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• Simplest distributed persistent key/value store that supports primary key range queries

  - by StaxMan

  I am looking for a properly distributed (i.e. not just sharded) and persisted (not bounded by available memory on single node, or cluster of nodes) key/value ("nosql") store that does support range queries by primary key. So far closest such system is Cassandra, which does above. However, it adds support for other features that are not essential for me. So while I like it (and will consider using it of course), I am trying to figure out if there might be other mature projects that implement what I need. Specifically, for me the only aspect of value I need is to access it as a blob. For key, however, I need range queries (as in, access values ordered, limited by start and/or end values). While values can have structures, there is no need to use that structure for anything on server side (can do client-side data binding, flexible value/content types etc). For added bonus, Cassandra style storage (journaled, all sequential writes) seems quite optimal for my use case. To help filter out answers, I have investigated some alternatives within general domain like: Voldemort (key/value, but no ordering) and CouchDB (just sharded, more batch-oriented); and am aware of systems that are not quite distributed while otherwise qualifying (bdb variants, tokyo cabinet itself (not sure if Tyrant might qualify), redis (in-memory store only)).

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• Large scale perspective lights casting shadow maps, in the most optimized way?

  - by meds

  I'm using projected texture shadows coupled with lights to light a large sports field at night. To do this I'm using shadow cameras which I place in the position of the stadiums lights and shine it down on the field at the appropriate angle. The problem with this method is the textures to which I render the shadows into have to be very large so they can keep sufficient detail over the entire stadium. This is incredibly under optimized since at any given point the players attention is only directed on a small portion of the field meaning large chunks of the texture just take up space wit no benefits. However the issue is the lights need to be perspective based as they come from actual directional lights hovering over the stadium. The way to solve this, I believe, is to figure out in the shadow cameras view matrix it would be to place the actual camera to render from, and adjust the view matrix accordingly to the position it is. So my question is, how can I calculate the optimal position to put the shadow camera and calculate its view matrix such that the shadows it projects will appear to be coming from the light source rather than the camera?

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• PHP package manager

  - by Mathias

  Hey, does anyone know a package manager library for PHP (as e.g. apt or yum for linux distros) apart from PEAR? I'm working on a system which should include a package management system for module management. I managed to get a working solution using PEAR, but using the PEAR client for anything else than managing a PEAR installation is not really the optimal solution as it's not designed for that. I would have to modify/extend it (e.g. to implement actions on installation/upgrade or to move PEAR specific files like lockfiles away from the system root) and especially the CLI client code is quite messy and PHP4. So maybe someone has some suggestions for an alternative PEAR client library which is easy to use and extend (the server side has some nice implementations like Pirum and pearhub) for completely different package management systems written in PHP (ideally including dependency tracking and different channels) for some general ideas how to implement such a PM system (yes, I'm still tinkering with the idea of implementing such a system from scratch) I know that big systems like Magento and symfony use PEAR for their PM. Magento uses a hacked version of the original PEAR client (which I'd like to avoid), symfony's implementation seems quite integrated with the framework, but would be a good starting point to at least write the client from scratch. Anyway, if anybody has suggestions: please :)

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• most efficient method of turning multiple 1D arrays into columns of a 2D array

  - by Ty W

  As I was writing a for loop earlier today, I thought that there must be a neater way of doing this... so I figured I'd ask. I looked briefly for a duplicate question but didn't see anything obvious. The Problem: Given N arrays of length M, turn them into a M-row by N-column 2D array Example: $id = [1,5,2,8,6] $name = [a,b,c,d,e] $result = [[1,a], [5,b], [2,c], [8,d], [6,e]] My Solution: Pretty straight forward and probably not optimal, but it does work: <?php // $row is returned from a DB query // $row['<var>'] is a comma separated string of values $categories = array(); $ids = explode(",", $row['ids']); $names = explode(",", $row['names']); $titles = explode(",", $row['titles']); for($i = 0; $i < count($ids); $i++) { $categories[] = array("id" => $ids[$i], "name" => $names[$i], "title" => $titles[$i]); } ?> note: I didn't put the name = value bit in the spec, but it'd be awesome if there was some way to keep that as well.

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• Caching issue with javascript and asp.net

  - by Ed Woodcock

  Hi guys: I asked a question a while back on here regarding caching data for a calendar/scheduling web app, and got some good responses. However, I have now decided to change my approach and stat caching the data in javascript. I am directly caching the HTML for each day's column in the calendar grid inside the $('body').data() object, which gives very fast page load times (almost unnoticable). However, problems start to arise when the user requests data that is not yet in the cache. This data is created by the server using an ajax call, so it's asynchronous, and takes about 0.2s per week's data. My current approach is simply to block for 0.5s when the user requests information from the server, and cache 4 weeks either side in the inital page load (and 1 extra week per page change request), however I doubt this is the optimal method. Does anyone have a suggestion as to how to improve the situation? To summarise: Each week takes 0.2s to retrieve from the server, asynchronously. Performance must be as close to real-time as possible. (however the data is not needed to be fully real-time: most appointments are added by the user and so we can re-cache after this) Currently 4 weeks are cached on either side of the inial week loaded: this is not enough. to cache 1 year takes ~ 21s, this is too slow for an initial load.

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• Implementation of MVC with SQLite and NSURLConnection, use cases?

  - by user324723

  I'm interested in knowing how others have implemented/designed database & web services in their iphone app and how they simplified it for the entire application. My application is dependent on these services and I can't figure out a efficient way to use them together due to the (semi)complexity of my requirements. My past attempts on combining them haven't been completely successful or at least optimal in my mind. I'm building a database driven iphone app that uses a relational database in sqlite and consumes web services based on missing content or user interaction. Like this hasn't been done before...right? Since I am using a relational database - any web services consumed requires normalization, parsing the result and persisting it to the database before it can be displayed in a table view controller. The applications UI consists of nested(nav controller) table views where a user can select a cell and be taken to the next table view where it attempts to populate the table views data source from the database. If nothing exists in the database then it will send a request via web services to download its content, thus download - parse - persist - query - display. Since the user has the ability to request a refresh of this data it still requires the same process. Quickly describing what I've implemented and tried to run with - 1st attempt - Used a singleton web service class that handled sending web service requests, parsing the result and returning it to the table view controller via delegate protocols. Once the controller received that data it would then be responsible for persisting it to the database and re-returning the result. I didn't like the idea of only preventing the case where the app delegate selector doesn't exists(released) causing the app to crash. 2nd attempt - Used NSNotificationCenter for easy access to both database and web services but later realized it was more complex due to adding and removing observers per view(which isn't advised anyways).

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• Java-Eclipse-Spring 3.1 - the fastest way to get familiar with this set

  - by Leron

  I, know almost all of you at some point of your life as a programmer get to the point where you know (more or less) different technologies/languages/IDEs and a times come when you want to get things together and start using them once - more efficient and second - more closely to the real life situation where in fact just knowing Java, or some experience with Eclipse doesn't mean nothing, and what makes you a programmer worth something is the ability to work with the combination of 2 or more combinations. Having this in mind here is my question - what do you think is the optimal way of getting into Java+Eclipse+Spring3.1 world. I've read, and I've read a lot. I started writing real code but almost every step is discovering the wheel again and again, wondering how to do thing you know are some what trivial, but you've missed that one article where this topic was discussed and so on. I don't mind for paying for a good tutorial like for example, after a bit of research I decided that instead of losing a lot of time getting the different parts together I'd rather pay for the videos in http://knpuniversity.com/screencast/starting-in-symfony2-tutorial and save myself a lot of time (I hope) and get as fast as possible to writing a real code instead of wondering what do what and so on. But I find it much more difficult to find such sources of info especially when you want something more specific as me and that's the reason to ask this question. I know a lot of you go through the hard way, and I won't give up if I have to do the same, but to be honest I really hope to get post with good tutorials on the subject (paid or not) because in my situation time is literally money. Thanks Leron

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• minimum L sum in a mxn matrix - 2

  - by hilal

  Here is my first question about maximum L sum and here is different and hard version of it. Problem : Given a mxn *positive* integer matrix find the minimum L sum from 0th row to the m'th row . L(4 item) likes chess horse move Example : M = 3x3 0 1 2 1 3 2 4 2 1 Possible L moves are : (0 1 2 2), (0 1 3 2) (0 1 4 2) We should go from 0th row to the 3th row with minimum sum I solved this with dynamic-programming and here is my algorithm : 1. Take a mxn another Minimum L Moves Sum array and copy the first row of main matrix. I call it (MLMS) 2. start from first cell and look the up L moves and calculate it 3. insert it in MLMS if it is less than exists value 4. Do step 2. until m'th row 5. Choose the minimum sum in the m'th row Let me explain on my example step by step: M[ 0 ][ 0 ] sum(L1 = (0, 1, 2, 2)) = 5 ; sum(L2 = (0,1,3,2)) = 6; so MLMS[ 0 ][ 1 ] = 6 sum(L3 = (0, 1, 3, 2)) = 6 ; sum(L4 = (0,1,4,2)) = 7; so MLMS[ 2 ][ 1 ] = 6 M[ 0 ][ 1 ] sum(L5 = (1, 0, 1, 4)) = 6; sum(L6 = (1,3,2,4)) = 10; so MLMS[ 2 ][ 2 ] = 6 ... the last MSLS is : 0 1 2 4 3 6 6 6 6 Which means 6 is the minimum L sum that can be reach from 0 to the m. I think it is O(8*(m-1)*n) = O(m*n). Is there any optimal solution or dynamic-programming algorithms fit this problem? Thanks, sorry for long question

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• How to map (large) integer on (small in size( alphanumeric string with PHP? (Cantor?)

  - by Glooh

  Dear all, I can't figure out how to optimally do the following in PHP: In a database, I have messages with a unique ID, like 19041985. Now, I want to refer to these messages in a short-url service but not using generated hashes but by simply 'calculate' the original ID. In other words, for example: http://short.url/sYsn7 should let me calculate the message ID the visitor would like to request. To make it more obvious, I wrote the following in PHP to generate these 'alphanumeric ID versions' and of course, the other way around will let me calculate the original message ID. The question is: Is this the optimal way of doing this? I hardly think so, but can't think of anything else. $alphanumString = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_'; for($i=0;$i < strlen($alphanumString);$i++) { $alphanumArray[$i] = substr($alphanumString,$i,1); } $id = 19041985; $out = ''; for($i=0;$i < strlen($id);$i++) { if(isset($alphanumString["".substr($id,$i,2).""]) && strlen($alphanumString["".substr($id,$i,2).""]) 0) { $out.=$alphanumString["".substr($id,$i,2).""]; } else { $out.=$alphanumString["".substr($id,$i,1).""]; $out.=$alphanumString["".substr($id,($i+1),1).""]; } $i++; } print $out;

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• Splitting a set of object into several subsets of 'similar' objects

  - by doublep

  Suppose I have a set of objects, S. There is an algorithm f that, given a set S builds certain data structure D on it: f(S) = D. If S is large and/or contains vastly different objects, D becomes large, to the point of being unusable (i.e. not fitting in allotted memory). To overcome this, I split S into several non-intersecting subsets: S = S1 + S2 + ... + Sn and build Di for each subset. Using n structures is less efficient than using one, but at least this way I can fit into memory constraints. Since size of f(S) grows faster than S itself, combined size of Di is much less than size of D. However, it is still desirable to reduce n, i.e. the number of subsets; or reduce the combined size of Di. For this, I need to split S in such a way that each Si contains "similar" objects, because then f will produce a smaller output structure if input objects are "similar enough" to each other. The problems is that while "similarity" of objects in S and size of f(S) do correlate, there is no way to compute the latter other than just evaluating f(S), and f is not quite fast. Algorithm I have currently is to iteratively add each next object from S into one of Si, so that this results in the least possible (at this stage) increase in combined Di size: for x in S: i = such i that size(f(Si + {x})) - size(f(Si)) is min Si = Si + {x} This gives practically useful results, but certainly pretty far from optimum (i.e. the minimal possible combined size). Also, this is slow. To speed up somewhat, I compute size(f(Si + {x})) - size(f(Si)) only for those i where x is "similar enough" to objects already in Si. Is there any standard approach to such kinds of problems? I know of branch and bounds algorithm family, but it cannot be applied here because it would be prohibitively slow. My guess is that it is simply not possible to compute optimal distribution of S into Si in reasonable time. But is there some common iteratively improving algorithm?

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• Doctrine2 - relationship

  - by Filip Golonka

  I'm developing an application, which is looking for optimal route and timetable in public transport. I have some experience about Doctrine1, but it's my first time with Doctrine2. There is soem new fields to describe relations (mappedBy and inversedBy) and also some new ways of mapping. I have following code: $query = $this->em->createQuery("SELECT partial cls.{stop}, partial t.{arriveTime, departureTime} FROM \Entities\Timetable t JOIN t.ride r JOIN t.carrierLineStop cls WHERE t.departureTime>=:time AND r.idCarrierLine=:carrierLine AND (cls.idStop=:firstStop OR cls.idStop=:lastStop)"); $query->setParameters(array( 'time' => $time, 'carrierLine' => $path->getLine(), 'firstStop' => $path->getFirstStop(), 'lastStop' => $path->getLastStop() )); When I try to execute that script I've got an error: [Semantical Error] line 0, col 24 near '}, partial t.{arriveTime,': Error: There is no mapped field named 'stop' on class Entities\CarrierLineStop. Mapping files: Entities\CarrierLineStop: type: entity table: carrier_line_stop fields: idCarrierLineStop: id: true type: integer unsigned: false nullable: false column: id_carrier_line_stop generator: strategy: IDENTITY nextStop: type: integer unsigned: false nullable: true column: next_stop manyToOne: idCarrierLine: targetEntity: Entities\CarrierLine cascade: { } mappedBy: null inversedBy: null joinColumns: id_carrier_line: referencedColumnName: id_carrier_line orphanRemoval: false stop: column: id_stop targetEntity: Entities\Stop cascade: { } mappedBy: null inversedBy: carrierLineStop joinColumns: id_stop: referencedColumnName: id_stop orphanRemoval: false lifecycleCallbacks: { } - Entities\Stop: type: entity table: stop fields: idStop: id: true type: integer unsigned: false nullable: false column: id_stop generator: strategy: IDENTITY name: type: string length: 45 fixed: false nullable: true miejscowosc: type: string length: 45 fixed: false nullable: true latitude: type: decimal nullable: true longitude: type: decimal nullable: true oneToMany: carrierLineStop: targetEntity: Entities\CarrierLineStop cascade: { } mappedBy: stop inversedBy: null joinColumns: id_stop: referencedColumnName: id_stop orphanRemoval: false lifecycleCallbacks: { } I have no idea about where the problem is...

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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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• How do I wait for a C# event to be raised?

  - by Evan Barkley

  I have a Sender class that sends a Message on a IChannel: public class MessageEventArgs : EventArgs { public Message Message { get; private set; } public MessageEventArgs(Message m) { Message = m; } } public interface IChannel { public event EventHandler<MessageEventArgs> MessageReceived; void Send(Message m); } public class Sender { public const int MaxWaitInMs = 5000; private IChannel _c = ...; public Message Send(Message m) { _c.Send(m); // wait for MaxWaitInMs to get an event from _c.MessageReceived // return the message or null if no message was received in response } } When we send messages, the IChannel sometimes gives a response depending on what kind of Message was sent by raising the MessageReceived event. The event arguments contain the message of interest. I want Sender.Send() method to wait for a short time to see if this event is raised. If so, I'll return its MessageEventArgs.Message property. If not, I return a null Message. How can I wait in this way? I'd prefer not to have do the threading legwork with ManualResetEvents and such, so sticking to regular events would be optimal for me.

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• Ruby Challenge - efficiently change the last character of every word in a sentence to a capital

  - by emson

  Hi All I recently was challenged to write some Ruby code to change the last character of every word in a sentence into a capital. Such that the string: "script to convert the last letter of every word to a capital" becomes "scripT tO converT thE lasT letteR oF everY worD tO A capitaL" This was my optimal solution however I'm sure you wizards have much better solutions and I would be really interested to hear them. "script to convert the last letter of every word to a capital".split.map{|w|w<<w.slice!(-1).chr.upcase}.join' ' For those interested as to what is going on here is an explanation. split will split the sentence up into an array, the default delimiter is a space and with Ruby you don't need to use brackets here. map the array from split is passed to map which opens a block and process each word (w) in the array. the block slice!(s) off the last character of the word and converts it to a chr (a character not ASCII code) and then capitalises upcase it. This character is now appended << to the word which is missing the sliced last letter. Finally the array of words is now join together with a ' ' to reform the sentence. Enjoy

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• Wasteful Ajax Page Loading

  - by Matt Dawdy

  I've started a new job, and the portion of the project I'm working has a very odd structure. Every pages is a .Net aspx page, and it loads just fine, but nothing is really done at load time. Everything is really loaded from a jquery document.onready handler. What is even more...interesting...is that the onready handler calls some ajax calls that drop entire .aspx pages into divs on the page, but first it strips out several parts of the the returned page. This is the "magic" script the previous programmer ran on all the returned html from his ajax calls: function CleanupResponseText(responseText, uniqueName) { responseText = responseText.replace("theForm.submit();", "SubmitSubForm(theForm, $(theForm).parent());"); responseText = responseText.replace(new RegExp("theForm", "g"), uniqueName); responseText = responseText.replace(new RegExp("doPostBack", "g"), "doPostBack" + uniqueName); return responseText; } He then intercepts any kind of form postback and runs his own form submission function: function SubmitSubForm(form, container) { //ShowLoading(container); $(form).ajaxSubmit( { url: $(form).attr("action"), success: function(responseText) { $(container).html(CleanupResponseText(responseText, form.id)); $("form", container).css("margin-top", "0").css("padding-top", "0"); //HideLoading(container); } } ); } Am I way offbase in thinking that this is less than optimal? I mean, how does a browser take out the html and head and other tags that don't have anything to do with what you are really trying to drop into that div? Also, he's returning things like asp:gridview controls, and the associate viewstate, which can be quite large if his dataset is big. Has anyone seen this before?

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• Combining XmlWriter objects?

  - by Kevin

  The way my application is structured, each component generates output as XML and returns an XmlWriter object. Before rendering the final output to the page, I combine all XML and perform an XSL transformation on that object. Below, is a simplified code sample of the application structure. Does it make sense to combine XmlWriter objects like this? Is there a better way to structure my application? The optimal solution would be one where I didn't have to pass a single XmlWriter instance as a parameter to each component. function page1Xml() { $content = new XmlWriter(); $content->openMemory(); $content->startElement('content'); $content->text('Sample content'); $content->endElement(); return $content; } function generateSiteMap() { $sitemap = new XmlWriter(); $sitemap->openMemory(); $sitemap->startElement('sitemap'); $sitemap->startElement('page'); $sitemap->writeAttribute('href', 'page1.php'); $sitemap->text('Page 1'); $sitemap->endElement(); $sitemap->endElement(); return $sitemap; } function output($content) { $doc = new XmlWriter(); $doc->openMemory(); $doc->writePi('xml-stylesheet', 'type="text/xsl" href="template.xsl"'); $doc->startElement('document'); $doc->writeRaw( generateSiteMap()->outputMemory() ); $doc->writeRaw( $content->outputMemory() ); $doc->endElement(); $doc->endDocument(); $output = xslTransform($doc); return $output; } $content = page1Xml(); echo output($content); Update: I may abandon XmlWriter altogether and use DomDocument instead. It is more flexible and it also seemed to perform better (at least on the crude tests I created).

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• How to query the SPView object

  - by Hugo Migneron

  I have a SPView object that contains a lot of SPListItem objects (there are many fields in the view). I am only interested in one of these fields. Let's call it specialField Given that view and specialField, I want to know if a value is contained in specialField. Here is a way of doing what I want to do : String specialField = "Special Field"; String specialValue = "value"; SPList list = SPContext.Current.Site.RootWeb.Lists["My List"]; SPView view = list.Views["My View"]; //This is the view I want to query SPQuery query = new SPQuery(); query.Query = view.Query; SPListItemCollection items = list.GetItems(query); foreach(SPListItem item in items) { var value = item[specialField]; if(value != null) && (value.ToString() == specialValue) { //My value is found. This is what I was looking for. //break out of the loop or return } } //My value is not found. However, iterating through each ListItem hardly seems optimal, especially as there might be hundreds of items. This query will be executed often, so I am looking for an efficient way to do this. EDIT I will not always be working with the same view, so my solution cannot be hardcoded (it has to be generic enough that the list, view and specialField can be changed.

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• In what order should the Python concepts be explained to absolute beginners?

  - by Tomaž Pisanski

  I am teaching Python to undergraduate math majors. I am interested in the optimal order in which students should be introduced to various Python concepts. In my view, at each stage the students should be able to solve a non-trivial programming problem using only the tools available at that time. Each new tool should enable a simpler solution to a familiar problem. A selection of numerous concepts available in Python is essential in order to keep students focused. They should also motivated and should appreciate each newly mastered tool without too much memorization. Here are some specific questions: For instance, my predecessor introduced lists before strings. I think the opposite is a better solution. Should function definitions be introduced at the very beginning or after mastering basic structured programming ideas, such as decisions (if) and loops (while)? Should sets be introduced before dictionaries? Is it better to introduce reading and writing files early in the course or should one use input and print for most of the course? Any suggestions with explanations are most welcome.

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• What is this: main:for(...){...} doing?

  - by David Murdoch

  I pulled up the NWmatcher source code for some light morning reading and noticed this odd bit of code I'd never seen in javascript before: main:for(/*irrelevant loop stuff*/){/*...*/} This snippet can be found in the compileGroup method on line 441 (nwmatcher-1.1.1) return new Function('c,s,d,h', 'var k,e,r,n,C,N,T,X=0,x=0;main:for(k=0,r=[];e=N=c[k];k++){' + SKIP_COMMENTS + source + '}return r;' ); Now I figured out what main: is doing on my own. If you have a loop within a loop and want to skip to the next iteration of the outer loop (without completing the inner OR the outer loop) you can execute continue main. Example: // This is obviously not the optimal way to find primes... function getPrimes(max) { var primes = [2], //seed sqrt = Math.sqrt, i = 3, j, s; outer: for (; i <= max; s = sqrt(i += 2)) { j = 3; while (j <= s) { if (i % j === 0) { // if we get here j += 2 and primes.push(i) are // not executed for the current iteration of i continue outer; } j += 2; } primes.push(i); } return primes; } What is this called? Are there any browsers that don't support it? Are there other uses for it other than continue?

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• Fast (de)serialization on iPhone

  - by Jacob Kuypers

  I'm developing a game/engine for iPhone OS. It's the first time I'm using Objective-C. I made my own binary format for geometry data and for textures I'm focusing on PVRTC. That should be the optimal approach as far as speed and space are concerned. I really want to keep loading time to a minimum and - if possible - be able to save very fast as well. So now I'm trying to make my "Entity" stuff persistent without sacrificing performance. First I wanted to use NSKeyedArchiver. From what I've heard, it's not very fast. Also, what I want to serialize is mostly structs made of floats with some ints and strings, so there isn't really a need for all that "object graph" overhead. NSArchiver would have been more appropriate, but they kicked that off the iphone for some reason. So now I'm thinking about making my own serialization scheme again. Am I wrong in thinking that NSKeyedArchiver is slow (I only read that, haven't tested it myself)? If so, what's the best way to encode/decode structs (with no pointers, mostly floats) without sacrificing speed?

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• Removing dotted border without setting NoFocus in Windows PyQt

  - by Cryptite

  There are a few questions on SO about this, all of which seem to say that the only way to remove the dotted border is to set the focusPolicy on widget/item in question to NoFocus. While this works as a temporary fix, this prevents further interaction with said widget/item in the realm of other necessary focusEvents. Said border in question: Here's an example of why this doesn't work. I have a Non-Modal widget popup, think a lightbox for an image. I want to detect a mousePressEvent outside of the widget and close the widget as a result. To do this, I should catch the focusOutEvent. However, if a vast majority of widgets in my program are set as NoFocus (to remove the border issue), then I cannot catch the focusOutEvent because, you guessed it, they have no focus policy. Here's another example: I have a QTreeWidget that is subclassed so I can catch keyPressEvents for various reasons. The QTreeWidget is also set as NoFocus to prevent the border. Because of this, however, the widget never has focus and therefore no keyPressEvents can be caught. A workaround for this (kludgy, imo) is to use the widget's grabKeyboard class, which is dangerous if I forget to releaseKeyboard later. This is not optimal. So then the question is, is there a way to remove this weird (mostly just ugly) dotted border without turning off focus for everything in my app? Thanks in advance!

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• Async task ASP.net HttpContext.Current.Items is empty - How do handle this?

  - by GuruC

  We are running a very large web application in asp.net MVC .NET 4.0. Recently we had an audit done and the performance team says that there were a lot of null reference exceptions. So I started investigating it from the dumps and event viewer. My understanding was as follows: We are using Asyn Tasks in our controllers. We rely on HttpContext.Current.Items hashtable to store a lot of Application level values. Task<Articles>.Factory.StartNew(() => { System.Web.HttpContext.Current = ControllerContext.HttpContext.ApplicationInstance.Context; var service = new ArticlesService(page); return service.GetArticles(); }).ContinueWith(t => SetResult(t, "articles")); So we are copying the context object onto the new thread that is spawned from Task factory. This context.Items is used again in the thread wherever necessary. Say for ex: public class SomeClass { internal static int StreamID { get { if (HttpContext.Current != null) { return (int)HttpContext.Current.Items["StreamID"]; } else { return DEFAULT_STREAM_ID; } } } This runs fine as long as number of parallel requests are optimal. My questions are as follows: 1. When the load is more and there are too many parallel requests, I notice that HttpContext.Current.Items is empty. I am not able to figure out a reason for this and this causes all the null reference exceptions. 2. How do we make sure it is not null ? Any workaround if present ? NOTE: I read through in StackOverflow and people have questions like HttpContext.Current is null - but in my case it is not null and its empty. I was reading one more article where the author says that sometimes request object is terminated and it may cause problems since dispose is already called on objects. I am doing a copy of Context object - its just a shallow copy and not a deep copy.

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• How to generate a monotone MART ROC in R?

  - by user1521587

  I am using R and applying MART (Alg. for multiple additive regression trees) on a training set to build prediction models. When I look at the ROC curve, it is not monotone. I would be grateful if someone can help me with how I should fix this. I am guessing the issue is that initially, MART generates n trees and if these trees are not the same for all the models I am building, the results will not be comparable. Here are the steps I take: 1) Fix the false-negative cost, c_fn. Let cost = c(0, 1, c_fn, 0). 2) use the following line to build the mart model: mart(x, y, lx, martmode='class', niter=2000, cost.mtx=cost) where x is the matrix of training set variables, y is the observation matrix, lx is the matrix which specifies which of the variables in x is numerical, which one categorical. 3) I predict the test set observations using the mart model found in step 2 using this line: y_pred = martpred(x_test, probs=T) 4) I compute the false-positive and false-negative errors as follows: t = 1/(1+c_fn) %threshold based on Bayes optimal rule where c_fp=1 and c_fn. p_0 = length(which(y_test==1))/dim(y_test)[1] p_01 = sum(1*(y_pred[,2]t & y_test==0))/dim(y_test)[1] p_11 = sum(1*(y_pred[,2]t & y_test==1))/dim(y_test)[1] p_fp = p_01/(1-p_0) p_tp = p_11/p_0 5) repeat step 1-4 for a new false-negative cost.

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• How to optimize shopping carts for minimal prices?

  - by tangens

  I have a list of items I want to buy. The items are offered by different shops and different prices. The shops have individual delivery costs. I'm looking for an optimal shopping strategy (and a java library supporting it) to purchase all of the items with a minimal total price. Example: Item1 is offered at Shop1 for $100, at Shop2 for $111. Item2 is offered at Shop1 for $90, at Shop2 for $85. Delivery cost of Shop1: $10 if total order < $150; $0 otherwise Delivery cost of Shop2: $5 if total order < $50; $0 otherwise If I buy Item1 and Item2 at Shop1 the total cost is $100 + $90 +$0 = $190. If I buy Item1 and Item2 at Shop2 the total cost is $111 + $85 +$0 = $196. If I buy Item1 at Shop1 and Item2 at Shop2 the total cost is $100 + $10 + $85 + $0 = 195. I get the minimal price if I order Item1 at Shop1 and Item2 at Shop2: $195 Question I need some hints which algorithms may help me to solve optimization problems of this kind for number of items about 100 and number of shops about 20. I already looked at apache-math and its optimization package, but I have no idea what algorithm to look for.

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• Need help extrapolating Java code

  - by Berlioz

  If anyone familiar with Rebecca Wirfs-Brock, she has a piece of Java code found in her book titled, Object Design: Roles, Responsibilities, and Collaborations. Here is the quote Applying Double Dispatch to a Specific Problem To implement the game Rock, Paper, Scissors we need to write code that determines whether one object “beats” another. The game has nine possible outcomes based on the three kinds of objects. The number of interactions is the cross product of the kinds of objects. Case or switch statements are often governed by the type of data that is being operated on. The object-oriented language equivalent is to base its actions on the class of some other object. In Java, it looks like this Here is the piece of Java code on page 16 ' import java.util.*; import java.lang.*; public class Rock { public static void main(String args[]) { } public static boolean beats(GameObject object) { if (object.getClass.getName().equals("Rock")) { result = false; } else if (object.getClass.getName().equals("Paper")) { result = false; } else if(object.getClass.getName().equals("Scissors")) { result = true; } return result; } }' ===This is not a very good solution. First, the receiver needs to know too much about the argument. Second, there is one of these nested conditional statements in each of the three classes. If new kinds of objects could be added to the game, each of the three classes would have to be modified. Can anyone share with me how to get this "less than optimal" piece of code to work in order to see it 'working'. She proceeds to demonstrate a better way, but I will spare you. Thanks

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