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• Is there a SortedList<T> class in .net ? (not SortedList<Key,Value> which is actually a kind of Sort

  - by Brann

  I need to sort some objects according to their contents (in fact according to one of their properties, which is NOT the key and may be duplicated between different objects) .net provides two classes (SortedDictionnary and SortedList), and both are some kind of Dictionaries. The only difference (AFAIK) is that SortedDictionnary uses a binary tree to maintain its state whereas SortedList does not and is accessible via an index. I could achieve what I want using a List, and then using its Sort() method with a custom implementation of IComparer, but it wouldn't be time-efficient as I would sort the whole List each time I insert a new object, whereas a good SortedList would just insert the item at the right position. What I need is a SortedList class with a RefreshPosition(int index) to move only the changed (or inserted) object rather than resorting the whole list each time an object inside changes. Am I missing something obvious ?

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• Java multi-threading - what is the best way to monitor the activity of a number of threads?

  - by MalcomTucker

  I have a number of threads that are performing a long runing task. These threads themselves have child threads that do further subdivisions of work. What is the best way for me to track the following: How many total threads my process has created What the state of each thread currently is What part of my process each thread has currently got to I want to do it in as efficient a way as possible and once threads finish, I don't want any references to them hanging around becasuse I need to be freeing up memory as early as possible. Any advice?

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• How to update an element with a List using LINQ and C#

  - by Addie

  I have a list of objects and I'd like to update a particular member variable within one of the objects. I understand LINQ is designed for query and not meant to update lists of immutable data. What would be the best way to accomplish this? I do not need to use LINQ for the solution if it is not most efficient. Would creating an Update extension method work? If so how would I go about doing that? EXAMPLE: (from trade in CrudeBalancedList where trade.Date.Month == monthIndex select trade).Update( trade => trade.Buy += optionQty);

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• Inserting only unique values into an array

  - by karl

  I have a set of values that I'm pushing into an array in the order they occur $valsArray = array(); //I process each value from a file (code removed for simplicity) //and then add into the array $valsArray[] = $val; How do I turn this into an associative array instead where the value gets inserted (as $key of associative array) only if it doesn't exist. If it does exist increment its count ($value of associative array) by 1. I'm trying to find a more efficient way of handling those values compared to what I'm doing now.

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• Reset form with jQuery

  - by da5id

  I have a form with a standard reset button coded thusly: <input type="reset" class="button standard" value="Clear" /> Trouble is, said form is of the multi-stage sort, so if a user fills out a stage & then returns later, the 'remembered' values for the various fields won't reset when the Clear button is clicked. I'm thinking that attaching a jQuery function to loop over all the fields and clear them 'manually' would do the trick. I'm already using jQuery within the form, but am only just getting up to speed & so am not sure how to go about this, other than individually referencing each field by ID, which doesn't seem very efficient. TIA for any help.

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• [wxWidgets] How to store wxImage into database, using C++?

  - by Thomas Matthews

  I have some wxImages and I would like to store them into a BLOB (Binary Large OBject) field in a MySQL database. There are no methods in wxImage nor wxBitmap for obtaining the binary data as an array of unsigned char so I can load into the database. My current workaround is to write the image to a temporary file, then load the BLOB field directly from the file. Is there a more efficient method to load and store a wxImage object into a MySQL BLOB field? I am using MySql C++ connector 1.05, MS Visual Studio 2008, wxWidgets and C++.

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• How to store or share live data between PHP Requests?

  - by Devyn

  Hi, I want to start a project for facebook and the application will be like real-time multiplayer chess game. The problem I'm having is I have no idea how to store the data when a player moves one piece and update the new position in player2 browser. I'm gonna use PHP, MySQL for server side and jQuery for Client Rendering. The simplest idea is to store the data in XML or MySQL and re-generate the result to player2 browser. But I know that when thousand of players are playing, it will not be an efficient way. Since I don't have time to study new language for this project, I'm gonna have to stick with PHP. I'm not going to use flash either because I want my client side light-weight and flash-free. So is there any way that will solve my problems?

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• Drawing Directed Acyclic Graphs: Minimizing edge crossing?

  - by Robert Fraser

  Laying out the verticies in a DAG in a tree form (i.e. verticies with no in-edges on top, verticies dependent only on those on the next level, etc.) is rather simple without graph drawing algorithms such as Efficient Sugimiya. However, is there a simple algorithm to do this that minimizes edge crossing? (For some graphs, it may be impossible to completely eliminate edge crossing.) A picture says a thousand words, so is there an algorithm that would suggest: instead of: EDIT: As the picture suggests, a vertex's inputs are always on top and outputs are always below, which is another barrier to just pasting in an existing layout algorithm.

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• Monitoring folders for changes

  - by blcArmadillo

  I'm working on a project that will require an application that watches a list of directories the user specifies for changes. Also, I'd like to give the users the option of running the application as a service or on an individual basis. Since users can choose to run it on an individual basis I don't think listening for some operating system event triggered by the addition or deletion of files (if such events exist) would be sufficient. I thought about maybe calculating a checksum for the deepest folder and then building up. I could then compare these checksums on subsequent scans to try and pinpoint where the changes have occurred. Would that be an appropriate solution; if not what would be the best way of doing this in an efficient manner? Also, I'm not quite sure what to tag this as so if you have any recommendations let me know and I'll as them as I see fit. EDIT: I'll need this method to work on Windows, OS X, and ideally Linux

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• Recursive function causing a stack overflow

  - by dbyrne

  I am trying to write a simple sieve function to calculate prime numbers in clojure. I've seen this question about writing an efficient sieve function, but I am not to that point yet. Right now I am just trying to write a very simple (and slow) sieve. Here is what I have come up with: (defn sieve [potentials primes] (if-let [p (first potentials)] (recur (filter #(not= (mod % p) 0) potentials) (conj primes p)) primes)) For small ranges it works fine, but causes a stack overflow for large ranges: user=> (sieve (range 2 30) []) [2 3 5 7 11 13 17 19 23 29] user=> (sieve (range 2 15000) []) java.lang.StackOverflowError (NO_SOURCE_FILE:0) I thought that by using recur this would be a non-stack-consuming looping construct? What am I missing?

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• Erlang bit indexing

  - by GTDev

  I am currently trying to learn erlang and what I am trying to do is to perform an operation on specific indices of an array stored in a bit array or int. If there is a 0 in a position, the index into the array at that position is not used. So envision the following: Example the array is: [1, 3, 5, 42, 23] My bit array is: 21 = 10101 in binary so I'm using indicies 1,3,5 so I'm calling a function on [1, 5, 23] my function is of the form my_function(Array, BitArray) -> SubArray = get_subarray_from_bitarray(Array, BitArray), process_subarray(SubArray). And I need help with the get_subarray_from_bitarray(). I know erlang has special syntax around bit strings (something like <<) so is there an efficient way of indexing into the bit array to get the indicies?

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• The sieve of Eratosthenes in F#

  - by IVlad

  I am interested in an implementation of the sieve of eratosthenes in purely functional F#. I am interested in an implementation of the actual sieve, not the naive functional implementation that isn't really the sieve, so not something like this: let rec PseudoSieve list = match list with | hd::tl -> hd :: (PseudoSieve <| List.filter (fun x -> x % hd <> 0) tl) | [] -> [] The second link above briefly describes an algorithm that would require the use of a multimap, which isn't available in F# as far as I know. The Haskell implementation given uses a map that supports an insertWith method, which I haven't seen available in the F# functional map. Does anyone know a way to translate the given Haskell map code to F#, or perhaps knows of alternative implementation methods or sieving algorithms that are as efficient and better suited for a functional implementation or F#?

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• Adding HTML to the DOM through the client.

  - by Mantorok

  Hi all Just wanted your views on the most efficient way to render content on demand, the reason this has come to light is that I'm maintaining a AA compliant website and we recently added video to it, and one of the techniques to avoid invalidation was to add the HTML for the video to the DOM after the page has loaded - which is fine and working ok. However, I found 2 possible techniques and I would appreciate some views, the one I'm currently using is an AJAX call that returns the HTML, the other technique is a hidden field that contains the HTML - I'm presently using the former. The main reason I'm asking the question is because there may be times when this particular control is also requested via an AJAX call, so I would end up with back-to-back AJAX calls, which seems a bit inefficient to me. I hope this makes sense, are there any better techniques to achieve this? Am I worrying too much over the consecutive AJAX calls? Thanks

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• Find top "n" nearby coordinates.

  - by John Hamelink

  I have a coordinate. I want to find the top "n" (n being a variable value) nearest coordinates out of several thousand rows stored on a MySQL database. I also want to be able to define maximum and minimum distances between the coordinate in question and the coordinates in the database. How best am I to go about this? Would it be bonkers to use PHP as I understand the syntax much better than MySQL? If I use a MySQL function, how do I move it between databases if I choose to switch servers? How is it stored? Lastly, what is the most efficient method of getting through all these coordinates accurately - the coordinates are all relatively close to one another? Thanks for your time, John.

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• All Permutations of a string when corresponding characters are not in the same place

  - by r20rock

  I need all possible permutations of a given string such that no character should remain at the same place as in the input string. Eg. : for input "ask" Output: all possible permutaions like "ksa", "kas"... such that 'a' is not in the 1st position , 's' is not in the 2nd positions and so on... in any permutation. I only need the count of such possible permutations I can do this by generating all permutations and filtering them but I need a very efficient way of doing this. All characters in the string are "UNIQUE" Preferred language C++.

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• Why Switch/Case and not If/Else If?

  - by OB OB

  This question in mainly pointed at C/C++, but I guess other languages are relevant as well. I can't understand why is switch/case still being used instead of if/else if. It seems to me much like using goto's, and results in the same sort of messy code, while the same results could be acheived with if/else if's in a much more organized manner. Still, I see these blocks around quite often. A common place to find them is near a message-loop (WndProc...), whereas these are among the places when they raise the heaviest havoc: variables are shared along the entire block, even when not propriate (and can't be initialized inside it). Extra attention has to be put on not dropping break's, and so on... Personally, I avoid using them, and I wonder wether I'm missing something? Are they more efficient than if/else's? Are they carried on by tradition?

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• real time updates for new page events

  - by Ben Ford

  I know there's a few questions knocking around on this topic but none quite the same. I'm currently searching by location for all the pages relating to a particular geographic location and caching their events in a database. The problem being I have to currently loop through all the pages i'm watching frequently to check for updates. At the moment the 10,000 Pages I'm keeping track of takes a good while to update. It would be much neater (and nicer to fb) to be notified instead of polling. Does anyone know of a more efficient to do this? Thanks Ben

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• Java paint speed relative to color model

  - by Jon

  I have a BufferedImage with an IndexColorModel. I need to paint that image onto the screen, but I've noticed that this is slow when using an IndexColorModel. However, if I run the BufferedImage through an identity affine transform it creates an image with a DirectColorModel and the painting is significantly faster. Here's the code I'm using AffineTransformOp identityOp = new AffineTransformOp(new AffineTransform(), AffineTransformOp.TYPE_BILINEAR); displayImage = identityOp.filter(displayImage, null); I have three questions 1. Why is painting the slower on an IndexColorModel? 2. Is there any way to speed up the painting of an IndexColorModel? 3. If the answer to 2. is no, is this the most efficient way to convert from an IndexColorModel to a DirectColorModel? I've noticed that this conversion is dependent on the size of the image, and I'd like to remove that dependency. Thanks for the help

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• MySqli Prepared Statment Fetch Row

  - by pws5068

  I'm looking for an efficient way to select a specific row with a php prepared statement. $iDB = new mysqliDB(); $stmt = $iDB->prepare($sql); $stmt->bind_param('s',$searhStr); $stmt->execute(); $stmt->store_result(); $stmt->bind_result($objID,$typeID,$year,$updated); // Now jump to row $rowNumber echo("Obj ID = {$objID}"); Any suggestions? Thanks!

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• SQL latest/top items in category

  - by drozzy

  What is a scalable way to select latest 10 items from each category. I have a schema list this: item category updated so I want to select 10 last update items from each category. The current solution I can come up with is to query for categories first and then issue some sort of union query: query = none for cat in categories: query += select top 10 from table where category=cat order by updated I am not sure how efficient this will be for bigger databases (1 million rows). If there is a way to do this in one go - that would be nice. Any help appreciated.

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• Help me understand Rails eager loading

  - by aaronrussell

  I'm a little confused as to the mechanics of eager loading in active record. Lets say a Book model has many Pages and I fetch a book using this query: @book = Book.find book_id, :include => :pages Now this where I'm confused. My understanding is that @book.pages is already loaded and won't execute another query. But suppose I want to find a specific page, what would I do? @book.pages.find page_id # OR... @book.pages.to_ary.find{|p| p.id == page_id} Am I right in thinking that the first example will execute another query, and therefore making the eager loading pointless, or is active record clever enough to know that it doesn't need to do another query? Also, my second question, is there an argument that in some cases eager loading is more intensive on the database and sometimes multiple small queries will be more efficient that a single large query? Thanks for your thoughts.

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• VS2010's "Public Property <PropertyName> As <DataType> vs. Public var

  - by Velika2

  In VS2008, I used to type Public Property <PropName> As <dataType> and hit the Enter key and the IDE editor would automatically expand it out to a full blown property block. Now, from what I understand, a new feature of 2010 is that the compiler automatically "expands" the short syntax above into the same IL code that you would get with the full property GET AND SET sub methods that were are accustomed to seeing before in the editor. But functionality, how the heck is this any different than just having a Public class level variable? If the only diff is what it compiles to and if otehrwise there is no functional difference, isn't the new way less efficient than the old since it involves more code than just having a class level memory variable? Public as I thought that if you weren't going to have code behind your properties that they were essentially the same. I guess the diffrenece is that they just added the keyword "Property" but functionality, their is no diff, eh?

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• Fastest way to put contents of Set<String> to a single String with words separated by a whitespace?

  - by Lars Andren

  I have a few Set<String>s and want to transform each of these into a single String where each element of the original Set is separated by a whitespace " ". A naive first approach is doing it like this Set<String> set_1; Set<String> set_2; StringBuilder builder = new StringBuilder(); for (String str : set_1) { builder.append(str).append(" "); } this.string_1 = builder.toString(); builder = new StringBuilder(); for (String str : set_2) { builder.append(str).append(" "); } this.string_2 = builder.toString(); Can anyone think of a faster, prettier or more efficient way to do this?

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• Make xargs execute the command once for each line of input

  - by Readonly

  How can I make xargs execute the command exactly once for each line of input given? It's default behavior is to chunk the lines and execute the command once, passing multiple lines to each instance. From http://en.wikipedia.org/wiki/Xargs: find /path -type f -print0 | xargs -0 rm In this example, find feeds the input of xargs with a long list of file names. xargs then splits this list into sublists and calls rm once for every sublist. This is more efficient than this functionally equivalent version: find /path -type f -exec rm '{}' \; I know that find has the "exec" flag. I am just quoting an illustrative example from another resource.

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• Searching with Linq

  - by Phil

  I have a collection of objects, each with an int Frame property. Given an int, I want to find the object in the collection that has the closest Frame. Here is what I'm doing so far: public static void Search(int frameNumber) { var differences = (from rec in _records select new { FrameDiff = Math.Abs(rec.Frame - frameNumber), Record = rec }).OrderBy(x => x.FrameDiff); var closestRecord = differences.FirstOrDefault().Record; //continue work... } This is great and everything, except there are 200,000 items in my collection and I call this method very frequently. Is there a relatively easy, more efficient way to do this?

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