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• c# multi threaded file processing

  - by user177883

  There is a folder that contains 1000 of small text files. I aim to parse and process all of them while more files are being populated in to the folder. My intention is to multithread this operation as the single threaded prototype took 6 minutes to process 1000 files. I like to have reader and writer thread(s) as following : while the reader thread(s) are reading the files, I d like to have writer thread(s) to process them. Once the reader is started reading a file, I d like to mark it as being processed, such as by renaming it, once it s read, rename it to completed. How to approach such multithreaded application ? Is it better to use a distributed hash table or a queue? Which data structure to use that would avoid locks? Would you have a better approach to this scheme that you like to share?

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

  - by jboxer

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

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• Why use hashing to create pathnames for large collections of files?

  - by Stephen

  Hi, I noticed a number of cases where an application or database stored collections of files/blobs using a has to determine the path and filename. I believe the intended outcome is a situation where the path never gets too deep, or the folders ever get too full - too many files (or folders) in a folder making for slower access. EDIT: Examples are often Digital libraries or repositories, though the simplest example I can think of (that can be installed in about 30s) is the Zotero document/citation database. Why do this? EDIT: thanks Mat for the answer - does this technique of using a hash to create a file path have a name? Is it a pattern? I'd like to read more, but have failed to find anything in the ACM Digital Library

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• Data Structure for a particular problem??

  - by AGeek

  Hi, Which data structure can perform insertion, deletion and searching operation in O(1) time in the worst case. We may assume the set of elements are integers drawn from a finite set 1,2,...,n, and initialization can take O(n) time. I can only think of implementing a hash table. Implementing it with Trees will not give O(1) time complexity for any of the operation. Or is it possible?? Kindly share your views on this, or any other data structure apart from these.. Thanks..

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• SHA-256 encryption wrong result in Android

  - by user642966

  I am trying to encrypt 12345 using 1111 as salt using SHA-256 encoding and the answer I get is: 010def5ed854d162aa19309479f3ca44dc7563232ff072d1c87bd85943d0e930 which is not same as the value returned by this site: http://hash.online-convert.com/sha256-generator Here's the code snippet: public String getHashValue(String entity, String salt){ byte[] hashValue = null; try { MessageDigest digest = MessageDigest.getInstance("SHA-256"); digest.update(entity.getBytes("UTF-8")); digest.update(salt.getBytes("UTF-8")); hashValue = digest.digest(); } catch (NoSuchAlgorithmException e) { Log.i(TAG, "Exception "+e.getMessage()); } catch (UnsupportedEncodingException e) { // TODO Auto-generated catch block e.printStackTrace(); } return BasicUtil.byteArrayToHexString(hashValue); } I have verified my printing method with a sample from SO and result is fine. Can someone tell me what's wrong here? And just to clarify - when I encrypt same value & salt in iOS code, the returned value is same as the value given by the converting site.

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• pipelined function

  - by user289429

  Can someone provide an example of how to use parallel table function in oracle pl/sql. We need to run massive queries for 15 years and combine the result. SELECT * FROM Table(TableFunction(cursor(SELECT * FROM year_table))) ...is what we want effectively. The innermost select will give all the years, and the table function will take each year and run massive query and returns a collection. The problem we have is that all years are being fed to one table function itself, we would rather prefer the table function being called in parallel for each of the year. We tried all sort of partitioning by hash and range and it didn't help. Also, can we drop the keyword PIPELINED from the function declaration? because we are not performing any transformation and just need the aggregate of the resultset.

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• Does to_json require parameters? what about within rails?

  - by Harry Wood

  Does to_json require parameters? what about within rails? I started getting the error "wrong number of arguments (0 for 1)" when doing myhash.to_json Unfortunately I'm not sure when this error started happening, but I guess it relates to some versions of either rails or the json gem. I suppose my code (in a rails controller) is using the ActiveSupport::JSON version of to_json, rather than the to_josn method supported by the json gem. ActiveSupport::JSON vs JSON In environment.rb I have RAILS_GEM_VERSION = '2.3.2' and also config.gem "json", :version=> '1.1.7' It's just a simple hash structure containing primitives which I want to convert in my controller, and it was working, but now I can't seem to run to_json without passing parameters.

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• Accessing GMail "View as HTML" content programatically?

  - by Amethi

  I love the "View as HTML" option in GMail when viewing attachments. I would love to be able to use this feature programatically, i.e. check a GMail inbox, read emails, if there are attachments, get the html view and use that content. I'm looking to do this in C Sharp (on a Mac, can't find the hash symbol). Does anyone know if this is possible or if there's another solution to easily get content from a GMail account, regardless of what format it's in? I.E html, pdf, Word doc, etc. The GMail Inbox Feed api isn't good enough and before I start trying to build an IMAP solution that pulls in PDF/Word doc converters, I thought it'd be good to ask here.

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• Best solution for language documentation.

  - by Simone Margaritelli

  I'm developing a new object oriented scripting language and the project itself is quite ready for audience now, so i'm starting to think about a serious (not as "drafty" as it is right now) way of document its grammar, functions from standard library and standard library classes. I've looked a bit around and almost every language hash its own web application for the documentation, Python uses Sphinx for instance. Which is the best PHP (don't have the time/will to install mod_who_knows_what on my server) application to accomplish this? I've used mediawiki a bit but i found its tag system a little bit hard to use in this context. Thanks for your answers.

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• How to make GhostScript PS2PDF stop subsetting fonts

  - by gavin-softyolk

  I am using the ps2pdf14 utility that ships with GhostScript, and I am having a problem with fonts. It does not seem to matter what instructions I pass to the command, it insists on subsetting any fonts it finds in the source document. e.g -dPDFSETTINGS#/prepress -dEmbedAllFonts#true -dSubsetFonts#false -dMaxSubsetPct#0 Note that the # is because the command is running on windows, it is the same as =. If anyone has any idea how to tell ps2pdf not to subset fonts, I would be very greatful. Thanks --------------------------Notes ------------------------------------------ The source file is a pdf containing embedded fonts, so it is the fonts already embedded in the source file, that I need to prevent being subset in the destination file. Currently all source file embedded fonts are subset, in some cases this is not apparent from the font name, i.e it contains no hash, and appears at first glance to be the full font, however the widths array has been subset in all cases.

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• resizing arrays when close to memory capacity

  - by user548928

  So I am implementing my own hashtable in java, since the built in hashtable has ridiculous memory overhead per entry. I'm making an open-addressed table with a variant of quadratic hashing, which is backed internally by two arrays, one for keys and one for values. I don't have the ability to resize though. The obvious way to do it is to create larger arrays and then hash all of the (key, value) pairs into the new arrays from the old ones. This falls apart though when my old arrays take up over 50% of my current memory, since I can't fit both the old and new arrays in memory at the same time. Is there any way to resize my hashtable in this situation Edit: the info I got for current hashtable memory overheads is from here How much memory does a Hashtable use? Also, for my current application, my values are ints, so rather than store references to Integers, I have an array of ints as my values.

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• does a switch idiom make sense in this case?

  - by the ungoverned

  I'm writing a parser/handler for a network protocol; the protocol is predefined and I am writing an adapter, in python. In the process of decoding the incoming messages, I've been considering using the idiom I've seen suggested elsewhere for "switch" in python: use a hash table whose keys are the field you want to match on (a string in this case) and whose values are callable expressions: self.switchTab = { 'N': self.handleN, 'M': self.handleM, ... } Where self.handleN, etc., are methods on the current class. The actual switch looks like this: self.switchTab[selector]() According to some profiling I've done with cProfile (and Python 2.5.2) this is actually a little bit faster than a chain of if..elif... statements. My question is, do folks think this is a reasonable choice? I can't imagine that re-framing this in terms of objects and polymorphism would be as fast, and I think the code looks reasonably clear to a reader.

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• What's the best way to match a query to a set of keywords?

  - by Ryan Detzel

  Pretty much what you would assume Google does. Advertisers come in and big on keywords, lets say "ipod", "ipod nano", "ipod 60GB", "used ipod", etc. Then we have a query, "I want to buy an ipod nano" or "best place to buy used ipods" what kind of algorithms and systems are used to match those queries to the keyword set. I would imagine that some of those keyword sets are huge, 100k keywords made up of one or more actual words. on top of that queries can be 1-n words as well. Any thoughts, links to wikipedia I can start reading? From what I know already I would use some stemmed hash in disk(CDB?) and a bloom filter to check to see if I should even go to disk.

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• Killing the mysqld process

  - by Josh K

  I have a table with ~800k rows. I ran an update users set hash = SHA1(CONCAT({about eight fields})) where 1; Now I have a hung Sequel Pro process and I'm not sure about the mysqld process. This is two questions: What harm can possibly come from killing these programs? I'm working on a separate database, so no damage should come to other databases on the system, right? Assume you had to update a table like this. What would be a quicker / more reliable method of updating without writing a separate script. I just checked with phpMyAdmin and it appears as though the query is complete. I still have Sequel Pro using 100% of both my cores though...

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• How does Hibernate detect dirty state of an entity object?

  - by ???'Lenik

  Is it using some kind of byte codes modification to the original classes? Or, maybe Hibernate get the dirty state by compare the given object with previously persisted version? I'm having a problem with hashCode() and equals() methods for complicated objects. I feel it would be very slow to compute hash code if the object has collection members, and cyclic references are also a problem. If Hibernate won't use hashCode()/equals() to check the dirty state, I guess I should not use equals()/hashCode() for the entity object (not value object), but I'm also afraid if the same operator (==) is not enough. So, the questions are: How does Hibernate know if a property of an object is changed? Do you suggest to override the hashCode()/equals() methods for complicated objects? What if they contains cyclic references? And, also, Would hashCode()/equals() with only the id field be enough?

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• How can i pass Twig sub parameter?

  - by aliocee

  hi, Help i cant pass my hash key to twig subroutine. here: foreach my $word (sort { $keywords{$a} <=> $keywords{$b} } keys (%keywords)) { my $t = XML::Twig->new( twig_roots => { 'Id' => \&insert($keywords{$word}) } ); $t->parse($docsums); sub insert { my($t, $id, $k)= @_; my $p = $id->text; my $query = "insert into pres (id, wid, p) values(DEFAULT, '$k', '$p')"; my $sql = $connect->prepare($query); $sql->execute( ); } } Thanks.

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• Whats the best data-structure for storing 2-tuple (a, b) which support adding, deleting tuples and c

  - by bhups

  Hi So here is my problem. I want to store 2-tuple (key, val) and want to perform following operations: - keys are strings and values are Integers - multiple keys can have same value - adding new tuples - updating any key with new value (any new value or updated value is greater than the previous one, like timestamps) - fetching all the keys with values less than or greater than given value - deleting tuples. Hash seems to be the obvious choice for updating the key's value but then lookups via values will be going to take longer (O(n)). The other option is balanced binary search tree with key and value switched. So now lookups via values will be fast (O(lg(n))) but updating a key will take (O(n)). So is there any data-structure which can be used to address these issues? Thanks.

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• PHP code cannot see query string param on return in Facebook oAuth flow

  - by TMC

  I am doing some integration with Facebook Open Graph using their oAuth flow and having issues with parsing query string parameters they return. On my callback URL, they pass back an "access_token" parameter with a hash (#). so the callback would be: http://mydomain.com/callback.php#access_token=foobar123 where foobar123 is my access token I'm trying to parse out. However, no matter what I do, my PHP code cannot see if and I've done every debug trick I know (even using phpinfo() to go through everything). The URL is stated only as http://mydomain.com/callback.php. It's as if the rest of the URL isn't really there! This code returns nothing: $token = $_REQUEST['access_token']; Any help would be greatly appreciated... I'm obviously missing something simple.

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• What's the best way of using a pair (triple, etc) of values as one value in C#?

  - by Yacoder

  That is, I'd like to have a tuple of values. The use case on my mind: Dictionary<Pair<string, int>, object> or Dictionary<Triple<string, int, int>, object> Are there built-in types like Pair or Triple? Or what's the best way of implementing it? Update There are some general-purpose tuples implementations described in the answers, but for tuples used as keys in dictionaries you should additionaly verify correct calculation of the hash code. Some more info on that in another question. Update 2 I guess it is also worth reminding, that when you use some value as a key in dictionary, it should be immutable.

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• Rails application and multilingual content, Model dilemma

  - by dakull

  I'm writing in Rails a website that will be multilingual, for the application translation part i will use the simple I18n gem, for messages and everything related. Yet, all the content must be translated, and we're talking about lots of pages, that will be stored into the database ( like articles, news, etc. ) For now, I'm thinking of two approaches: Lets say i have a Pages table, the content in diff. languages, i will be storing it in a different table called PagesContent that will belong_to Pages and also to a Languages table. The problem here, is that I'll essentially duplicate the no. of tables needed. Pros: flexibility, in the box validation To skip that duplication i can serialize a hash into the content column of Pages, containing the translation. The problem here, is validation, arguably more code to write, and less flexibility when adding a new language. Pros: Less tables. Any other idea ?

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• how to store passwords in database?

  - by rgksugan

  I use jsp and servlets in my web application. i need to store passwords in the database. I found that hashing will be the best way to do that. I used this code to do it. java.security.MessageDigest d = null; d = java.security.MessageDigest.getInstance("SHA-1"); d.reset(); d.update(pass.getBytes("UTF-8")); byte b[] = d.digest(); String tmp = (new BASE64Encoder()).encode(b); When i tried to print the value of tmp, i get some other value.i guess its the hash value of the password. But when i persist this data to the database the original password gets saved there other than the value in tmp.. What is the problem???

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• call value inside a JS variable as a JS function name

  - by user1640668

  Hello I have a function to perform actions but name of the function is inside a variable... below code will get the URL's hashed part example: #JHON and remove # and store it inside URLHASH variable..example: JHON var urlhash = document.location.hash; urlhash = urlhash.replace(/^.*#/, ''); always there is a function name from that value inside variable and i want to call value inside that variable as a function name window.onload=function() { Value inside URLHASH variable should run as a name of a variable. example: jhon(); }; Is it possible ? I tried some codes but it calls variable name as a function not value inside the variable..help me..

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• What is the best way to implement this composite GetHashCode()

  - by Frank Krueger

  I have a simple class: public class TileName { int Zoom, X, Y; public override bool Equals (object obj) { var o = obj as TileName; return (o != null) && (o.Zoom == Zoom) && (o.X == X) && (o.Y == Y); } public override int GetHashCode () { return (Zoom + X + Y).GetHashCode(); } } I was curious if I would get a better distribution of hash codes if I instead did something like: public override int GetHashCode () { return Zoom.GetHashCode() + X.GetHashCode() + Y.GetHashCode(); } This class is going to be used as a Dictionary key, so I do want to make sure there is a decent distribution.

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• ActiveRecord Create (not !) Throwing Exception on Validation

  - by myferalprofessor

  So I'm using ActiveRecord model validations to validate a form in a RESTful application. I have a create action that does: @association = Association.new and the receiving end of the form creates a data hash of attributes from the form parameters to save to the database using: @association = user.associations.create(data) I want to simply render the create action if validation fails. The problem is that the .create (not !) method is throwing an exception in cases where the model validation fails. Example: validates_format_of :url, :with => /(^$)|(^(http|https):\/\/[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(([0-9]{1,5})?\/.*)?$)/ix, :message => "Your url doesn't seem valid." in the model produces: ActiveRecord::RecordInvalid Exception: Validation failed: Url Your url doesn't seem valid. I thought .create! is supposed throw an exception whereas .create is not. Am I missing something here? Ruby 1.8.7 patchlevel 173 & rails 2.3.3

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• Facebook like iframe ignores my specified href

  - by Zhami

  I have Javascript that imputes (computes and injects) HTML into my DOM for the Facebook "Like" function. I need to specify a "canonical" URL because the actual URL doesn't reflect all the DOM manipulations that have been made (driven by user activity on the Web "page"). Alas, Facebook's code doesn't use the url I supply but the window.location value (which has #hash aspects that influence the page's presentation, but that aren't accessible to the server). Anyway... why is FB's code ignoring the url I give to it? I generate the HTML thus: var html = '<iframe src="http://www.facebook.com/plugins/like.php?href=' + encodeURI(url) + '&layout=standard&show_faces=false&width=100&action=recommend&font=arial&colorscheme=light" style="border:none; overflow:hidden; width:270px; height:26px;" allowTransparency="true" frameborder="0" scrolling="no"</iframe'

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