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• how would you like computer science classes to be taught?

  - by aaa

  hello I am a graduate student now, and hopefully someday I will teach. my interests are C++, Python, embedded languages, and scientific computing. Meanwhile I daydream about how I would teach. I was not quite happy with my undergraduate university as I found many computer science classes lacking. so I would like to ask you, if you were a student, how would you like your computer science classes to be taught? I understand it is a very subjective question, but nevertheless I think it's important to know what people want. Some specific points I am interested in: should computer languages be taught explicitly, or should students be required to pick up language on their own? what is better for learning, tests, projects, some sort of take-home exam? how do you think classtime should be used? theory, introduction, explanations, etc.? do you think the group projects are important? how much about computer architecture do you want to learn in computer science class, not necessarily assembler class. should particular operating system/editor be mandated or encouraged? Thanks thank you for your comments. Question has been closed because it is a discussion question rather than Q&A. If you know appropriate website for discussions of such sort with low noise ratio, please let me know.

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• Associating an object with another object for GC clearup

  - by thecoop

  Is there any way of associating an object instance (object A) with a second object (object B) in a generalised way, so that when B gets collected A becomes eligable for collection? The same behaviour that would happen if B had an instance variable pointing to A, but without explicitly changing the class definition of B, and being able to do this in a dynamic way? The same sort of effect could be done by using the Component.Disposed event in a funky way, but I don't want to make B disposable EDIT I'm basically creating a cache of objects that are associated with a single 'root' object, and I don't want the cache to be static, as there can be lots of root objects using different caches, so lots of memory will be used up when a root object is no longer used but the cached objects are still around. So, I want a collection of cached objects to be associated with each 'root' object, without changing the root object definition. Sort of like metadata of an extra object reference attached to each root object instance. That way, each collection will get collected when the root object is collected, and not hang around like they would if a static cache was used.

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• Cobol web development/hosting resources

  - by felixm

  Hello, I'm employed at a fairly big company here in Germany and got the job to create the main website for it which will feature: Static contents; Information and Presentations An employee area (around 6000 employees) featuring various things from calenders, job descriptions, some sort of groups Too many other dynamic things I can't list here I have decided to use COBOL for the job, it may be very underrated but it is a very powerful language, especially for business apps and, as my co-workers say, web (2.0) development too. I also need to use COBOL because all the backend and transactions system of the company is programmed in it (some small parts were programmed in LISP too, idk exactly why). I also have received an API that makes it possible to use COBOL with MySQL easily. This is a big project and it will probably take more than 2 months programming it. What do I have to expect when building a huge web app in COBOL? Are there web frameworks for COBOL available? Some sort of MVC? Are there any good resources for practical web-development with COBOL? Thanks in advance

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• Cookie not working after mod rewrite rule

  - by moonwalker

  Hi all, I have a simple Cookie to set the chosen language: $lang = $_GET['lang']; $myLang = $_COOKIE["myLang"]; if (!isset($_COOKIE["myLang"])){ setcookie("myLang", "en", $expire); include "languages/en.php"; $myLang = "en"; }else{ include "languages/$myLang.php"; } // One year to expire $expire = time()+60*60*24*30*365; // Put $languages in a common header file. $languages = array('en' => 1, 'fr' => 2, 'nl' => 3); if (array_key_exists($lang, $languages)) { include "languages/{$lang}.php"; setcookie("myLang", $lang, $expire); $myLang = $lang; } After using some rewrite rules, it just doesn't work anymore. I tried the following: setcookie("myLang", "en", $expire, "/" , false); No luck at all. This is my .htaccess file: <IfModule mod_rewrite.c> Options +FollowSymLinks Options +Indexes RewriteEngine On RewriteBase / RewriteRule ^sort/([^/]*)/([^/]*)$ /3arsi2/sort.php?mode=$1&cat=$2 [L] RewriteRule ^category/([^/]*)$ /3arsi2/category.php?cat=$1 [L] RewriteRule ^category/([^/]*)/([^/]*)$ /3arsi2/category.php?cat=$1&lang=$2 [L] RewriteRule ^search/([^/]*)$ /3arsi2/search.php?mode=$1 [L] RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule ^u/([^/]+)/?$ 3arsi2/user.php?user=$1 [NC,L] RewriteRule ^u/([^/]+)/(images|videos|music)/?$ 3arsi2/user.php?user=$1&page=$2 [NC,L] RewriteRule ^([^\.]+)$ 3arsi2/$1.php [NC,L] </IfModule> Any idea how to solve this? I'm still new to the mod rewrite thing, so I still don't really understand the logic behind it all. Thanks for any help you can provide.

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• usort - more parameters

  - by pgfonline

  Hallo, how can I pass more parameters to usort? I have different functions, which are very similar in structure, I want to have just one function: <?php $arr = array( array('number' => 100, 'string'=>'aaa'), array('number'=>50, 'string'=>'bdef'), array('number'=>150, 'string'=>'cbba') ); usort($arr, 'sortNumberDesc'); //How can I use just a single function? //How can I pass further parameters to usort? function sortNumberDesc($a, $b){ $a = $a['number']; $b = $b['number']; if ($a == $b) return 0; return ($a > $b) ? -1 : +1; } function sortNumberAsc($a, $b){ $a = $a['number']; $b = $b['number']; if ($a == $b) return 0; return ($a < $b) ? -1 : +1; } //I want to do the same with just one function: //Sort ID is the search index, reverse DESC or ASC function sort($a, $b, $sortId='number', $reverse = 0){ $a = $a[$sortId]; $b = $b[$sortId]; if ($a == $b) return 0; if($reverse == false) return ($a > $b) ? -1 : +1; else return ($a < $b) ? -1 : +1; } print_r($arr); ?>

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• why MVC instead of good old asp.net? Still not grasping why I should go this route??

  - by RJ

  I know this question has been asked before and I read all the answers but they still don't give me the answers I am looking for. I need something concrete. I volunteered to give a presentation on MVC to other developers in our group which forces me to learn it. The big question everyone has is: "What can MVC bring to the table that we can't do in asp.net or MVC can do faster. I have just gone through Nerd Dinner and actually created a complete website that sort of mimics Nerd Dinner. But as great a job that Scott Guthrie did on it, there are big gaps that aren't answered such as, how do I throw a textbox on the listing page with a button and do a simple search. In asp.net, I would throw a textbox, button and grid on the page and bind it to a sproc and away I go. What is the equivalent in MVC. I guess I need a really good tutorial on how to use MVC without using Linq-to-Sql. I know I am sort of babbling on about this but it is a very serious question that still seems to go unanswered. On a side note, the View page of MVC brings back nightmares of classic asp with all the in-line code that we got away from way back when with code behind pages. Yes, MVC has Controller and Model classes which are great but I still don't like the classic asp tags in the html. Help me out here, I really like the concept of MVC and want it to be successful but I need more!

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• Rails helper module undefined method `sort'

  - by Magicked

  I'm trying to create a simple helper module in rails, and I'm stumped on the following error message from my new person form (app/views/people/new.html.erb): undefined method `sort' for 97:Fixnum Extracted source (around line #17): 14: <p> 15: <% nations = { 'United States of America' => 'USA', 'Canada' => 'Canada', 'Mexico' => 'Mexico', 'United Kingdom' => 'UK' } %> 16: <%= f.label :country %><br /> 17: <%= radio_buttons(:person, :country, nations) %> 18: 19: </p> 20: <p> radio_buttons is a helper module I have created for my view. Here it is (app/helpers/people_helper.rb): module PeopleHelper def radio_buttons(model_name, target_property, button_source) html='' list = button_source.sort list.each do |x| html << radio_buttons(model_name, target_property, x[1]) html << h(x[0]) html << '<br />' end return html end end The problem appears to be on the "list = button_source.sort", but I'm not sure why it says the method is undefined. I have been able to use it directly within my view code. Am I not able to use methods like this within helper modules? Do I need to include something? Thanks for any help!

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• Django: Applying Calculations To A Query Set

  - by TheLizardKing

  I have a QuerySet that I wish to pass to a generic view for pagination: links = Link.objects.annotate(votes=Count('vote')).order_by('-created')[:300] This is my "hot" page which lists my 300 latest submissions (10 pages of 30 links each). I want to now sort this QuerySet by an algorithm that HackerNews uses: (p - 1) / (t + 2)^1.5 p = votes minus submitter's initial vote t = age of submission in hours Now because applying this algorithm over the entire database would be pretty costly I am content with just the last 300 submissions. My site is unlikely to be the next digg/reddit so while scalability is a plus it is required. My question is now how do I iterate over my QuerySet and sort it by the above algorithm? For more information, here are my applicable models: class Link(models.Model): category = models.ForeignKey(Category, blank=False, default=1) user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add=True) modified = models.DateTimeField(auto_now=True) url = models.URLField(max_length=1024, unique=True, verify_exists=True) name = models.CharField(max_length=512) def __unicode__(self): return u'%s (%s)' % (self.name, self.url) class Vote(models.Model): link = models.ForeignKey(Link) user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add=True) def __unicode__(self): return u'%s vote for %s' % (self.user, self.link) Notes: I don't have "downvotes" so just the presence of a Vote row is an indicator of a vote or a particular link by a particular user.

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• Sorting by custom field and fetching whole tree from DB

  - by Niaxon

  Hello everyone, I am trying to do file browser in a tree form and have a problem to sort it somehow. I use PHP and MySQL for that. I've created mixed (nested set + adjacency) table 'element' with the following fields: element_id, left_key, right_key, level, parent_id, element_name, element_type (enum: 'folder','file'), element_size. Let's not discuss right now that it is better to move information about element (name, type, size) into other table. Function to scan specified directory and fill table work correctly. Noteworthy, i am adding elements to tree in specific order: folders first and then files. After that i can easily fetch and display whole table on the page using simple query: SELECT * FROM element WHERE 1=1 ORDER BY left_key With the result of that query and another function i can generate correct html code (<ul><li>... and so on). to display tree. Now back to the question (finally, huh?). I am struggling to add sorting functionality. For example i want to order my result by size. Here i need to keep in my mind whole hierarchy of tree and rule: folders first, files later. I believe i can do that by generating in PHP recursive query: SELECT * FROM element WHERE parent_id = {$parentId} ORDER BY element_type (so folders would be first), size (or name for example) asc/desc After that for each result which has type = 'folder' i will send another query to get it's content. Also it's possible to fetch whole tree by left_key and after that sort it in PHP as array but i guess that would be worse :) I wonder if there is better and more efficient way to do such a thing?

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• How to not use JavaScript with in the elements events attributes but still load via AJAX

  - by thecoshman

  I am currently loading HTMl content via AJAX. I have code for things on different elements onclick attributes (and other event attributes). It does work, but I am starting to find that the code is getting rather large, and hard to read. I have also read that it is considered bad practice to have the event code 'inline' like this and that I should really do by element.onclick = foobar and have foobar defined somewhere else. I understand how with a static page it is fairly easy to do this, just have a script tag at the bottom of the page and once the page is loaded have it executed. This can then attach any and all events as you need them. But how can I get this sort of affect when loading content via AJAX. There is also the slight case that the content loaded can very depending on what is in the database, some times certain sections of HTML, such as tables of results, will not even be displayed there will be something else entirely. I can post some samples of code if any body needs them, but I have no idea what sort of things would help people with this one. I will point out, that I am using Jquery already so if it has some helpful little functions that would be rather sweet¬

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• How to make placeholder varablies in jquery validate 1.7?

  - by chobo2

  Hi I am using jquery 1.4.2 and jquery validate 1.7(http://bassistance.de/jquery-plugins/jquery-plugin-validation/) Say I have this example that I just grabbed off some random site(http://www.webreference.com/programming/javascript/jquery/form_validation/) 8 <script type="text/javascript"> 9 $(document).ready(function() { 10 $("#form1").validate({ 11 rules: { 12 name: "required",// simple rule, converted to {required:true} 13 email: {// compound rule 14 required: true, 15 email: true 16 }, 17 url: { 18 url: true 19 }, 20 comment: { 21 required: true 22 } 23 }, 24 messages: { 25 comment: "Please enter a comment." 26 } 27 }); 28 }); 29 </script> now is it possible to do something like this 10 $("#form1").validate({ var NameHolder = "name" 11 rules: { 12 NameHolder: "required",// simple rule, converted to {required:true} 13 email: {// compound rule 14 required: true, 15 email: true So basically I want to make sort of a global variable to hold theses rule names( what correspond to the names on that html control). My concern is the names of html controls can change and it kinda sucks that I will have to go around and change it in many places of my code to make it work again. So basically I am wondering is there away to make a global variable to store this name. So if I need to change the name I only have to change it in one spot in my javascript file sort of the way stopping magic numbers ?

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• __toString magic and type coercion

  - by TomcatExodus

  I've created a Template class for managing views and their associated data. It implements Iterator and ArrayAccess, and permits "sub-templates" for easy usage like so: <p><?php echo $template['foo']; ?></p> <?php foreach($template->post as $post): ?> <p><?php echo $post['bar']; ?></p> <?php endforeach; ?> Anyways, rather than using inline core functions, such as hash() or date(), I figured it would be useful to create a class called TemplateData, which would act as a wrapper for any data stored in the templates. This way, I can add a list of common methods for formatting, for example: echo $template['foo']->asCase('upper'); echo $template['bar']->asDate('H:i:s'); //etc.. When a value is set via $template['foo'] = 'bar'; in the controllers, the value of 'bar' is stored in it's own TemplateData object. I've used the magic __toString() so when you echo a TemplateData object, it casts to (string) and dumps it's value. However, despite the mantra controllers and views should not modify data, whenever I do something like this: $template['foo'] = 1; echo $template['foo'] + 1; //exception It dies on a Object of class TemplateData could not be converted to int; Unless I recast $template['foo'] to a string: echo ((string) $template['foo']) + 1; //outputs 2 Sort of defeats the purpose having to jump through that hoop. Are there any workarounds for this sort of behavior that exist, or should I just take this as it is, an incidental prevention of data modification in views?

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• TFS query mixing Tasks and Bugs, sorted by Priority

  - by Val

  We're using TFS with MSF for Agile 4.2 on a project, and I have a bunch of work to do, both Tasks and Bugs. Both are prioritized by our managers, and assigned due dates and target releases. I use a Work Item query as my main TODO list, and I want to list all the Work Items assigned to me, in order by due date and priority. Problem: I can't seem to find a way to write a unified query that will list both Tasks and Bugs sorted by date and then priority. The problem is that Tasks and Bugs use different fields for Priority. So, my query currently lists the tasks by Due Date, then by Task Priority, then it lists Bugs by Due Date, then by Priority. So, I see tasks that are due later than bugs: Title Due Date Priority Task Priority task1 4/23/2010 Medium task2 4/23/2010 High task3 4/30/2010 Low task4 4/30/2010 Medium bug1 4/23/2010 1 bug2 4/23/2010 2 What I want: Title Due Date Priority Task Priority task1 4/23/2010 Medium task2 4/23/2010 High bug1 4/23/2010 1 bug2 4/23/2010 2 task3 4/30/2010 Low task4 4/30/2010 Medium I don't care if the bugs come before or after the tasks on the same due date; I just want all the work items grouped together by due date, so I never see Tasks for a later due date before Bugs for an earlier one. Another problem is the sorting on Task Priority -- alpha sort means I can't get them to sort by the meaning of the priority. But that's a minor problem I can live with if I can get the Tasks and Bugs intermingled. Any way to do this in a single query?

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• Why rails app is redirecting unexpectedly instead of matching the route?

  - by ruevaughn

  I asked this question earlier and thought it was fixed, but it's not. Previous question here My problem is I am trying to set my routes so that when I type in localhost:3000/sites/admin It should redirect to localhost:3000/en/sites/admin here is my routes.rb file scope ":locale", locale: /#{I18n.available_locales.join("|")}/ do get "log_out" => "sessions#destroy", as: "log_out" get "log_in" => "sessions#new", as: "log_in" resources :sites, except: [:new, :edit, :index, :show, :update, :destroy, :create] do collection do get :home get :about_us get :faq get :discounts get :services get :contact_us get :admin get :posts end end resources :users resources :abouts resources :sessions resources :coupons resources :monthly_posts resources :reviews resources :categories do collection { post :sort } resources :children, :controller => :categories, :only => [:index, :new, :create, :new_subcategory] end resources :products do member do put :move_up put :move_down end end resources :faqs do collection { post :sort } end root :to => 'sites#home' match "/savesort" => 'sites#savesort' end match '', to: redirect("/#{I18n.default_locale}") match '*path', to: redirect("/#{I18n.default_locale}/%{path}") But as of right now, it redirects to /en/en/en/en/en/en/en/en/en/en/sites/admin (adds en until browser complains). Any thoughts why it keeps adding /en?

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• How do I use price data in one table for a calculation that is stored in another table?

  - by shane

  I'm still leanring PHP/MySQL but have learned quite a bit thanks to codies on StackOverflow. I'm trying to setup a sort of room reservations system using two tables: SETUP: Room price table: Has, prices for a type room a client may want to rent as well as the dates (day of week) they wish to use it. Pricing varies based on day of the week and per room. I've setup a different table for each room type as each room type carries different pricing for each day of the week. So, There is an Alpha room table, Bravo room, etc. Within Alpha table are headers for the days of the week with pricing pre-entered into the rows. Client info table: Has the name, address, date of room use, etc data for the specific client. EXAMPLE: Alpha-room price table: Sun = $100; Mon = $200; Tue=$300 and so on. Bravo-room price table: Sun = $100; Mon = $200; Tue=$300 and so on. Client data table: ClientName; date-of-room-use; address; day_subtotal; grand_total. QUESTION: I'm trying to find PHP code that will: look at the date of room use in the client data table, look up the associated cost for that date in the specific room pricing table, record that unit cost in the day subtotal of the client data table and sum a grand total in the grand total row of the client data table (assuming the room may be used more than one day by the customer). I know there's something to do with join but I'm finding it difficult to grasp the concept and, if someone can demonstrate using this example, I think I will have a better understanding of how to work this sort of transaction. Thank you ALL in advance for your suggestions or alternatvie approaches.

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• How important is it to use SSL on every page of your website?

  - by Mark

  Recently I installed a certificate on the website I'm working on. I've made as much of the site as possible work with HTTP, but after you log in, it has to remain in HTTPS to prevent session hi-jacking, doesn't it? Unfortunately, this causes some problems with Google Maps; I get warnings in IE saying "this page contains insecure content". I don't think we can afford Google Maps Premier right now to get their secure service. It's sort of an auction site so it's fairly important that people don't get charged for things they didn't purchase because some hacker got into their account. All payments are done through PayPal though, so I'm not saving any sort of credit card info, but I am keeping personal contact information. Fraudulent charges could be reversed fairly easily if it ever came to that. What do you guys suggest I do? Should I take the bulk of the site off HTTPS and just secure certain pages like where ever you enter your password, and that's it? That's what our competition seems to do.

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• Online file storage similar to Amazon S3

  - by Joel G

  I am looking to code a file storage application in perl similar to amazon s3. I already have a amazon s3 clone that I found online called parkplace but its in ruby and is old also isn't built for high loads. I am not really sure what modules and programs I should use so id like some help picking them out. My requirements are listed below (yes I know there are lots but I could start simple then add more once I get it going): Easy API implementation for client side apps. (maybe RESTful but extras like mkdir and cp (?) Centralized database server for the USERDB (maybe PostgreSQL (?). Logging of all connections, bandwidth used, well pretty much everything to a centralized server (maybe PostgreSQL again (?). Easy server side configuration (config file(s) stored on the servers). Web based control panel for admin(s) and user(s) to show logs. (could work just running queries from the databases) Fast High Uptime Low memory usage Some sort of load distribution/load balancer (maybe a dns based or pound or perlbal or something else (?). Maybe a cache of some sort (memcached or parlbal or something else (?). Thanks in advance

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• Properly maintain sorted state of Array/Set

  - by Jeff

  I'm trying to get data out of my MOC and then create some new objects based on those objects, and put it all back together, while keeping my sort state. The securities come out of the MOC in proper order. And everything seems to be fine until I do the assignment to the game at the bottom from setWithArray. The documentation says that setWithArray removed the duplicate objects, if there are any. I'm wonder if that's messing up my data, but I don't see a good alternative. The data is ultimately being pulled out into a UITableView. When I add items to the game manually, then they stay sorted, so I don't think the breaking of the sort is beyond the scope of what I've included here. NSError *error; NSArray *allTheSecurities = [managedObjectContext executeFetchRequest:request error:&error]; if (allTheSecurities == nil) { // Handle the error. } [request release]; /**/ NSLog( @"Enumerate..." ); NSEnumerator *enumerator = [allTheSecurities objectEnumerator]; id anObject; NSMutableArray *portfolioStocks = [[NSMutableArray alloc] init]; while (anObject = [enumerator nextObject]) { NSLog( @"Iteration... %@", [anObject name] ); NSLog( @"Build a stock..." ); PortfolioStocks *this_stock = (PortfolioStocks *)[NSEntityDescription insertNewObjectForEntityForName:@"PortfolioStocks" inManagedObjectContext:context]; NSLog( @"Set a value..." ); [this_stock setSecurity:(Security *)anObject]; [this_stock setQuantity:[NSNumber numberWithInt:0]]; NSLog( @"Add to portfolioStocks..." ); [portfolioStocks addObject:this_stock]; } //Sorted properly up to here! NSLog( @"Add to portfolio..." ); [game setPortfolio:[NSSet setWithArray:portfolioStocks]]; // <-- This is where it's not sorted anymore.

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• Some optimization about the code (computing ranks of a vector)?

  - by user1748356

  The following code is a function (performance-critical) to compute tied ranks of a vector: mergeSort(x,inds,ci); //a sort function to sort vector x of length ci, also returns keys (inds) of x. int tj=0; double xi=x[0]; for (int j = 1; j < ci; ++j) { if (x[j] > xi) { double rankvalue = 0.5 * (j - 1 + tj); for (int k = tj; k < j; ++k) { ranks[inds[k]]=rankvalue; }; tj = j; xi = x[j]; }; }; double rankvalue = 0.5 * (ci - 1 + tj); for (int k = tj; k < ci; ++k) { ranks[inds[k]]=rankvalue; }; The problem is, the supposed performance bottleneck mergeSort(), which is O(NlogN) is several times faster than the other part of codes (which is O(N)), which suggests there is room for huge improvment with the other part of the codes, any advices?

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• IComparer for integers with and empty strings at end

  - by paulio

  Hi, I've written the following IComparer but I need some help. I'm trying to sort a list of numbers but some of the numbers may not have been filled in. I want these numbers to be sent to the end of the list at all times.. for example... [EMPTY], 1, [EMPTY], 3, 2 would become... 1, 2, 3, [EMPTY], [EMPTY] and reversed this would become... 3, 2, 1, [EMPTY], [EMPTY] Any ideas? public int Compare(ListViewItem x, ListViewItem y) { int comparison = int.MinValue; ListViewItem.ListViewSubItem itemOne = x.SubItems[subItemIndex]; ListViewItem.ListViewSubItem itemTwo = y.SubItems[subItemIndex]; if (!string.IsNullOrEmpty(itemOne.Text) && !string.IsNullOrEmpty(itemTwo.Text)) { uint itemOneComparison = uint.Parse(itemOne.Text); uint itemTwoComparison = uint.Parse(itemTwo.Text); comparison = itemOneComparison.CompareTo(itemTwoComparison); } else { // ALWAYS SEND TO BOTTOM/END OF LIST. } // Calculate correct return value based on object comparison. if (OrderOfSort == SortOrder.Descending) { // Descending sort is selected, return negative result of compare operation. comparison = (-comparison); } else if (OrderOfSort == SortOrder.None) { // Return '0' to indicate they are equal. comparison = 0; } return comparison; } Cheers.

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• incremental way of counting quantiles for large set of data

  - by Gacek

  I need to count the quantiles for a large set of data. Let's assume we can get the data only through some portions (i.e. one row of a large matrix). To count the Q3 quantile one need to get all the portions of the data and store it somewhere, then sort it and count the quantile: List<double> allData = new List<double>(); foreach(var row in matrix) // this is only example. In fact the portions of data are not rows of some matrix { allData.AddRange(row); } allData.Sort(); double p = 0.75*allData.Count; int idQ3 = (int)Math.Ceiling(p) - 1; double Q3 = allData[idQ3]; Now, I would like to find a way of counting this without storing the data in some separate variable. The best solution would be to count some parameters od mid-results for first row and then adjust it step by step for next rows. Note: These datasets are really big (ca 5000 elements in each row) The Q3 can be estimated, it doesn't have to be an exact value. I call the portions of data "rows", but they can have different leghts! Usually it varies not so much (+/- few hundred samples) but it varies! This question is similar to this one: http://stackoverflow.com/questions/1058813/on-line-iterator-algorithms-for-estimating-statistical-median-mode-skewness But I need to count quantiles. ALso there are few articles in this topic, i.e.: http://web.cs.wpi.edu/~hofri/medsel.pdf http://portal.acm.org/citation.cfm?id=347195&dl But before I would try to implement these, I wanted to ask you if there are maybe any other, qucker ways of counting the 0.25/0.75 quantiles?

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• Achieving Thread-Safety

  - by Smasher

  Question How can I make sure my application is thread-safe? Are their any common practices, testing methods, things to avoid, things to look for? Background I'm currently developing a server application that performs a number of background tasks in different threads and communicates with clients using Indy (using another bunch of automatically generated threads for the communication). Since the application should be highly availabe, a program crash is a very bad thing and I want to make sure that the application is thread-safe. No matter what, from time to time I discover a piece of code that throws an exception that never occured before and in most cases I realize that it is some kind of synchronization bug, where I forgot to synchronize my objects properly. Hence my question concerning best practices, testing of thread-safety and things like that. mghie: Thanks for the answer! I should perhaps be a little bit more precise. Just to be clear, I know about the principles of multithreading, I use synchronization (monitors) throughout my program and I know how to differentiate threading problems from other implementation problems. But nevertheless, I keep forgetting to add proper synchronization from time to time. Just to give an example, I used the RTL sort function in my code. Looked something like FKeyList.Sort (CompareKeysFunc); Turns out, that I had to synchronize FKeyList while sorting. It just don't came to my mind when initially writing that simple line of code. It's these thins I wanna talk about. What are the places where one easily forgets to add synchronization code? How do YOU make sure that you added sync code in all important places?

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• C# - Advantages/Disadvantages of different implementations for Comparing Objects

  - by Kevin Crowell

  This questions involves 2 different implementations of essentially the same code. First, using delegate to create a Comparison method that can be used as a parameter when sorting a collection of objects: class Foo { public static Comparison<Foo> BarComparison = delegate(Foo foo1, Foo foo2) { return foo1.Bar.CompareTo(foo2.Bar); }; } I use the above when I want to have a way of sorting a collection of Foo objects in a different way than my CompareTo function offers. For example: List<Foo> fooList = new List<Foo>(); fooList.Sort(BarComparison); Second, using IComparer: public class BarComparer : IComparer<Foo> { public int Compare(Foo foo1, Foo foo2) { return foo1.Bar.CompareTo(foo2.Bar); } } I use the above when I want to do a binary search for a Foo object in a collection of Foo objects. For example: BarComparer comparer = new BarComparer(); List<Foo> fooList = new List<Foo>(); Foo foo = new Foo(); int index = fooList.BinarySearch(foo, comparer); My questions are: What are the advantages and disadvantages of each of these implementations? What are some more ways to take advantage of each of these implementations? Is there a way to combine these implementations in such a way that I do not need to duplicate the code? Can I achieve both a binary search and an alternative collection sort using only 1 of these methods?

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• Permuting a binary tree without the use of lists

  - by Banang

  I need to find an algorithm for generating every possible permutation of a binary tree, and need to do so without using lists (this is because the tree itself carries semantics and restraints that cannot be translated into lists). I've found an algorithm that works for trees with the height of three or less, but whenever I get to greater hights, I loose one set of possible permutations per height added. Each node carries information about its original state, so that one node can determine if all possible permutations have been tried for that node. Also, the node carries information on weather or not it's been 'swapped', i.e. if it has seen all possible permutations of it's subtree. The tree is left-centered, meaning that the right node should always (except in some cases that I don't need to cover for this algorithm) be a leaf node, while the left node is always either a leaf or a branch. The algorithm I'm using at the moment can be described sort of like this: if the left child node has been swapped swap my right node with the left child nodes right node set the left child node as 'unswapped' if the current node is back to its original state swap my right node with the lowest left nodes' right node swap the lowest left nodes two childnodes set my left node as 'unswapped' set my left chilnode to use this as it's original state set this node as swapped return null return this; else if the left child has not been swapped if the result of trying to permute left child is null return the permutation of this node else return the permutation of the left child node if this node has a left node and a right node that are both leaves swap them set this node to be 'swapped' The desired behaviour of the algoritm would be something like this: branch / | branch 3 / | branch 2 / | 0 1 branch / | branch 3 / | branch 2 / | 1 0 <-- first swap branch / | branch 3 / | branch 1 <-- second swap / | 2 0 branch / | branch 3 / | branch 1 / | 0 2 <-- third swap branch / | branch 3 / | branch 0 <-- fourth swap / | 1 2 and so on... Sorry for the ridiculisly long and waddly explanation, would really, really apreciate any sort of help you guys could offer me. Thanks a bunch!

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• PHP -- automatic SQL injection protection?

  - by ashgromnies

  I took over maintenance of a PHP app recently and I'm not super familiar with PHP but some of the things I've been seeing on the site are making me nervous that it could be vulnerable to a SQL injection attack. For example, see how this code for logging into the administrative section works: $password = md5(HASH_SALT . $_POST['loginPass']); $query = "SELECT * FROM `administrators` WHERE `active`='1' AND `email`='{$_POST['loginEmail']}' AND `password`='{$password}'"; $userInfo = db_fetch_array(db_query($query)); if($userInfo['id']) { $_SESSION['adminLoggedIn'] = true; // user is logged in, other junk happens here, not important The creators of the site made a special db_query method and db_fetch_array method, shown here: function db_query($qstring,$print=0) { return @mysql(DB_NAME,$qstring); } function db_fetch_array($qhandle) { return @mysql_fetch_array($qhandle); } Now, this makes me think I should be able to do some sort of SQL injection attack with an email address like: ' OR 'x'='x' LIMIT 1; and some random password. When I use that on the command line, I get an administrative user back, but when I try it in the application, I get an invalid username/password error, like I should. Could there be some sort of global PHP configuration they have enabled to block these attacks? Where would that be configured? Here is the PHP --version information: # php --version PHP 5.2.12 (cli) (built: Feb 28 2010 15:59:21) Copyright (c) 1997-2009 The PHP Group Zend Engine v2.2.0, Copyright (c) 1998-2009 Zend Technologies with the ionCube PHP Loader v3.3.14, Copyright (c) 2002-2010, by ionCube Ltd., and with Zend Optimizer v3.3.9, Copyright (c) 1998-2009, by Zend Technologies

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