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  • Best similarity metric for collaborative filtering?

    - by allclaws
    I'm trying to decide on the best similarity metric for a product recommendation system using item-based collaborative filtering. This is a shopping basket scenario where ratings are binary valued - the user has either purchased an item or not - there is no explicit rating system (eg, 5-stars). Step 1 is to compute item-to-item similarity, though I want to look at incorporating more features later on. Is the Tanimoto coefficient the best way to go for binary values? Or are there other metrics that are appropriate here? Thanks.

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  • What to do of exceptions when implementing java.lang.Iterator

    - by Vincent Robert
    The java.lang.Iterator interface has 3 methods: hasNext, next and remove. In order to implement a read-only iterator, you have to provide an implementation for 2 of those: hasNext and next. My problem is that these methods does not declare any exceptions. So if my code inside the iteration process declares exceptions, I must enclose my iteration code inside a try/catch block. My current policy has been to rethrow the exception enclosed in a RuntimeException. But this has issues because the checked exceptions are lost and the client code no longer can catch those exceptions explicitly. How can I work around this limitation in the Iterator class? Here is a sample code for clarity: class MyIterator implements Iterator { @Override public boolean hasNext() { try { return implementation.testForNext(); } catch ( SomethingBadException e ) { throw new RuntimeException(e); } } @Override public boolean next() { try { return implementation.getNext(); } catch ( SomethingBadException e ) { throw new RuntimeException(e); } } ... }

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  • php : echo"", print(), printf()

    - by marc-andre menard
    Is there a better way to output data to html page with PHP ? if i like to make a div with some var in php i will write something like that print ('<div>'.$var.'</div>); or echo "'<div>'.$var.'</div>'"; what is the PROPER way to do that ? or a better way, fill a $tempvar and print it once? like that: $tempvar = '<div>'.$var.'</div>' print ($tempvar); in fact, in real life, the var will be fill with much more !

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  • Using the using statement with WinForms... Good Practice?

    - by Nate Heinrich
    I understand the concept and reasons behind using the using statement, and I use it with things like file resources and remote connections, I was wondering if it is good practice to use the using statement with WinForm forms and dialogs? using (MyDialog dlg = new MyDialog()) { if (dlg.ShowDialog() == EDialogResult.OK) { // Do Something } } Thanks!

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  • Programming Concepts: What should be done when an exception is thrown?

    - by Dooms101
    This does not really apply to any language specifically, but if it matters I am using VB.NET in Visual Studio 2008. I can't seem to find anything really that useful using Google about this topic, but I was wondering what is common practice when an exception is thrown and caught but since it has been thrown the application cannot continue operating. For example I have exceptions that are thrown by my FileLoader class when a file cannot be found or when a file is deemed corrupt. The exception is only thrown within the class and is not handled really. If the error is detected, then the exception is thrown and whatever function is was thrown is basically quits. So in the code trying to create that object or call one of its members I use a Try...Catch statement. However, I was wondering, what should even do when this exception is caught? My application needs these files to be intact, and if they are not, the application is almost useless. So far I just pop up a message box telling the user their is an error and to reinstall. What else can I do, or better, what's common practice in these situations?

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  • Best Image Replacement Technique

    - by Josh Stodola
    What is the best (as in cross-browser) technique to do image replacement in CSS? I am using sprites to do my navigation, but I want the markup to remain SEO friendly. Given the following HTML structure... <div id="menu"> <ul> <li><a href="#">Test</a></li> <li><a href="#">Tester</a></li> <li><a href="#">Testing Testing</a></li> </ul> </div> What is the best way to replace the text with a background image using CSS only? I am currently using this... text-indent: -9999px; But, it fails with CSS on, and images off.

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  • Extending Throwable in Java

    - by polygenelubricants
    Java lets you create an entirely new subtype of Throwable, e.g: public class FlyingPig extends Throwable { ... } Now, very rarely, I may do something like this: throw new FlyingPig("Oink!"); and of course elsewhere: try { ... } catch (FlyingPig porky) { ... } My questions are: Is this a bad idea? And if so, why? What could've been done to prevent this subtyping if it is a bad idea? Since it's not preventable (as far as I know), what catastrophies could result? If this isn't such a bad idea, why not? How can you make something useful out of the fact that you can extends Throwable?

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  • Blackberry User Interface Design - Customizable UI?

    - by John Stewart
    I am trying to design a Blackberry Application and I am wondering if there are any resources on how to create custom user interface elements, skin existing ones and what other possibilities are there? I have developed a few iPhone applications with custom UI and stuff, so not sure what BB world offers in terms of UI development. Any tips, suggestions or ideas would be great.

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  • Optimal UI For Single Zip Code Entry on iPhone

    - by sylvanaar
    I need to prompt the user to enter his/her zip code at certain times in my iPhone application. I cannot store it or get it from the user's current location. What is the optimal input method? I started with a 5 wheel picker. This seemed like a bad direction, so I opted for a PIN-like entry screen. My implepentation is about the same as the 'enter passcode' screen you see when unlocking the iphone - including automatically ending input on the 5th digit instead of providing a return/enter button. Does this seem optimal? Or is there a better way? Note: I only need to accept a 5 digit US zip code.

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  • Binning a numeric variable in R

    - by McPeterson
    I have a vector X that contains positive numbers that I want to bin/discretize. For this vector, I want the numbers [0, 10) to show up just as they exist in the vector, but numbers [10,∞) to be 10+. I'm using: x <- c(0,1,3,4,2,4,2,5,43,432,34,2,34,2,342,3,4,2) binned.x <- as.factor(ifelse(x > 10,"10+",x)) but this feels klugey to me. Does anyone know a better solution or a different approach? mcpeterson

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  • How do I delete a file from depot, but leave local copy in tact?

    - by Gary
    I'm trying to learn Perforce and want to delete a file from the depot(easy to do with p4 delete, p4 submit), but that deletes it from the client machine dir structure as well. I want to keep my local file in my directory intact. The only way I can see to do this would be to move it out of the hierarchy that is under Perforce control before deleting. I was able to get my file back by syncing an earlier version. Maybe I set up my client workspace wrong? Or am I misunderstanding a fundamental concept of source control? The client workspace is /home/user and I did it this way so I could add any file under my home directory without getting an error about the file not being under client's root. FYI - Linux client and server running P4D/LINUX26X86/2009.1/222893 (2009/11/12) Any advice appreciated. Thanks.

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  • Is it good to use .settings for storing controls text data?

    - by Zenya
    In my WinForms applications I often put the controls text data (form title, labels texts, button captions, etc.) into a .settings (feature automatically generated by Visual Studio - based on the ApplicationSettingsBase class). In particular, Add a form or a control. In Solution Explorer add a new string item into the application scope of the settings file. Bind the control text property with the corresponding item of the settings file (through the property binding). Good point of this is that all my text data is collected in one place and easy to check and edit. Also it is convenient when I want to use the same text for several controls. However, I haven't heard that somebody uses the .settings such way. In tutorials for creating multilingual applications, for example, it is recommended to enter texts directly into the control property. So, is it good practice to use .settings for storing controls text data? Brief conclusion from the answers: Storing controls text data in the .settings is not common practice.

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  • Using different languages in one project

    - by Tarbal
    I recently heard about the use of several different languages in a (big) project, I also read about famous services such as Twitter using Rails as frontend, mixed with some other languages, and Scala I think it was as backend. Is this common practice? Who does that? I'm sure there are disadvantages to this. I think that you will have problems with the different interpreters/compilers and seamlessly connecting the different languages. Is this true? Why is this actually done? For performance?

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  • How much of STL is too much?

    - by Darius Kucinskas
    I am using a lot of STL code with std::for_each, bind, and so on, but I noticed that sometimes STL usage is not good idea. For example if you have a std::vector and want to do one action on each item of the vector, your first idea is to use this: std::for_each(vec.begin(), vec.end(), Foo()) and it is elegant and ok, for a while. But then comes the first set of bug reports and you have to modify code. Now you should add parameter to call Foo(), so now it becomes: std::for_each(vec.begin(), vec.end(), std::bind2nd(Foo(), X)) but that is only temporary solution. Now the project is maturing and you understand business logic much better and you want to add new modifications to code. It is at this point that you realize that you should use old good: for(std::vector::iterator it = vec.begin(); it != vec.end(); ++it) Is this happening only to me? Do you recognise this kind of pattern in your code? Have you experience similar anti-patterns using STL?

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  • How doe we name test methods where we are checking for more than one condition?

    - by Sandbox
    I follow the technique specified in Roy Osherove's The Art Of Unit Testing book while naming test methods - MethodName_Scenario_Expectation. It suits perfectly well for my 'unit' tests. But,for tests that I write in 'controller' or 'coordinator' class, there isn't necessarily a method which I want to test. For these tests, I generate multiple conditions which make up one scenario and then I verify the expectation. For example, I may set some properties on different instances, generate an event and then verify that my expectations from controller/coordinator is being met. Now, my controller handles events using a private event handler. Here my scenario is that, I set some properties, say 3 condition1,condition2 and condition3 Also, my scenario includes an event is raised I don't have a method name as my event handler is private. How do I name such a test method?

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  • What should be the "trunk" development, or release

    - by Nix
    I have the unfortunate opportunity of source control via Borland's StarTeam. It unfortunately does very few things well, and one supreme weakness is its view management. I love SVN and come from an SVN mindset. Our issue is post production release we are spending countless hours merging changes into a "production support" environment. Please do not harass me this was not my doing, I inherited it and am trying to present a better way of managing the repository. It is not an option to switch to a different SCM tool. Current setup Product.1.0 (TRUNK, current production code, and at this level are pending bug fixes) Product.2.0(true trunk anything checked in gets tested, and then released next production cycle, a lot of changes occur in this view) My proposal is going to be to swap them, have all development be done on the trunk (Production), tag on releases, and as needed create child views to represent production support bug fixes. Production Production.2.0.SP.1 I can not find any documentation to support the above proposal so I am trying to get feedback on whether or not the change is a good idea and if there is anything you would recommend doing differently.

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  • Bad method names and what it says about code structure.

    - by maxfridbe
    (Apologies in advance if this is a re-post but I didn't find similar posts) What bad method name patterns have you seen in code and what did it tell you about the code. For instance, I keep seeing: public void preform___X___IfNecessary(...); I believe that this is bad because the operation X has an inversion of conditions. Note that this is a public method because classes methods might legitimately require private helpers like this

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  • How much user data should be required to grant a password reset?

    - by Andrew Heath
    I'm looking to add password-reset functionality to my site and have been browsing the numerous threads discussing various aspects of that issue here on SO. One thing I haven't really seen clarified is how much information to require from the user for confirmation before sending out the reset email. is email alone enough? email + account username? email + account username + some other identifying value all accounts must input? I don't want my site to seem like an old wrinkly nun with a ruler, but I don't want people to be able to abuse the password reset system willy-nilly. Suggestions?

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  • How to design a class for managing file path ?

    - by remi bourgarel
    Hi All In my app, I generate some xml file for instance : "/xml/product/123.xml" where 123 is the product's id and 123.xml contains informations about this product. I also have "/xml/customer/123.xml" where 123.xml contains informations about the client ... 123 How can I manage these file paths : 1/ - I create the file path directly in the seralization method ? 2/ I create 2 static class : CustomerSerializationPathManager and ProductSerializationPathManager with 1 method : getPath(int customerID) and getPath(int productID) 3/ I create one static class : SerializationPathManager with 2 method : getCustomerPath(int customerID) and getProductPath(int productID) 4/ something else I'd prefer the solution 3 cause if I think there's only one reason to change this class : I change the root directory. So I'd like to have your thoughts about it... thx

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  • What is the basic pattern for using (N)Hibernate?

    - by Vilx-
    I'm creating a simple Windows Forms application with NHibernate and I'm a bit confused about how I'm supposed to use it. To quote the manual: ISession (NHibernate.ISession) A single-threaded, short-lived object representing a conversation between the application and the persistent store. Wraps an ADO.NET connection. Factory for ITransaction. Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier. Now, suppose I have the following scenario: I have a simple classifier which is a MSSQL table with two columns - ID (auto_increment) and Name (nvarchar). To edit this classifier I create a form which contains a single gridview and two buttons - OK and Cancel. The user can nearly directly edit the table in the gridview, and when he hits OK the changes he made are persisted to the DB (or if he hits cancel, nothing happens). Now, I have several questions about how to organize this: What should the lifetime of my ISession be? Should I create a single ISession for my whole application; an ISession for each of my forms (the application is single-threaded MDI); or an ISession for every DB operation/transaction? Does NHibernate offer some kind of built-in dirty tracking or must I do this myself? The manual mentions something like it here and there but does not go into details. How is this done? Is there not a huge overhead? Is it somehow tied with the cache(s) that NHibernate has? What are these caches for? Are they not specific to a single ISession? That is, if I use a seperate ISession for every transaction, won't it break the dirty tracking? How does the built-in dirty tracking detect deleted objects?

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  • Rounded Corners Image Change on Hover

    - by Sarfraz
    Hello, I created a rounded box/button and sliced its first corner, the middle bar (which repeats horizontally to adjust the width of the button text/content) and the last corner and used following markup: <div id="left-corner"></div> <div id="middle-bar">About Us</div> <div id="right-corner"></div> These divs have corresponding images from CSS and are floated left. Those three divs create a single rounded button wiht text About Us which is fine. Problem: I have also created similar three slices of hover images but I wonder how to apply hover to those buttons because if I use :hover with these hovered slices, then even hovering on corner images also creates hovering effect. One alternative is to use fixed width buttons and slice buttons completely but I do not want to do that.

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  • Is there a way to generate a short random id, avoiding collisions, without hitting persistent storag

    - by bshacklett
    If you've used GoToMeeting, that's the type of ID I want. I'd like it to be random so that it obfuscates the number of items being tracked and short, so that it's easy to reference manually; UUIDs are way too long. I'd like to avoid hitting persistent storage merely for performance reasons, but I can't think of any other way to avoid collisions. Is 9 digits enough to do something time-based?

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