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  • Representing Sparse Data in PostgreSQL

    - by Chris S
    What's the best way to represent a sparse data matrix in PostgreSQL? The two obvious methods I see are: Store data in a single a table with a separate column for every conceivable feature (potentially millions), but with a default value of NULL for unused features. This is conceptually very simple, but I know that with most RDMS implementations, that this is typically very inefficient, since the NULL values ususually takes up some space. However, I read an article (can't find its link unfortunately) that claimed PG doesn't take up data for NULL values, making it better suited for storing sparse data. Create separate "row" and "column" tables, as well as an intermediate table to link them and store the value for the column at that row. I believe this is the more traditional RDMS solution, but there's more complexity and overhead associated with it. I also found PostgreDynamic, which claims to better support sparse data, but I don't want to switch my entire database server to a PG fork just for this feature. Are there any other solutions? Which one should I use?

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  • How to determine the data type of a CvMat

    - by Chris
    When using the CvMat type, the type of data is crucial to keeping your program running. For example, depending on whether your data is type float or unsigned char, you would choose one of these two commands: cvmGet(mat, row, col); cvGetReal2D(mat, row, col); Is there a universal approach to this? If the wrong data type matrix is passed to these calls, they crash at runtime. This is becoming an issue, since a function I have defined is getting passed several different types of matrices. How do you determine the data type of a matrix so you can always access its data? I tried using the "type()" function as such. CvMat* tmp_ptr = cvCreateMat(t_height,t_width,CV_8U); std::cout << "type = " << tmp_ptr->type() << std::endl; This does not compile, saying "term does not evaluate to a function taking 0 arguments". If I remove the brackets after the word type, I get a type of 1111638032 EDIT minimal application that reproduces this... int main( int argc, char** argv ) { CvMat *tmp2 = cvCreateMat(10,10, CV_32FC1); std::cout << "tmp2 type = " << tmp2->type << " and CV_32FC1 = " << CV_32FC1 << " and " << (tmp2->type == CV_32FC1) << std::endl; } Output: tmp2 type = 1111638021 and CV_32FC1 = 5 and 0

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  • Get remote image using cURL then resample.

    - by Chris
    I want to be able to retrieve a remote image from a webserver, resample it, and then serve it up to the browser AND save it to a file. Here is what I have so far: $ch = curl_init(); // set URL and other appropriate options curl_setopt($ch, CURLOPT_URL, "$rURL"); curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); curl_setopt($ch, CURLOPT_HEADER, 0); // grab URL and pass it to the browser $out = curl_exec($ch); // close cURL resource, and free up system resources curl_close($ch); $imgRes = imagecreatefromstring($out); imagejpeg($imgRes, $filename, 70); header("Content-Type: image/jpg"); header("Content-length: ".filesize($filename)); header("Content-Transfer-Encoding: binary"); header("Content-Length: ".filesize($filename)); readfile("$filename"); exit(); Update Updated code to include imjpeg step to save the image as lower quality. But how do I then, efficiently, serve this up to the browser. I currently, later in the code, do this readfile("$filename"); along with some header information but that means I'm reading the file back in again which seems inefficient.

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  • qtableview (libqt) how do I correctly create a QModelIndex

    - by Chris Camacho
    I'm trying to enter edit mode on a specific cell like this void MainWindow::on_addButton_released(void) { tm->addRow(); tableView->scrollToBottom(); int ec=tm->firstWritableColumn(); int r=tm->rowCount(QModelIndex()); QModelIndex id = tm->index(r, ec, QModelIndex()); tableView->setCurrentIndex(id); tableView->edit(id); qDebug() << "row:" << r << " col:" << ec << "index:" << id; } my model creates an index like this QModelIndex TableModel::index(int row,int column,QModelIndex parent) const { Q_UNUSED(parent); return createIndex(row,column,0); } the debug output looks like this row: 9 col: 1 index: QModelIndex(9,1,0x0,TableModel(0xbf3f50) ) I'm fairly sure that the index is somehow invalid as setCurrentIndex doesn't seem to be working

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  • How to delete a user in MSCRM 4.0

    - by Chris Richner
    Do you know of a way to get rid of CRM User accounts in MSCRM 4.0? After some user accounts have been deleted in AD we're faced a lot of issues while importing the organisation to another server stating that there are issues with the user mapping. What kind of idea is behind the fact that no user accounts can be deleted from the crm installation? Is there any tool or undocumented Webservice API call to get rid of crm users? Thanks for sharing yours insights

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  • How much of the "Objective-C" I'm learning is universal Objective-C, and not Apple's frameworks?

    - by Chris Cooper
    This question is related to one of my others about C: What can you do in C without “std” includes? Are they part of “C,” or just libraries? I've become curious lately as to what is really contained the the core Objective-C language, and what parts of the Objective-C I've done for iPhone/OS X development is specific to Apple platforms. I know that things like syntax are the same, but for instance, is NSObject and its torrent of NS-subclasses actually part of "standard" Objective-C? Could I use them in, say, Windows? What parts are universal for the most part, and what parts would I only find on an Apple platform? If you want, giving an example of Objective-C used elsewhere as an example of what is more "universal" would help me as well. Thanks! =)

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  • Java Future and infinite computation

    - by Chris
    I'm trying to optimize an (infinite) computation algorithm. I have an infinte Sum to calculate ( Summ_{n- infinity} (....) ) My idea was to create several threads using the Future < construct, then combine the intermediate results together. My problem hoewer is that I need a certain precision. So I need to constantly calculate the current result while other threads keep calculating. My question is: Is there some sort of result queue where each finished thread can put its results in, while a main thread can receive those results and then either lets the computation continues or terminate the whole ExecutorService? Any Help would really be appreciated! Thanks!

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  • StructureMap resolve dependency through injection instead of service location

    - by Chris Marisic
    In my project I register many ISerializers implementations with the assembly scanner. FWIW this is the code that registers my ISerializers Scan(scanner => { scanner.AssemblyContainingType<ISerializer>(); scanner.AddAllTypesOf<ISerializer>().NameBy(type => type.Name); scanner.WithDefaultConventions(); }); Which then correctly registers ISerializer (...ISerializer) Scoped as: Transient JsonSerializer Configured Instance of ...JsonSerializer BsonSerializer Configured Instance of ...BsonSerializer And so forth. Currently the only way I've been able to figure out how to resolve the serializer I want is to hardcode a service location call with jsonSerializer = ObjectFactory.GetNamedInstance<ISerializer>("JsonSerializer"); Now I know in my class that I specifically want the jsonSerializer so is there a way to configure a rule or similar that says for ISerializer's to connect the named instance based on the property name? So that I could have MySomeClass(ISerializer jsonSerializer, ....) And StructureMap correctly resolve this scenario? Or am I approaching this wrong and perhaps I should just register the concrete type that implements ISerializer and then just specifically use MySomeClass(JsonSerializer jsonSerializer, ....) for something along these lines with the concrete class?

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  • IE8 Debugger: how to load external javascript files?

    - by Chris Barnhill
    I have downloaded and installed IE8. I was playing around with the debugger, but I could not figure out how to load external javascript files. It displays the javascript from the main page, but I need to debug the script in the external files. I have googled various articles that show a screenshot of an IE8 debugger with a drop-down for selecting which script to debug, but my debugger does not feature this. Can anyone help me with this? Thanks.

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  • Lazy Loading wpf Combobox items

    - by Chris McGrath
    I have an IEnumerable< which lazy loads it's data. I want to just set a Combobox's ItemsSource to the IEnumerable, but when I do it goes and loads all the data anyway (which removes the point of lazy loading). I've tried it with Linq-To-Sql as well since it seems to be a similar theory and it also loads all the data. Is there an easy way to do this?

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  • Silverlight solution builds in VS2008 but fails with MSBuild

    - by Chris Nicola
    I have a Silverlight solution that I want to create a build script for. I have a simple script that looks like this call "c:\Program Files\Microsoft Visual Studio 9.0\VC\bin\vcvars32.bat" msbuild %CD%\V1\Incentive.sln /target:Rebuild /property:Configuration=DEBUG;WarningLevel=2 msbuild %CD%\UI\IncentiveUI.sln /target:Rebuild /property:Configuration=DEBUG;WarningLevel=2 pause However when I run this I get a failure, with some complaints about classes that are in a project with linked files: http://pastebin.com/JRE3tWfh This solution compiles fine in VS2008 so I can't figure out what the problem is. I have to guess something is wrong with the way I am using msbuild here.

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  • Shortest-path algorithms which use a space-time tradeoff?

    - by Chris Mounce
    I need to find shortest paths in an unweighted, undirected graph. There are algorithms which can find a shortest path between two nodes, but this can take time. There are also algorithms for computing shortest paths for all pairs of nodes in the graph, but storing such a lookup table would take lots of disk space. What I'm wondering: Is there an algorithm which offers a space-time tradeoff that's somewhere between these two extremes? In other words, is there a way to speed up a shortest-path search, while using less disk space than would be occupied by an all-pairs shortest-path table? I know there are ways to efficiently store lookup tables for this problem, and I already have a couple of ideas for speeding up shortest-path searches using precomputed data. But I don't want to reinvent the wheel if there's already some established algorithm that solves this problem.

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  • Why do multiline cells in my CSV file appear with a question mark at the end of each line in Excel?

    - by Chris Lindsay
    I'm currently working on a project where we'd like to allow a user to export their data to CSV. Some of the data we present has multiple values for a single cell, and so we use the standard CSV method of putting each value on its own line: Column A, Column B, Column C Value A, "Value B1 Value B2", Value C Most of the time this works fine, but some people are reporting seeing a small question mark in a box character appear at the end of each line when they load the file in Excel. Why is this happening?

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  • CryptographicException: Padding is invalid and cannot be removed and Validation of viewstate MAC fai

    - by Chris Marisic
    Monitoring my global exception logs this error seems to be impossible to remove no matter what I do, I thought I finally got rid of it but it's back again. You can see a strack trace of the error on a similar post here. Notes about the environment: IIS 6.0, .NET 3.5 SP1 single server ASP.NET application Steps already taken: <system.web> <machineKey validationKey="big encryption key" decryptionKey="big decryption key" validation="SHA1" decryption="AES" /> In my Page Base for all of my pages protected override void OnInit(EventArgs e) { const string viewStateKey = "big key value"; Page.ViewStateUserKey = viewStateKey; } Also in the source of the page I can see that all of the ASP.NET generated hidden fields are correctly at the top of the page.

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  • Javafx - Clipview to a Group?

    - by Chris-NTA
    Can I apply clipview to a vertical expanding Group? Time to time I'm appending text to a group and want to use scrollbar to navigate in that group. The scrollbar part is working when I assign it to the group itself but want to limit the size of the group by using clipview. Anyone having experience in this?

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  • Resolving Circular References for Objects Implementing ISerializable

    - by Chris
    I'm writing my own IFormatter implementation and I cannot think of a way to resolve circular references between two types that both implement ISerializable. Here's the usual pattern: [Serializable] class Foo : ISerializable { private Bar m_bar; public Foo(Bar bar) { m_bar = bar; m_bar.Foo = this; } public Bar Bar { get { return m_bar; } } protected Foo(SerializationInfo info, StreamingContext context) { m_bar = (Bar)info.GetValue("1", typeof(Bar)); } public void GetObjectData(SerializationInfo info, StreamingContext context) { info.AddValue("1", m_bar); } } [Serializable] class Bar : ISerializable { private Foo m_foo; public Foo Foo { get { return m_foo; } set { m_foo = value; } } public Bar() { } protected Bar(SerializationInfo info, StreamingContext context) { m_foo = (Foo)info.GetValue("1", typeof(Foo)); } public void GetObjectData(SerializationInfo info, StreamingContext context) { info.AddValue("1", m_foo); } } I then do this: Bar b = new Bar(); Foo f = new Foo(b); bool equal = ReferenceEquals(b, b.Foo.Bar); // true // Serialise and deserialise b equal = ReferenceEquals(b, b.Foo.Bar); If I use an out-of-the-box BinaryFormatter to serialise and deserialise b, the above test for reference-equality returns true as one would expect. But I cannot conceive of a way to achieve this in my custom IFormatter. In a non-ISerializable situation I can simply revisit "pending" object fields using reflection once the target references have been resolved. But for objects implementing ISerializable it is not possible to inject new data using SerializationInfo. Can anyone point me in the right direction?

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  • Wordpress sidebar classes

    - by Chris J. Lee
    There any way i could add a class for the specific order of widget item? i.e. the class name would be widgetorder-1 (for the first appearing widget), widgetorder-2 (for the widget appearing in the 2nd order), etc. I looked into filters but wasn't sure how that worked.

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  • strange redefined symbols

    - by Chris H
    I included this header into one of my own: http://codepad.org/lgJ6KM6b When I compiled I started getting errors like this: CMakeFiles/bin.dir/SoundProjection.cc.o: In function `Gnuplot::reset_plot()': /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include/g++-v4/new:105: multiple definition of `Gnuplot::reset_plot()' CMakeFiles/bin.dir/main.cc.o:project/gnuplot-cpp/gnuplot_i.hpp:962: first defined here CMakeFiles/bin.dir/SoundProjection.cc.o: In function `Gnuplot::set_smooth(std::basic_string, std::allocator const&)': project/gnuplot-cpp/gnuplot_i.hpp:1041: multiple definition of `Gnuplot::set_smooth(std::basic_string, std::allocator const&)' CMakeFiles/bin.dir/main.cc.o:project/gnuplot-cpp/gnuplot_i.hpp:1041: first defined here CMakeFiles/bin.dir/SoundProjection.cc.o:/usr/include/eigen2/Eigen/src/Core/arch/SSE/PacketMath.h:41: multiple definition of `Gnuplot::m_sGNUPlotFileName' I know it's hard to see in this mess, but look at where the redefinitions are taking place. They take place in files like /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include/g++-v4/new:105. How is the new operator getting information about a gnuplot header? I can't even edit that file. How could that ever even be possible? I'm not even sure how to start debugging this. I hope I've provided enough information. I wasn't able to reproduce this in a small project. I mostly just looking for tips on how to find out why this is happening, and how to track it down. Thanks.

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  • Cakephp: Correct way to resolve hasMany - hasMany relation

    - by Chris
    I have three models: Company, Car, Passenger Company hasMany Cars Car hasMany Passenger These relations seem to work independetly: Car shows all Passengers and Company shows all Cars. But I cannot resolve the Company - Passenger (Show all Passengers of a Company). My controller for Company: function index(){ //grab all companies and pass it to the view: $companies = $this->Company->find('all'); $this->set('companies', $companies); } This displays all companies with all their respective cars. However the array does not contain an entry for passenger. What do I have to do to completely resovle the Company - Car - Passenger relation?

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  • Inserting Multiple Records in SQL2000

    - by Chris M
    I have a web app that currently is inserting x (between 1 + 40) records into a table that contains about 5 fields, via a linq-2-sql-stored procedure in a loop. Would it be better to manually write the SQL Inserts to say a string builder and run them against the database when the loops completed rather than 30 transactions? or should I just accept this is negligible for such a small number of inserts.

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  • C String literals: Where do they go?

    - by Chris Cooper
    I have read a lot of posts about "string literals" on SO, most of which have been about best-practices, or where the literal is NOT located in memory. I am interested in where the string DOES get allocated/stored, etc. I did find one intriguing answer here, saying: Defining a string inline actually embeds the data in the program itself and cannot be changed (some compilers allow this by a smart trick, don't bother). but, it had to do with C++, not to mention that it says not to bother. I am bothering. =D So my question is, again, where and how is my string literal kept? Why should I not try to alter it? Does the implementation vary by platform? Does anyone care to elaborate on the "smart trick?" Thanks for any explanations.

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