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• Remove redundant entries, scala way

  - by andersbohn

  Edit: Added the fact, that the list is sorted, and realizing 'duplicate' is misleading, replaced that with 'redundant' in the title. I have a sorted list of entries stating a production value in a given interval. Entries stating the exact same value at a later time adds no information and can safely be left out. case class Entry(minute:Int, production:Double) val entries = List(Entry(0, 100.0), Entry(5, 100.0), Entry(10, 100.0), Entry(20, 120.0), Entry(30, 100.0), Entry(180, 0.0)) Experimenting with the scala 2.8 collection functions, so far I have this working implementation: entries.foldRight(List[Entry]()) { (entry, list) => list match { case head :: tail if (entry.production == head.production) => entry :: tail case head :: tail => entry :: list case List() => entry :: List() } } res0: List[Entry] = List(Entry(0,100.0), Entry(20,120.0), Entry(30,100.0), Entry(180,0.0)) Any comments? Am I missing out on some scala magic?

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• Java - JPA - Generators - @SequenceGenerator

  - by Yatendra Goel

  I am learning JPA and have confusion in the @SequenceGenerator annotation. Upto my understanding, it automatically assigns a value to numeric identity fields/properties of an entity. Q1. Does this sequence generator make use of the database's increasing numeric value generating capability or generates the number on his own? Q2. If JPA uses database auto increement feauture, then will it work with datastores that don't have auto increement feature? Q3. If JPA generate numeric value on his own, then how the JPA implementation knows which value to generate next? Does it consult with the database first to see what value was stored last so as to generate the value (last + 1). ====================================================================================== Q4. Please also throw some light on sequenceName and allocationSize properties of @SequenceGenerator annotation.

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• undefined reference to static member variable

  - by Max

  Hi. I have this class that has a static member. it is also a base class for several other classes in my program. Here's its header file: #ifndef YARL_OBJECT_HPP #define YARL_OBJECT_HPP namespace yarlObject { class YarlObject { // Member Variables private: static int nextID; // keeps track of the next ID number to be used int ID; // the identifier for a specific object // Member Functions public: YarlObject(): ID(++nextID) {} virtual ~YarlObject() {} int getID() const {return ID;} }; } #endif and here's its implementation file. #include "YarlObject.hpp" namespace yarlObject { int YarlObject::nextID = 0; } I'm using g++, and it returns three undefined reference to 'yarlObject::YarlObject::nextID linker errors. If I change the ++nextID phrase in the constructor to just nextID, then I only get one error, and if I change it to 1, then it links correctly. I imagine it's something simple, but what's going on?

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• Archiving Database Tables using Java

  - by HonorGod

  My application demands archiving database tables between sybase and db2 and vice-a-versa and within(db2 to db2 and sybase to sybase) using java. I am trying to understand the best strategies around in terms performance, implementation, ease of use and scalability. Here is my current process - source and destination tables with the acceptable parameters (from java) are defined within xml. the application reads the source and destination configurations and execute them sequentially. destination is sometime optional when source is just deleting data from a specific table or when the source is just calling a stored procedure. dataset between source and destination is extremely large (in millions) From top of my head, it looks like I can define dependencies between multiple source and destination combination and have them execute in parallel in multiple treads. But will this improve any performance(i hope it will)? Are there any open-source frameworks for data archiving using java? Any other thoughts on the implements side will be really helpful. Thanks

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• Want to add a new property to a class, can I use anonymous functions for this?

  - by Blankman

  I have 2 Lists: List<User> List<UserStats> So I want to add a property Count to User (it doesn't have one now, and I can't change the implementation at this point). For a web service call, that returns json, I want to modify the User object. Basically I add the Users to a collection. So I want to add a modified user class (via anonymous functions?) to the collection before I serialize it to json. So something like: loop users { user.Count = userstats[user.ID].Count; list.Add(user); } is this possible? how?

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• Grouped UITableView's cell separator missing when setting backgroundView with an image

  - by Howard Spear

  I have a grouped UITableView with a custom UITableViewCell class and I am adding a custom background image to each cell. However, when I do this, the cell's separator is not visible. If simply switch the table style to Plain instead of Grouped, the separator is showing up. I need the grouped table - how do I make the separator show up? Here's my code: @interface MyCustomTableViewCell : UITableViewCell @end @implementation MyCustomTableViewCell // because I'm loading the cell from a xib file - (id)initWithCoder:(NSCoder *)coder { self = [super initWithCoder:coder]; if (self) { // Create a background image view. self.backgroundView = [[UIImageView alloc] init]; } return self; } // MyViewController - (UITableViewCell *)tableView:(UITableView *)aTableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { // // standard cell dequeue + create cell code here // // // Configure the cell background now // UIImage *backgroundImage = [UIImage imageNamed:@"odd_row.png"]; if (indexPath.row % 2 == 0) { backgroundImage = [UIImage imageNamed:@"even_row.png"]; } UIImageView *backgroundView = (UIImageView *)cell.backgroundView; backgroundView.image = backgroundImage; }

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• Instance where embedded C++ compilers don't support multiple inheritance?

  - by Nathan

  I read a bit about a previous attempt to make a C++ standard for embedded platforms where they specifically said multiple inheritance was bad and thus not supported. From what I understand, this was never implemented as a mainstream thing and most embedded C++ compilers support most standard C++ constructs. Are there cases where a compiler on a current embedded platform (i.e. something not more than a few years old) absolutely does not support multiple inheritance? I don't really want to do multiple inheritance in a sense where I have a child with two full implementations of a class. What I am most interested in is inheriting from a single implementation of a class and then also inheriting one or more pure virtual classes as interfaces only. This is roughly equivalent to Java/.Net where I can extend only one class but implement as many interfaces as I need. In C++ this is all done through multiple inheritance rather than being able to specifically define an interface and declare a class implements it.

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• How to override the attr_protected?

  - by KandadaBoggu

  I have STI implementation as follows: class Automobile < ActiveRecord::Base end class Car < Automobile end class Truck < Automobile end class User < ActiveRecord::Base has_many :automobiles accepts_nested_attributes_for :automobiles end I am creating a list of automobiles for a user. For each automobile, the UI sets the type field and the properties associated with the automobile.While form submission, the type field is ignored as it is a protected attribute. How do I work around this issue? Is there a declarative way to unprotect a protected attribute?

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• Aspect Oriented Programming vs List<IAction> To execute methods based on conditions

  - by David Robbins

  I'm new to AOP so bear with me. Consider the following scenario: A state machine is used in a workflow engine, and after the state of the application is changed, a series of commands are executed. Depending on the state, different types of commands should be executed. As I see it, one implementation is to create List<IAction> and have each individual action determine whether it should execute. Would a Aspect Oriented process work as well? That is, could you create an aspect that notifies a class when a property changes, and execute the appropriate processes from that class? Would this help centralize the state specific rules?

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• How to synchronize static method in java.

  - by Summer_More_More_Tea

  Hi there: I come up with this question when implementing singleton pattern in Java. Even though the example listed blow is not my real code, yet very similar to the original one. public class ConnectionFactory{ private static ConnectionFactory instance; public static synchronized ConnectionFactory getInstance(){ if( instance == null ){ instance = new ConnectionFactory(); } return instance; } private ConnectionFactory(){ // private constructor implementation } } Because I'm not quite sure about the behavior of a static synchronized method, I get some suggestion from google -- do not have (or as less as possible) multiple static synchronized methods in the same class. I guess when implementing static synchronized method, a lock belongs to Class object is used so that multiple static synchronized methods may degrade performance of the system. Am I right? or JVM use other mechanism to implement static synchronized method? What's the best practice if I have to implement multiple static synchronized methods in a class? Thank you all! Kind regards!

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• How to efficiently deal with a large amount of HTML5 canvas pixel data over websockets

  - by user730569

  Using imageData = context.getImageData(0, 0, width, height); JSON.stringify(imageData.data); I grab the pixel data, convert it to a string, and then send it over the wire via websockets. However, this string can be pretty large, depending on the size of the canvas object. I tried using the compression technique found here: JavaScript implementation of Gzip but socket.io throws the error Websocket message contains invalid character(s). Is there an effective way to compress this data so that it can be sent over websockets?

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• Simplest LINQ in C# troubleshooting.

  - by Jay

  I'm trying to learn a bit of LINQ but I'm having compile issues right off the bat. Is there any specific reason why this won't work? using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace HelloLINQ { class HelloLINQ { public static void Main() { Example1(); } public static void Example1() { var numbers = new int[] { 1, 5, 3, 7, 3, 8, 9, 3, 6, 6, 2 }; var under5 = from n in numbers select n; foreach (var n in under5) { Console.WriteLine(n); } } } } The error is: Could not find an implementation of the query pattern for source type 'int[]'. 'Select' not found. Are you missing a reference to 'System.Core.dll' or a using directive for 'System.Linq'?

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• Auto pointer for unsigned char array?

  - by Gianluca

  I'd need a class like std::auto_ptr for an array of unsigned char*, allocated with new[]. But auto_ptr only calls delete and not delete[], so i can't use it. I also need to have a function which creates and returns the array. I came out with my own implementation within a class ArrayDeleter, which i use like in this example: #include <Utils/ArrayDeleter.hxx> typedef Utils::ArrayDeleter<unsigned char> Bytes; void f() { // Create array with new unsigned char* xBytes = new unsigned char[10]; // pass array to constructor of ArrayDeleter and // wrap it into auto_ptr return std::auto_ptr<Bytes>(new Bytes(xBytes)); } ... // usage of return value { auto_ptr<Bytes> xBytes(f()); }// unsigned char* is destroyed with delete[] in destructor of ArrayDeleter Is there a more elegant way to solve this? (Even using another "popular" library)

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• What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

  - by fabrizioM

  I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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• C5 Generics Collection IntervalHeap<T> -- getting an IPriorityQueueHandle from a T for Replace or De

  - by Jared Updike

  I'm using the Generics Collection library C5 (server down :-( ) and I have an IntervalHeap(T) and I need to Delete or Replace a T that is not the Max or Min. How do I get an IPriorityQueueHandle from my T? The C5 library source code shows that IPriorityQueueHandle(T) has no methods or properties to implement and the compiler thinks my implementation of IPriorityQueueHandle(T) for my T is acceptable. I try to use a T like this: q.Replace(t, t); and the C5 library throws an InvalidCastException because it cannot convert my T to a (Handle).

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• calling resize on std vector of pointers crashed

  - by user11869

  The problem can be reproduced using VS 2013 Express. It crashed when internal vector implementation tried to deallocate the original vector. However, the problem can solved by using 'new' instead of 'malloc'. Anyone can shed some light on this? struct UndirectedGraphNode { int label; vector<UndirectedGraphNode *> neighbors; UndirectedGraphNode(int x) : label(x) {}; }; int main(int argc, char** argv) { UndirectedGraphNode* node1 = (UndirectedGraphNode*)malloc(sizeof(UndirectedGraphNode)); node1->label = 0; node1->neighbors.resize(2); return 0; }

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• How to detect touchEvent across multiple objects?

  - by RobGThai

  In short: I need to find a way to implement swipe action (touchEvent) for my Calendar just like the default Android Calendar one. I am using GridView to make a calendar for my application. When I touch any date, I launch an activity to display details on that date. My problem is that now I tried to implement swipe to change month/year to display but I dont know a way to do it. I tried to use setOnTouchListener on GridView but it seems like detecting for each grid separately instead of the whole grid as one. Further problem would be that it overridden my onItemClick implementation as well.

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• Simple Serialization Faster Than JSON? (in Ruby)

  - by Sinan Taifour

  I have an application written in ruby (that runs in the JRuby VM). When profiling it, I realized that it spends a lot (actually almost all of) its time converting some hashes into JSON. These hashes have keys of symbols, values of other similar hashes, arrays, strings, and numbers. Is there a serialization method that is suitable for such an input, and would typically run faster than JSON? It would preferable if it is has a Java or JRuby-compatible gem, too. I am currently using the jruby-json gem, which is the fastest JSON implementation in JRuby (as I am told), so the move will most likely be to a different serialization method rather than just a different library. Any help is appreciated! Thanks.

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• Why I can't called my doSomething method?

  - by Tattat

  This is my DrawSomethingCmd: #import "Command.h"; @interface DrawSomethingCmd : Command { } -(void)doSomething; -(void)execute; @end and the DrawSomethingCmd.m's doSomething method is like that: -(void)doSomething{ NSLog(@"did"); } The Command.h: #import <Foundation/Foundation.h> @interface Command : NSObject { } -(void)execute; And the Command.m: #import "Command.h" @implementation Command -(id)init{ return self; } -(void)execute{ } @end And I have the method like this: DrawSomethingCmd *tempCmd = [[DrawSomethingCmd alloc] init]; [tempCmd doSomething]; But my Console did't show any things on that, what's going on?

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• C++ - how does Sleep() and cin work?

  - by quano

  Just curious. How does actually the function Sleep() work (declared in windows.h)? Maybe not just that implementation, but anyone. With that I mean - how is it implemented? How can it make the code "stop" for a specific time? Also curious about how cin and those actually work. What do they do exactly? The only way I know how to "block" something from continuing to run is with a while loop, but considering that that takes a huge amount of processing power in comparison to what's happening when you're invoking methods to read from stdin (just compare a while (true) to a read from stdin), I'm guessing that isn't what they do.

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• How to save state of the app when app terminates?

  - by user164589

  Hi guys. I am trying to save the app state by encoding when the app terminates. I've found the solution related this issue. But I don't know how to use. I am really trying to make encoding and decoding like this: http://cocoaheads.byu.edu/wiki/nscoding in CustomObject.h @interface CustomObject : NSObject <NSCoding> { NSArray *someArray; } in CustomObject.m @implementation CustomObject // Other method implementations here - (void) encodeWithCoder:(NSCoder*)encoder { [encoder encodeObject:someArray forKey:@"someArray"]; } - (id) initWithCoder:(NSCoder*)decoder { if (self = [super init]) { someArray = [[decoder decodeObjectForKey:@"someArray"] retain]; } return self; } @end My object to save is another NSArray. Not "someArray" in CustomObject. We call it that "MySaveObject". I want to pass "MySaveObject" to "someArray" in CustomObject. Actually I don't know how to encode "MySaveObject" and to pass to "someArray" in CustomObject. Thanks in advance.

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• Gwt-ext. Bean to record and record to bean.

  - by den bardadym

  I write a RIA application and my JPA beans must be decoded to push it in Store. My decisions are: Brute Force. If I have property 'aProp' in bean (and getter/setter for it) i create RecordDef, then Record, then Recrod.set('aProp', bean.getAProp()) and so on.. (it is terrible) I can write generator for creating a Factory of Records (it is my desision and i write it). For example: RecordFactory<User> factory = GWT.create(User.class); //User is entity I now that i need a reflection, BUT GWT have no implementation of reflection (some libraries emulates this, but they builds on generators) Exists the best way? Thanks, Den Bardadym.

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• What do the external JSF libraries/frameworks add?

  - by kgrad

  I have seen mention of a bunch of external JSF Libraries such as ICEfaces, Richfaces, etc. However, I am unsure as to what these libraries actually add over just using JSF 2.0. Are they just additional components that are pre-built? I know that PrettyFaces adds URL rewriting, and I Believe that ICEFaces/Richfaces add Ajax enabled components? What are some other major component libraries, what are their benefits / why should people use them? Additionally, what does a framework like SEAM add over using straight JSF2 with EJB? Is MYFaces simply a different implementation of JSF?

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• Are volatile data members trivially copyable?

  - by Lightness Races in Orbit

  Whilst writing this answer I realised that I'm not as confident about my conclusions as I usually would ensure before hitting Post Your Answer. I can find a couple of reasonably convincing citations for the argument that the trivial-copyability of volatile data members is either implementation defined or flat-out false: https://groups.google.com/forum/?fromgroups=#!topic/comp.std.c++/5cWxmw71ktI http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48118 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3159.html#496 But I haven't been able to back this up in the standard1 itself. Particularly "worrying" is that there's no sign of the proposed wording change from that n3159 issues list in the actual standard's final wording. So, what gives? Are volatile data members trivially copyable, or not? 1   C++11

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• Implementing Transparent Persistence

  - by Jules

  Transparent persistence allows you to use regular objects instead of a database. The objects are automatically read from and written to disk. Examples of such systems are Gemstone and Rucksack (for common lisp). Simplified version of what they do: if you access foo.bar and bar is not in memory, it gets loaded from disk. If you do foo.bar = baz then the foo object gets updated on disk. Most systems also have some form of transactions, and they may have support for sharing objects across programs and even across a network. My question is what are the different techniques for implementing these kind of systems and what are the trade offs between these implementation approaches?

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