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  • How can I combine sequential expression trees into a fast method?

    - by chillitom
    Suppose I have the following expressions: Expression<Action<T, StringBuilder>> expr1 = (t, sb) => sb.Append(t.Name); Expression<Action<T, StringBuilder>> expr2 = (t, sb) => sb.Append(", "); Expression<Action<T, StringBuilder>> expr3 = (t, sb) => sb.Append(t.Description); I'd like to be able to compile these into a method/delegate equivalent to the following: void Method(T t, StringBuilder sb) { sb.Append(t.Name); sb.Append(", "); sb.Append(t.Description); } What is the best way to approach this? I'd like it to perform well, ideally with performance equivalent to the above method.

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  • Any tips of how to handle hierarchical trees in relational model?

    - by George
    Hello all. I have a tree structure that can be n-levels deep, without restriction. That means that each node can have another n nodes. What is the best way to retrieve a tree like that without issuing thousands of queries to the database? I looked at a few other models, like flat table model, Preorder Tree Traversal Algorithm, and so. Do you guys have any tips or suggestions of how to implement a efficient tree model? My objective in the real end is to have one or two queries that would spit the whole tree for me. With enough processing i can display the tree in dot net, but that would be in client machine, so, not much of a big deal. Thanks for the attention

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  • What is the max LINQ Expression Trees can do?

    - by yeeen
    What is the maximun that LINQ expression Tree can do? Can it define a class? How about a method, with all the declared name, modifiers, parametertype and return type? Must the program always define the tree himself? Is it possible to generate the tree from a given C# file? Where can I get resources to learn about writing basic to advanced Expression Tree and Expression Tree Visitor? (articles and videos will be great) Thanks for those who are able to help...

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  • Any tips of how to handle hierarchial trees in relational model?

    - by George
    Hello all. I have a tree structure that can be n-levels deep, without restriction. That means that each node can have another n nodes. What is the best way to retrieve a tree like that without issuing thousands of queries to the database? I looked at a few other models, like flat table model, Preorder Tree Traversal Algorithm, and so. Do you guys have any tips or suggestions of how to implement a efficient tree model? My objective in the real end is to have one or two queries that would spit the whole tree for me. With enough processing i can display the tree in dot net, but that would be in client machine, so, not much of a big deal. Thanks for the attention

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  • Spatial Index for Rectangles With Fast Insert

    - by TheCloudlessSky
    Hello, I'm looking for a data structure that provides indexing for Rectangles. I need the insert algorithm to be as fast as possible since the rectangles will be moving around the screen (think of dragging a rectangle with your mouse to a new position). I've looked into R-Trees, R+Trees, kD-Trees, Quad-Trees and B-Trees but from my understanding insert's are usually slow. I'd prefer to have inserts at sub-linear time complexity so maybe someone can prove me wrong about either of the listed data structures. I should be able to query the data structure for what rectangles are at point(x, y) or what rectangles intersect rectangle(x, y, width, height). EDIT: The reason I want insert so fast is because if you think of a rectangle being moved around the screen, they're going to have to be removed and then re-inserted. Thanks!

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  • List of fundamental data structures - what am I missing?

    - by jboxer
    I've been studying my fundamental data structures a bunch recently, trying to make sure I've got them down cold. By "fundamental", I mean the real basic ones. Fancy ones like Red-Black Trees and Bloom Filters are clearly worth knowing, but they're usually either enhancements of fundamental ones (Red-Black Trees are binary search trees with special properties to keep them balanced) or they're only useful in very specific situations (Bloom Filters). So far, I'm "fluent" in the following data structures: Arrays Linked Lists Stacks/Queues Binary Search Trees Heaps/Priority Queues Hash Tables However, I feel like I'm missing something. Are there any fundamental ones that I'm forgetting about? EDIT: Added these after posting the question Strings (suggested by catchmeifyoutry) Sets (suggested by Peter) Graphs (suggested by Nick D and aJ) B-Trees (Suggested by tloach) I'm a little on-the-fence about whether these are too fancy or not, but I think they're different enough from the fundamental structures (and important enough) to be worth studying as fundamental.

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  • Asymptotic runtime of list-to-tree function

    - by Deestan
    I have a merge function which takes time O(log n) to combine two trees into one, and a listToTree function which converts an initial list of elements to singleton trees and repeatedly calls merge on each successive pair of trees until only one tree remains. Function signatures and relevant implementations are as follows: merge :: Tree a -> Tree a -> Tree a --// O(log n) where n is size of input trees singleton :: a -> Tree a --// O(1) empty :: Tree a --// O(1) listToTree :: [a] -> Tree a --// Supposedly O(n) listToTree = listToTreeR . (map singleton) listToTreeR :: [Tree a] -> Tree a listToTreeR [] = empty listToTreeR (x:[]) = x listToTreeR xs = listToTreeR (mergePairs xs) mergePairs :: [Tree a] -> [Tree a] mergePairs [] = [] mergePairs (x:[]) = [x] mergePairs (x:y:xs) = merge x y : mergePairs xs This is a slightly simplified version of exercise 3.3 in Purely Functional Data Structures by Chris Okasaki. According to the exercise, I shall now show that listToTree takes O(n) time. Which I can't. :-( There are trivially ceil(log n) recursive calls to listToTreeR, meaning ceil(log n) calls to mergePairs. The running time of mergePairs is dependent on the length of the list, and the sizes of the trees. The length of the list is 2^h-1, and the sizes of the trees are log(n/(2^h)), where h=log n is the first recursive step, and h=1 is the last recursive step. Each call to mergePairs thus takes time (2^h-1) * log(n/(2^h)) I'm having trouble taking this analysis any further. Can anyone give me a hint in the right direction?

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  • Random forests for short texts

    - by Jasie
    Hi all, I've been reading about Random Forests (1,2) because I think it'd be really cool to be able to classify a set of 1,000 sentences into pre-defined categories. I'm wondering if someone can explain to me the algorithm better, I think the papers are a bit dense. Here's the gist from 1: Overview We assume that the user knows about the construction of single classification trees. Random Forests grows many classification trees. To classify a new object from an input vector, put the input vector down each of the trees in the forest. Each tree gives a classification, and we say the tree "votes" for that class. The forest chooses the classification having the most votes (over all the trees in the forest). Each tree is grown as follows: If the number of cases in the training set is N, sample N cases at random - but with replacement, from the original data. This sample will be the training set for growing the tree. If there are M input variables, a number m « M is specified such that at each node, m variables are selected at random out of the M and the best split on these m is used to split the node. The value of m is held constant during the forest growing. Each tree is grown to the largest extent possible. There is no pruning. So, does this look right? I'd have N = 1,000 training cases (sentences), M = 100 variables (let's say, there are only 100 unique words across all sentences), so the input vector is a bit vector of length 100 corresponding to each word. I randomly sample N = 1000 cases at random (with replacement) to build trees from. I pick some small number of input variables m « M, let's say 10, to build a tree off of. Do I build tree nodes randomly, using all m input variables? How many classification trees do I build? Thanks for the help!

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  • Chromium OS Build: How can I use a prebuilt chromium in my OS build?

    - by trees
    I'm attempting to build chromium-os from source and am having some issues integrating the browser into the build. I have a zip of a prebuilt version but I have not been able to find documentation on what to do with it. I've been following the guide that google provides and have just setup the board, but now I am stuck, the directions for building/including chromium in the OS are far to vague. Any help would be greatly appreciated

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  • How to structure classes in the filesystem?

    - by da_b0uncer
    I have a few (view) classes. Table, Tree, PagingColumn, SelectionColumn, SparkLineColumn, TimeColumn. currently they're flat under app/view like this: app/view/Table app/view/Tree app/view/PagingColumn ... I thought about restructuring it, because the Trees and Tables use the columns, but there are some columns, which only work in a tree, some who work in trees and tables and in the future there are probably some who only work in tables, I don't know. My first idea was like this: app/view/Table app/view/Tree app/view/column/PagingColumn app/view/column/SelectionColumn app/view/column/SparkLineColumn app/view/column/TimeColumn But since the SelectionColumn is explicitly for trees, I have the fear that future developers could get the idea of missuse them. But how to restructure it probably? Like this: app/view/table/panel/Table app/view/tree/panel/Tree app/view/tree/column/PagingColumn app/view/tree/column/SelectionColumn app/view/column/SparkLineColumn app/view/column/TimeColumn Or like this: app/view/Table app/view/Tree app/view/column/SparkLineColumn app/view/column/TimeColumn app/view/column/tree/PagingColumn app/view/column/tree/SelectionColumn

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  • Collision Detection in Java for a game

    - by gordsmash
    Im making a game in Java with a few other people but we are stuck on one part of it, making the collision detection. The game is an RPG and I know how to do the collision detection with the characters using Rectangles, but what I dont know how to do is the collision detection for the maps. What I mean by that is like so the character cant walk over trees or water and that stuff but using rectangles doesnt seem like the best option here. Well to explain what the game maps are gonna look like, here is an example http://i980.photobucket.com/albums/ae287/gordsmash/7-8.jpg Now I could use rectangles to get bounds and stop the player from walking over the trees and water but that would take a lot of them. But is there another easier way to prevent the player from walking over the trees and obstacles besides using Rectangles?

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  • Using Instance Nodes, worth it?

    - by Twitch
    I am making a 2d game where there are various environments with lots and lots of objects. There is a forest scene with like 1200 objects in total(trees mainly), of which around 100 are visible on the camera at any given time, as you move through the level. These are comprised of around 20 different kind of trees and other props. Each object is usually 2-6 triangles with a transparent texture. My developer asked me to replace each object in the scene with a node, and keeping only a minimal amount of actual objects which would be 300+ or so(?), since there are a few modified unique meshes. So he can instantiate the actual objects to keep the game light. Is this actually effective? And if so how much? I 've read about draw calls and such and I suppose that if I combine each texture (10 kinds of trees) in 1 mesh it will have the same effect?

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  • Objects disappear when zoomed out in Unity

    - by Starkers
    Ignore the palm trees here. I have some oak-like trees when I'm zoomed in: They disappear when I zoom out: Is this normal? Is this something to do with draw distance? How can I change this so my trees don't disappear? The reason I ask is because my installation had a weird terrain glitch. If this isn't normal I'm going to reinstall right away because I'm always thinking 'is that a feature? Or a glitch'?

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  • Tic-Tac-Toe AI: How to Make the Tree?

    - by cam
    I'm having a huge block trying to understand "trees" while making a Tic-Tac-Toe bot. I understand the concept, but I can't figure out to implement them. Can someone show me an example of how a tree should be generated for such a case? Or a good tutorial on generating trees? I guess the hard part is generating partial trees. I know how to implement generating a whole tree, but not parts of it.

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  • Find location using only distance and range?

    - by pinnacler
    Triangulation works by checking your angle to three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and it's to my right at 90 degrees." Repeat 2 more times for different targets and angles. Trilateration works by checking your distance from three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and I'm 100 meters away from that." Repeat 2 more times for different targets and ranges. But both of those methods rely on knowing WHAT you're looking at. Say you're in a forest and you can't differentiate between trees, but you know where key trees are. These trees have been hand picked as "landmarks." You have a robot moving through that forest slowly. Do you know of any ways to determine location based solely off of angle and range, exploiting geometry between landmarks? Note, you will see other trees as well, so you won't know which trees are key trees. Ignore the fact that a target may be occluded. Our pre-algorithm takes care of that. 1) If this exists, what's it called? I can't find anything. 2) What do you think the odds are of having two identical location 'hits?' I imagine it's fairly rare. 3) If there are two identical location 'hits,' how can I determine my exact location after I move the robot next. (I assume the chances of having 2 occurrences of EXACT angles in a row, after I reposition the robot, would be statistically impossible, barring a forest growing in rows like corn). Would I just calculate the position again and hope for the best? Or would I somehow incorporate my previous position estimate into my next guess? If this exists, I'd like to read about it, and if not, develop it as a side project. I just don't have time to reinvent the wheel right now, nor have the time to implement this from scratch. So if it doesn't exist, I'll have to figure out another way to localize the robot since that's not the aim of this research, if it does, lets hope it's semi-easy.

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  • Find location using only distance and bearing?

    - by pinnacler
    Triangulation works by checking your angle to three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and it's to my right at 90 degrees." Repeat 2 more times for different targets and angles. Trilateration works by checking your distance from three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and I'm 100 meters away from that." Repeat 2 more times for different targets and ranges. But both of those methods rely on knowing WHAT you're looking at. Say you're in a forest and you can't differentiate between trees, but you know where key trees are. These trees have been hand picked as "landmarks." You have a robot moving through that forest slowly. Do you know of any ways to determine location based solely off of angle and range, exploiting geometry between landmarks? Note, you will see other trees as well, so you won't know which trees are key trees. Ignore the fact that a target may be occluded. Our pre-algorithm takes care of that. 1) If this exists, what's it called? I can't find anything. 2) What do you think the odds are of having two identical location 'hits?' I imagine it's fairly rare. 3) If there are two identical location 'hits,' how can I determine my exact location after I move the robot next. (I assume the chances of having 2 occurrences of EXACT angles in a row, after I reposition the robot, would be statistically impossible, barring a forest growing in rows like corn). Would I just calculate the position again and hope for the best? Or would I somehow incorporate my previous position estimate into my next guess? If this exists, I'd like to read about it, and if not, develop it as a side project. I just don't have time to reinvent the wheel right now, nor have the time to implement this from scratch. So if it doesn't exist, I'll have to figure out another way to localize the robot since that's not the aim of this research, if it does, lets hope it's semi-easy.

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  • Behaviour tree code example?

    - by jokoon
    http://altdevblogaday.org/2011/02/24/introduction-to-behavior-trees/ Obviously the most interesting article I found on this website. What do you think about it ? It lacks some code example, don't you know any ? I also read that state machines are not very flexible compared to behaviour trees... On top of that I'm not sure if there is a true link between state machines and the state pattern... is there ?

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  • When and why are certain data structures used in the context of web development?

    - by Ein Doofus
    While browsing around the MSDN I came across: http://msdn.microsoft.com/en-us/library/aa287104%28v=vs.71%29 which lists various data structures such as: Queues Stacks Hashtables Binary Trees Binary Search Trees Graphs (I believe there are also Lists) and I was hoping to get a high-level overview of when these various data structures can be used in the broad context of web development, and when used, why one data structure is generally used instead of any other one.

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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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  • The Latest News About SAP

    - by jmorourke
    Like many professionals, I get a lot of my news from Google e-mail alerts that I’ve set up to keep track of key industry trends and competitive news.  In the past few weeks, I’ve been getting a number of news alerts about SAP.  Below are a few recent examples: Warm weather cuts short US maple sugaring season – by Toby Talbot, AP MILWAUKEE – Temperatures in Wisconsin had already hit the high 60s when Gretchen Grape and her family began tapping their 850 maple trees. They had waited for the state's ceremonial tapping to kick off the maple sugaring season. It was moved up five days, but that didn't make much difference. For Grape, the typically month-long season ended nine days later. The SAP had stopped flowing in a record-setting heat wave, and the 5-quart collection bags that in a good year fill in a day were still half-empty. Instead of their usual 300 gallons of syrup, her family had about 40. Maple syrup producers across the North have had their season cut short by unusually warm weather. While those with expensive, modern vacuum systems say they've been able to suck a decent amount of sap from their trees, producers like Grape, who still rely on traditional taps and buckets, have seen their year ruined. "It's frustrating," said the 69-year-old retiree from Holcombe, Wis. "You put in the same amount of work, equipment, investment, and then all of a sudden, boom, you have no SAP." Home & Garden: Too-Early Spring Means Sugaring Woes  - by Georgeanne Davis for The Free Press Over this past weekend, forsythia and daffodils were blooming in the southern parts of the state as temperatures climbed to 85 degrees, and trees began budding out, putting an end to this year's maple syrup production even as the state celebrated Maine Maple Sunday. Maple sugaring needs cold nights and warm days to induce SAP flows. Once the trees begin budding, SAP can still flow, but the SAP is bitter and has an off taste. Many farmers and dairymen count on sugaring for extra income, so the abbreviated season is a real financial loss for them, akin to the shortened shrimping season's effect on Maine lobstermen. SAP season comes to a sugary Sunday finale – Kennebec Journal, March 26th, 2012 Rebecca Manthey stood out in the rain at the entrance of Old Fort Western keeping watch over a cast iron kettle of boiling SAP hooked to a tripod over a wood fire.  Manthey and the rest of the Old Fort Western staff -- decked out in 18th-century attire -- joined sugar houses across the state in observance of Maine Maple Sunday. The annual event is sponsored by the Department of Agriculture and the Maine Maple Producers Association.  She said the rain hadn't kept people from coming to enjoy all the events at the fort surrounding the production of Maple syrup.  "In the 18th century, you would be boiling SAP in the woods, so I would be in the woods," Manthey explained to the families who circled around her. "People spent weeks and weeks in the woods. You don't want to cook it to fast or it would burn. When it looks like the right consistency then you send it (into the kitchen) to be made into sugar." Manthey said she enjoyed portraying an 18th-century woman, even in the rain, which didn't seem to bother visitors either. There was a steady stream of families touring the fort and enjoying the maple syrup demonstrations. I hope you enjoy these updates on SAP – Happy April Fool’s Day!

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  • Searching Natural Language Sentence Structure

    - by Cerin
    What's the best way to store and search a database of natural language sentence structure trees? Using OpenNLP's English Treebank Parser, I can get fairly reliable sentence structure parsings for arbitrary sentences. What I'd like to do is create a tool that can extract all the doc strings from my source code, generate these trees for all sentences in the doc strings, store these trees and their associated function name in a database, and then allow a user to search the database using natural language queries. So, given the sentence "This uploads files to a remote machine." for the function upload_files(), I'd have the tree: (TOP (S (NP (DT This)) (VP (VBZ uploads) (NP (NNS files)) (PP (TO to) (NP (DT a) (JJ remote) (NN machine)))) (. .))) If someone entered the query "How can I upload files?", equating to the tree: (TOP (SBARQ (WHADVP (WRB How)) (SQ (MD can) (NP (PRP I)) (VP (VB upload) (NP (NNS files)))) (. ?))) how would I store and query these trees in a SQL database? I've written a simple proof-of-concept script that can perform this search using a mix of regular expressions and network graph parsing, but I'm not sure how I'd implement this in a scalable way. And yes, I realize my example would be trivial to retrieve using a simple keyword search. The idea I'm trying to test is how I might take advantage of grammatical structure, so I can weed-out entries with similar keywords, but a different sentence structure. For example, with the above query, I wouldn't want to retrieve the entry associated with the sentence "Checks a remote machine to find a user that uploads files." which has similar keywords, but is obviously describing a completely different behavior.

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  • Interval tree algorithm that supports merging of intervals with no overlap

    - by Dave Griffiths
    I'm looking for an interval tree algorithm similar to the red-black interval tree in CLR but that supports merging of intervals by default so that there are never any overlapping intervals. In other words if you had a tree containing two intervals [2,3] and [5,6] and you added the interval [4,4], the result would be a tree containing just one interval [2,6]. Thanks Update: the use case I'm considering is calculating transitive closure. Interval sets are used to store the successor sets because they have been found to be quite compact. But if you represent interval sets just as a linked list I have found that in some situations they can become quite large and hence so does the time required to find the insertion point. Hence my interest in interval trees. Also there may be quite a lot of merging one tree with another (i.e. a set OR operation) - if both trees are large then it may be better to create a new tree using inorder walks of both trees rather than repeated insertions of each interval.

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  • Metalanguage like BNF or XML-Schema to validate a tree-instance against a tree-model

    - by Stefan
    Hi! I'm implementing a new machine learning algorithm in Java that extracts a prototype datastructure from a set of structured datasets (tree-structure). As im developing a generic library for that purpose, i kept my design independent from concrete data-representations like XML. My problem now is that I need a way to define a data model, which is basically a ruleset describing valid trees, against which a set of trees is being matched. I thought of using BNF or a similar dialect. Basically I need a way to iterate through the space of all valid TreeNodes defined by the ModelTree (Like a search through the search space for algorithms like A*) so that i can compare my set of concrete trees with the model. I know that I'll have to deal with infinite spaces there but first things first. I know, it's rather tricky (and my sentences are pretty bumpy) but I would appreciate any clues. Thanks in advance, Stefan

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