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• OpenCV: How to copy CvSeq data into CvMat?

  - by Can Bal

  I have a CvSeq structure at hand, which is the output of an available OpenCV function. This holds 128 bytes of data in each of the sequence elements. I want to copy each of these 128-byte elements into rows of a CvMat structure to form a N-by-128 of type CV_32FC1. What would be the most efficient way to do this? I thought of using memcpy but I couldn't come up with a working solution. For the details, I want to calculate the SURF features in an image by cvExtractSURF() function, and copy the SURF descriptors into a matrix for passing it to the cvKMeans2().

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• Integer Linear Programming Java: Multiple Open Source and Commercial tools are available. Which one

  - by Sandeep Jindal

  Hi, I need to use Integer Linear Programming API/Tool for my application. Though my application is in Java but I don’t mind calling an EXE (Tool) from Java providing input using file (MPS, etc). My search analysis is as follows: There are multiple Open Source and Commercial tools available to solve ILP Following I found and think are useful for my needs. 1. Gnu LP Kit(GLPK): I think this is the oldest and probably most stable and efficient 2. IP_Solve: Has good reviews about it. 3. JavaILP: Found this, but not much reviews about it 4. Apache Common-Math: Supports LP but not ILP, so ruled out. 5. Coin-OR Can you please suggest which one shall be the best in terms of stability, efficiency, acceptance, etc Regards Sandeep Jindal

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• perl one liner alternative to this bash "chain"?

  - by Michael Mao

  Hello everyone: I am trying to comprehend Perl following the way describe in the book "Minimal Perl". I've uploaded all source txt files onto my own server : results folder I got the output from using several bash commands in a "chain" like this: cat run*.txt | grep '^Bank[[:space:]]Balance'| cut -d ':' -f2 | grep -E '\$[0-9]+' I know this is far from the most concise and efficient, but at least it works... As our uni subject now moves onto the Perl part, I'd like to know if there is a way to get the same results in one line? I am trying something like the following code but stuck in the middle: Chenxi Mao@chenxi-a6b123bb /cygdrive/c/eMarket/output $ perl -wlne 'print; if $n=~/^Bank Balance/' syntax error at -e line 1, near "if $n" Execution of -e aborted due to compilation errors.

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• Language Design: Combining Gotos and Functions

  - by sub

  I'm designing and currently rethinking a low-level interpreted programming language with similarities to assembler. I very soon came across the functions/loops/gotos decision problem and thought that while loops like while and for would be too high-level and unfitting, gotos would be too low level, unmaintainable and generally evil again. Functions like you know them from most languages that have return values and arguments aren't fitting in the language's concept either. So I tried to figure out something between a function and a goto which is capable of Recursion Efficient loops After some thinking I came up with the idea of subroutines: They have a beginning and an end like a function They have a name but no arguments like a goto You can go into one with jump and go out of it again before its end with return (doesn't give back any result, only stops the subroutine) Handled just like normal code - Global scope like goto So I wanted to know: Is the idea above good? What are the (dis)advantages? Would there be a better combination of function and goto or even a completely new idea?

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• Aaron Hillegass Chapter 18 Challenge Question

  - by jasonbogd

  I am working through Aaron Hillegass' Cocoa Programming for Mac OS X and am doing the challenge for Chapter 18. Basically, the challenge is to write an app that can draw ovals using your mouse, and then additionally, add saving/loading and undo support. I'm trying to think of a good class design for this app that follows MVC. Here's what I had in mind: Have a NSView-subclass that represents an oval (say JBOval) that I can use to easily draw an oval. Have a main view (JBDrawingView) that holds JBOvals and draws them. The thing is that I wasn't sure how to add archiving. Should I archive each JBOval? I think this would work, but archiving an NSView doesn't seem very efficient. Any ideas on a better class design? Thanks.

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• F# currying efficiency?

  - by Eamon Nerbonne

  I have a function that looks as follows: let isInSet setElems normalize p = normalize p |> (Set.ofList setElems).Contains This function can be used to quickly check whether an element is semantically part of some set; for example, to check if a file path belongs to an html file: let getLowerExtension p = (Path.GetExtension p).ToLowerInvariant() let isHtmlPath = isInSet [".htm"; ".html"; ".xhtml"] getLowerExtension However, when I use a function such as the above, performance is poor since evaluation of the function body as written in "isInSet" seems to be delayed until all parameters are known - in particular, invariant bits such as (Set.ofList setElems).Contains are reevaluated each execution of isHtmlPath. How can best I maintain F#'s succint, readable nature while still getting the more efficient behavior in which the set construction is preevaluated. The above is just an example; I'm looking for a general pattern that avoids bogging me down in implementation details - where possible I'd like to avoid being distracted by details such as the implementation's execution order since that's usually not important to me and kind of undermines a major selling point of functional programming.

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• C# Multithreading File IO (Reading)

  - by washtik

  We have a situation where our application needs to process a series of files and rather than perform this function synchronously, we would like to employ multi-threading to have the workload split amongst different threads. Each item of work is: 1. Open a file for read only 2. Process the data in the file 3. Write the processed data to a Dictionary We would like to perform each file's work on a new thread? Is this possible and should be we better to use the ThreadPool or spawn new threads keeping in mind that each item of "work" only takes 30ms however its possible that hundreds of files will need to be processed. Any ideas to make this more efficient is appreciated.

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• PHP DateTime Regex

  - by CogitoErgoSum

  Hey, long story short I have inherited some terrible code. As a result a string comparison is buggy when comparing dates due to the format of the date. I am trying to convert the date to a valid DateFormat syntax so I can run a proper comparison. These are some samples of the current format: 12/01/10 at 8:00PM 12/31/10 at 12:00PM 12/10/09 at 5:00AM and so forth. I'd like to convert this to a YYYYMMDDHHMM format i.e 201012012000 for comparison purposes. If anyone can give me a quick regex snippet to do this that'd be appreciated as right now i'm hitting a brick wall for a regex. I can do it by exploding the string over several times etc but I'd rather do it in a more efficient manner. Thanks!

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• Algorithm and data structure learning resources for dynamic programming

  - by Pranav

  Im learning dynamic programming now, and while I know the theory well, designing DP algorithms for new problems is still difficult. This is what i would really like now- A book or a website, which poses a problem which can be solved by dynamic programming. Also there is the solution with an explanation available, which i would like to see if i cant solve the problem even after butting my head at it for a few hours. Is there some resource that provides this sort of a thing for several categories of algorithms- like graph algorithms, dynamic programming, etc? P.S. I considered Topcoder, but the solutions there are not really appropriate for learning to implement efficient solutions.

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• iPhone – Best method to import/drawing UI graphic elements? CGContextDrawPDFPage?

  - by Ross

  Hello, What is the best way to use the custom UI graphics on the iPhone? I've come across CGContextDrawPDFPage and Panic's Shrinkit. Should I be using storing my vector ui graphics as PDF's and loading them using CGContextDrawPDFPage to draw them. I did previously asked what way Apple store their UI graphics and was answered crushed png. The options as I see it, but I would really want to know what technique other people use. This question is for vector graphics only. Looking for what is standard / most effective / most efficient. PNG (bitmapped image) Custom UIView drawing code (generated from Opacity) PDF (I've not used this method, is it with CGContextDrawPDFPage?) Many thanks Ross

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• sql query to incrementally modify where condition until result contains what is required

  - by iamrohitbanga

  I need an sql query to select some items from a table based on some condition which is based on a category field. As an example consider a list of people and I fetch the people from a particular age group from the database. I want to check if the result contains at least one result from each of a number of categories. If not I want to modify the age group by extending it and check the results again. This is repeated until I get an age group for which one result is present for each category. Right now i am doing this by analyzing the results and modifying the sql query. So a number of sql select queries are sent. What is the most efficient way of doing this? I am invoking the select queries from a java program using jdbc. I am using mysql database.

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• .NET and P2P - writing a P2P messenger

  - by brovar

  Hi there, Does anyone have any advice how to write such app? Or maybe knows some nice tutorial? I would like to use System.Net.PeerToPeer namespace, but everything I can find about it is MSDN which I can't read without getting mad. Or maybe using "old-school" TCP/IP would more efficient? I will appreciate every piece of advice. Every sample code I will shower with gold ;) And please, don't send me back to Google for I have searched for a long time for sth useful - maybe inaccurately but time is running out and I really need some help.

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• ASP.net 2.0 Gridview with Expanding Panel Rows -- How to build Panel "on the fly"

  - by jlrolin

  I'm currently building a Gridview that has expandable rows. Each row contains a dynamically created Panel of Form elements. Right now, I have a javascript function that expands (or in my case, makes visible) the panel when an Image is clicked on the Gridview row. My question is... is there a more efficient way of doing this. Instead of pulling all my data to begin with and building each new row as I Databind, is there a way to simple create the row with the Panel full of textboxes and dropdownlists on the fly when the user clicks the Expand button?" I'd like to limit the server calls by doing it that way instead of how I'm currently doing it, looping through every row and creating a new panel with form elements and inserting that into a row that is hidden.

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• Two Key HashSet?

  - by athena

  I need a HashSet implementation where the elements are a pair of Integers eg. Set s = { {1,2} , {3,4} , {1,4}}. Here the set s has 3 elements. This kind of two key HashSet is needed in many situations like, I have a relation in my database where the candidate key is a combination of two columns. Is there some library which already provides this? If no such implementation is available, then rather then implementing the entire data structure from scratch, will it be easier (and efficient?) to extend the HashSet implementation in Java?

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• One pass multiple whitespace replace to single whitespace and eliminate leading and trailing whitesp

  - by Phoenix

  void RemoveSpace(char *String) { int i=0,y=0; int leading=0; for(i=0,y=0;String[i]!='\0';i++,y++) { String[y]=String[i]; // let us copy the current character. if(isspace(String[i])) // Is the current character a space? { if(isspace(String[i+1])||String[i+1]=='\0'||leading!=1) // leading space y--; } else leading=1; } String[y]='\0'; } Does this do the trick of removing leading and trailing whitespaces and replacing multiple whitespaces with single ones ?? i tested it for null string, all whitespaces, leading whitespaces and trailing whitespaces. Do you think this is an efficient one pass solution ??

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• Spatial index for geo coordinates?

  - by Michael Borgwardt

  What kind of data structure could be used for an efficient nearest neighbor search in a large set of geo coordinates? With "regular" spatial index structures like R-Trees that assume planar coordinates, I see two problems (Are there others I have overlooked?): Wraparound at the poles and the International Date Line Distortion of distances near the poles How can these factors be allowed for? I guess the second one could compensated by transforming the coordinates. Can an R-Tree be modified to take wraparound into account? Or are there specialized geo-spatial index structures?

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• Help me finish this Python 3.x self-challenge.

  - by Hamish Grubijan

  This is not a homework. I saw this article praising Linq library and how great it is for doing combinatorics stuff, and I thought to myself: Python can do it in a more readable fashion. After half hour of dabbing with Python I failed. Please finish where I left off. Also, do it in the most Pythonic and efficient way possible please. from itertools import permutations from operator import mul from functools import reduce glob_lst = [] def divisible(n): return (sum(j*10^i for i,j in enumerate(reversed(glob_lst))) % n == 0) oneToNine = list(range(1, 10)) twoToNine = oneToNine[1:] for perm in permutations(oneToNine, 9): for n in twoToNine: glob_lst = perm[1:n] #print(glob_lst) if not divisible(n): continue else: # Is invoked if the loop succeeds # So, we found the number print(perm) Thanks!

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• EF4, MVC 3, Azure and Code First or Traditional

  - by RichardAlanA

  I am planning to build a web application using ASP MVC3 that runs on Azure with a SQL Azure back end. I would like to use the Microsoft stack and have no plans to ever change to another stack. I am looking into the use of WCF and WF but that would be in the future. I looked at the traditional and Code First approach to using Entity Framework but I can't see if there is any advantage in using one or the other approach. Sure they each have advantages but for me I don't care if my classes do inherit from EF classes. All I want is to find the most efficient solution. Can anyone out there give me some advice as to which approach might be the best. thanks very much Richard

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• Help me finish this Python self-challenge.

  - by Hamish Grubijan

  This is not a homework. I saw this article praising Linq library and how great it is for doing combinatorics stuff, and I thought to myself: Python can do it in a more readable fashion. After half hour of dabbing with Python I failed. Please finish where I left off. Also, do it in the most Pythonic and efficient way possible please. from itertools import permutations from operator import mul from functools import reduce glob_lst = [] def divisible(n): return (sum(j*10^i for i,j in enumerate(reversed(glob_lst))) % n == 0) oneToNine = list(range(1, 10)) twoToNine = oneToNine[1:] for perm in permutations(oneToNine, 9): for n in twoToNine: glob_lst = perm[1:n] #print(glob_lst) if not divisible(n): continue else: # Is invoked if the loop succeeds # So, we found the number print(perm) Thanks!

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• Browser Detection Python / mod_python?

  - by cka

  I want to keep some statistics about users and locations in a database. For instance, I would like to store "Mozilla","Firefox","Safari","Chrome","IE", etc... as well as the versions, and possibly the operating system. What I am trying to locate from Python is this string; Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.14) Gecko/2009090216 Ubuntu/9.04 (jaunty) Firefox/3.0.14 Is there an efficient way to use Python or mod_python to detect the http user agent/browser?

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• How do you use pip, virtual_env and Fabric to handle deployement?

  - by e-satis

  What are your settings, your tricks, and above all, your work flow? These tools are great but they are still no best practices attached to their usage, so I don't know what is the most efficient way to use them. Do you use pip bundles or always download? Do you set up Apache/Cherokee/MySQL by hand or do you have a script for than. Do you put everything in virtual_env and use --no-site-package? Do you use one virtual_env for several projects? What do you use Fabric for (which part of your deployment do you script)? Do you put your Fabric scripts in on the client or the server? How do you handle database and media file migration? Do you even need a build tool such as SCons? What are the steps of your deployment? How often do you perform each of them? etc.

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• The subscription model behind CSS selectors?

  - by Martin Kristiansen

  With CSS selectors a query string body > h1.span subscribes to a specific type of nodes in the tree. Does anyone know how this is done? Selectors for transformations, how does the browser select the result set? And is there a trick to making it efficient? I imagine there being some sort of hierarchical type-tree for the entire structure to which the nodes subscribe and which is what is used when doing the selector queries — but this is only a guess. Does anyone know the real answer? Or even more interesting, what would be the best way to do dynamic lookups on a tree based on jQuery/CSS search queries?

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• When is calculating or variable-reading faster?

  - by Andreas Hornig

  hi, to be honest, I don't really know what the "small green men" in my cpu and compiler do, so I sometimes would like to know :). Currently I would like to know what's faster, so that I can design my code in a more efficient way. So for example I want to calclate something at different points in my sourcecode, when will it be faster to calculate it once and store it in a variable that's read and used for the next points it's needed and when is it faster to calculate it everytime? I think it's depending on how "complex" and "long" the calculation is and how fast then cache is, where variables are stored, but I don't have any clue what's faster :). Thanks for any reply to my tiny but important question! Andreas PS: perhaps it's important to know that I code in JAVA, but it's more a genral question.

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• Message Queue or Scheduler

  - by Walter White

  Hi all, I am currently using Quartz Scheduler for asynchronous tasks such as sending an email when an exception occurs, sending an email from the web interface, or periodically analyzing traffic. Should I use a message queue for sending an email? Is it any more efficient or correct to do it that way? The scheduler approach works just fine. If I use a queue and the email failed to send, is it possible for the queue to retry sending the email at a later time? The queue approach looks simpler than the scheduler for tasks that need to happen immediately, but for scheduler tasks, the scheduler still, unless there is more to the queue than I am aware of. I have not yet used JMS, so this is what I have read. Walter

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• Fine tune some SQL called multiple times

  - by Carl

  Hi all, I currently have an SQL query which is currently called multiple times like this (pseudo code): foreach(KeyValuePair kvp in someMapList) { select col1 from table where col2 = kvp.key and col3 = kvp.value; //do some processing on the returned value } The above could obviously call the database a large number of times if it is a big list of pairs. Can anyone think of a more efficient piece of SQL which could essentially return a list of specific values based on a list of two unique pieces of information so that the processing can be done in bulk? One obvious one would be to build up a big piece of SQL with ORs but this would probably be quite inefficient? Thanks Carl

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