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  • Use format strings that contain %1, %2 etc. instead of %d, %s etc. - Linux, C++

    - by rursw1
    Hello, As a follow-up of this question (Message compiler replacement in Linux gcc), I have the following problem: When using MC.exe on Windows for compiling and generating messages, within the C++ code I call FormatMessage, which retrieves the message and uses the va_list *Arguments parameter to send the varied message arguments. For example: messages.mc file: MessageId=1 Severity=Error SymbolicName=MULTIPLE_MESSAGE_OCCURED Language=English message %1 occured %2 times. . C++ code: void GetMsg(unsigned int errCode, wstring& message,unsigned int paramNumber, ...) { HLOCAL msg; DWORD ret; LANGID lang = GetUserDefaultLangID(); try { va_list argList; va_start( argList, paramNumber ); const TCHAR* dll = L"MyDll.dll"; _hModule = GetModuleHandle(dll); ret =::FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_HMODULE|FORMAT_MESSAGE_IGNORE_INSERTS, _hModule, errCode, lang, (LPTSTR) &msg, 0, &argList ); if ( 0 != ret ) { unsigned int count = 0 ; message = msg; if (paramNumber>0) { wstring::const_iterator iter; for (iter = message.begin();iter!=message.end();iter++) { wchar_t xx = *iter; if (xx ==L'%') count++; } } if ((count == paramNumber) && (count >0)) { ::LocalFree( msg ); ret =::FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_HMODULE, _hModule, errCode, GetUserDefaultLangID(), (LPTSTR) &msg, 0, &argList ); } else if (count != paramNumber) { wstringstream tmp; wstring messNumber; tmp << (errCode & 0xFFFF); tmp >> messNumber; message = message +L"("+ messNumber + L"). Bad Format String. "; } } ::LocalFree( msg ); } catch (...) { message << L"last error: " << GetLastError(); } va_end( argList ); } Caller code: wstring message; GetMsg(MULTIPLE_MESSAGE_OCCURED, message,2, "Error message", 5); Now, I wrote a simple script to generate a .msg file from the .mc file, and then I use gencat to generate a catalog from it. But is there a way to use the formatted strings as they contain %1, %2, etc. and NOT the general (%d, %s...) format? Please note, that the solution has to be generic enough for each possible message with each posible types\ arguments order... Is it possible at all? Thank you.

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  • Refactoring Singleton Overuse

    - by drharris
    Today I had an epiphany, and it was that I was doing everything wrong. Some history: I inherited a C# application, which was really just a collection of static methods, a completely procedural mess of C# code. I refactored this the best I knew at the time, bringing in lots of post-college OOP knowledge. To make a long story short, many of the entities in code have turned out to be Singletons. Today I realized I needed 3 new classes, which would each follow the same Singleton pattern to match the rest of the software. If I keep tumbling down this slippery slope, eventually every class in my application will be Singleton, which will really be no logically different from the original group of static methods. I need help on rethinking this. I know about Dependency Injection, and that would generally be the strategy to use in breaking the Singleton curse. However, I have a few specific questions related to this refactoring, and all about best practices for doing so. How acceptable is the use of static variables to encapsulate configuration information? I have a brain block on using static, and I think it is due to an early OO class in college where the professor said static was bad. But, should I have to reconfigure the class every time I access it? When accessing hardware, is it ok to leave a static pointer to the addresses and variables needed, or should I continually perform Open() and Close() operations? Right now I have a single method acting as the controller. Specifically, I continually poll several external instruments (via hardware drivers) for data. Should this type of controller be the way to go, or should I spawn separate threads for each instrument at the program's startup? If the latter, how do I make this object oriented? Should I create classes called InstrumentAListener and InstrumentBListener? Or is there some standard way to approach this? Is there a better way to do global configuration? Right now I simply have Configuration.Instance.Foo sprinkled liberally throughout the code. Almost every class uses it, so perhaps keeping it as a Singleton makes sense. Any thoughts? A lot of my classes are things like SerialPortWriter or DataFileWriter, which must sit around waiting for this data to stream in. Since they are active the entire time, how should I arrange these in order to listen for the events generated when data comes in? Any other resources, books, or comments about how to get away from Singletons and other pattern overuse would be helpful.

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  • How do we simplify this kind of code in Java? Something like macros in C?

    - by Terry Li
    public static boolean diagonals(char[][] b, int row, int col, int l) { int counter = 1; // because we start from the current position char charAtPosition = b[row][col]; int numRows = b.length; int numCols = b[0].length; int topleft = 0; int topright = 0; int bottomleft = 0; int bottomright = 0; for (int i=row-1,j=col-1;i>=0 && j>=0;i--,j--) { if (b[i][j]==charAtPosition) { topleft++; } else { break; } } for (int i=row-1,j=col+1;i>=0 && j<=numCols;i--,j++) { if (b[i][j]==charAtPosition) { topright++; } else { break; } } for (int i=row+1,j=col-1;i<=numRows && j>=0;i++,j--) { if (b[i][j]==charAtPosition) { bottomleft++; } else { break; } } for (int i=row+1,j=col+1;i<=numRows && j<=numCols;i++,j++) { if (b[i][j]==charAtPosition) { bottomright++; } else { break; } } return topleft + bottomright + 1 >= l || topright + bottomleft + 1 >= l; //in this case l is 5 } After I was done posting the code above here, I couldn't help but wanted to simplify the code by merging the four pretty much the same loops into one method. Here's the kind of method I want to have: public int countSteps(char horizontal, char vertical) { } Two parameters horizontal and vertical can be either + or - to indicate the four directions to walk in. What I want to see if possible at all is i++; is generalized to i horizontal horizontal; when horizontal taking the value of +. What I don't want to see is if or switch statements, for example: public int countSteps(char horizontal, char vertical) { if (horizontal == '+' && vertical == '-') { for (int i=row-1,j=col+1;i>=0 && j<=numCols;i--,j++) { if (b[i][j]==charAtPosition) { topright++; } else { break; } } } else if (horizontal == '+' && vertical == '+') { for (int i=row+1,j=col+1;i>=0 && j<=numCols;i++,j++) { if (b[i][j]==charAtPosition) { topright++; } else { break; } } } else if () { } else { } } Since it is as tedious as the original one. Note also that the comparing signs for the loop condition i>=0 && j<=numCols; for example, >= && <= have correspondence with the value combination of horizontal and vertical. Sorry for my bad wording, please let me know if anything is not clear.

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  • Optimize slow ranking query

    - by Juan Pablo Califano
    I need to optimize a query for a ranking that is taking forever (the query itself works, but I know it's awful and I've just tried it with a good number of records and it gives a timeout). I'll briefly explain the model. I have 3 tables: player, team and player_team. I have players, that can belong to a team. Obvious as it sounds, players are stored in the player table and teams in team. In my app, each player can switch teams at any time, and a log has to be mantained. However, a player is considered to belong to only one team at a given time. The current team of a player is the last one he's joined. The structure of player and team is not relevant, I think. I have an id column PK in each. In player_team I have: id (PK) player_id (FK -> player.id) team_id (FK -> team.id) Now, each team is assigned a point for each player that has joined. So, now, I want to get a ranking of the first N teams with the biggest number of players. My first idea was to get first the current players from player_team (that is one record top for each player; this record must be the player's current team). I failed to find a simple way to do it (tried GROUP BY player_team.player_id HAVING player_team.id = MAX(player_team.id), but that didn't cut it. I tried a number of querys that didn't work, but managed to get this working. SELECT COUNT(*) AS total, pt.team_id, p.facebook_uid AS owner_uid, t.color FROM player_team pt JOIN player p ON (p.id = pt.player_id) JOIN team t ON (t.id = pt.team_id) WHERE pt.id IN ( SELECT max(J.id) FROM player_team J GROUP BY J.player_id ) GROUP BY pt.team_id ORDER BY total DESC LIMIT 50 As I said, it works but looks very bad and performs worse, so I'm sure there must be a better way to go. Anyone has any ideas for optimizing this? I'm using mysql, by the way. Thanks in advance Adding the explain. (Sorry, not sure how to format it properly) id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t ALL PRIMARY NULL NULL NULL 5000 Using temporary; Using filesort 1 PRIMARY pt ref FKplayer_pt77082,FKplayer_pt265938,new_index FKplayer_pt77082 4 t.id 30 Using where 1 PRIMARY p eq_ref PRIMARY PRIMARY 4 pt.player_id 1 2 DEPENDENT SUBQUERY J index NULL new_index 8 NULL 150000 Using index

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  • Do you use an exception class in your Perl programs? Why or why not?

    - by daotoad
    I've got a bunch of questions about how people use exceptions in Perl. I've included some background notes on exceptions, skip this if you want, but please take a moment to read the questions and respond to them. Thanks. Background on Perl Exceptions Perl has a very basic built-in exception system that provides a spring-board for more sophisticated usage. For example die "I ate a bug.\n"; throws an exception with a string assigned to $@. You can also throw an object, instead of a string: die BadBug->new('I ate a bug.'); You can even install a signal handler to catch the SIGDIE psuedo-signal. Here's a handler that rethrows exceptions as objects if they aren't already. $SIG{__DIE__} = sub { my $e = shift; $e = ExceptionObject->new( $e ) unless blessed $e; die $e; } This pattern is used in a number of CPAN modules. but perlvar says: Due to an implementation glitch, the $SIG{DIE} hook is called even inside an eval(). Do not use this to rewrite a pending exception in $@ , or as a bizarre substitute for overriding CORE::GLOBAL::die() . This strange action at a distance may be fixed in a future release so that $SIG{DIE} is only called if your program is about to exit, as was the original intent. Any other use is deprecated. So now I wonder if objectifying exceptions in sigdie is evil. The Questions Do you use exception objects? If so, which one and why? If not, why not? If you don't use exception objects, what would entice you to use them? If you do use exception objects, what do you hate about them, and what could be better? Is objectifying exceptions in the DIE handler a bad idea? Where should I objectify my exceptions? In my eval{} wrapper? In a sigdie handler? Are there any papers, articles or other resources on exceptions in general and in Perl that you find useful or enlightening.

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  • Incorrect string encodings

    - by James
    Note: I have read all of the related PHP, UTF-8, character encoding articles that are usually suggested, but my question relates to data inserted before I applied such techniques. I am wishing to retrospectively fix all character encoding problems. Now all connections are set as utf8 using PDO. PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8' Unfortunately, a large amount of data was inserted that is of questionable encoding before I had implemented correct character encoding practices. As displayed by: $sql = "SELECT name FROM data LIMIT 3"; foreach ($pdo->query($sql) as $row) { $name = $row['name']; echo $name . "\n"; echo utf8_encode($name) . "\n"; echo utf8_decode($name) . "\n"; echo htmlspecialchars($name, ENT_QUOTES, 'UTF-8') . "\n"; echo htmlspecialchars(utf8_encode($name), ENT_QUOTES, 'UTF-8') . "\n"; echo htmlspecialchars(utf8_decode($name), ENT_QUOTES, 'UTF-8') . "\n"; echo '<hr/>'; } Which produces: Antonín Dvořák AntonÃÆín DvoÃâ¦Ãâ¢ÃÆák Anton??­n Dvo??????¡k Antonín Dvořák AntonÃÆín DvoÃâ¦Ãâ¢ÃÆák ---------- Ô±Ö€Õ¡Õ´ Ô½Õ¡Õ¹Õ¡Õ¿Ö€ÕµÕ¡Õ¶ ñÃâ¬Ã¡Ã´ ýáùáÿÃâ¬ÃµÃ¡Ã¶ ????? ?????????? Ô±Ö€Õ¡Õ´ Ô½Õ¡Õ¹Õ¡Õ¿Ö€ÕµÕ¡Õ¶ ñÃâ¬Ã¡Ã´ ýáùáÿÃâ¬ÃµÃ¡Ã¶ ---------- Tiësto Tiësto Tiësto Tiësto Tiësto Tiësto ---------- When removing 'SET NAMES utf8' with PDO it produces the data: Antonín DvoÅák Antonín DvoÃÂák Antonín Dvorák Antonín DvoÅák Antonín DvoÃÂák Antonín Dvorák ---------- ???? ????????? Ô±ÖÕ¡Õ´ Ô½Õ¡Õ¹Õ¡Õ¿ÖÕµÕ¡Õ¶ ???? ????????? ???? ????????? Ô±ÖÕ¡Õ´ Ô½Õ¡Õ¹Õ¡Õ¿ÖÕµÕ¡Õ¶ ???? ????????? ---------- Tiësto Tiësto Ti?sto Tiësto Tiësto ---------- And here is a dump of the database rows concerned: DROP TABLE IF EXISTS `data`; CREATE TABLE IF NOT EXISTS `data` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(80) NOT NULL, PRIMARY KEY (`id`), KEY `name` (`name`(10)), ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=0; INSERT INTO `data` (`id`, `name`) VALUES (0, 'Antonín Dvořák'), (1, 'Ô±Ö€Õ¡Õ´ Ô½Õ¡Õ¹Õ¡Õ¿Ö€ÕµÕ¡Õ¶'), (2, 'Tiësto'); The 3rd and 6th lines of the 3rd row "Tiësto" are then correctly echoed. I'm just unsure what is the best way to correct encodings/detect the encodings of bad strings and correct, etc.

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  • MVC EditorFor bind to type in array

    - by BradBrening
    I have a ViewModel that, among other properties, contains an array of 'EmailAddress' objects. EmailAddress itself has properties such as "Address", and "IsPrimary". My view model breakdown is: public class UserDetailsViewModel { public BUser User { get; set; } public string[] Roles { get; set; } public EmailAddress[] EmailAddresses { get; set; } } I am showing a "User Details" page that is pretty standard. For example, I'm displaying data using @Html.DisplayFor(model => model.User.UserName) and @Html.DisplayFor(model => model.User.Comment) I also have a section on the page that lists all of the EmailAddress objects associated with the user: @if(Model.EmailAddresses.Length > 0) { foreach (var address in Model.EmailAddresses) { <div> @Html.DisplayFor(model => address.Address) </div> } } else { <div class="center">User does not have any email addresses.</div> } My problem is that I would like to show an "Add Email Address" form above the list of email addresses. I thought I would take the "normal" approach thusly: @using(Html.BeginForm(new { id=Model.User.UserName, action="AddUserEmailAddress" })) { <text>Address:</text> @Html.EditorFor(model => ** HERE I AM STUCK **) <input type="submit" value="Add Email" class="button" /> } As you may be able to tell, I am stuck here. I've tried model => Model.EmailAddresses[0] and model => Model.EmailAddresses.FirstOrDefault(). Both of these have failed horribly. I am sure that I am going about this all wrong. I've even thought of adding a "dummy" property to my ViewModel of type EmailAddress just so that I can bind to that in my EditorFor - but that seems to be a really bad hack. There has to be something simple that I'm overlooking! I would appreciate any help anyone can offer with this matter. Thank you in advance!

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  • Understanding C++ dynamic allocation

    - by kiokko89
    Consider the following code: class CString { private: char* buff; size_t len; public: CString(const char* p):len(0), buff(nullptr) { cout << "Constructor called!"<<endl; if (p!=nullptr) { len= strlen(p); if (len>0) { buff= new char[len+1]; strcpy_s(buff, len+1, p); } } } CString (const CString& s) { cout << "Copy constructor called!"<<endl; len= s.len; buff= new char[len+1]; strcpy_s(buff, len+1, s.buff); } CString& operator = (const CString& rhs) { cout << "Assignment operator called!"<<endl; if (this != &rhs) { len= rhs.len; delete[] buff; buff= new char[len+1]; strcpy_s(buff, len+1, rhs.buff); } return *this; } CString operator + (const CString& rhs) const { cout << "Addition operator called!"<<endl; size_t lenght= len+rhs.len+1; char* tmp = new char[lenght]; strcpy_s(tmp, lenght, buff); strcat_s(tmp, lenght, rhs.buff); return CString(tmp); } ~CString() { cout << "Destructor called!"<<endl; delete[] buff; } }; int main() { CString s1("Hello"); CString s2("World"); CString s3 = s1+s2; } My problem is that I don't know how to delete the memory allocated in the addition operator function(char* tmp = new char[length]). I couldn't do this in the constructor(I tried delete[] p) because it is also called from the main function with arrays of chars as parameters which are not allocated on the heap...How can I get around this? (Sorry for my bad English...)

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  • Symfony2 Forms: is it possible to bind a form in an "unconventional way"?

    - by DonCallisto
    Imagine this scenario: in our company there is an employee that "play" around graphic,css,html and so on. Our new project will born under symfony2 so we're trying some silly - but "real" - stuff (like authentication from db, submit data from a form and persist it to db and so on..) The problem As far i know, learnt from symfony2 "book" that i found on the site (you can find it here), there is an "automated" way for creating and rendering forms: 1) Build the form up into a controller in this way $form = $this->createFormBuilder($task) ->add('task','text'), ->add('dueDate','date'), ->getForm(); return $this->render('pathToBundle:Controller:templateTwig', array('form'=>$form->createview()); 2) Into templateTwig render the template {{ form_widget(form) }} // or single rows method 3) Into a controller (the same that have a route where you can submit data), take back submitted information if($rquest->getMethod()=='POST'){ $form->bindRequest($request); /* and so on */ } Return to scenario Our graphic employee don't want to access controllers, write php and other stuff like those. So he'll write a twig template with a "unconventional" (from symfony2 point of view, but conventional from HTML point of view) method: /* into twig template */ <form action="{{ path('SestanteUserBundle_homepage') }}" method="post" name="userForm"> <div> USERNAME: <input type="text" name="user_name" value="{{ user.username}}"/> </div> <div> EMAIL: <input type="text" name="user_mail" value="{{ user.email }}"/> </div> <input type="hidden" name="user_id" value="{{ id }}" /> <input type="submit" value="modifica i dati"> </form> Now, if into the controller that handle the submission of data we do something like that public function indexAction(Request $request) { if($request->getMethod() == 'POST'){ // sono arrivato per via di un submit, quindi devo modificare i dati prima di farli vedere a video $defaultData = array('message'=>'ho visto questa cosa in esempio, ma non capisco se posso farne a meno'); $form = $this->createFormBuilder($defaultData) ->add('user_name','text') ->add('user_mail','email') ->add('user_id','integer') ->getForm(); $form->bindRequest($request); //bindo la form ad una request $data = $form->getData(); //mi aspetto un'array chiave=>valore /* .... */ We expected that $data will contain an array with key,value from the submitted form. We found that it isn't true. After googling for a while and try with other "bad" ideas, we're frozen into that. So, if you have a "graphic office" that can't handle directly php code, how can we interface from form(s) to controller(s) ? UPDATE It seems that Symfony2 use a different convention for form's field name and lookup once you've submitted that. In particular, if my form's name is addUser and a field is named userName, the field's name will be AddUser[username] so maybe it have a "dynamic" lookup method that will extract form's name, field's name, concat them and lookup for values. Is it possible?

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  • Postgresql count+sort performance

    - by invictus
    I have built a small inventory system using postgresql and psycopg2. Everything works great, except, when I want to create aggregated summaries/reports of the content, I get really bad performance due to count()'ing and sorting. The DB schema is as follows: CREATE TABLE hosts ( id SERIAL PRIMARY KEY, name VARCHAR(255) ); CREATE TABLE items ( id SERIAL PRIMARY KEY, description TEXT ); CREATE TABLE host_item ( id SERIAL PRIMARY KEY, host INTEGER REFERENCES hosts(id) ON DELETE CASCADE ON UPDATE CASCADE, item INTEGER REFERENCES items(id) ON DELETE CASCADE ON UPDATE CASCADE ); There are some other fields as well, but those are not relevant. I want to extract 2 different reports: - List of all hosts with the number of items per, ordered from highest to lowest count - List of all items with the number of hosts per, ordered from highest to lowest count I have used 2 queries for the purpose: Items with host count: SELECT i.id, i.description, COUNT(hi.id) AS count FROM items AS i LEFT JOIN host_item AS hi ON (i.id=hi.item) GROUP BY i.id ORDER BY count DESC LIMIT 10; Hosts with item count: SELECT h.id, h.name, COUNT(hi.id) AS count FROM hosts AS h LEFT JOIN host_item AS hi ON (h.id=hi.host) GROUP BY h.id ORDER BY count DESC LIMIT 10; Problem is: the queries runs for 5-6 seconds before returning any data. As this is a web based application, 6 seconds are just not acceptable. The database is heavily populated with approximately 50k hosts, 1000 items and 400 000 host/items relations, and will likely increase significantly when (or perhaps if) the application will be used. After playing around, I found that by removing the "ORDER BY count DESC" part, both queries would execute instantly without any delay whatsoever (less than 20ms to finish the queries). Is there any way I can optimize these queries so that I can get the result sorted without the delay? I was trying different indexes, but seeing as the count is computed it is possible to utilize an index for this. I have read that count()'ing in postgresql is slow, but its the sorting that are causing me problems... My current workaround is to run the queries above as an hourly job, putting the result into a new table with an index on the count column for quick lookup. I use Postgresql 9.2.

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  • Which is the "best" data access framework/approach for C# and .NET?

    - by Frans
    (EDIT: I made it a community wiki as it is more suited to a collaborative format.) There are a plethora of ways to access SQL Server and other databases from .NET. All have their pros and cons and it will never be a simple question of which is "best" - the answer will always be "it depends". However, I am looking for a comparison at a high level of the different approaches and frameworks in the context of different levels of systems. For example, I would imagine that for a quick-and-dirty Web 2.0 application the answer would be very different from an in-house Enterprise-level CRUD application. I am aware that there are numerous questions on Stack Overflow dealing with subsets of this question, but I think it would be useful to try to build a summary comparison. I will endeavour to update the question with corrections and clarifications as we go. So far, this is my understanding at a high level - but I am sure it is wrong... I am primarily focusing on the Microsoft approaches to keep this focused. ADO.NET Entity Framework Database agnostic Good because it allows swapping backends in and out Bad because it can hit performance and database vendors are not too happy about it Seems to be MS's preferred route for the future Complicated to learn (though, see 267357) It is accessed through LINQ to Entities so provides ORM, thus allowing abstraction in your code LINQ to SQL Uncertain future (see Is LINQ to SQL truly dead?) Easy to learn (?) Only works with MS SQL Server See also Pros and cons of LINQ "Standard" ADO.NET No ORM No abstraction so you are back to "roll your own" and play with dynamically generated SQL Direct access, allows potentially better performance This ties in to the age-old debate of whether to focus on objects or relational data, to which the answer of course is "it depends on where the bulk of the work is" and since that is an unanswerable question hopefully we don't have to go in to that too much. IMHO, if your application is primarily manipulating large amounts of data, it does not make sense to abstract it too much into objects in the front-end code, you are better off using stored procedures and dynamic SQL to do as much of the work as possible on the back-end. Whereas, if you primarily have user interaction which causes database interaction at the level of tens or hundreds of rows then ORM makes complete sense. So, I guess my argument for good old-fashioned ADO.NET would be in the case where you manipulate and modify large datasets, in which case you will benefit from the direct access to the backend. Another case, of course, is where you have to access a legacy database that is already guarded by stored procedures. ASP.NET Data Source Controls Are these something altogether different or just a layer over standard ADO.NET? - Would you really use these if you had a DAL or if you implemented LINQ or Entities? NHibernate Seems to be a very powerful and powerful ORM? Open source Some other relevant links; NHibernate or LINQ to SQL Entity Framework vs LINQ to SQL

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  • Akka framework support for finding duplicate messages

    - by scala_is_awesome
    I'm trying to build a high-performance distributed system with Akka and Scala. If a message requesting an expensive (and side-effect-free) computation arrives, and the exact same computation has already been requested before, I want to avoid computing the result again. If the computation requested previously has already completed and the result is available, I can cache it and re-use it. However, the time window in which duplicate computation can be requested may be arbitrarily small. e.g. I could get a thousand or a million messages requesting the same expensive computation at the same instant for all practical purposes. There is a commercial product called Gigaspaces that supposedly handles this situation. However there seems to be no framework support for dealing with duplicate work requests in Akka at the moment. Given that the Akka framework already has access to all the messages being routed through the framework, it seems that a framework solution could make a lot of sense here. Here is what I am proposing for the Akka framework to do: 1. Create a trait to indicate a type of messages (say, "ExpensiveComputation" or something similar) that are to be subject to the following caching approach. 2. Smartly (hashing etc.) identify identical messages received by (the same or different) actors within a user-configurable time window. Other options: select a maximum buffer size of memory to be used for this purpose, subject to (say LRU) replacement etc. Akka can also choose to cache only the results of messages that were expensive to process; the messages that took very little time to process can be re-processed again if needed; no need to waste precious buffer space caching them and their results. 3. When identical messages (received within that time window, possibly "at the same time instant") are identified, avoid unnecessary duplicate computations. The framework would do this automatically, and essentially, the duplicate messages would never get received by a new actor for processing; they would silently vanish and the result from processing it once (whether that computation was already done in the past, or ongoing right then) would get sent to all appropriate recipients (immediately if already available, and upon completion of the computation if not). Note that messages should be considered identical even if the "reply" fields are different, as long as the semantics/computations they represent are identical in every other respect. Also note that the computation should be purely functional, i.e. free from side-effects, for the caching optimization suggested to work and not change the program semantics at all. If what I am suggesting is not compatible with the Akka way of doing things, and/or if you see some strong reasons why this is a very bad idea, please let me know. Thanks, Is Awesome, Scala

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  • ACL implementation

    - by Kirzilla
    First question Please, could you explain me how simpliest ACL could be implemented in MVC. Here is the first approach of using Acl in Controller... <?php class MyController extends Controller { public function myMethod() { //It is just abstract code $acl = new Acl(); $acl->setController('MyController'); $acl->setMethod('myMethod'); $acl->getRole(); if (!$acl->allowed()) die("You're not allowed to do it!"); ... } } ?> It is very bad approach, and it's minus is that we have to add Acl piece of code into each controller's method, but we don't need any additional dependencies! Next approach is to make all controller's methods private and add ACL code into controller's __call method. <?php class MyController extends Controller { private function myMethod() { ... } public function __call($name, $params) { //It is just abstract code $acl = new Acl(); $acl->setController(__CLASS__); $acl->setMethod($name); $acl->getRole(); if (!$acl->allowed()) die("You're not allowed to do it!"); ... } } ?> It is better than previous code, but main minuses are... All controller's methods should be private We have to add ACL code into each controller's __call method. The next approach is to put Acl code into parent Controller, but we still need to keep all child controller's methods private. What is the solution? And what is the best practice? Where should I call Acl functions to decide allow or disallow method to be executed. Second question Second question is about getting role using Acl. Let's imagine that we have guests, users and user's friends. User have restricted access to viewing his profile that only friends can view it. All guests can't view this user's profile. So, here is the logic.. we have to ensure that method being called is profile we have to detect owner of this profile we have to detect is viewer is owner of this profile or no we have to read restriction rules about this profile we have to decide execute or not execute profile method The main question is about detecting owner of profile. We can detect who is owner of profile only executing model's method $model-getOwner(), but Acl do not have access to model. How can we implement this? I hope that my thoughts are clear. Sorry for my English. Thank you.

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  • Casting between variant and bstr_t causing inconsisten crash in Windows 2008

    - by user58470
    We have a C# application, calling a simple C++ wrapper class, that then calls an existing C++ DLL. The C++ code is all VC++ 6.0. We are getting inconsistent behaviour, but the crash, when it happens, always happens within the C++ wrapper DLL, and always in the same spot (have confirmed using painful logging statements). It never happens on any environment except on Windows 2008, so we suspect some bad-but-not-fatal memory trashing is going on that somehow Windows 2008 is being more mindful of. Here's the relevant code, if anyone has any ideas on why this might be crashing it would be much appreciated. We've been tearing our hair out for a few days and project timelines are slipping all for the want of being able to return a simple string back to C#... I've been told we've tried setting the VARIANT vresult using VariantInit, and clearing it when we are done with VariantClear, but that didn't help. // JobMgrDll.cpp : Defines the entry point for the DLL application. // #include "stdafx.h" #include "JobMgrDll.h" #include "jobmgr.h" CString gcontext; CString guser; CString ghost; CString glog; JOBMGRDLL_API int nJobMgrDll=0; extern "C" JOBMGRDLL_API char* perform_billcalc(char* cmd, char* context, char* user,char* host,BSTR* log,int* loglen) { char* result = new char[1000]; memset(result,0,999); result[999] = '\0'; bstr_t bt_command = cmd; UUID uuid = __uuidof(BRLib::Rules); VARIANT vresult; char *p_rv; gcontext = context; guser = user; ghost = host; write_log("execute_job"); p_rv = execute_job(uuid, "none", bt_command, &vresult); write_log("DONE execute_job"); CString message; write_log ("Intializing bstr_t with variant"); // WE ALWAYS GET HERE bstr_t res(vresult); //message.Format("%s result = %s",p_rv,res); //write_log(message); write_log("copying Result"); // WE DON'T ALWAYS GET HERE, BUT SOMETIMES WE DO strcpy(result,(char*)res); write_log(CString(result)); *loglen = glog.GetLength(); *log = glog.AllocSysString(); return result; } Again, any ideas much, much appreciated.

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  • ZF Autoloader to load ancestor and requested class

    - by Pekka
    I am integrating Zend Framework into an existing application. I want to switch the application over to Zend's autoloading mechanism to replace dozens of include() statements. I have a specific requirement for the autoloading mechanism, though. Allow me to elaborate. The existing application uses a core library (independent from ZF), for example: /Core/Library/authentication.php /Core/Library/translation.php /Core/Library/messages.php this core library is to remain untouched at all times and serves a number of applications. The library contains classes like class ancestor_authentication { ... } class ancestor_translation { ... } class ancestor_messages { ... } in the application, there is also a Library directory: /App/Library/authentication.php /App/Library/translation.php /App/Library/messages.php these includes extend the ancestor classes and are the ones that actually get instantiated in the application. class authentication extends ancestor_authentication { } class translation extends ancestor_translation { } class messages extends ancestor_messages { } usually, these class definitions are empty. They simply extend their ancestors and provide the class name to instantiate. $authentication = new authentication(); The purpose of this solution is to be able to easily customize aspects of the application without having to patch the core libraries. Now, the autoloader I need would have to be aware of this structure. When an object of the class authentication is requested, the autoloader would have to: 1. load /Core/Library/authentication.php 2. load /App/Library/authentication.php My current approach would be creating a custom function, and binding that to Zend_Loader_Autoloader for a specific namespace prefix. Is there already a way to do this in Zend that I am overlooking? The accepted answer in this question kind of implies there is, but that may be just a bad choice of wording. Are there extensions to the Zend Autoloader that do this? Can you - I am new to ZF - think of an elegant way, conforming with the spirit of the framework, of extending the Autoloader with this functionality? I'm not necessary looking for a ready-made implementation, some pointers (This should be an extension to the xyz method that you would call like this...) would already be enough.

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  • Supersized image captions - render outside of JavaScript

    - by Sol
    I am using the jQuery supersized script for a full screen slideshow (not the WordPress plugin as this didn't give me enough control). However, one issue that I am trying to tackle is how to render the image caption text outside of the javascript slides[ ] call - and instead, render them within the page div - to improve SEO on the page. My code works fine right now, images and the caption text are correctly displaying, but looking at the source code, there is very little text outside of the javascript (which is bad for SEO), so I would just like to improve it, if possible. I haven't been able to find any other topic on this subject and so far, I've been unsuccessful at improving on the current code, which is as follows; <!-- Supersized 3.2.7 - By Sam Dunn / One Mighty Roar (www.onemightyroar.com) Released under MIT License / GPL License --> <script type="text/javascript"> var slides=[]; <?php $my_query = new WP_Query ( array( 'post_status' => 'publish', 'post_type' => 'featured', //'numberposts' => 5, 'orderby' => 'menu_order', 'order' => 'ASC', 'showposts' => 50 )); while( $my_query->have_posts() ) : $my_query->the_post(); $slink = get_post_meta($post->ID,'FS_link',true); ?> slides.push({image : '<?php echo get_image_path(get_post_meta($post->ID, 'FS_slideimage_src', true)); ?>', title : '<div class="slidecaptioninside"><h1><?php echo the_title(); ?></h1><p><?php echo strip_tags(get_post_meta($post->ID, 'FS_fitemcaption', true)); ?>...<a href="<?php echo $slink;?>">find out more</a></p></div>', url : '<?php echo $slink;?>'}); <?php endwhile; ?> // start supersized JS $j = jQuery.noConflict(); $j(window).load(function() { $j.supersized({ //Functionality slideshow: 1, // ..... additional functions go here... slide_captions : 1, //Slide caption (Pull from "title" in slides array) slides : slides, slide_links : 'blank', progress_bar : 1, mouse_scrub: 1 }); }); </script> <div id="slidecontainer"> <div id="slidecaption"></div> <!--Thumbnail Navigation--> <div id="prevthumb"></div> <div id="nextthumb"></div> <!--additional tray divs here--> </div><!--slidecontainer--> I have tried to get Supersized to output the content into a parent div [div id="supersized"] using $j('#supersized').supersized({ but this doesn't appear to work. Has anyone managed to do this differently to improve page SEO?

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  • Combining FileStream and MemoryStream to avoid disk accesses/paging while receiving gigabytes of data?

    - by w128
    I'm receiving a file as a stream of byte[] data packets (total size isn't known in advance) that I need to store somewhere before processing it immediately after it's been received (I can't do the processing on the fly). Total received file size can vary from as small as 10 KB to over 4 GB. One option for storing the received data is to use a MemoryStream, i.e. a sequence of MemoryStream.Write(bufferReceived, 0, count) calls to store the received packets. This is very simple, but obviously will result in out of memory exception for large files. An alternative option is to use a FileStream, i.e. FileStream.Write(bufferReceived, 0, count). This way, no out of memory exceptions will occur, but what I'm unsure about is bad performance due to disk writes (which I don't want to occur as long as plenty of memory is still available) - I'd like to avoid disk access as much as possible, but I don't know of a way to control this. I did some testing and most of the time, there seems to be little performance difference between say 10 000 consecutive calls of MemoryStream.Write() vs FileStream.Write(), but a lot seems to depend on buffer size and the total amount of data in question (i.e the number of writes). Obviously, MemoryStream size reallocation is also a factor. Does it make sense to use a combination of MemoryStream and FileStream, i.e. write to memory stream by default, but once the total amount of data received is over e.g. 500 MB, write it to FileStream; then, read in chunks from both streams for processing the received data (first process 500 MB from the MemoryStream, dispose it, then read from FileStream)? Another solution is to use a custom memory stream implementation that doesn't require continuous address space for internal array allocation (i.e. a linked list of memory streams); this way, at least on 64-bit environments, out of memory exceptions should no longer be an issue. Con: extra work, more room for mistakes. So how do FileStream vs MemoryStream read/writes behave in terms of disk access and memory caching, i.e. data size/performance balance. I would expect that as long as enough RAM is available, FileStream would internally read/write from memory (cache) anyway, and virtual memory would take care of the rest. But I don't know how often FileStream will explicitly access a disk when being written to. Any help would be appreciated.

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  • How to implement a caching model without violating MVC pattern?

    - by RPM1984
    Hi Guys, I have an ASP.NET MVC 3 (Razor) Web Application, with a particular page which is highly database intensive, and user experience is of the upmost priority. Thus, i am introducing caching on this particular page. I'm trying to figure out a way to implement this caching pattern whilst keeping my controller thin, like it currently is without caching: public PartialViewResult GetLocationStuff(SearchPreferences searchPreferences) { var results = _locationService.FindStuffByCriteria(searchPreferences); return PartialView("SearchResults", results); } As you can see, the controller is very thin, as it should be. It doesn't care about how/where it is getting it's info from - that is the job of the service. A couple of notes on the flow of control: Controllers get DI'ed a particular Service, depending on it's area. In this example, this controller get's a LocationService Services call through to an IQueryable<T> Repository and materialize results into T or ICollection<T>. How i want to implement caching: I can't use Output Caching - for a few reasons. First of all, this action method is invoked from the client-side (jQuery/AJAX), via [HttpPost], which according to HTTP standards should not be cached as a request. Secondly, i don't want to cache purely based on the HTTP request arguments - the cache logic is a lot more complicated than that - there is actually two-level caching going on. As i hint to above, i need to use regular data-caching, e.g Cache["somekey"] = someObj;. I don't want to implement a generic caching mechanism where all calls via the service go through the cache first - i only want caching on this particular action method. First thought's would tell me to create another service (which inherits LocationService), and provide the caching workflow there (check cache first, if not there call db, add to cache, return result). That has two problems: The services are basic Class Libraries - no references to anything extra. I would need to add a reference to System.Web here. I would have to access the HTTP Context outside of the web application, which is considered bad practice, not only for testability, but in general - right? I also thought about using the Models folder in the Web Application (which i currently use only for ViewModels), but having a cache service in a models folder just doesn't sound right. So - any ideas? Is there a MVC-specific thing (like Action Filter's, for example) i can use here? General advice/tips would be greatly appreciated.

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  • B-trees, databases, sequential inputs, and speed.

    - by IanC
    I know from experience that b-trees have awful performance when data is added to them sequentially (regardless of the direction). However, when data is added randomly, best performance is obtained. This is easy to demonstrate with the likes of an RB-Tree. Sequential writes cause a maximum number of tree balances to be performed. I know very few databases use binary trees, but rather used n-order balanced trees. I logically assume they suffer a similar fate to binary trees when it comes to sequential inputs. This sparked my curiosity. If this is so, then one could deduce that writing sequential IDs (such as in IDENTITY(1,1)) would cause multiple re-balances of the tree to occur. I have seen many posts argue against GUIDs as "these will cause random writes". I never use GUIDs, but it struck me that this "bad" point was in fact a good point. So I decided to test it. Here is my code: SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[T1]( [ID] [int] NOT NULL CONSTRAINT [T1_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO CREATE TABLE [dbo].[T2]( [ID] [uniqueidentifier] NOT NULL CONSTRAINT [T2_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO declare @i int, @t1 datetime, @t2 datetime, @t3 datetime, @c char(300) set @t1 = GETDATE() set @i = 1 while @i < 2000 begin insert into T2 values (NEWID(), @c) set @i = @i + 1 end set @t2 = GETDATE() WAITFOR delay '0:0:10' set @t3 = GETDATE() set @i = 1 while @i < 2000 begin insert into T1 values (@i, @c) set @i = @i + 1 end select DATEDIFF(ms, @t1, @t2) AS [Int], DATEDIFF(ms, @t3, getdate()) AS [GUID] drop table T1 drop table T2 Note that I am not subtracting any time for the creation of the GUID nor for the considerably extra size of the row. The results on my machine were as follows: Int: 17,340 ms GUID: 6,746 ms This means that in this test, random inserts of 16 bytes was almost 3 times faster than sequential inserts of 4 bytes. Would anyone like to comment on this? Ps. I get that this isn't a question. It's an invite to discussion, and that is relevant to learning optimum programming.

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  • .NET Free memory usage (how to prevent overallocation / release memory to the OS)

    - by Ronan Thibaudau
    I'm currently working on a website that makes large use of cached data to avoid roundtrips. At startup we get a "large" graph (hundreds of thouthands of different kinds of objects). Those objects are retrieved over WCF and deserialized (we use protocol buffers for serialization) I'm using redgate's memory profiler to debug memory issues (the memory didn't seem to fit with how much memory we should need "after" we're done initializing and end up with this report Now what we can gather from this report is that: 1) Most of the memory .NET allocated is free (it may have been rightfully allocated during deserialisation, but now that it's free, i'd like for it to return to the OS) 2) Memory is fragmented (which is bad, as everytime i refresh the cash i need to redo the memory hungry deserialisation process and this, in turn creates large object that may throw an OutOfMemoryException due to fragmentation) 3) I have no clue why the space is fragmented, because when i look at the large object heap, there are only 30 instances, 15 object[] are directly attached to the GC and totally unrelated to me, 1 is a char array also attached directly to the GC Heap, the remaining 15 are mine but are not the cause of this as i get the same report if i comment them out in code. So my question is, what can i do to go further with this? I'm not really sure what to look for in debugging / tools as it seems my memory is fragmented, but not by me, and huge amounts of free spaces are allocated by .net , which i can't release. Also please make sure you understand the question well before answering, i'm not looking for a way to free memory within .net (GC.Collect), but to free memory that is already free in .net , to the system as well as to defragment said memory. Note that a slow solution is fine, if it's possible to manually defragment the large heap i'd be all for it as i can call it at the end of RefreshCache and it's ok if it takes 1 or 2 second to run. Thanks for your help! A few notes i forgot: 1) The project is a .net 2.0 website, i get the same results running it in a .net 4 pool, idem if i run it in a .net 4 pool and convert it to .net 4 and recompile. 2) These are results of a release build, so debug build can not be the issue. 3) And this is probably quite important, i do not get these issues at all in the webdev server, only in IIS, in the webdev i get memory consumption rather close to my actual consumption (well more, but not 5-10X more!)

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  • Twitter RSS feed, [domdocument.load]: failed to open stream:

    - by dave1019
    hi i'm using the following: <?php $doc = new DOMDocument(); $doc->load('http://twitter.com/statuses/user_timeline/XXXXXX.rss'); $arrFeeds = array(); foreach ($doc->getElementsByTagName('item') as $node) { $itemRSS = array ( 'title' => $node->getElementsByTagName('title')->item(0)->nodeValue, 'desc' => $node->getElementsByTagName('description')->item(0)->nodeValue, 'link' => $node->getElementsByTagName('link')->item(0)->nodeValue, 'date' => $node->getElementsByTagName('pubDate')->item(0)->nodeValue ); array_push($arrFeeds, $itemRSS); } for($i=0;$i<=3;$i++) { $tweet=substr($arrFeeds[$i]['title'],17); $tweetDate=strtotime($arrFeeds[$i]['date']); $newDate=date('G:ia l F Y ',$tweetDate); if($i==0) { $b='style="border:none;"'; } $tweetsBox.='<div class="tweetbox" ' . $b . '> <div class="tweet"><p>' . $tweet . '</p> <div class="tweetdate"><a href="http://twitter.com/XXXXXX">@' . $newDate .'</a></div> </div> </div>'; } return $tweetsBox; ?> to return the 4 most recent tweets from a given timeline (XXXXX is the relevant feed) It seems to work fine but i've recently been getting the following error sporadically: PHP error debug Error: DOMDocument::load(http://twitter.com/statuses/user_timeline/XXXXXX.rss) [domdocument.load]: failed to open stream: HTTP request failed! HTTP/1.1 502 Bad Gateway I've read that the above code is dependant on Twitter beign available and I know it gets rather busy sometimes. Is there either a better way of receiving twits, or is there any kind of error trapping i could do to just to display "tweets are currently unavailable..." ind of message rather than causing an error. I'm usnig ModX CMS so any parse error kills the site rather than just ouputs a warning. thanks.

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  • EXC_BAD_ACCESS when simply casting a pointer in Obj-C

    - by AlexChilcott
    Hi all, Frequent visitor but first post here on StackOverflow, I'm hoping that you guys might be able to help me out with this. I'm fairly new to Obj-C and XCode, and I'm faced with this really... weird... problem. Googling hasn't turned up anything whatsoever. Basically, I get an EXC_BAD_ACCESS signal on a line that doesn't do any dereferencing or anything like that that I can see. Wondering if you guys have any idea where to look for this. I've found a work around, but no idea why this works... The line the broken version barfs out on is the line: LevelEntity *le = entity; where I get my bad access signal. Here goes: THIS VERSION WORKS NSArray *contacts = [self.body getContacts]; for (PhysicsContact *contact in contacts) { PhysicsBody *otherBody; if (contact.bodyA == self.body) { otherBody = contact.bodyB; } if (contact.bodyB == self.body) { otherBody = contact.bodyA; } id entity = [otherBody userData]; if (entity != nil) { LevelEntity *le = entity; CGPoint point = [contact contactPointOnBody:otherBody]; } } THIS VERSION DOESNT WORK NSArray *contacts = [self.body getContacts]; for (NSUInteger i = 0; i < [contacts count]; i++) { PhysicsContact *contact = [contacts objectAtIndex:i]; PhysicsBody *otherBody; if (contact.bodyA == self.body) { otherBody = contact.bodyB; } if (contact.bodyB == self.body) { otherBody = contact.bodyA; } id entity = [otherBody userData]; if (entity != nil) { LevelEntity *le = entity; CGPoint point = [contact contactPointOnBody:otherBody]; } } Here, the only difference between the two examples is the way I enumerate through my array. In the first version (which works) I use for (... in ...), where as in the second I use for (...; ...; ...). As far as I can see, these should be the same. This is seriously weirding me out. Anyone have any similar experience or idea whats going on here? Would be really great :) Cheers, Alex

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  • Is It possible to use the second part of this code for repository patterns and generics

    - by newToCSharp
    Is there any issues in using version 2,to get the same results as version 1. Or is this just bad coding. Any Ideas public class Customer { public int CustomerID { get; set; } public string EmailAddress { get; set; } int Age { get; set; } } public interface ICustomer { void AddNewCustomer(Customer Customer); void AddNewCustomer(string EmailAddress, int Age); void RemoveCustomer(Customer Customer); } public class BALCustomer { private readonly ICustomer dalCustomer; public BALCustomer(ICustomer dalCustomer) { this.dalCustomer = dalCustomer; } public void Add_A_New_Customer(Customer Customer) { dalCustomer.AddNewCustomer(Customer); } public void Remove_A_Existing_Customer(Customer Customer) { dalCustomer.RemoveCustomer(Customer); } } public class CustomerDataAccess : ICustomer { public void AddNewCustomer(Customer Customer) { // MAKE DB CONNECTION AND EXECUTE throw new NotImplementedException(); } public void AddNewCustomer(string EmailAddress, int Age) { // MAKE DB CONNECTION AND EXECUTE throw new NotImplementedException(); } public void RemoveCustomer(Customer Customer) { // MAKE DB CONNECTION AND EXECUTE throw new NotImplementedException(); } } // VERSION 2 public class Customer_New : DataRespository<CustomerDataAccess> { public int CustomerID { get; set; } public string EmailAddress { get; set; } public int Age { get; set; } } public class DataRespository<T> where T:class,new() { private T item = new T(); public T Execute { get { return item; } set { item = value; } } public void Update() { //TO BE CODED } public void Save() { //TO BE CODED } public void Remove() { //TO BE CODED } } class Program { static void Main(string[] args) { Customer_New cus = new Customer_New() { Age = 10, EmailAddress = "[email protected]" }; cus.Save(); cus.Execute.RemoveCustomer(new Customer()); // Repository Version Customer customer = new Customer() { EmailAddress = "[email protected]", CustomerID = 10 }; BALCustomer bal = new BALCustomer(new CustomerDataAccess()); bal.Add_A_New_Customer(customer); } } }

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  • How would you structure your entity model for storing arbitrary key/value data with different data t

    - by Nathan Ridley
    I keep coming across scenarios where it will be useful to store a set of arbitrary data in a table using a per-row key/value model, rather than a rigid column/field model. The problem is, I want to store the values with their correct data type rather than converting everything to a string. This means I have to choose either a single table with multiple nullable columns, one for each data type, or a set of value tables, one for each data type. I'm also unsure as to whether I should use full third normal form and separate the keys into a separate table, referencing them via a foreign key from the value table(s), or if it would be better to keep things simple and store the string keys in the value table(s) and accept the duplication of strings. Old/bad: This solution makes adding additional values a pain in a fluid environment because the table needs to be modified regularly. MyTable ============================ ID Key1 Key2 Key3 int int string date ---------------------------- 1 Value1 Value2 Value3 2 Value4 Value5 Value6 Single Table Solution This solution allows simplicity via a single table. The querying code still needs to check for nulls to determine which data type the field is storing. A check constraint is probably also required to ensure only one of the value fields contains non-nulll data. DataValues ============================================================= ID RecordID Key IntValue StringValue DateValue int int string int string date ------------------------------------------------------------- 1 1 Key1 Value1 NULL NULL 2 1 Key2 NULL Value2 NULL 3 1 Key3 NULL NULL Value3 4 2 Key1 Value4 NULL NULL 5 2 Key2 NULL Value5 NULL 6 2 Key3 NULL NULL Value6 Multiple-Table Solution This solution allows for more concise purposing of each table, though the code needs to know the data type in advance as it needs to query a different table for each data type. Indexing is probably simpler and more efficient because there are less columns that need indexing. IntegerValues =============================== ID RecordID Key Value int int string int ------------------------------- 1 1 Key1 Value1 2 2 Key1 Value4 StringValues =============================== ID RecordID Key Value int int string string ------------------------------- 1 1 Key2 Value2 2 2 Key2 Value5 DateValues =============================== ID RecordID Key Value int int string date ------------------------------- 1 1 Key3 Value3 2 2 Key3 Value6 How do you approach this problem? Which solution is better? Also, should the key column be separated into a separate table and referenced via a foreign key or be should it be kept in the value table and bulk updated if for some reason the key name changes?

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  • In R, how do you get the best fitting equation to a set of data?

    - by Matherion
    I'm not sure wether R can do this (I assume it can, but maybe that's just because I tend to assume that R can do anything :-)). What I need is to find the best fitting equation to describe a dataset. For example, if you have these points: df = data.frame(x = c(1, 5, 10, 25, 50, 100), y = c(100, 75, 50, 40, 30, 25)) How do you get the best fitting equation? I know that you can get the best fitting curve with: plot(loess(df$y ~ df$x)) But as I understood you can't extract the equation, see Loess Fit and Resulting Equation. When I try to build it myself (note, I'm not a mathematician, so this is probably not the ideal approach :-)), I end up with smth like: y.predicted = 12.71 + ( 95 / (( (1 + df$x) ^ .5 ) / 1.3)) Which kind of seems to approximate it - but I can't help to think that smth more elegant probably exists :-) I have the feeling that fitting a linear or polynomial model also wouldn't work, because the formula seems different from what those models generally use (i.e. this one seems to need divisions, powers, etc). For example, the approach in Fitting polynomial model to data in R gives pretty bad approximations. I remember from a long time ago that there exist languages (Matlab may be one of them?) that do this kind of stuff. Can R do this as well, or am I just at the wrong place? (Background info: basically, what we need to do is find an equation for determining numbers in the second column based on the numbers in the first column; but we decide the numbers ourselves. We have an idea of how we want the curve to look like, but we can adjust these numbers to an equation if we get a better fit. It's about the pricing for a product (a cheaper alternative to current expensive software for qualitative data analysis); the more 'project credits' you buy, the cheaper it should become. Rather than forcing people to buy a given number (i.e. 5 or 10 or 25), it would be nicer to have a formula so people can buy exactly what they need - but of course this requires a formula. We have an idea for some prices we think are ok, but now we need to translate this into an equation.

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