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• Subset generation by rules

  - by Sazug

  Let's say that we have a 5000 users in database. User row has sex column, place where he/she was born column and status (married or not married) column. How to generate a random subset (let's say 100 users) that would satisfy these conditions: 40% should be males and 60% - females 50% should be born in USA, 20% born in UK, 20% born in Canada, 10% in Australia 70% should be married and 30% not. These conditions are independent, that is we cannot do like this: (0.4 * 0.5 * 0.7) * 100 = 14 users that are males, born in USA and married (0.4 * 0.5 * 0.3) * 100 = 6 users that are males, born in USA and not married. Is there an algorithm to this generation?

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• Why does this give a segmentation fault?

  - by nightcracker

  I'm stunned, why does this code give me a segmentation fault? #include <stdio.h> #define LIMIT 1500000 typedef struct { int p; int a; int b; } triplet; int main(int argc, char **argv) { int i; triplet triplets[LIMIT]; for (i = 0; i < 5; i++) { triplets[i].p = 9; // remove this line and everything works fine } printf("%d\n", triplets[15].p); return 0; } EDIT: After changing LIMIT to 150 I no longer get a segmentation fault, it prints random numbers instead.

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• Design: How to declare a specialized memory handler class

  - by Michael Dorgan

  On an embedded type system, I have created a Small Object Allocator that piggy backs on top of a standard memory allocation system. This allocator is a Boost::simple_segregated_storage< class and it does exactly what I need - O(1) alloc/dealloc time on small objects at the cost of a touch of internal fragmentation. My question is how best to declare it. Right now, it's scope static declared in our mem code module, which is probably fine, but it feels a bit exposed there and is also now linked to that module forever. Normally, I declare it as a monostate or a singleton, but this uses the dynamic memory allocator (where this is located.) Furthermore, our dynamic memory allocator is being initialized and used before static object initialization occurs on our system (as again, the memory manager is pretty much the most fundamental component of an engine.) To get around this catch 22, I added an extra 'if the small memory allocator exists' to see if the small object allocator exists yet. That if that now must be run on every small object allocation. In the scheme of things, this is nearly negligable, but it still bothers me. So the question is, is there a better way to declare this portion of the memory manager that helps decouple it from the memory module and perhaps not costing that extra isinitialized() if statement? If this method uses dynamic memory, please explain how to get around lack of initialization of the small object portion of the manager.

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• is this a secure approach in ActiveRecords in Rails?

  - by Adnan

  Hello, I am using the following for my customers to unsubscribe from my mailing list; def index @user = User.find_by_salt(params[:subscribe_code]) if @user.nil? flash[:notice] = "the link is not valid...." render :action => 'index' else Notification.delete_all(:user_id => @user.id) flash[:notice] = "you have been unsubscribed....." redirect_to :controller => 'home' end end my link looks like; http://site.com/unsubscribe/32hj5h2j33j3h333 so the above compares the random string to a field in my user table and accordingly deletes data from the notification table. My question; is this approach secure? is there a better/more efficient way for doing this? All suggestions are welcome.

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• xpath help substring expression

  - by NA

  Hi i have a document from which i am trying to extract a date. But the problem is within the node along with the date their is some text too. Something like <div class="postHeader"> Posted on July 20, 2009 9:22 PM PDT </div> From this tag i just want the date item not the Posted on text. something like ./xhtml:div[@class = 'postHeader'] is getting everything. and to be precise, the document i have is basically a nodelist of this elements for eg i will get 10 nodes of these elements with different date values but to be worse the problem is sometime inside these tags some random other tags also pops us like anchors etc. Can i write a universal expath which will just get the date out of the div tag?

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• This PHP/Smarty doesn't work in IE

  - by Kyle Sevenoaks

  I'm starting to get sick of IE's random problems. Page link. (Add things to the cart with the kjøp button and handlevogn) I have this little tiny code here, {foreach $cart.taxes.$currency as $tax} <div id="subTotalCaption2"><p style="width:100px;">{$tax.name_lang}:</p></div> <div id="taxAmount2"><p>{$tax.formattedAmount}</p></div> {/foreach} That's meant to display the amount of total tax for each of the items in the basket. (MVA 25%) This works in every other browser but not IE. Why? Why not? Just why? Any help at all would be very much appreciated.

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• Bitwise operators versus .NET abstractions for bit manipulation in C# prespective

  - by Leron

  I'm trying to get basic skills in working with bits using C#.NET. I posted an example yesterday with a simple problem that needs bit manipulation which led me to the fact that there are two main approaches - using bitwise operators or using .NET abstractions such as BitArray (Please let me know if there are more build-in tools for working with bits other than BitArray in .NET and how to find more info for them if there are?). I understand that bitwise operators work faster but using BitArray is something much more easier for me, but one thing I really try to avoid is learning bad practices. Even though my personal preferences are for the .NET abstraction(s) I want to know which i actually better to learn and use in a real program. Thinking about it I'm tempted to think that .NET abstractions are not that bad at, after all there must be reason to be there and maybe being a beginner it's more natural to learn the abstraction and later on improve my skills with low level operations, but this is just random thoughts.

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• Can PHP Perform Magic Instantiation?

  - by Aiden Bell

  Despite PHP being a pretty poor language and ad-hoc set of libraries ... of which the mix of functions and objects, random argument orders and generally ill-thought out semantics mean constant WTF moments.... ... I will admit, it is quite fun to program in and is fairly ubiquitous. (waiting for Server-side JavaScript to flesh out though) question: Given a class class RandomName extends CommonAppBase {} is there any way to automatically create an instance of any class extending CommonAppBase without explicitly using new? As a rule there will only be one class definition per PHP file. And appending new RandomName() to the end of all files is something I would like to eliminate. The extending class has no constructor; only CommonAppBase's constructor is called. Strange question, but would be nice if anyone knows a solution. Thanks in advance, Aiden (btw, my PHP version is 5.3.2) Please state version restrictions with any answer.

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• Python - Using "Google AJAX Search" API's Local Search Objects

  - by user330739

  Hi! I've just started using Google's search API to find addresses and the distances between those addresses. I used geopy for this, but, I often had the problem of not getting the correct addresses for my queries. I decided to experiment, therefore, with Google's "Local Search" (http://code.google.com/apis/ajaxsearch/local.html). Anyway, I wanted to ask if I could use the "Local Search" objects provided by the API within python. Something tells me that I can't and that I have to use json. Does anyone know if there is a work around? PS: Im trying to make something like this: http://www.google.com/uds/samples/random/lead.html ... except a matrix type deal where the insides will be filled with distances between the addresses. Thanks for reading!

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• jquery - lose click() event after ajax call???

  - by niczoom

  At the following webpage liamharding.com/pgi.php I have an option panel on the left side of the page which opens and closes upon clicking the panels 'arrow', this works fine until you select a market (for testing use one of the 'Random Walk' markets and click 'Show/Refesh Graphs'), this then makes an ajax call using get_graph(forexName, myCount, divIsNew) function. Once this call is completed a graph(s) is displayed and then my options panels click() event does not work? The ajax call returns the data in a variable ajax_data, the problem happens when I perform the following code var jq_ajax_data = $("<div/>").html(ajax_data); . I need to wrap it in a so I can extract data from it using jQuery. If this line of code is commented out the click() event works fine ?? Hope somebody can help, I have spent a lot of time but cant find what the problem is.

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• SQL Server Express 2008 Stored Procedure execution time spikes periodically

  - by user156241

  I have a big stored procedure on a SQL Server 2008 Express SP2 database that gets run about every 200 ms. Normal execution time is about 50ms. What I am seeing is large inconsistencies in this run time. It will execute for while, say 50-100 times at 40-60ms which is expected, then seemingly at random the same stored procedure will take way longer, say 900ms or 1.5 seconds to run. Sometimes more than one call of the same procedure in a row will take longer too. It appears that something is causing sql server to slow down dramatically every minute or so, but I can't figure out what. There is no timing pattern between the occurences. I have the same setup on two different computers, one of which is a clean XP Pro load with no virus checking and nothing installed except SQL server. Also, The recovery options for all the databases are set to "Simple".

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• Intel MKL memory management and exceptions

  - by Andrew

  Hello everyone, I am trying out Intel MKL and it appears that they have their own memory management (C-style). They suggest using their MKL_malloc/MKL_free pairs for vectors and matrices and I do not know what is a good way to handle it. One of the reasons for that is that memory-alignment is recommended to be at least 16-byte and with these routines it is specified explicitly. I used to rely on auto_ptr and boost::smart_ptr a lot to forget about memory clean-ups. How can I write an exception-safe program with MKL memory management or should I just use regular auto_ptr's and not bother? Thanks in advance. EDIT http://software.intel.com/sites/products/documentation/hpc/mkl/win/index.htm this link may explain why I brought up the question UPDATE I used an idea from the answer below for allocator. This is what I have now: template <typename T, size_t TALIGN=16, size_t TBLOCK=4> class aligned_allocator : public std::allocator<T> { public: pointer allocate(size_type n, const void *hint) { pointer p = NULL; size_t count = sizeof(T) * n; size_t count_left = count % TBLOCK; if( count_left != 0 ) count += TBLOCK - count_left; if ( !hint ) p = reinterpret_cast<pointer>(MKL_malloc (count,TALIGN)); else p = reinterpret_cast<pointer>(MKL_realloc((void*)hint,count,TALIGN)); return p; } void deallocate(pointer p, size_type n){ MKL_free(p); } }; If anybody has any suggestions, feel free to make it better.

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• C++: Efficiently adding integers to strings

  - by Shinka

  I know how to add integers to strings, but I'm not sure I'm doing it in an efficient matters. I have a class where I often have to return a string plus an integer (a different integer each time), in Java I would do something like public class MyClass { final static String S = "MYSTRING"; private int id = 0; public String getString() { return S + (id++); } } But in C++ I have to do; class MyClass { private: std::string S; // For some reason I can't do const std::string S = "MYSTRING"; int id; public: MyClass() { S = "MYSTRING"; id = 0; } std::string getString() { std::ostringstream oss; oss << S << id++; return oss.str(); } } An additional constraint: I don't want (in fact, in can't) use Boost or any other librairies, I'll have to work with the standard library. So the thing is; the code works, but in C++ I have to create a bunch of ostringstream objects, so it seems inefficient. To be fair, perhaps Java do the same and I just don't notice it, I say it's inefficient mostly because I know very little about strings. Is there a more efficient way to do this ?

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• How can I improve the performance of LinqToSql queries that use EntitySet properties?

  - by DanM

  I'm using LinqToSql to query a small, simple SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of what makes LinqToSql so appealing. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance besides resorting to doing all the joins manually? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view. Update Here are the table definitions for the example I used in my question: create table Order ( Id int identity(1, 1) primary key, ProductName ntext null ) create table Customer ( Id int identity(1, 1) primary key, OrderId int null references Order (Id) )

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• Efficient synchronization of querying an array of resources

  - by Erel Segal Halevi

  There is a list of N resources, each of them can be queried by at most a single thread at a time. There are serveral threads that need to do the same thing at approximately the same time: query each of the resources (each thread has a different query), in arbitrary order, and collect the responses. If each thread loops over the resources in the same order, from 0 to N-1, then they will probably have to wait for each other, which is not efficient. I thought of letting the threads loop over the resources in a random permutation, but this seems too complex and also not so efficient, for example, for 2 resources and 2 threads, in half the cases they will choose the same order and wait for each other. Is there a simple and more efficient way to solve this?

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• What's the "Hello World!" of genetic algorithms good for?

  - by JohnIdol

  I found this very cool C++ sample , literally the "Hello World!" of genetic algorithms. I so decided to re-code the whole thing in C# and this is the result. Now I am asking myself: is there any practical application along the lines of generating a target string starting from a population of random strings? EDIT: my buddy on twitter just tweeted that "is useful for transcription type things such as translation. Does not have to be Monkey's". I wish I had a clue.

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• How to store static content across branches in a single location in version control

  - by Shravan

  [Just a random thought] I have a pdf doc that is downloaded when the user clicks on 'help' on my website. Now, this is a pretty huge document and is saved in version control (SVN) and is thus copied for all branches that exist in SVN. This is static content and something that developers are not working on, and does not change often. Is there a more efficient way to store it (that would not hamper local deployments) that would make SVN checkouts and updates relatively faster. I know the benefit we get is not huge, this is something that came to my head none the less.

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• Does this variable need to be declared volatile?

  - by titaniumdecoy

  Does the out variable in the MyThread class need to be declared volatile in this code or will the "volatility" of the stdout variable in the ThreadTest class carry over? import java.io.PrintStream; class MyThread implements Runnable { int id; PrintStream out; // should this be declared volatile? MyThread(int id, PrintStream out) { this.id = id; this.out = out; } public void run() { try { Thread.currentThread().sleep((int)(1000 * Math.random())); out.println("Thread " + id); } catch (InterruptedException e) { e.printStackTrace(); } } } public class ThreadTest { static volatile PrintStream stdout = System.out; public static void main(String[] args) { for (int i = 0; i < 10; i++) { new Thread(new MyThread(i, stdout)).start(); } } }

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• session timeout urgent help needed

  - by nandu

  hi! in my website when session gets timed out nd after that we click on any button or perform action it gives random error as input string not in correct format.. how do i resolve problem?? i've 500 pages in whole website...and 20 master pages...so can't check for session on each page... i wrote code in global.asax application_error method...tht if error occur and session is null than redirect to default page..it worked....but when page is in frame..it does not refresh the whole pahe..only frame redirects the page...so the panel of master page remains same..

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• Chrome starts to load image then show broken link icon

  - by Clare A Keith Ward

  Chrome (21.0.1180.79 m) On several random pages it has started to load an image and then suddenly the image disappears and there's only the broken image icon. If I right click the icon and choose to open the image in another window then the image opens, so it seems to me that it isn't a problem with the page? Here's one of the pages that it does it on; http://welshjournals.llgc.org.uk/browse/viewpage/llgc-id:1048090/llgc-id:1048951/llgc-id:1048969/get650 I'm running Kaspersky Internet Security 2012 Any help would be appreciated. Thanks Clare

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• Python: Count lines and differentiate between them

  - by Mister X

  I'm using an application that gives a timed output based on how many times something is done in a minute, and I wish to manually take the output (copy paste) and have my program, and I wish to count how many times each minute it is done. An example output is this: 13:48 An event happened. 13:48 Another event happened. 13:49 A new event happened. 13:49 A random event happened. 13:49 An event happened. So, the program would need to understand that 2 things happened at 13:48, and 3 at 13:49. I'm not sure how the information would be stored, but I need to average them after, to determine an average of how often it happens. Sorry for being so complicated!

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• Android RelativeLayout spacing

  - by fordays

  Hi, I'm just putting the finishing touches to my Android app. Unfortunately, I dug straight into development without reading the documentation and built my layout with AbsoluteLayout and it turned out to look terrible when I loaded the app on my phone. Now I'm redoing the UI in a RelativeLayout and I want to put empty canvas space in between my ViewGroups in the y-direction. I am currently achieving this by putting random TextView sentences that are of the same color as my View's background in order to make psuedo-empty space. Is there a better way to do this, because right now when I define a specific ViewGroup to be placed below another View, it gets stuck right below the top View. As I was writing this, it dawned upon me that using padding might be the answer.... Any other suggestions?

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• mkmapview cpu usage on iphone 3G

  - by mozveren

  Hello all, I have some troubles with iphone 3G and Mkmapview. After a certain random time, my application freeze. When I launch with performances tool, I can see that the application a lot of time to retrieve map tiles in cache. 19.6 7006 Foundation +[NSURLConnection(NSURLConnectionReallyInternal) 18.5 6613 GMM GMM::TileCachePrivate::runCacheThread() Its seems that the MkMapView component launch several threads to load the tiles in caches. How I can avoid this behavior ? The behavior seems to not make troubles on 3GS. Thanks

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• Unique serial number in a java web application.

  - by Zenzen

  I've been wondering what's the correct practice for generating unique ids? The thing is in my web app I'll have a plugin system, when a user registers a plugin I want to generate a unique serial ID for it. I've been thinking about storing all numbers in a DB or a file on the server, generating a random number and checking whether it already exists in the DB/file, but that doesn't seem that good. Are there other ways to do it? Would using the UUID be the preferred way to go?

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• GVim highlighting with matchadd eventually slows down?

  - by Kyle MacFarlane

  I have the following in ~/.vim/ftplugin/python.vim to highlight long lines, accidental tabs and extra whitespace in Python files: hi CustomPythonErrors ctermbg=red ctermfg=white guibg=#592929 au BufWinEnter *.py call matchadd('CustomPythonErrors', '\%>80v.\+', -1) au BufWinEnter *.py call matchadd('CustomPythonErrors', '/^\t\+/', -1) au BufWinEnter *.py call matchadd('CustomPythonErrors', '\s\+$', -1) au BufWinLeave *.py call clearmatches() The BufWinLeave is so that the matches are cleared when I switch to another file in case that file isn't a .py file. It's an essential feature for me when working with something like Django. It all works fine for random amounts of time; from ten minutes to hours (my guess is it depends on how many files I open/close). But eventually when any line over 80 characters is displayed GVim slows to a halt and requires a restart. Does anyone have any ideas why this would eventually slow down?

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