Convert this information to a Python expression like True or (True or False) and eval it? Create a binary tree where a node is either a bool or Conjunction/Disjunction object and recursively evaluate it? Convert it into nested S-expressions and use a Lisp parser? Something else? Suggestions welcome.

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• Scala: working around the "illegal cyclic reference"

  - by Paul Milovanov

  Hi all, I'm trying to implement a HashMap-based tree that'd support O(1) subtree lookup for a given root key. To that goal, I'm trying to do the following: scala> type Q = HashMap[Char, Q] <console>:6: error: illegal cyclic reference involving type Q type Q = HashMap[Char, Q] ^ So the question is, is there a way for me to do something of the sort without resorting to the ugly HashMap[Char, Any] with subsequent casting of values to HashMap[Char, Any]? Now, I also see that I can use something like the following to avoid the cyclic-reference error, and it might even be cleaner -- but it'd be nice to find out how to correctly do it the first way, just for the educational value. import collections.mutable.HashMap class LTree { val children = new HashMap[Char, LTree] } Thanks a bunch.

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• What's the best general programming book to review basic development concepts?

  - by Charles S.

  I'm looking for for a programming book that reviews basic concepts like implementing linked lists, stacks, queues, hash tables, tree traversals, search algorithms, etc. etc. Basically, I'm looking for a review of everything I learned in college but have forgotten. I prefer something written in the last few years that includes at least a decent amount of code in object-oriented languages. This is to study for job interview questions but I already have the "solving interview questions" books. I'm looking for something with a little more depth and explanation. Any good recommendations?

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• Best design for generating code from an AST?

  - by Sam Washburn

  I'm working on a pretty complex DSL that I want to compile down into a few high level languages. The whole process has been a learning experience. The compiler is written in java. I was wondering if anyone knew a best practice for the design of the code generator portion. I currently have everything parsed into an abstract syntax tree. I was thinking of using a template system, but I haven't researched that direction too far yet as I would like to hear some wisdom first from stack overflow. Thanks!

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• Recursive Function To Create Array

  - by mTuran

  Hi, i use kohana framework and i am trying to code recursive function to create category tree. My Categories Table id int(11) NO PRI NULL auto_increment name varchar(50) NO NULL parent_id int(11) NO NULL projects_count int(11) NO NULL My Example Which Is Not Work public static function category_list($parent_id = 0) { $result = Database::instance()->query(' SELECT name, projects_count FROM project_categories WHERE parent_id = ?', array($parent_id) ); $project_categories = array(); foreach($result as $row) { $project_categories[] = $row; Project_Categories_Model::factory()->category_list($parent_id + 1); } return $project_categories; }

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• Get HTML DOM with CSS

  - by 2x2p1p

  CSS can apply styles in elements through one ID, class or pseudo-selector, but I would like to get the HTML tree, something like in javascript: <script type = "text/javascript"> window.onload = function () { var div = document.getElementsByTagName ("div"); div[0].style.backgroundColor = "gray"; div[0].style.padding = "20px"; } </script> So for example: <style type = "text/css"> div[0] { /* Wrong but i tried :( */ background-color: gray; padding: 20px; } </style> <div > <div>...</div> </div> I'm tired of assign IDs to millions and millions of elements; is there a way to do this?

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• Problem understanding treesort in Haskell

  - by Jerry

  I am trying to figure out how exactly does treesort from here work (I understand flatten, insert and foldr). I suppose what's being done in treesort is applying insert for each element on the list thus generating a tree and then flattening it. The only problem I can't overcome here is where the list (that is the argument of the function) is hiding (because it is not written anywhere as an argument except for the function type declaration). One more thing: since dot operator is function composition, why is it an error when I change: treesort = flatten . foldr insert Leaf to treesort = flatten( foldr insert Leaf )?

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• Json to treeview (<ul>)

  - by Pieter

  Hi I get the following data back from my WCF Data Service (I cut out the metadata) { "d" : [ {"CodeId": 6, "Title": "A Child Sub Item", "Parent":}, {"CodeId": 5, "Title": "Another Root Item", "Parent": -1}, {"CodeId": 4, "Title": "Child Item", "Parent": 2}, {"CodeId": 2, "Title": "Root Item", "Parent": -1} ] } I am trying to get this into a <ul> style tree with Parent = -1 as root and then the rest as sub items of their parent id's. Can anyone help me please, preferably in jQuery? I will use this in jstree if someone knows of a better way to do this. Thanks

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• Turn database result into array

  - by Industrial

  Hi everyone, I have just made the update/add/delete part for the "Closure table" way of organizing query hierarchical data that are shown on page 70 in this slideshare: http://www.slideshare.net/billkarwin/sql-antipatterns-strike-back My database looks like this: Table Categories: ID Name 1 Top value 2 Sub value1 Table CategoryTree: child parent 1 1 2 2 2 1 However, I have a bit of an issue getting the full tree back as an multidimensional array from a single query. Here's what I would like to get back: array ( 'topvalue' = array ( 'Subvalue', 'Subvalue2', 'Subvalue3' = array ('Subvalue 1', 'Subvalue 2', 'Subvalue 3' ) ); ); Update: Found this link, but I still have a hard time to convert it into an array: http://karwin.blogspot.com/2010/03/rendering-trees-with-closure-tables.html

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• mySQL INSERT INTO SELECT not working

  - by Industrial

  Hi everyone, I am trying to implement the "Closure Table" structure in a php/mySQL webapp from Bill Karwins "SQL Antipatterns" slideshare presentation: http://www.slideshare.net/billkarwin/sql-antipatterns-strike-back The first step is to insert some stuff into my tree (page 73 in slide): Easy to insert a new child of comment #5: INSERT INTO Comments ... (Generates comment #8) INSERT INTO TreePaths (ancestor, descendant) VALUES (8, 8); INSERT INTO TreePaths (ancestor, descendant) SELECT ancestor, 8 FROM TreePaths WHERE descendant = 5; I try to translate all this into Codeigniters active record db-style language, and that's about where I get stuck. I cant understand how the second insert gets it's values. Is there anyone out there who can help me out with this?

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• Updating cached counts in MySQL

  - by phleet

  In order to fix a bug, I have to iterate over all the rows in a table, updating a cached count of children to what its real value should be. The structure of the things in the table form a tree. In rails, the following does what I want: Thing.all.each do |th| Thing.connection.update( " UPDATE #{Thing.quoted_table_name} SET children_count = #{th.children.count} WHERE id = #{th.id} " ) end Is there any way of doing this in a single MySQL query? Alternatively, is there any way of doing this in multiple queries, but in pure MySQL? I want something like UPDATE table_name SET children_count = ( SELECT COUNT(*) FROM table_name AS tbl WHERE tbl.parent_id = table_name.id ) except the above doesn't work (I understand why it doesn't).

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• Don’t be a dinosaur. Use Calendar Tree!

  - by jamiet

  If one spends long enough in my company one will likely eventually have to listen to me bark on about subscribable calendars. I was banging on about them way back in 2009, I’ve cajoled SQLBits into providing one, provided one myself for the World Cup, and opined that they could be transformative for the delivery of BI. I believe subscribable calendars can change the world but have never been good at elucidating why I thought so, for that reason I always direct people to read a blog by Scott Adams (yes, the guy who draws Dilbert) entitled Calendar as Filter. In that blog post Scott writes: I think the family calendar is the organizing principle into which all external information should flow. I want the kids' school schedules for sports and plays and even lunch choices to automatically flow into the home calendar. Everything you do has a time dimension. If you are looking for a new home, the open houses are on certain dates, and certain houses that fit your needs are open at certain times. If you are shopping for some particular good, you often need to know the store hours. Your calendar needs to know your shopping list and preferences so it can suggest good times to do certain things I think the biggest software revolution of the future is that the calendar will be the organizing filter for most of the information flowing into your life. You think you are bombarded with too much information every day, but in reality it is just the timing of the information that is wrong. Once the calendar becomes the organizing paradigm and filter, it won't seem as if there is so much. I wholly agree and hence was delighted to discover (via the Hanselminutes podcast) that Scott has a startup called CalendarTree.com whose raison d’etre is to solve this very problem. What better way to describe a Scott Adams startup than with a Scott Adams comic: I implore you to check out Calendar Tree and make the world a tiny bit better by using it to share any information that has a time dimension to it. Don’t be a dinosaur, use Calendar tree! @Jamiet

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