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  • What is the most efficient functional version of the following imperative code?

    - by justin.r.s.
    I'm learning Scala and I want to know the best way of expressing this imperative pattern using Scala's functional programming capabilities. def f(l: List[Int]): Boolean = { for (e <- l) { if (test(e)) return true } } return false } The best I can come up with is along the lines of: l map { e => test(e) } contains true But this is less efficient since it calls test() on each element, whereas the imperative version stops on the first element that satisfies test(). Is there a more idiomatic functional programming technique I can use to the same effect? The imperative version seems awkward in Scala.

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  • Missing something with Reader monad - passing the damn thing around everywhere

    - by Richard Huxton
    Learning Haskell, managing syntax, have a rough grasp of what monads etc are about but I'm clearly missing something. In main I can read my config file, and supply it as runReader (somefunc) myEnv just fine. But somefunc doesn't need access to the myEnv the reader supplies, nor do the next couple in the chain. The function that needs something from myEnv is a tiny leaf function. So - how do I get access to the environment in a function without tagging all the intervening functions as (Reader Env)? That can't be right because otherwise you'd just pass myEnv around in the first place. And passing unused parameters through multiple levels of functions is just ugly (isn't it?). There are plenty of examples I can find on the net but they all seem to have only one level between runReader and accessing the environment.

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  • What's the deal with all of the abstract stuff?

    - by JustVenting
    I see a lot of talk about MVVM, MVC, Design Patterns etc... You know, some guy has a blog, and he spent the last six months learning about one these things and desiging a program centered around that concept and then he goes on and on about it like its better than sliced bread. I read all of this crap and I wonder, whatever happened to simple logical programming? Not self-absorbed huge frameworks of design patterns and mvc and whatever else you can think of... just simple linear programming, perhaps a few classes to encapsulate things here and there.

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  • Change function into dependencyproperty

    - by Jaya Willianto
    Hi everyone.. I am new to XAML and WPF and I am learning about DependencyProperty and Path. For example, I have a function like this public byte[] DownloadPicture() { WebClient webClient = new WebClient(); byte[] data; data = webClient.DownloadData("https://graph.facebook.com/4/picture&type=large"); return data; } and I have dependencyproperty like this public static DependencyProperty DownloadPicProperty = DependencyProperty.Register("DownloadPic", typeof(byte), typeof(ImageControl), new PropertyMetadata(false)); How can I connect the DependencyProperty with the DownloadPicture function I wrote? Any suggestions? What should I write in the CLR wrapper?

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  • A way of allocating multidimensional arrays dynamically

    - by C77431
    salute.. I am learning dynamic allocations for multidimensional arrays in a book and I found some ways for that, And now haven't problem in it. But the author of the book shows us a way, but it doesn't work correctly. It is this: pbeans = new double [3][4]; // Allocate memory for a 3x4 array And this is the error: error C2440: '=' : cannot convert from 'int (*)[4]' to 'int *' how should i define pbeans ( if this type of coding is legal)? and what is the problem exactly? Regards.

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  • Calculation of derived field in sql

    - by Matt
    Taking Sql this quarter and not having any luck with the following question: The height of players in feet (inches/12). Include their name. Hint: Calculation or derived field. Be sure to give the calculated field a column header. We're learning the basic Select statment and didn't find any reference on how to make custom data at w3schools. I'm using Microsoft SQL server Management Express Here's my statment so far: select nameLast, nameFirst, height from Master where height (I assume its something like 'Player_Height' = height/12) order by nameLast, nameFirst, height Thanks for the help

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  • Start diving into large open source projetcs

    - by Vanangamudi
    How to start learning and reading the source of large and complex projects like Blender3D and Gimp, for instance. Since the developers busy improving it and there is no docs exist at present, how do we start developing and customizing these projects. Linux kernel deserve to have several books on its code, also these kind of project do deserve the same. And there are no unit tests available for this kind of projects. Say I'm going to read and understand the source code blender. How do I start. How to setup the development environment for developing the app? If it includes several dependencies, and assume that their source code also available how to setup this kind of inter-related, coherent source code to debug?

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  • How many real world developers are involved with the Demoscene?

    - by spoulson
    I grew up learning to code based on what I've experienced with the demoscene. It seems to be a pretty sparse subculture in the US. How many developers watch or participate in the scene? Teaser: If you haven't checked out the scene before, take a look at one of my favorites: Debris by Farbrausch. Watch on demoscene.tv or download the app (179k) and run it yourself. No video, all realtime rendering and audio. Think, a small group of guys wrote this for a competition on their free time.

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  • Creating Html Helper Method - MVC Framework

    - by nettguy
    I am learning MVC from Stephen Walther tutorials on MSDN website. He suggests that we can create Html Helper method. Say Example using System; namespace MvcApplication1.Helpers { public class LabelHelper { public static string Label(string target, string text) { return String.Format("<label for='{0}'>{1}</label>", target, text); } } } My Question under which folder do i need to create these class? View folder or controller folder? or can i place it in App_Code folder?

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  • Caching vector addition over changing collections

    - by DRMacIver
    I have the following setup: I have a largish number of uuids (currently about 10k but expected to grow unboundedly - they're user IDs) and a function f : id - sparse vector with 32-bit integer values (no need to worry about precision). The function is reasonably expensive (not outrageously so, but probably on the order of a few 100ms for a given id). The dimension of the sparse vectors should be assumed to be infinite, as new dimensions can appear over time, but in practice is unlikely to ever exceed about 20k (and individual results of f are unlikely to have more than a few hundred non-zero values). I want to support the following operations efficiently: add a new ID to the collection invalidate an existing ID retrieve sum f(id) in O(changes since last retrieval) i.e. I want to cache the sum of the vectors in a way that's reasonable to do incrementally. One option would be to support a remove ID operation and treat invalidation as a remove followed by an add. The problem with this is that it requires us to keep track of all the old values of f, which is expensive in space. I potentially need to use many instances of this sort of cached structure, so I would like to avoid that. The likely usage pattern is that new IDs are added at a fairly continuous rate and are frequently invalidated at first. Ids which have been invalidated recently are much more likely to be invalidated again than ones which have remained valid for a long time, but in principle an old Id can still be invalidated. Ideally I don't want to do this in memory (or at least I want a way that lets me save the result to disk efficiently), so an idea which lets me piggyback off an existing DB implementation of some sort would be especially appreciated.

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  • How is the syntax for stl iterators implemented?

    - by Liberalkid
    I've been working on writing a library in my spare time to familiarize myself more with c++ and singular value decomposition. I've been working on writing an Iterator class and I'm entirely capable of writing the functionality and I have already for my own currently MatrixIterator class. I'm guessing that it involves namespaces because: vector<int>::iterator Would appear to be an iterator from the namespace vector, but namespaces are another topic which I'm not familiar with. Mainly I'm asking what would it involve to implement an iterator such that it could be referenced in a similar way to the stl iterators. I'm also aware that I could use boost.iterators or something similar to save myself a lot of work, but I'm more interested in learning all of the details that go into something like this.

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  • JQuery Ajax returned blank data

    - by kwokwai
    Hi all, I am learning how to use JQuery to help check data availability. I have written a function in a Controller for checking data input, and the URL is like this: http://www.mywebsite.com/controllers/action/avariable but the returned data was blank. <Script language="javascript"> $(document).ready(function(){ $(document).change(function(){ var usr = $("#data\\[User\\]\\[name\\]").val(); $.post{"http://www.mywebsite.com/controllers/action/", usr, function(msg){alert(msg);} } }); }); </Script> <div id="username"> <input type=text name="data[User][name]" id="data[User][name]"> </div> Here is the code of the Action: function action($data=null){ $this->autoRender = false; $result2=$this->__avail($udata); if($result2==1) {return "OK";} else {return "NOT";} }

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  • What Should be the Structure of a C++ Project?

    - by Ell
    I have recently started learning C++ and coming from a Ruby environment I have found it very hard to structure a project in a way that it still compiles correctly, I have been using Code::Blocks which is brilliant but a downside is that when I add a new header file or c++ source file, it will generate some code and even though it is only a mere 3 or 4 lines, I do not know what these lines do. First of all I would like to ask this question: What do these lines do? #ifndef TEXTGAME_H_INCLUDED #define TEXTGAME_H_INCLUDED #endif // TEXTGAME_H_INCLUDED My second question is, do I need to #include both the .h file and the .cpp file, and in which order. My third question is where can I find the GNU GCC Compiler that, I beleive, was packaged with Code::Blocks and how do I use it without Code::Blocks? I would rather develop in a notepad++ sort of way because that is what I'm used to in Ruby but since C++ is compiled, you may think differently (please give advice and views on that as well) Thanks in advance, ell.

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  • Difference between var and Class class in object creation

    - by Divine
    Its a silly question, however shocked to see different behaviors. Learning a lot. Lets say I have two classes below Class A { public void Display() { } } Class B : A { public void Display() { } } Class C : B { public void Display() { } } Class Final { static void Main() { var c = new C(); // B c = new C(); //My doubt is, both of the above gives different results. May I know B c = new C() creates object of B or C? What I understood is, it creates object of B. Then why we say "new C()"? I agree with C c = new C(); But I thought, B b = new C(); creates object of B. Where we use this style? Only when utilizing runtime polymorphism? (Overriding methods)? } }

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  • How would you use version control for personal data, like a personal website?

    - by nn
    This is more a use-case question, but I generate static files for a personal website using txt2tags. I was thinking of maybe storing this information in a git repository. Normally I use RCS since it's simplest, and I'm only a single user. But there just seems to be a large trend of people using git/svn/cvs/etc. for personal data, and I thought this may also be a good way to at least learn some of the basics of the tool. Obviously most of the learning is done in an environment where you collaborate. So back to the question: how would you use use a version control system such as git, to manage a personal website?

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  • What is the most efficient algorithm for reversing a String in Java?

    - by Hultner
    I am wondering which way to reverse a string in Java that is most efficient. Should I use some sort of xor method? The easy way would be to put all the chars in a stack and put them back into a string again but I doubt that's a very efficient way to do it. And please do not tell me to use some built in function in Java. I am interested in learning how to do it not to use an efficient function but not knowing why it's efficient or how it's built up.

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  • After C++ - Python or Java?

    - by carleeto
    I'm fast approaching the point in my coding where I would like to quickly write object oriented code in languages other than C++ for a variety of reasons. After a lot of research, my choices have pretty much narrowed down to Python and Java. I'm leaning towards Python because of its relationship to C, but with Java, from what I can see, I get a good introduction to using and creating test suites with Eclipse - there is also Processing which is pulling me towards Java. I'm not the kind of guy to tackle two languages at once, so which one would you recommend and why? What I want at the end is to have an additional language I can use for rapid development. Ease of learning isn't important to me as I'm willing to put in the time regardless. Ability to use the new language widely is.

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  • Errors when using a Ruby On Rails scaffold with a data type of interger

    - by bublebboy
    I am learning Ruby On Rails. I am on a shared hosting with Ruby version 1.8.1 and Rails version 2.3.10. I am working my way through a tutorial at http://railstutorial.org/chapters/a-demo-app?version=2.3#top and at one point in the tutorial it has me run: script/generate scaffold Micropost content:string user_id:interger The tutorial is using the default database, SQLite3. The command works and I use rake db:migrate to create the database. I can view the page listing the microposts (which is empty), but when I try to add a micropost (microposts/new) I get an error undefined method `user_id' for #<Micropost:0x7f710e4988e8> After doing some testing on my own it seems I experience the problem by using the data type of interger. While I understand that using a scaffold is not the best way of building a ruby on rails, I'm just beginning and would still like to know why I am experiencing this problem to help me better understand how rails works.

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  • Hibernate - One design problem

    - by Yatendra Goel
    I am learning Hibernate from the tutorial on JBoss website. I have a confusion in a code example located here. There is a Cat class code at 4.1. A simple POJO example. This Cat class has a reference to his mother as private Cat mother; Q1. If the class has an identifier property as id, then wouldn't it be better to store the cat's mother's id instead of cat's mother object. means instead of private Cat mother; wouldn't it be better to have private long motherId; `

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  • How do I get a MessageBox like information window to appear in Java?

    - by John McClane
    I'm learning Java and I have no idea how to do this. I dragged a button on the form in Netbeans, double clicked it and it created this event: @Action public void HelloClickMethod() { JOptionPane.showMessageDialog(this, "The message!", "This is supposed to be the MessageBox title."); } This is the exception the IDE brings up. Cannot find symbol. Symbol: showMessageDialog() Edit 1 Now I changed it to this: @Action public void HelloClickMethod() { JOptionPane.showMessageDialog(this, "The message!", "This is supposed to be the MessageBox title.",JOptionPane.ERROR_MESSAGE); } However the IDE is saying I have an error in the word 'this'. "Cannot find symbol". I don't understand. Why is it so dificult and why are the errors so esoteric. :P

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  • c# how to get keydown and button click to do the same thing??

    - by myax
    I am new to C#.I am learning to make a calculator just like ms windows calculator.the buttons work when i click it, but I want the numpad to work too. Suppose the user types '0', it should be the same as if he clicked the 0 button on my gui. here is my button click event for 0. private void button0_Click(object sender, EventArgs e) { checkifequa(); textBox1.Text = textBox1.Text + "0"; } how do i get the keydown to work?

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  • How many variables is to many when storing in _SESSION?

    - by steve
    Hi - I'm looking for an idea of best practices here. I have a web based application that has a number of hooks into other systems. Let's say 5, and each of these 5 systems has a number of flags to determine different settings the user has selected in said systems, lets say 5 settings per system (so 5*5). I am storing the status of these settings in the user sesion variables and was wondering is that a sufficient way of doing it? I'm learning php as I go along so not sure about any pitfalls that this could run me into!

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  • C# connectionString encryption questions

    - by 5YrsLaterDBA
    I am learning how to encrypt the ConnectionString for our C# (3.5) Application. I read the .Net Framwork Developer Guide (http://msdn.microsoft.com/en-us/library/89211k9b(VS.80).aspx) about securing connection string. but not fully understand the contents. It says "The connection string can only be decrypted on the computer on which it was encrypted." We have a release machine which will build our application which will generate the OurApp.exe.config and then install it to many product machines. Is that meam we have to have this encryption process separated with our application and run it at individual product machine? We may use the "RSAProtectedConfigurationProvider". It mentioned we need encryption key for that provider. when and how we should provide the encryption key? thanks,

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  • is counter has certain value inside a class in python

    - by mazlor
    i am learning classes in python and when i was reading the documentation i found this example that i didn't understand : class MyClass: """A simple example class""" def __init__(self): self.data = [] i = 12345 def f(self): return 'hello world' then if we assign : x = MyClass() x.counter = 1 now if we implement while loop : while x.counter < 10: x.counter = x.counter * 2 so the value of x.counter will be : 16 while for example if we have a variable y : y = 1 while y < 1 : y = y *2 then if we look for the value of y we find it 1 so i don't know how is the value of counter became 16 . thanks

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  • Creating custom ribbon with SQL Server linked Access application

    - by andy
    I'm just learning about creating custom ribbons in Access 2010, but I'm running into an issue. The Access application I'm working with is connected to a SQL Server backend (connected, not just linked tables). As I understand it, the USysRibbons table needs to exist in the Access application itself, and not in a connected SQL Server. How does one go about creating a table in an Access application that is already linked to a SQL Server? I tried creating the table in a blank database and then importing it into the Access application without any luck.

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