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• Good way to identify similar images?

  - by Nick

  I've developed a simple and fast algorithm in PHP to compare images for similarity. Its fast (~40 per second for 800x600 images) to hash and a unoptimised search algorithm can go through 3,000 images in 22 mins comparing each one against the others (3/sec). The basic overview is you get a image, rescale it to 8x8 and then convert those pixels for HSV. The Hue, Saturation and Value are then truncated to 4 bits and it becomes one big hex string. Comparing images basically walks along two strings, and then adds the differences it finds. If the total number is below 64 then its the same image. Different images are usually around 600 - 800. Below 20 and extremely similar. Are there any improvements upon this model I can use? I havent looked at how relevant the different components (hue, saturation and value) are to the comparison. Hue is probably quite important but the others? To speed up searches I could probably split the 4 bits from each part in half, and put the most significant bits first so if they fail the check then the lsb doesnt need to be checked at all. I dont know a efficient way to store bits like that yet still allow them to be searched and compared easily. I've been using a dataset of 3,000 photos (mostly unique) and there havent been any false positives. Its completely immune to resizes and fairly resistant to brightness and contrast changes.

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• Best way to create a SPARQL endpoint for a RDBMS (MySQL database)

  - by Ankur

  I am doing (want to do) some experiments with Linked Open Datasets particularly those put out by governments. I have a RDBMS (more specifically MySQL). I designed it with semantic web ideas in mind i.e. I have a information stored as objects, predicates and classes which define objects. In turn all objects are related to each other though statements of the form subject -- predicate -- object (where the subjects are from the objects table). I want to be able to query other RDF triple stores from my application and let other triple stores query my data. Is it possible to "set something up" so that this is possible? I have looked at Jena. Using Jena seems to mean I have to it as a storage application rather than MySQL - the only problem with this is that I include a new concept called a category (which I don't think is part of the semantic web languages). I will use categories to help with displaying information (they don't have any other meaning) but using Jena seems to mean that I can't organise predicates under categories for more convenient viewing. I am using Java so a JAVA API is preferred. It's also possible I misunderstood the purpose of Jena, and maybe that can be of use, but I am not sure how. I am sure four days from now this question will seem rather silly, but at the moment I am somewhat confused about how to proceed.

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• [MySQL] Efficiently store last X records per item

  - by Saif Bechan

  I want to store the last X records in an MySQL database in an efficient way. So when the 4th record is stored the first should be deleted. The way I do this not is first run a query getting the items. Than check what I should do then insert/delete. There has to be a better way to do this. Any suggestions? Edit I think I should add that the records stored do not have a unique number. They have a mixed par. For example article_id and user_id. Then I want to make a table with the last X items for user_x. Just selecting the article from the table grouped by user and sorted by time is not an option for me. The table where I do the sort and group on has millions of records and gets hit a lot for no reason. So making a table in between with the last X records is way more effient. PS. I am not using this for articles and users.

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• Database abstraction/adapters for ruby

  - by Stiivi

  What are the database abstractions/adapters you are using in Ruby? I am mainly interested in data oriented features, not in those with object mapping (like active record or data mapper). I am currently using Sequel. Are there any other options? I am mostly interested in: simple, clean and non-ambiguous API data selection (obviously), filtering and aggregation raw value selection without field mapping: SELECT col1, col2, col3 = [val1, val2, val3] not hash of { :col1 = val1 ...} API takes into account table schemas 'some_schema.some_table' in a consistent (and working) way; also reflection for this (get schema from table) database reflection: get list of table columns, their database storage types and perhaps adaptor's abstracted types table creation, deletion be able to work with other tables (insert, update) in a loop enumerating selection from another table without requiring to fetch all records from table being enumerated Purpose is to manipulate data with unknown structure at the time of writing code, which is the opposite to object mapping where structure or most of the structure is usually well known. I do not need the object mapping overhead. What are the options, including back-ends for object-mapping libraries?

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• IPad SQLite Push and Pull Data from external MS SQL Server DB

  - by MattyD

  This carries on from my previous post (http://stackoverflow.com/questions/4182664/ipad-app-pull-and-push-relational-data). My plan is that when the ipad application starts I am going to pull data (config data i.e. Departments, Types etc etc relational data that is used across the system) from a webhosted MS SQL Server DB via a webservice and populate it into an SQL Lite DB on the IPad. Then when I load a listing I will pull the data over the line again via a webservice and populate it into the SQL Lite db on the ipad (than just run select commands to populate the listing). My questions are: 1. What is the most efficient way to transfer data across the line via the web? Everyone seems to do it a different way. My idea is that I will have a webService for each type of data pull (e.g. RetrieveContactListing) that will query the db and than convert that data into "something" to send across the line. My question really is what is the "something" that it should be converting into? 2. Everyone talks about odata services. Is this suited for applications where complex read and writes are needed? Ive created a simple iphone app before that talked to an sql server db (i just sent my own structured xml across the line) but now with this app the data calls are going to be a lot larger so efficiency is key.

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• A good data model for finding a user's favorite stories

  - by wings

  Original Design Here's how I originally had my Models set up: class UserData(db.Model): user = db.UserProperty() favorites = db.ListProperty(db.Key) # list of story keys # ... class Story(db.Model): title = db.StringProperty() # ... On every page that displayed a story I would query UserData for the current user: user_data = UserData.all().filter('user =' users.get_current_user()).get() story_is_favorited = (story in user_data.favorites) New Design After watching this talk: Google I/O 2009 - Scalable, Complex Apps on App Engine, I wondered if I could set things up more efficiently. class FavoriteIndex(db.Model): favorited_by = db.StringListProperty() The Story Model is the same, but I got rid of the UserData Model. Each instance of the new FavoriteIndex Model has a Story instance as a parent. And each FavoriteIndex stores a list of user id's in it's favorited_by property. If I want to find all of the stories that have been favorited by a certain user: index_keys = FavoriteIndex.all(keys_only=True).filter('favorited_by =', users.get_current_user().user_id()) story_keys = [k.parent() for k in index_keys] stories = db.get(story_keys) This approach avoids the serialization/deserialization that's otherwise associated with the ListProperty. Efficiency vs Simplicity I'm not sure how efficient the new design is, especially after a user decides to favorite 300 stories, but here's why I like it: A favorited story is associated with a user, not with her user data On a page where I display a story, it's pretty easy to ask the story if it's been favorited (without calling up a separate entity filled with user data). fav_index = FavoriteIndex.all().ancestor(story).get() fav_of_current_user = users.get_current_user().user_id() in fav_index.favorited_by It's also easy to get a list of all the users who have favorited a story (using the method in #2) Is there an easier way? Please help. How is this kind of thing normally done?

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• SQL Structure of DB table with different types of columns

  - by Dmitry Dvornikov

  I have a problem with the optimization of the structure of the database. I'll try to explain it exactly. I create a project, where we can add different values??, but this values must have different types of the columns in the database (eg, int, double , varchar). What is the best way to store the different types of values ??in the database. In the project I'm using Propel 1.6. The point is availability to add value with 'int', 'varchar' and other columns types, to search the table was efficient. In total, I have two ideas. The first is to create a table of "value", which will have columns: "id ", "value_int", "value_double", "value_varchar", etc - with the corresponding column types. Depending on the type of values??, records will be saved with the value in the appropriate column (the rest will be NULL). The second solution is to create separate tables such as "value_int", "value_varchar" etc. There would be columns: "id", "value", which correspond to the relevant types of "value" (ie, such as int, varchar, etc). I must admit that I do not believe any of the above solutions, originally I was thinking about one table "value", where the column would be a "text" type - but this solution would probably be even worse. I would like to know your opinion on this topic, maybe something else would be better. Thanks in advance. EDIT: For example : We have three tables: USER: [table of users] * id * name FIELD: [table of profile fields - where the column 'type' is the type of field, eg int or varchar) * id * type * name VALUE : * id * User_id - ( FK user.id ) * Field_id - ( FK field.id ) * value So we have in each row an user in USER table, and the profile is stored in the VALUE table. Bit each profile field may have a different type (column 'type' in the FIELD table), and based on that I would want this value to add to the appropriate column of the appropriate type.

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• Am I understanding premature optimization correctly?

  - by Ed Mazur

  I've been struggling with an application I'm writing and I think I'm beginning to see that my problem is premature optimization. The perfectionist side of me wants to make everything optimal and perfect the first time through, but I'm finding this is complicating the design quite a bit. Instead of writing small, testable functions that do one simple thing well, I'm leaning towards cramming in as much functionality as possible in order to be more efficient. For example, I'm avoiding multiple trips to the database for the same piece of information at the cost of my code becoming more complex. One part of me wants to just not worry about redundant database calls. It would make it easier to write correct code and the amount of data being fetched is small anyway. The other part of me feels very dirty and unclean doing this. :-) I'm leaning towards just going to the database multiple times, which I think is the right move here. It's more important that I finish the project and I feel like I'm getting hung up because of optimizations like this. My question is: is this the right strategy to be using when avoiding premature optimization?

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• Mimic Coldfusion's debug output in PHP?

  - by TekiusFanatikus

  I'm trying to mimic Coldfusion's debug output in PHP. Here's an example of what it looks like (ie. Execution Time section): I've turned to XDebug. Ideally, the exception stack error output would be what I'd be looking for. However, it only shows up when an exception occurs. I also tried something like (in our CMS-ish app) this (original question here): $content.= "<?php xdebug_start_trace('e:/xdebug/trace');?>"; $content.= "<?php require('".$page['file_'.LG]."'); ?>"; $content.= "<?php xdebug_stop_trace();?>"; ... $content.= "<?php echo readfile('e:/xdebug/trace.xt');?>"; However, I get an insane, browser crashing HTML table dropped at the bottom of page. Not very efficient. My php.ini config: xdebug.trace_format = 2 xdebug.collect_vars = 1 xdebug.collect_params = 4 xdebug.dump_globals = 1 xdebug.dump.SERVER = 'REQUEST_URI' xdebug.show_local_vars = 1 xdebug.show_mem_delta = 1 I'm just wondering if someone has already done something similar?

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• Why do I get "Bad File Descriptor" when I try to read a file with Perl?

  - by Magicked

  I'm trying to read a binary file 40 bytes at a time, then check to see if all those bytes are 0x00, and if so ignore them. If not, it will write them back out to another file (basically just cutting out large blocks of null bytes). This may not be the most efficient way to do this, but I'm not worried about that. However, right now I'm getting a "Bad File Descriptor" error and I cannot figure out why. my $comp = "\x00" * 40; my $byte_count = 0; my $infile = "/home/magicked/image1"; my $outfile = "/home/magicked/image1_short"; open IN, "<$infile"; open OUT, ">$outfile"; binmode IN; binmode OUT; my ($buf, $data, $n); while (read (IN, $buf, 40)) { ### Problem is here ### $boo = 1; for ($i = 0; $i < 40; $i++) { if ($comp[$i] != $buf[$i]) { $i = 40; print OUT $buf; $byte_count += 40; } } } die "Problems! $!\n" if $!; close OUT; close IN; I marked with a comment where it is breaking. Thanks for any help!

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• Is There a Better Way to Feed Different Parameters into Functions with If-Statements?

  - by FlowofSoul

  I've been teaching myself Python for a little while now, and I've never programmed before. I just wrote a basic backup program that writes out the progress of each individual file while it is copying. I wrote a function that determines buffer size so that smaller files are copied with a smaller buffer, and bigger files are copied with a bigger buffer. The way I have the code set up now doesn't seem very efficient, as there is an if loop that then leads to another if loops, creating four options, and they all just call the same function with different parameters. import os import sys def smartcopy(filestocopy, dest_path, show_progress = False): """Determines what buffer size to use with copy() Setting show_progress to True calls back display_progress()""" #filestocopy is a list of dictionaries for the files needed to be copied #dictionaries are used as the fullpath, st_mtime, and size are needed if len(filestocopy.keys()) == 0: return None #Determines average file size for which buffer to use average_size = 0 for key in filestocopy.keys(): average_size += int(filestocopy[key]['size']) average_size = average_size/len(filestocopy.keys()) #Smaller buffer for smaller files if average_size < 1024*10000: #Buffer sizes determined by informal tests on my laptop if show_progress: for key in filestocopy.keys(): #dest_path+key is the destination path, as the key is the relative path #and the dest_path is the top level folder copy(filestocopy[key]['fullpath'], dest_path+key, callback = lambda pos, total: display_progress(pos, total, key)) else: for key in filestocopy.keys(): copy(filestocopy[key]['fullpath'], dest_path+key, callback = None) #Bigger buffer for bigger files else: if show_progress: for key in filestocopy.keys(): copy(filestocopy[key]['fullpath'], dest_path+key, 1024*2600, callback = lambda pos, total: display_progress(pos, total, key)) else: for key in filestocopy.keys(): copy(filestocopy[key]['fullpath'], dest_path+key, 1024*2600) def display_progress(pos, total, filename): percent = round(float(pos)/float(total)*100,2) if percent <= 100: sys.stdout.write(filename + ' - ' + str(percent)+'% \r') else: percent = 100 sys.stdout.write(filename + ' - Completed \n') Is there a better way to accomplish what I'm doing? Sorry if the code is commented poorly or hard to follow. I didn't want to ask someone to read through all 120 lines of my poorly written code, so I just isolated the two functions. Thanks for any help.

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• Reverse geocode street name and city as text

  - by Taylor Satula

  Hello, I have been having some trouble finding a good way to output just the street name and city as text (Infinite Loop, Cupertino shown here) that can be displayed in my iPhone app. This needs to be able to dynamically change as you change streets and city. I don't have the slightest idea of how to do this, I hope someone can help. I have attached a very rough image of what I am trying to acheave. I have found this (http://code.google.com/apis/maps/documentation/javascript/services.html#Geocoding) for google maps about how to reverse geocode using javascript, but what I do not understand is how this would be done in a iPhone development setting. I work in web design and I see how it would be done in HTML but I am very new to iPhone development and don't have the slightest clue of how it would be done here. If someone could spell out how to do this I would be extremely grateful. I cannot seem to find what I am looking for by searching Google. Reference picture: http://www.threepixeldrift.com/images/deep-storage/reversegeocodeiphoneapp.jpg

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• gl_FragColor and glReadPixels

  - by chun0216

  I am still trying to read pixels from fragment shader and I have some questions. I know that gl_FragColor returns with vec4 meaning RGBA, 4 channels. After that, I am using glReadPixels to read FBO and write it in data GLubyte *pixels = new GLubyte[640*480*4]; glReadPixels(0, 0, 640,480, GL_RGBA, GL_UNSIGNED_BYTE, pixels); This works fine but it really has speed issue. Instead of this, I want to just read RGB so ignore alpha channels. I tried: GLubyte *pixels = new GLubyte[640*480*3]; glReadPixels(0, 0, 640,480, GL_RGB, GL_UNSIGNED_BYTE, pixels); instead and this didn't work though. I guess it's because gl_FragColor returns 4 channels and maybe I should do something before this? Actually, since my returned image (gl_FragColor) is grayscale, I did something like float gray = 0.5 //or some other values gl_FragColor = vec4(gray,gray,gray,1.0); So is there any efficient way to use glReadPixels instead of using the first 4 channels method? Any suggestion? By the way, this is on opengl es 2.0 code.

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• MS SQL - Multi-Column substring matching

  - by hamlin11

  One of my clients is hooked on multi-column substring matching. I understand that Contains and FreeText search for words (and at least in the case of Contains, word prefixes). However, based upon my understanding of this MSDN book, neither of these nor their variants are capable of searching substrings. I have used LIKE rather extensively (Select * from A where A.B Like '%substr%') Sample table A: ID | Col1 | Col2 | Col3 | ------------------------------------- 1 | oklahoma | colorado | Utah | 2 | arkansas | colorado | oklahoma | 3 | florida | michigan | florida | ------------------------------------- The following code will give us row 1 and row 2: select * from A where Col1 like '%klah%' or Col2 like '%klah%' or Col3 like '%klah%' This is rather ugly, probably slow, and I just don't like it very much. Probably because the implementations that I'm dealing with have 10+ columns that need searched. The following may be a slight improvement as code readability goes, but as far as performance, we're still in the same ball park. select * from A where (Col1 + ' ' + Col2 + ' ' + Col3) like '%klah%' I have thought about simply adding insert, update, and delete triggers that simply add the concatenated version of the above columns into a separate table that shadows this table. Sample Shadow_Table: ID | searchtext | --------------------------------- 1 | oklahoma colorado Utah | 2 | arkansas colorado oklahoma | 3 | florida michigan florida | --------------------------------- This would allow us to perform the following query to search for '%klah%' select * from Shadow_Table where searchtext like '%klah%' I really don't like having to remember that this shadow table exists and that I'm supposed to use it when I am performing multi-column substring matching, but it probably yields pretty quick reads at the expense of write and storage space. My gut feeling tells me there there is an existing solution built into SQL Server 2008. However, I don't seem to be able to find anything other than research papers on the subject. Any help would be appreciated.

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• Validating JSP's and HTML Forms, Server-side or Client-side, or both?

  - by CitadelCSAlum

  I am aware that I can Google "HTML Form Validation" and would get a billion tutorials. I am well aware that I can use simple JavaScript to validate form input, but I have been told that this is not necessarily an efficient method. I have also heard that it is a best practice to validate both client and server-side code. OK! Well, What exactly does this mean besides writing code on both? Does it mean I do some with JavaScript and other with Servlet's or does it mean that I write identical validation methods on both? My real question is can anybody give me insight and direction as how to go about validation my HTML forms. I am using JSP's and Servlet's and I have tons of form validation to do. I have already done minor form validation with regex in Java, but want to figure out if Im heading in the right track before I write any more code. Only productive answers please, If I wanted negative feedback on how inexperienced I was, I would have gone to Reddit. Thanks!

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• Negative number representation across multiple architechture

  - by Donotalo

  I'm working with OKI 431 micro controller. It can communicate with PC with appropriate software installed. An EEPROM is connected in the I2C bus of the micro which works as permanent memory. The PC software can read from and write to this EEPROM. Consider two numbers, B and C, each is two byte integer. B is known to both the PC software and the micro and is a constant. C will be a number so close to B such that B-C will fit in a signed 8 bit integer. After some testing, appropriate value for C will be determined by PC and will be stored into the EEPROM of the micro for later use. Now the micro can store C in two ways: The micro can store whole two byte representing C The micro can store B-C as one byte signed integer, and can later derive C from B and B-C I think that two's complement representation of negative number is now universally accepted by hardware manufacturers. Still I personally don't like negative numbers to be stored in a storage medium which will be accessed by two different architectures because negative number can be represented in different ways. For you information, 431 also uses two's complement. Should I get rid of the headache that negative number can be represented in different ways and accept the one byte solution as my other team member suggested? Or should I stick to the decision of the two byte solution because I don't need to deal with negative numbers? Which one would you prefer and why?

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• Fastest XML parser for small, simple documents in Java

  - by Varkhan

  I have to objectify very simple and small XML documents (less than 1k, and it's almost SGML: no namespaces, plain UTF-8, you name it...), read from a stream, in Java. I am using JAXP to process the data from my stream into a Document object. I have tried Xerces, it's way too big and slow... I am using Dom4j, but I am still spending way too much time in org.dom4j.io.SAXReader. Does anybody out there have any suggestion on a faster, more efficient implementation, keeping in mind I have very tough CPU and memory constraints? [Edit 1] Keep in mind that my documents are very small, so the overhead of staring the parser can be important. For instance I am spending as much time in org.xml.sax.helpers.XMLReaderFactory.createXMLReader as in org.dom4j.io.SAXReader.read [Edit 2] The result has to be in Dom format, as I pass the document to decision tools that do arbitrary processing on it, like switching code based on the value of arbitrary XPaths, but also extracting lists of values packed as children of a predefined node. [Edit 3] In any case I eventually need to load/parse the complete document, since all the information it contains is going to be used at some point. (This question is related to, but different from, http://stackoverflow.com/questions/373833/best-xml-parser-for-java )

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• Advanced search engine or server for relational database [closed]

  - by Pawel

  In my current project we are storing big volume of data in relational database. One of the recent key requirements is to enrich application by adding some advanced search capabilities. In the Project, performance is one of the important factors due to very large tables (10+ milions of records) with parent-children relations (for example: multi-level parent-child relationship, where I am looking for all parents with specific children). The search engine should also be able to check these references for hits. I have found some potential engines on stack overflow, however it looks like that all of them are dedicated rather for text search than relational db and hosted on linux os: lucene Solr Sphinx As I understand some of them use documents as a source of searching, but is it possible or efficient to create programmaticaly documents based on my relational data? As I am not familiar with all of their features/capabilities can anyone please make some recommendations or propose some different solution? To summarize my requirements: framework/engine to search relational database including decendants. support for Microsoft SQL Server can be used in .NET applications preferably hosted on Windows systems Does any of mentioned above are able to solve my problem? do you know any better solution?

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• Firefox extension js object initialization

  - by Michael

  Note: this is about Firefox extension, not a js general question. In Firefox extension project I need my javascript object to be initialized just once per Firefox window. Otherwise each time I open my window a new timers will be engaged, new properties will be used, so everything will start from scratch. hope example below will demystify my question :) var StupidExtension { statusBarValue: "Not Initialized Yet", startup: function () { ... // Show statusBarValue in Status Bar Panel }, initTimerToRetrieveStatusBarValueFromNetwork: function () { ... } } so each time you hit Ctrl+N a new window you will see "Not Initialized Yet" and then new timer will be fired, so after some time it retrieve data from network you will see value also on second window and so on. Ideally would be to have just a single timer function running and updating all status bar panels in all Firefox windows. Of course I can do some caching, like saving the value in prefs or some other storage, then show it from there. But I feel like this is artificial. So the question will be is there "native" technique of making static some parts of the object among all Firefox window instances?

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• Change a finder method w/ parameters to an association

  - by Sai Emrys

  How do I turn this into a has_one association? (Possibly has_one + a named scope for size.) class User < ActiveRecord::Base has_many :assets, :foreign_key => 'creator_id' def avatar_asset size = :thumb # The LIKE is because it might be a .jpg, .png, or .gif. # More efficient methods that can handle that are OK. ;) self.assets.find :first, :conditions => ["thumbnail = '#{size}' and filename LIKE ?", self.login + "_#{size}.%"] end end EDIT: Cuing from AnalogHole on Freenode #rubyonrails, we can do this: has_many :assets, :foreign_key => 'creator_id' do def avatar size = :thumb find :first, :conditions => ["thumbnail = ? and filename LIKE ?", size.to_s, proxy_owner.login + "_#{size}.%"] end end ... which is fairly cool, and makes syntax a bit better at least. However, this still doesn't behave as well as I would like. Particularly, it doesn't allow for further nice find chaining (such that it doesn't execute this find until it's gotten all its conditions). More importantly, it doesn't allow for use in an :include. Ideally I want to do something like this: PostsController def show post = Post.get_cache(params[:id]) { Post.find(params[:id], :include => {:comments => {:users => {:avatar_asset => :thumb}} } ... end ... so that I can cache the assets together with the post. Or cache them at all, really - e.g. get_cache(user_id){User.find(user_id, :include => :avatar_assets)} would be a good first pass. This doesn't actually work (self == User), but is correct in spirit: has_many :avatar_assets, :foreign_key => 'creator_id', :class_name => 'Asset', :conditions => ["filename LIKE ?", self.login + "_%"] (Also posted on Refactor My Code.)

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• Internal loop only runs once, containing loop runs endlessly

  - by Mark

  noob question I'm afraid. I have a loop that runs and rotates the hand of a clock and an internal loop that checks the angle of the hand if it is 90, 180, 270 and 360. On these 4 angles the corresponding div is displayed and its siblings removed. The hand loops and loops eternally, which is what I want, but the angle check only runs the loop once through the whole 360. As the hand passes through the angles it is correctly displaying and removing divs but is doesn't continue after the first revolution of the clock. I've obviously messed up somewhere and there is bound to be a more efficient way of doing all this. I am using jQueryRotate.js for my rotations. Thanks for your time. jQuery(document).ready(function(){ var angle = 0; setInterval(function(){ jQuery("#hand").rotate(angle); function movehand(){ if (angle == 90) { jQuery("#intervention").fadeIn().css("display","block").siblings().css("display","none"); } else if (angle == 180) { jQuery("#management").fadeIn().css("display","block").siblings().css("display","none"); } else if (angle == 270) { jQuery("#prevention").fadeIn().css("display","block").siblings().css("display","none"); } else if (angle == 360) { jQuery("#reaction").fadeIn().css("display","block").siblings().css("display","none"); } else {movehand;} }; movehand(); angle+=1; },10); });

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• Multithreaded linked list traversal

  - by Rob Bryce

  Given a (doubly) linked list of objects (C++), I have an operation that I would like multithread, to perform on each object. The cost of the operation is not uniform for each object. The linked list is the preferred storage for this set of objects for a variety of reasons. The 1st element in each object is the pointer to the next object; the 2nd element is the previous object in the list. I have solved the problem by building an array of nodes, and applying OpenMP. This gave decent performance. I then switched to my own threading routines (based off Windows primitives) and by using InterlockedIncrement() (acting on the index into the array), I can achieve higher overall CPU utilization and faster through-put. Essentially, the threads work by "leap-frog'ing" along the elements. My next approach to optimization is to try to eliminate creating/reusing the array of elements in my linked list. However, I'd like to continue with this "leap-frog" approach and somehow use some nonexistent routine that could be called "InterlockedCompareDereference" - to atomically compare against NULL (end of list) and conditionally dereference & store, returning the dereferenced value. I don't think InterlockedCompareExchangePointer() will work since I cannot atomically dereference the pointer and call this Interlocked() method. I've done some reading and others are suggesting critical sections or spin-locks. Critical sections seem heavy-weight here. I'm tempted to try spin-locks but I thought I'd first pose the question here and ask what other people are doing. I'm not convinced that the InterlockedCompareExchangePointer() method itself could be used like a spin-lock. Then one also has to consider acquire/release/fence semantics... Ideas? Thanks!

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• Read/Write/Find/Replace huge csv file

  - by notapipe

  I have a huge (4,5 GB) csv file.. I need to perform basic cut and paste, replace operations for some columns.. the data is pretty well organized.. the only problem is I cannot play with it with Excel because of the size (2000 rows, 550000 columns). here is some part of the data: ID,Affection,Sex,DRB1_1,DRB1_2,SENum,SEStatus,AntiCCP,RFUW,rs3094315,rs12562034,rs3934834,rs9442372,rs3737728 D0024949,0,F,0101,0401,SS,yes,?,?,A_A,A_A,G_G,G_G D0024302,0,F,0101,7,SN,yes,?,?,A_A,G_G,A_G,?_? D0023151,0,F,0101,11,SN,yes,?,?,A_A,G_G,G_G,G_G I need to remove 4th, 5th, 6th, 7th, 8th and 9th columns; I need to find every _ character from column 10 onwards and replace it with a space ( ) character; I need to replace every ? with zero (0); I need to replace every comma with a tab; I need to remove first row (that has column names; I need to replace every 0 with 1, every 1 with 2 and every ? with 0 in 2nd column; I need to replace F with 2, M with 1 and ? with 0 in 3rd column; so that in the resulting file the output reads: D0024949 1 2 A A A A G G G G D0024302 1 2 A A G G A G 0 0 D0023151 1 2 A A G G G G G G (both input and output should read one line per row, ne extra blank row) Is there a memory efficient way of doing that with java(and I need a code to do that) or a usable tool for playing with this large data so that I can easily apply Excel functionality..

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• Data structure to build and lookup set of integer ranges

  - by actual

  I have a set of uint32 integers, there may be millions of items in the set. 50-70% of them are consecutive, but in input stream they appear in unpredictable order. I need to: Compress this set into ranges to achieve space efficient representation. Already implemented this using trivial algorithm, since ranges computed only once speed is not important here. After this transformation number of resulting ranges is typically within 5 000-10 000, many of them are single-item, of course. Test membership of some integer, information about specific range in the set is not required. This one must be very fast -- O(1). Was thinking about minimal perfect hash functions, but they do not play well with ranges. Bitsets are very space inefficient. Other structures, like binary trees, has complexity of O(log n), worst thing with them that implementation make many conditional jumps and processor can not predict them well giving poor performance. Is there any data structure or algorithm specialized in integer ranges to solve this task?

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• Help ! How do I get the total number rows from my mssql paging procedure ?

  - by The_AlienCoder

  Ok I have a table in my MSSQL database that stores comments. My desire is to be able to page though the records using [Back],[Next], page numbers & [Last] buttons in my datalist. I figured the most efficient way was to use a stored procedure that only returns a certain number of rows within a partcular range. Here is what I came up with @PageIndex INT, @PageSize INT, @postid int AS SET NOCOUNT ON begin WITH tmp AS ( SELECT comments.*, ROW_NUMBER() OVER (ORDER BY dateposted ASC) AS Row FROM comments WHERE (comments.postid = @postid)) SELECT tmp.* FROM tmp WHERE Row between (@PageIndex - 1) * @PageSize + 1 and @PageIndex*@PageSize end RETURN Now everything works fine and I have been able implement [Next] and [Back] buttons in my datalist pager.Now I need the total number of all comments(not in the cuurent page) so that I can implement my page numbers and the[Last] button on my pager. In other words I want to return the total number of rows in my first select statement i.e WITH tmp AS ( SELECT comments.*, ROW_NUMBER() OVER (ORDER BY dateposted ASC) AS Row FROM comments WHERE (comments.postid = @postid)) set @TotalRows = @@rowcount @@rowcount doesnt work and raises an error.I also cant get count.* to work either. Is there another way to get the total amount of rows or is my approach doomed.

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