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• Performance intensive string splitting and manipulation in java

  - by juhanic

  What is the most efficient way to split a string by a very simple separator? Some background: I am porting a function I wrote in C with a bunch of pointer arithmetic to java and it is incredibly slow(After some optimisation still 5* slower). Having profiled it, it turns out a lot of that overhead is in String.split The function in question takes a host name or ip address and makes it generic: 123.123.123.123-*.123.123.123 a.b.c.example.com-*.example.com This can be run over several million items on a regular basis, so performance is an issue.

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• Again, what version control system to choose?

  - by Ivan

  Please excuse me for probably a newbie hundred-times-chewed question. I have no experience with version control systems except of using Visual Source Safe in a project done by 2 people sitting in front of each other (which has shown VSS quite sack of boulders, not anything useful). Right now I am looking to grok-in using some modern VCS. Here are the preferences in descending priority order: Platform-agnostic. Pretty pleasant to use With Visual Studio 2010 on Windows as well as With NetBeans 6.9 and Eclipse 3.6 on Linux and Mac. Convenient and efficient for mutually-dependent projects done by teams of 1-10 and consisting of files of quite a diverse selection of types. Including early-stage projects with unstable design and experimenting. Modern. As fresh and future-technology-feature-rich as possible. Free & open-source. Should I take a closer look at SVN, Mercurial, GIT, Bazaar, or something else?

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• Parsing dbpedia JSON in Python

  - by givp

  Hello, I'm trying to get my head around the dbpedia JSON schema and can't figure out an efficient way of extracting a specific node: This is what dbpedia gives me: http://dbpedia.org/data/Ceramic_art.json I've got the whole thing as a JSON object in Python but don't really understand how to get the english abstract from this data. I've gotten this far: u = "http://dbpedia.org/data/Ceramic_art.json" data = urlfetch.fetch(url=u) json_data = json.loads(data.content) for j in json_data["http://dbpedia.org/resource/Ceramic_art"]: if(j == "http://dbpedia.org/ontology/abstract"): print "it's here" Not sure how to proceed from here. As you can see there are multiple languages. I need to get the english abstract. Thanks for your help, g

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• Django gives "I/O operation on closed file" error when reading from a saved ImageField

  - by Rob Osborne

  I have a model with two image fields, a source image and a thumbnail. When I update the new source image, save it and then try to read the source image to crop/scale it to a thumbnail I get an "I/O operation on closed file" error from PIL. If I update the source image, don't save the source image, and then try to read the source image to crop/scale, I get an "attempting to read from closed file" error from PIL. In both cases the source image is actually saved and available in later request/response loops. If I don't crop/scale in a single request/response loop but instead upload on one page and then crop/scale in another page this all works fine. This seems to be a cached buffer being reused some how, either by PIL or by the Django file storage. Any ideas on how to make an ImageField readable after saving?

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• Complicated MySQL query?

  - by Scott

  I have two tables: RatingsTable that contains a ratingname and a bit whether it is a positive or negative rating: Good 1 Bad 0 Fun 1 Boring 0 FeedbackTable that contains feedback on things...the person rating, the rating and the thing rated. The feedback can be determined if it's a positive or negative rating based on RatingsTable. Jim Chicken Good Jim Steak Bad Ted Waterskiing Fun Ted Hiking Fun Nancy Hiking Boring I am trying to write an efficient MySQL query for the following: On a page, I want to display the the top 'things' that have the highest proportional positive ratings. I want to be sure that the items from the feedback table are unique...meaning, that if Jim has rated Chicken Good 20 times...it should only be counted once. At some point I will want to require a minimum number of ratings (at least 10) to be counted for this page as well. I'll want to to do the same for highest proportional negative ratings, but I am sure I can tweak the one for positive accordingly.

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• SQL Query: Using Cursors

  - by user2953138

  I need some directions for SQL Server & Cursors: I have a table named Order: OrderID Item Amount 1 A 10 1 B 1 2 A 5 2 C 4 2 D 21 3 B 11 I have a second table named Storage: Item Amount A 40 B 44 C 20 D 1 For every OrderID, I want to check if enough items are available. If not, I want to return an error message. How can this be done with Cursors at all? Are nested cursors the solution to this? My main issue is to understand how I can fetch the OrderID as actual "Group" of ID=1, 2, 3 etc. instead of line by line

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• Faster way to convert from 24 bit wav pcm format to float?

  - by LMO

  I need to read data in from a wav file in 24 bit pcm format, and convert to float. I'm using Python 2.7.2. The wave package reads the data in as a string, so what I've tried is: # read in entire wav file wdata = f.readframes(nFrames) # unpack into signed integers and convert to float data = array.array('f') for i in range(0,nFrames*3,3): data.append(float(struct.unpack('<i', '\x00'+ wdata[i:i+3])[0])) # normalize sample values data = data / 0x800000 This is quite a bit faster than my earlier approaches, but still quite slow. Can anyone suggest a more efficient method?

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• Javascript: gradually adding to string in each iteration ?

  - by Kim Jong Woo

  I have a string like this that is split up: var tokens = "first>second>third>last".split(">"); What I would like in each iteration is for it to return Iteration 0: "last" Iteration 1: "third>last" Iteration 2: "second>third>last" Iteration 3: "first>second>third>last" I am thinking of using decrementing index for loop.... but is there a more efficient approach ? for (int w = tokens.length-1; w == 0; w--) { }

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• Keeping iPhone application in sync with GWT application.

  - by Reflog

  Hi, I'm working on an iPhone application that should work in offline and online modes. In it's online mode it's supposed to feed all the information the user enters to a webservice backed by GWT/GAE. In it's offline mode it's supposed to store the information locally, and when connection is available sync it up to the web service. Currently my plan is as follows: Provide a connection between an app and a webservice using Protobuffers for efficient over-the-wire communication Work with local DB using Core Data Poll the network status, and when available sync the database and keep some sort of local-db-to-remote-db key synchronization. The question is - am I in the right direction? Are the standard patterns for implementing this? Maybe someone can point me to an open-source application that works in a similar fashion? I am really new to iPhone coding, and would be very glad to hear any suggestions. Thanks

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• Adding items to Model Collection in ASP.NET MVC

  - by Stacey

  In an ASP.NET MVC application where I have the following model.. public class EventViewModel { public Guid Id { get; set; } public List<Guid> Attendants { get; set; } } passed to a view... public ActionResult Create(EventViewModel model) { // ... } I want to be able to add to the "Attendants" Collection from the View. The code to add it works just fine - but how can I ensure that the View model retains the list? Is there any way to do this without saving/opening/saving etc? I am calling my addition method via jQuery $.load. public void Insert(Guid attendant) { // add the attendant to the attendees list of the model - called via $.load } I would also like to add there is no database. There is no storage persistence other than plain files.

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• Populate properties decorated with an attribute

  - by PUT

  Are there any frameworks that assist me with this: (thinking that perhaps StructureMap can help me) Whenever I create a new instance of "MyClass" or any other class that inherits from IMyInterface I want all properties decorated with [MyPropertyAttribute] to be populated with values from a database or some other data storage using the property Name in the attribute. public class MyClass : IMyInterface { [MyPropertyAttribute("foo")] public string Foo { get; set; } } [AttributeUsage(AttributeTargets.Property)] public sealed class MyPropertyAttribute : System.Attribute { public string Name { get; private set; } public MyPropertyAttribute(string name) { Name = name; } }

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• [C++] instantiating bitset using hex character.

  - by bndz

  Hey, I'm trying to figure out how to instantiate a 4 bit bitset based on a hex character. For instance, If I have a character with value 'F', I want to create a bitset of size 4 initialized to 1111 or if it is A, i want to initialize it to 1010. I could use a bunch of if statements like so: fn(char c) { bitset<4 temp; if(c == 'F') temp.set(); //... if(c == '9') { temp.set(1); temp.set(3); } //... } This isn't efficient, is there a way of easily converting the string to a decimal integer and constructing the bitset using the last 4 bits of the int? Thanks for any help.

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• Strategy to structure a search index in a relational database

  - by neilc

  I am interested in suggestions for building an efficient and robust structure for indexing products in a new database I am building (i'm using MySql) When a product is entered through the form there are three parts I am interested in indexing for searching purposes. The product title The product description Tags The most important is title, followed by tags, followed by the description. I was thinking of using the following structure CREATE TABLE `searchindex` ( `id` INT NOT NULL , `word` VARCHAR( 255 ) NOT NULL , `weighting` INT NOT NULL , `product_id` INT NOT NULL , PRIMARY KEY ( `id` ) ) Then each time a product is created I would split apart the title, description and tags (removing common words) and award them a weighting. Then it is trivial to select out the words and corresponding products and order them by weighting. Is there a better way to do this? I would be worried that this strategy would slow down over time and as the database filled up.

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• Zend_Session: unserialize session data

  - by takeshin

  I'm using session SaveHandler to persist session data in the database. Sample session_data column from the database: Messenger|a:1:{s:13:"page_messages";a:0:{}}userSession|a:1:{s:7:"referer";s:32:"http://cms.dev/user/profile/view";}Zend_Auth|a:1:{s:7:"storage";O:19:"User_Model_Identity":3:{s:2:"id";s:1:"1";s:8:"username";s:13:"administrator";s:4:"slug";s:13:"administrator";}} I want to delete Zend_Auth object from this session data. How can I unserialize those objects and remove object I need? I suspect, that I don't have to write my custom parser, that Zend_Session already has a method to do this. I have tried different combinations of unserialize but it still returns false. I'm using autoloader from ZF 1.10.2 and Doctrine 1.2

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• How can I use SiteMap more efficiently?

  - by Bipul

  So, in our website we are using SiteMap. For each request we render some menu and to do that we do SiteMap.RootNode in the helper function. Now, when I have done the profiling of my website using dotTrace, I saw the get_RootNode() is taking lot's of time(around 70-75 millisecond). But we know that the SiteMap is static. So, I am thinking in somehow I will get the SiteMap.RootNode only once in Application_Start and will access that through out each request. So, my questions are, Is my approach correct? How should I do that? Or is there any efficient way that I can use SiteMap.RootNode Thanks.

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• non-servlet JSP

  - by h2g2java

  I realise there are EL and near EL frameworks like StringTemplate, JUEL, Velocity, etc. However, I am not asking for list of alternatives to JSTL/EL. I came across a package more than a year ago, someone who wrote a util that emulates the functionality of JSP for non-servlet env, i.e., JSP composition which does not need a "servlet container" to function. I ignored it and now I think it would be helpful to me and I need help to recall what it is. My actual motivation is similar to what StringTemplate, JUEL, Velocity would offer to help me compose SQL blocks, HTML blocks but I am thinking that JSPs are precompiled into bytecode and JSPs are more run-time efficient since run-time parsing is done no more than once. So actually, recommendation for alternatives would be acceptable as long as the templates are precompiled into bytecode. But I still prefer the JSP emulator.

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• Setting up Maven for a team

  - by Bytecode Ninja

  I have used Maven extensively for my personal projects, but now I have to set it up for a small team of 5-7 developers. My main question is, what's the recommended approach for managing dependencies to commercial libraries that are not available in the Maven repos? How can I manage the dependency of these commercial libraries on the open source libraries that they use and are available in Maven repos? Also, are there any other recommendations and advices that I should know or implement to make the setup as efficient, effective, and smooth as possible? Thanks in advance.

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• Question about AJAX

  - by Doug

  function showHint(str) { if (window.XMLHttpRequest) { xmlhttp=new XMLHttpRequest(); } else { xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); } xmlhttp.onreadystatechange=function() { if (xmlhttp.readyState==4 && xmlhttp.status==200) { document.getElementById("games").innerHTML=xmlhttp.responseText; } } xmlhttp.open("GET","hw9.database.php?name="+str,true); xmlhttp.send(); } I'm learning AJAX at the moment. The code here basically receives the echo from the PHP and then puts it in element id games. My question is, if I wanted to have AJAX send 3 different http requests to 3 different PHP scripts and if I wanted to retrieve data from each one and then put it in 3 different element id's then would I make 3 copies of this same function? I would imagine that there should be a more efficient way. Thanks!

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• "conveyor belt" cache architecture

  - by Andrew Matthews

  I'm producing an application with a few peculiar internal communication characteristics that make the usual suspects for data storage and transport (Qs and RDBMSs) ill-fitted. I'm wondering whether there is a product out there that matches the following characteristics: all data put into it is peristent all reads are delivered out of memory data is universally available data lives where it is most needed data is versioned (nice to have) updates are transactional (I'd like ACID characteristics) data is potentially replicated, but always in sync works on windows is based on or has bindings for .NET is really fast is really robust is redundant is scalable I'm looking at things like Microsoft codename "Velocity", but I am not sure whether it fits all of the above characteristics. Likewise, Memcached is not a perfect fit either. The current version of this app opts for an RDBMS with a signaling system for inter-system sync, but latency is too high and versioning of the DB is a pain. I need all the robustness, but with none of the trade-offs.

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• Java 2D clip area to shape

  - by user2923880

  I'm quite new to graphics in java and I'm trying to create a shape that clips to the bottom of another shape. Here is an example of what I'm trying to achieve: Where the white line at the base of the shape is the sort of clipped within the round edges. The current way I am doing this is like so: g2.setColor(gray); Shape shape = getShape(); //round rectangle g2.fill(shape); Rectangle rect = new Rectangle(shape.getBounds().x, shape.getBounds().y, width, height - 3); Area area = new Area(shape); area.subtract(new Area(rect)); g2.setColor(white); g2.fill(area); I'm still experimenting with the clip methods but I can't seem to get it right. Is this current method ok (performance wise, since the component repaints quite often) or is there a more efficient way? Thanks in advance.

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• CUDA small kernel 2d convolution - how to do it

  - by paulAl

  I've been experimenting with CUDA kernels for days to perform a fast 2D convolution between a 500x500 image (but I could also vary the dimensions) and a very small 2D kernel (a laplacian 2d kernel, so it's a 3x3 kernel.. too small to take a huge advantage with all the cuda threads). I created a CPU classic implementation (two for loops, as easy as you would think) and then I started creating CUDA kernels. After a few disappointing attempts to perform a faster convolution I ended up with this code: http://www.evl.uic.edu/sjames/cs525/final.html (see the Shared Memory section), it basically lets a 16x16 threads block load all the convolution data he needs in the shared memory and then performs the convolution. Nothing, the CPU is still a lot faster. I didn't try the FFT approach because the CUDA SDK states that it is efficient with large kernel sizes. Whether or not you read everything I wrote, my question is: how can I perform a fast 2D convolution between a relatively large image and a very small kernel (3x3) with CUDA?

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• JSON documents and SQL database tables

  - by Sharmi

  Do JSON documents in RavenDB cost more than the SQL Server tables in terms of the storage and query costs. And also for centralized access, which one is better? What are the disadvantages of NON-SQL databases like RavenDB,CouchDB,MongoDB, etc... ? I can get that some of these are open source and support more datatypes like enums,objects,etc. but otherwise i don't see any big advantage? Currently there is a problem of storing huge amount of logs from various locations. I am planning to suggest these to my manager so just need a clear idea.

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• Conceptual question about NSAutoreleasePools

  - by ryyst

  In my Cocoa program, wouldn't a really simple way of dealing with autoreleased objects be to just create a timer object inside the app delegate that calls the following method e.g. every 10 seconds: if (pool) { // Release & drain the current pool to free the memory. [pool release]; } // Create a new pool. pool = [[NSAutoreleasePool alloc] init]; The only problems I can imagine are: 1) If the above code runs in a separate thread, an object might get autoreleased between the release call to the old pool and the creation of the new pool - that seems highly unlikely though. 2) It's obviously not that efficient, because the pool might get released if there's nothing in it. Likewise, in the 10 second gap, many many objects might be autoreleased, causing the pool to grow a lot. Still, the above solution seems pretty suitable to small and simple projects. Why doesn't anybody use it? What's the best practice of using NSAutoreleasePools?

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• Embarrassingly parallel workflow creates too many output files

  - by Hooked

  On a Linux cluster I run many (N > 10^6) independent computations. Each computation takes only a few minutes and the output is a handful of lines. When N was small I was able to store each result in a separate file to be parsed later. With large N however, I find that I am wasting storage space (for the file creation) and simple commands like ls require extra care due to internal limits of bash: -bash: /bin/ls: Argument list too long. Each computation is required to run through a qsub scheduling algorithm so I am unable to create a master program which simply aggregates the output data to a single file. The simple solution of appending to a single fails when two programs finish at the same time and interleave their output. I have no admin access to the cluster, so installing a system-wide database is not an option. How can I collate the output data from embarrassingly parallel computation before it gets unmanageable?

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• How should my application keep clients in sync with schema changes to HTML5 databases?

  - by Chad Johnson

  I'm wanting to incorporate HTML5 database storage into my web application to make it online-accessible. I've done lots of development in server-side environments with databases, and we all know that database schema additions and modifications are often necessary. I am wondering what should happen if my application uses an offline database schema, and that schema changes. How do I prevent the application from breaking on the client side? How do I ensure the database is always up to date on the client end? Anyone have any solutions?

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