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• Where should an application's default folder live?

  - by HotOil

  Hi: I'm creating a little app that configures a connected device and then saves the config information in a file. The filename cannot be chosen by the user, but its location can be chosen. Where is the best place for the app's default save-to folder? I have seen examples out there where it is the "MyDocuments" location (eg Visual Studio does this). I have seen a folder created right at the top of the C:\ drive. I find that to be a little obnoxious, personally. It could be in the Program Files[Manufacturer] or Program Files[Product Name], or wherever the app was installed. I have used this location in the past; I dislike it because Windows Explorer does not allow a user to browse to there very easily ('browsability'). Going with this last notion that 'browsability' is a factor, I suppose MyDocuments is the best choice. Is this the most common, most widely accepted practice? I think historically we have chosen the install folder because that co-locates the data with the device management utilities. But I would really like to get away from that. I don't want the user to have to go pawing through system files to find his/her data, esp if that person is not too Windows-savvy. Also, I am using the .NET WinForms FolderBrowserDialog, and the "Environment.SpecialFolders" enum isn't helpful in setting up the dialog to point into the Program Files folder. Thanks for your input! Suz.

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• ImageViews sometimes not displaying in FrameLayout activity

  - by Ken

  The top level layout in my activity is a framelayout. I have completed, debugged and tested this app and it works exactly like it should in all respects on my g1 and on various emulators. But on 3.7-inch displays running 2.1+, some imageviews packed in a linearlayout are periodically not visible. I know that they are there because you can touch and drag them with effect in the app. So I assume somehow they have gotten under the SurfaceView that is the main component of the app. This is apparently so even though the SurfaceView is declared in the xml prior to the LinearLayout. However, the ImageViews IN the LinearLayout are added programmatically towards the end of onCreate(). Framelayout stacks everything that is added to it, one on top of the other--the only way you will see more than one child of a frame layout is if they are smaller than the screen and are placed apart from eachother. Oddly, sometimes the imageviews ARE visible--it is random. Anyway, I've been trying to combat this with framelayout.bringChildToFront(View v) on the linearlayout without success. I wonder if anyone has any insight into how the behavior could be random like that, and how I should code these imageviews to keep this from happening, and why the problem appears only to occur on 3.7 vs 3.2 inch screens (as it happens, the two 3.2-inch screens were both htc, so vendor might be factor too). [edit] Actually, I've determined that this is a 2.2 issue, not a screen size (or even vendor) issue. Can't ensure that ImageViews added to a framelayout with a SurfaceView in it will appear on top of the surfaceview. I ran some tests in the respective onDraw() methods and the imageviews are 'visible' (0), and nothing does anything to the alpha of the drawables, which are there as well at ondraw(). [/edit] Any insight would be welcomed. Ken T.

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• I'm having an issue to use GLshort for representing Vertex, and Normal.

  - by Xylopia

  As my project gets close to optimization stage, I notice that reducing Vertex Metadata could vastly improve the performance of 3D rendering. Eventually, I've dearly searched around and have found following advices from stackoverflow. Using GL_SHORT instead of GL_FLOAT in an OpenGL ES vertex array How do you represent a normal or texture coordinate using GLshorts? Advice on speeding up OpenGL ES 1.1 on the iPhone Simple experiments show that switching from "FLOAT" to "SHORT" for vertex and normal isn't tough, but what troubles me is when you're to scale back verticies to their original size (with glScalef), normals are multiplied by the reciprocal of the scale. Natural remedy for this is to multiply the normals w/ scale before you submit to GPU. Then, my short normals almost become 0, because the scale factor is usually smaller than 0. Duh! How do you use "short" for both vertex and normal at the same time? I've been trying this and that for about a full day, but I could only go for "float vertex w/ byte normal" or "short vertex w/ float normal" so far. Your help would be truly appreciated.

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• Does it ever make sense to make a fundamental (non-pointer) parameter const?

  - by Scott Smith

  I recently had an exchange with another C++ developer about the following use of const: void Foo(const int bar); He felt that using const in this way was good practice. I argued that it does nothing for the caller of the function (since a copy of the argument was going to be passed, there is no additional guarantee of safety with regard to overwrite). In addition, doing this prevents the implementer of Foo from modifying their private copy of the argument. So, it both mandates and advertises an implementation detail. Not the end of the world, but certainly not something to be recommended as good practice. I'm curious as to what others think on this issue. Edit: OK, I didn't realize that const-ness of the arguments didn't factor into the signature of the function. So, it is possible to mark the arguments as const in the implementation (.cpp), and not in the header (.h) - and the compiler is fine with that. That being the case, I guess the policy should be the same for making local variables const. One could make the argument that having different looking signatures in the header and source file would confuse others (as it would have confused me). While I try to follow the Principle of Least Astonishment with whatever I write, I guess it's reasonable to expect developers to recognize this as legal and useful.

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• Doctrine - get the offset of an object in a collection (implementing an infinite scroll)

  - by dan

  I am using Doctrine and trying to implement an infinite scroll on a collection of notes displayed on the user's browser. The application is very dynamic, therefore when the user submits a new note, the note is added to the top of the collection straightaway, besides being sent (and stored) to the server. Which is why I can't use a traditional pagination method, where you just send the page number to the server and the server will figure out the offset and the number of results from that. To give you an example of what I mean, imagine there are 20 notes displayed, then the user adds 2 more notes, therefore there are 22 notes displayed. If I simply requests "page 2", the first 2 items of that page will be the last two items of the page currently displayed to the user. Which is why I am after a more sophisticated method, which is the one I am about to explain. Please consider the following code, which is part of the server code serving an AJAX request for more notes: // $lastNoteDisplayedId is coming from the AJAX request $lastNoteDisplayed = $repository->findBy($lastNoteDisplayedId); $allNotes = $repository->findBy($filter, array('createdAt' => 'desc')); $offset = getLastNoteDisplayedOffset($allNotes, $lastNoteDisplayedId); // retrieve the page to send back so that it can be appended to the listing $notesPerPage = 30 $notes = $repository->findBy( array(), array('createdAt' => 'desc'), $notesPerPage, $offset ); $response = json_encode($notes); return $response; Basically I would need to write the method getLastNoteDisplayedOffset, that given the whole set of notes and one particoular note, it can give me its offset, so that I can use it for the pagination of the previous Doctrine statement. I know probably a possible implementation would be: getLastNoteDisplayedOffset($allNotes, $lastNoteDisplayedId) { $i = 0; foreach ($allNotes as $note) { if ($note->getId() === $lastNoteDisplayedId->getId()) { break; } $i++; } return $i; } I would prefer not to loop through all notes because performance is an important factor. I was wondering if Doctrine has got a method itself or if you can suggest a different approach.

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• To OpenID or not to OpenID? Is it worth it?

  - by Eloff

  Does OpenID improve the user experience? Edit Not to detract from the other comments, but I got one really good reply below that outlined 3 advantages of OpenID in a rational bottom line kind of way. I've also heard some whisperings in other comments that you can get access to some details on the user through OpenID (name? email? what?) and that using that it might even be able to simplify the registration process by not needing to gather as much information. Things that definitely need to be gathered in a checkout process: Full name Email (I'm pretty sure I'll have to ask for these myself) Billing address Shipping address Credit card info There may be a few other things that are interesting from a marketing point of view, but I wouldn't ask the user to manually enter anything not absolutely required during the checkout process. So what's possible in this regard? /Edit (You may have noticed stackoverflow uses OpenID) It seems to me it is easier and faster for the user to simply enter a username and password in a signup form they have to go through anyway. I mean you don't avoid entering a username and password either with OpenID. But you avoid the confusion of choosing a OpenID provider, and the trip out to and back from and external site. With Microsoft making Live ID an OpenID provider (More Info), bringing on several hundred million additional accounts to those provided by Google, Yahoo, and others, this question is more important than ever. I have to require new customers to sign up during the checkout process, and it is absolutely critical that the experience be as easy and smooth as possible, every little bit harder it becomes translates into lost sales. No geek factor outweighs cold hard cash at the end of the day :) OpenID seems like a nice idea, but the implementation is of questionable value. What are the advantages of OpenID and is it really worth it in my scenario described above?

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• Entity Framework DateTime update extremely slow

  - by Phyxion

  I have this situation currently with Entity Framework: using (TestEntities dataContext = DataContext) { UserSession session = dataContext.UserSessions.FirstOrDefault(userSession => userSession.Id == SessionId); if (session != null) { session.LastAvailableDate = DateTime.Now; dataContext.SaveChanges(); } } This is all working perfect, except for the fact that it is terribly slow compared to what I expect (14 calls per second, tested with 100 iterations). When I update this record manually through this command: dataContext.Database.ExecuteSqlCommand(String.Format("update UserSession set LastAvailableDate = '{0}' where Id = '{1}'", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss.fffffff"), SessionId)); I get 55 calls per second, which is more than fast enough. However, when I don't update the session.LastAvailableDate but I update an integer (e.g. session.UserId) or string with Entity Framework, I get 50 calls per second, which is also more than fast enough. Only the datetime field is terrible slow. The difference of a factor 4 is unacceptable and I was wondering how I can improve this as I don't prefer using direct SQL when I can also use the Entity Framework. I'm using Entity Framework 4.3.1 (also tried 4.1).

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• What is a good approach to preloading data?

  - by Bob Horn

  Are there best practices out there for loading data into a database, to be used with a new installation of an application? For example, for application foo to run, it needs some basic data before it can even be started. I've used a couple options in the past: TSQL for every row that needs to be preloaded: IF NOT EXISTS (SELECT * FROM Master.Site WHERE Name = @SiteName) INSERT INTO [Master].[Site] ([EnterpriseID], [Name], [LastModifiedTime], [LastModifiedUser]) VALUES (@EnterpriseId, @SiteName, GETDATE(), @LastModifiedUser) Another option is a spreadsheet. Each tab represents a table, and data is entered into the spreadsheet as we realize we need it. Then, a program can read this spreadsheet and populate the DB. There are complicating factors, including the relationships between tables. So, it's not as simple as loading tables by themselves. For example, if we create Security.Member rows, then we want to add those members to Security.Role, we need a way of maintaining that relationship. Another factor is that not all databases will be missing this data. Some locations will already have most of the data, and others (that may be new locations around the world), will start from scratch. Any ideas are appreciated.

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• Running Different Modules on Tomcat/Server

  - by umesh awasthi

  Hi All, I have started working on my own project idea but on the starting i have strucked in the structure decision may be lack of knowledge is the promary factor. i am wondering how we can make 2 different modules to co-operate on the server.Here is is explanation of what i am trying to ask as per my design i need 2 modules for my application 1. Back end handling where i can do all content handling as well as other admin task a console which will be capable of handling everything from ceating importing contents to everything. 2 USer end which is only an interface to the end user to use the application. to visualize the things its kinda e-commerce application one is back office management and other is user end of web-shop. since these two module will be very much interlinked but i don't want them to mix up i want them to develop independently since admin is one which is core and it will also going to serve user interface. my question is how i can develop two module independently but on the other hand i want them to co-operate to accomplish the task as a whole. Really sorry in advance if i am not making any sense. Thanks in advance

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• Using child visitor in C#

  - by Thomas Matthews

  I am setting up a testing component and trying to keep it generic. I want to use a generic Visitor class, but not sure about using descendant classes. Example: public interface Interface_Test_Case { void execute(); void accept(Interface_Test_Visitor v); } public interface Interface_Test_Visitor { void visit(Interface_Test_Case tc); } public interface Interface_Read_Test_Case : Interface_Test_Case { uint read_value(); } public class USB_Read_Test : Interface_Read_Test_Case { void execute() { Console.WriteLine("Executing USB Read Test Case."); } void accept(Interface_Test_Visitor v) { Console.WriteLine("Accepting visitor."); } uint read_value() { Console.WriteLine("Reading value from USB"); return 0; } } public class USB_Read_Visitor : Interface_Test_Visitor { void visit(Interface_Test_Case tc) { Console.WriteLine("Not supported Test Case."); } void visit(Interface_Read_Test_Case rtc) { Console.WriteLine("Not supported Read Test Case."); } void visit(USB_Read_Test urt) { Console.WriteLine("Yay, visiting USB Read Test case."); } } // Code fragment USB_Read_Test test_case; USB_Read_Visitor visitor; test_case.accept(visitor); What are the rules the C# compiler uses to determine which of the methods in USB_Read_Visitor will be executed by the code fragment? I'm trying to factor out dependencies of my testing component. Unfortunately, my current Visitor class contains visit methods for classes not related to the testing component. Am I trying to achieve the impossible?

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• Partitioning data set in r based on multiple classes of observations

  - by Danny

  I'm trying to partition a data set that I have in R, 2/3 for training and 1/3 for testing. I have one classification variable, and seven numerical variables. Each observation is classified as either A, B, C, or D. For simplicity's sake, let's say that the classification variable, cl, is A for the first 100 observations, B for observations 101 to 200, C till 300, and D till 400. I'm trying to get a partition that has 2/3 of the observations for each of A, B, C, and D (as opposed to simply getting 2/3 of the observations for the entire data set since it will likely not have equal amounts of each classification). When I try to sample from a subset of the data, such as sample(subset(data, cl=='A')), the columns are reordered instead of the rows. To summarize, my goal is to have 67 random observations from each of A, B, C, and D as my training data, and store the remaining 33 observations for each of A, B, C, and D as testing data. I have found a very similar question to mine, but it did not factor in multiple variables. I feel silly asking this question because it seems so simple, but I'm stumped. Also, this is my first question on this site, so I apologize in advance for any faux pas on my part.

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• What is the fastest way to find duplicates in multiple BIG txt files?

  - by user2950750

  I am really in deep water here and I need a lifeline. I have 10 txt files. Each file has up to 100.000.000 lines of data. Each line is simply a number representing something else. Numbers go up to 9 digits. I need to (somehow) scan these 10 files and find the numbers that appear in all 10 files. And here comes the tricky part. I have to do it in less than 2 seconds. I am not a developer, so I need an explanation for dummies. I have done enough research to learn that hash tables and map reduce might be something that I can make use of. But can it really be used to make it this fast, or do I need more advanced solutions? I have also been thinking about cutting up the files into smaller files. To that 1 file with 100.000.000 lines is transformed into 100 files with 1.000.000 lines. But I do not know what is best: 10 files with 100 million lines or 1000 files with 1 million lines? When I try to open the 100 million line file, it takes forever. So I think, maybe, it is just too big to be used. But I don't know if you can write code that will scan it without opening. Speed is the most important factor in this, and I need to know if it can be done as fast as I need it, or if I have to store my data in another way, for example, in a database like mysql or something. Thank you in advance to anybody that can give some good feedback.

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• convert variable with mixed date formats to one format in r

  - by jalapic

  A sample of my dataframe: date 1 25 February 1987 2 20 August 1974 3 9 October 1984 4 18 August 1992 5 19 September 1995 6 16-Oct-63 7 30-Sep-65 8 22 Jan 2008 9 13-11-1961 10 18 August 1987 11 15-Sep-70 12 5 October 1994 13 5 December 1984 14 03/23/87 15 30 August 1988 16 26-10-1993 17 22 August 1989 18 13-Sep-97 I have a large dataframe with a date variable that has multiple formats for dates. Most of the formats in the variable are shown above- there are a couple of very rare others too. The reason why there are multiple formats is that the data were pulled together from various websites that each used different formats. I have tried using straightforward conversions e.g. strftime(mydf$date,"%d/%m/%Y") but these sorts of conversion will not work if there are multiple formats. I don't want to resort to multiple gsub type editing. I was wondering if I am missing a more simple solution? Code for example: structure(list(date = structure(c(12L, 8L, 18L, 6L, 7L, 4L, 14L, 10L, 1L, 5L, 3L, 17L, 16L, 11L, 15L, 13L, 9L, 2L), .Label = c("13-11-1961", "13-Sep-97", "15-Sep-70", "16-Oct-63", "18 August 1987", "18 August 1992", "19 September 1995", "20 August 1974", "22 August 1989", "22 Jan 2008", "03/23/87", "25 February 1987", "26-10-1993", "30-Sep-65", "30 August 1988", "5 December 1984", "5 October 1994", "9 October 1984"), class = "factor")), .Names = "date", row.names = c(NA, -18L), class = "data.frame")

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• Why is my quick sort so slow?

  - by user513075

  Hello, I am practicing writing sorting algorithms as part of some interview preparation, and I am wondering if anybody can help me spot why this quick sort is not very fast? It appears to have the correct runtime complexity, but it is slower than my merge sort by a constant factor of about 2. I would also appreciate any comments that would improve my code that don't necessarily answer the question. Thanks a lot for your help! Please don't hesitate to let me know if I have made any etiquette mistakes. This is my first question here. private class QuickSort implements Sort { @Override public int[] sortItems(int[] ts) { List<Integer> toSort = new ArrayList<Integer>(); for (int i : ts) { toSort.add(i); } toSort = partition(toSort); int[] ret = new int[ts.length]; for (int i = 0; i < toSort.size(); i++) { ret[i] = toSort.get(i); } return ret; } private List<Integer> partition(List<Integer> toSort) { if (toSort.size() <= 1) return toSort; int pivotIndex = myRandom.nextInt(toSort.size()); Integer pivot = toSort.get(pivotIndex); toSort.remove(pivotIndex); List<Integer> left = new ArrayList<Integer>(); List<Integer> right = new ArrayList<Integer>(); for (int i : toSort) { if (i > pivot) right.add(i); else left.add(i); } left = partition(left); right = partition(right); left.add(pivot); left.addAll(right); return left; } }

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• A scripting engine for Ruby?

  - by Earlz

  Hello, I am creating a Ruby On Rails website, and for one part it needs to be dynamic so that (sorta) trusted users can make parts of the website work differently. For this, I need a scripting language. In a sort of similar project in ASP.Net, I wrote my own scripting language/DSL. I can not use that source code(written at work) though, and I don't want to make another scripting language if I don't have to. So, what choices do I have? The scripting must be locked down and not be able to crash my server or anything. I'd really like if I could use Ruby as the scripting language, but it's not strictly necessary. Also, this scripting part will be called on almost every request for the website, sometimes more than once. So, speed is a factor. I looked at the RubyLuaBridge but it is Alpha status and seems dead. What choices for a scripting language do I have in a Ruby project? Also, I will have full control over where this project is deployed(root access), so there are no real limits..

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• Is memory allocation in linux non-blocking?

  - by Mark

  I am curious to know if the allocating memory using a default new operator is a non-blocking operation. e.g. struct Node { int a,b; }; ... Node foo = new Node(); If multiple threads tried to create a new Node and if one of them was suspended by the OS in the middle of allocation, would it block other threads from making progress? The reason why I ask is because I had a concurrent data structure that created new nodes. I then modified the algorithm to recycle the nodes. The throughput performance of the two algorithms was virtually identical on a 24 core machine. However, I then created an interference program that ran on all the system cores in order to create as much OS pre-emption as possible. The throughput performance of the algorithm that created new nodes decreased by a factor of 5 relative the the algorithm that recycled nodes. I'm curious to know why this would occur. Thanks. *Edit : pointing me to the code for the c++ memory allocator for linux would be helpful as well. I tried looking before posting this question, but had trouble finding it.

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• Why can't you return a List from a Compiled Query?

  - by Andrew

  I was speeding up my app by using compiled queries for queries which were getting hit over and over. I tried to implement it like this: Function Select(ByVal fk_id As Integer) As List(SomeEntity) Using db As New DataContext() db.ObjectTrackingEnabled = False Return CompiledSelect(db, fk_id) End Using End Function Shared CompiledSelect As Func(Of DataContext, Integer, List(Of SomeEntity)) = _ CompiledQuery.Compile(Function(db As DataContext, fk_id As Integer) _ (From u In db.SomeEntities _ Where u.SomeLinkedEntity.ID = fk_id _ Select u).ToList()) This did not work and I got this error message: Type : System.ArgumentNullException, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 Message : Value cannot be null. Parameter name: value However, when I changed my compiled query to return IQueryable instead of List like so: Function Select(ByVal fk_id As Integer) As List(SomeEntity) Using db As New DataContext() db.ObjectTrackingEnabled = False Return CompiledSelect(db, fk_id).ToList() End Using End Function Shared CompiledSelect As Func(Of DataContext, Integer, IQueryable(Of SomeEntity)) = _ CompiledQuery.Compile(Function(db As DataContext, fk_id As Integer) _ From u In db.SomeEntities _ Where u.SomeLinkedEntity.ID = fk_id _ Select u) It worked fine. Can anyone shed any light as to why this is? BTW, compiled queries rock! They sped up my app by a factor of 2.

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• Entity Framework LINQ Query using Custom C# Class Method - Once yes, once no - because executing on the client or in SQL?

  - by BrooklynDev

  I have two Entity Framework 4 Linq queries I wrote that make use of a custom class method, one works and one does not: The custom method is: public static DateTime GetLastReadToDate(string fbaUsername, Discussion discussion) { return (discussion.DiscussionUserReads.Where(dur => dur.User.aspnet_User.UserName == fbaUsername).FirstOrDefault() ?? new DiscussionUserRead { ReadToDate = DateTime.Now.AddYears(-99) }).ReadToDate; } The linq query that works calls a from after a from, the equivalent of SelectMany(): from g in oc.Users.Where(u => u.aspnet_User.UserName == fbaUsername).First().Groups from d in g.Discussions select new { UnReadPostCount = d.Posts.Where(p => p.CreatedDate > DiscussionRepository.GetLastReadToDate(fbaUsername, p.Discussion)).Count() }; The query that does not work is more like a regular select: from d in oc.Discussions where d.Group.Name == "Student" select new { UnReadPostCount = d.Posts.Where(p => p.CreatedDate > DiscussionRepository.GetLastReadToDate(fbaUsername, p.Discussion)).Count(), }; The error I get is: LINQ to Entities does not recognize the method 'System.DateTime GetLastReadToDate(System.String, Discussion)' method, and this method cannot be translated into a store expression. My question is, why am I able to use my custom GetLastReadToDate() method in the first query and not the second? I suppose this has something to do with what gets executed on the db server and what gets executed on the client? These queries seem to use the GetLastReadToDate() method so similarly though, I'm wondering why would work for the first and not the second, and most importantly if there's a way to factor common query syntax like what's in the GetLastReadToDate() method into a separate location to be reused in several different places LINQ queries. Please note all these queries are sharing the same object context.

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• parse.json of authenticated play request

  - by niklassaers

  I've set up authentication in my application like this, always allow when a username is supplied and the API-key is 123: object Auth { def IsAuthenticated(block: => String => Request[AnyContent] => Result) = { Security.Authenticated(RetrieveUser, HandleUnauthorized) { user => Action { request => block(user)(request) } } } def RetrieveUser(request: RequestHeader) = { val auth = new String(base64Decode(request.headers.get("AUTHORIZATION").get.replaceFirst("Basic", ""))) val split = auth.split(":") val user = split(0) val pass = split(1) Option(user) } def HandleUnauthorized(request: RequestHeader) = { Results.Forbidden } def APIKey(apiKey: String)(f: => String => Request[AnyContent] => Result) = IsAuthenticated { user => request => if(apiKey == "123") f(user)(request) else Results.Forbidden } } I want then to define a method in my controller (testOut in this case) that uses the request as application/json only. Now, before I added authentication, I'd say "def testOut = Action(parse.json) {...}", but now that I'm using authentication, how can I add parse.json in to the mix and make this work? def testOut = Auth.APIKey("123") { username => implicit request => var props:Map[String, JsValue] = Map[String, JsValue]() request.body match { case JsObject(fields) => { props = fields.toMap } case _ => {} // Ok("received something else: " + request.body + '\n') } if(!props.contains("UUID")) props.+("UUID" -> UniqueIdGenerator.uuid) if (!props.contains("entity")) props.+("entity" -> "unset") props.+("username" -> username) Ok(props.toString) } As a bonus question, why is only UUID added to the props map, not entity and username? Sorry about the noob factor, I'm trying to learn Scala and Play at the same time. :-) Cheers Nik

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• Out-of-memory algorithms for addressing large arrays

  - by reve_etrange

  I am trying to deal with a very large dataset. I have k = ~4200 matrices (varying sizes) which must be compared combinatorially, skipping non-unique and self comparisons. Each of k(k-1)/2 comparisons produces a matrix, which must be indexed against its parents (i.e. can find out where it came from). The convenient way to do this is to (triangularly) fill a k-by-k cell array with the result of each comparison. These are ~100 X ~100 matrices, on average. Using single precision floats, it works out to 400 GB overall. I need to 1) generate the cell array or pieces of it without trying to place the whole thing in memory and 2) access its elements (and their elements) in like fashion. My attempts have been inefficient due to reliance on MATLAB's eval() as well as save and clear occurring in loops. for i=1:k [~,m] = size(data{i}); cur_var = ['H' int2str(i)]; %# if i == 1; save('FileName'); end; %# If using a single MAT file and need to create it. eval([cur_var ' = cell(1,k-i);']); for j=i+1:k [~,n] = size(data{j}); eval([cur_var '{i,j} = zeros(m,n,''single'');']); eval([cur_var '{i,j} = compare(data{i},data{j});']); end save(cur_var,cur_var); %# Add '-append' when using a single MAT file. clear(cur_var); end The other thing I have done is to perform the split when mod((i+j-1)/2,max(factor(k(k-1)/2))) == 0. This divides the result into the largest number of same-size pieces, which seems logical. The indexing is a little more complicated, but not too bad because a linear index could be used. Does anyone know/see a better way?

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• Matlab fft function

  - by CTZStef

  The code below is from the Matlab 2011a help about fft function. I think there is a problem here : why do they multiply t(1:50) by Fs, and then say it's time in millisecond ? Certainly, it happens to be true in this very particular case, but change the value of Fs to, say, 2000, and it won't work anymore, obviously because of this factor of 2. Right ? Quite misleading, isn't it ? What do I miss ? Fs = 1000; % Sampling frequency T = 1/Fs; % Sample time L = 1000; % Length of signal t = (0:L-1)*T; % Time vector % Sum of a 50 Hz sinusoid and a 120 Hz sinusoid x = 0.7*sin(2*pi*50*t) + sin(2*pi*120*t); y = x + 2*randn(size(t)); % Sinusoids plus noise plot(Fs*t(1:50),y(1:50)) title('Signal Corrupted with Zero-Mean Random Noise') xlabel('time (milliseconds)') Clearer with this : fs = 2000; % Sampling frequency T = 1 / fs; % Sample time L = 1000; % Length of signal t2 = (0:L-1)*T; % Time vector f = 50; % signal frequency s2 = sin(2*pi*f*t2); figure, plot(fs*t2(1:50),s2(1:50)); % NOT good figure, plot(t2(1:50),s2(1:50)); % good

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• Programming texts and reference material for my Kindle DX, creating the ultimate reference device?

  - by mwilliams

  (Revisiting this topic with the release of the Kindle DX) Having owned both generation Kindle readers and now getting a Kindle DX; I'm very excited for true PDF handling on an e-ink device! An image of _Why's book on my Kindle (from my iPhone). This gives me a device capable of storing hundreds of thousands of pages that are full text search capable in the form factor of a magazine. What references (preferably PDF to preserve things such as code samples) would you recommend? Ultimately I would like reference material for every modern and applicable programming language (C, C++, Objective-C, Python, Ruby, Java, .NET (C#, Visual Basic, ASP.NET), Erlang, SQL references) as well as general programming texts and frameworks (algorithms, design patterns, theory, Rails, Django, Cocoa, ORMs, etc) and anything else that could be thought of. With so many developers here using such a wide array of languages, as a professional in your particular field, what books or references would you recommend to me for my Kindle? Creative Commons material a plus (translate that to free) as well as the material being in the PDF file format. File size is not an issue. If this turns out to be a success, I will update with a follow-up with a compiled list generated from all of the answers. Thanks for the assistance and contributing! UPDATE I have been using the Kindle DX a lot now for technical books. Check out this blog post I did for high resolution photos of different material: http://www.matthewdavidwilliams.com/2009/06/12/technical-document-pdfs-on-the-kindle-dx/

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• Information about PTE's (Page Table Entries) in Windows

  - by Patrick

  In order to find more easily buffer overflows I am changing our custom memory allocator so that it allocates a full 4KB page instead of only the wanted number of bytes. Then I change the page protection and size so that if the caller writes before or after its allocated piece of memory, the application immediately crashes. Problem is that although I have enough memory, the application never starts up completely because it runs out of memory. This has two causes: since every allocation needs 4 KB, we probably reach the 2 GB limit very soon. This problem could be solved if I would make a 64-bit executable (didn't try it yet). even when I only need a few hundreds of megabytes, the allocations fail at a certain moment. The second problem is the biggest one, and I think it's related to the maximum number of PTE's (page table entries, which store information on how Virtual Memory is mapped to physical memory, and whether pages should be read-only or not) you can have in a process. My questions (or a cry-for-tips): Where can I find information about the maximum number of PTE's in a process? Is this different (higher) for 64-bit systems/applications or not? Can the number of PTE's be configured in the application or in Windows? Thanks, Patrick PS. note for those who will try to argument that you shouldn't write your own memory manager: My application is rather specific so I really want full control over memory management (can't give any more details) Last week we had a memory overwrite which we couldn't find using the standard C++ allocator and the debugging functionality of the C/C++ run time (it only said "block corrupt" minutes after the actual corruption") We also tried standard Windows utilities (like GFLAGS, ...) but they slowed down the application by a factor of 100, and couldn't find the exact position of the overwrite either We also tried the "Full Page Heap" functionality of Application Verifier, but then the application doesn't start up either (probably also running out of PTE's)

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• Stuck in a loop

  - by Luke

  while (true) { //read in the file StreamReader convert = new StreamReader("../../convert.txt"); //define variables string line = convert.ReadLine(); double conversion; int numberIn; double conversionFactor; //ask for the conversion information Console.WriteLine("Enter the conversion in the form (Amount, Convert from, Convert to)"); String inputMeasurement = Console.ReadLine(); string[] inputMeasurementArray = inputMeasurement.Split(','); //loop through the lines looking for a match while (line != null) { string[] fileMeasurementArray = line.Split(','); if (fileMeasurementArray[0] == inputMeasurementArray[1]) { if (fileMeasurementArray[1] == inputMeasurementArray[2]) { Console.WriteLine("The conversion factor for {0} to {1} is {2}", inputMeasurementArray[1], inputMeasurementArray[2], fileMeasurementArray[2]); //convert to int numberIn = Convert.ToInt32(inputMeasurementArray[0]); conversionFactor = Convert.ToDouble(fileMeasurementArray[2]); conversion = (numberIn * conversionFactor); Console.WriteLine("{0} {1} is {2} {3} \n", inputMeasurementArray[0], inputMeasurementArray[1], conversion, inputMeasurementArray[2]); break; } } else { Console.WriteLine("Please enter two valid conversion types \n"); break; } line = convert.ReadLine(); } } The file consists of the following: ounce,gram,28.0 pound,ounce,16.0 pound,kilogram,0.454 pint,litre,0.568 inch,centimetre,2.5 mile,inch,63360.0 The user will input something like 6,ounce,gram The idea is that it finds the correct line by checking if the first and second words in the file are the same as the second and third the user enters. The problem is that if it checks the first line and it fails the if statement, if goes through to the else statement and stops. I am trying to find a way where it will stop after the it finds the correct line but not until. If someone types in a value that isn't in the file, then it should show an error.

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• How lucene indexing ?

  - by user312140

  Hello I read some document about lucene ; also i read the document in this link ( http://lucene.sourceforge.net/talks/pisa ) . I don't really understand how lucene index documents and don't understand lucene work with which algorithm for indexing ? On above link , said lucene use this algorithm for indexing : * incremental algorithm: o maintain a stack of segment indices o create index for each incoming document o push new indexes onto the stack o let b=10 be the merge factor; M=8 for (size = 1; size < M; size *= b) { if (there are b indexes with size docs on top of the stack) { pop them off the stack; merge them into a single index; push the merged index onto the stack; } else { break; } } How this algorithm help us to have an optimize indexing ? Does lucene use B-tree algorithm or any other algorithm like that for indexing or have a paticular algorithm ? Thank you for reading my post .

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