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• Can I create a collection in Scala that uses different equals/hashCode/compare implementations?

  - by Willis Blackburn

  I'm looking for as simple way to create an identity set. I just want to be able to keep track of whether or not I've "seen" a particular object while traversing a graph. I can't use a regular Set because Set uses "==" (the equals method in Scala) to compare elements. What I want is a Set that uses "eq." Is there any way to create a Set in Scala that uses some application-specified method for testing equality rather than calling equals on the set elements? I looked for some kind of "wrapEquals" method that I could override but did not find it. I know that I could use Java's IdentityHashMap, but I'm looking for something more general-purpose. Another idea I had was to just wrap each set element in another object that implements equals in terms of eq, but it's wasteful to generate tons of new objects just to get a new equals implementation. Thanks!

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• Microsoft SQL Server 2008 Web Edition: is it suitable for "closed" websites?

  - by micha12

  Can Microsoft SQL Server 2008 Web Edition be used in "closed" websites, which are hosted on the Internet, but require users to log in? We are developing a web application for banks. This is a website for clients of the bank; it allows clients to log in and view information on their personal banking accounts, stock portfolios, etc. Can this web app use SQL Server 2008 Web Edition? Here is information on this edition of SQL Server: http://www.microsoft.com/sqlserver/2008/en/us/web.aspx It is said on this page that Web Edition can be used only on "public and Internet accessible ... Web applications". Technically, the web app we are developing is public and Internet accessible - although it requires authentication. Won't using Web Edition in our web app violate SQL Server license terms? Thank you.

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• 2d parabolic projectile

  - by ndg

  I'm looking to create a basic Javascript implementation of a projectile that follows a parabolic arc (or something close to one) to arrive at a specific point. I'm not particularly well versed when it comes to complex mathematics and have spent days reading material on the problem. Unfortunately, seeing mathematical solutions is fairly useless to me. I'm ideally looking for pseudo code (or even existing example code) to try to get my head around it. Everything I find seems to only offer partial solutions to the problem. In practical terms, I'm looking to simulate the flight of an arrow from one location (the location of the bow) to another. It strikes me there are two distinct problems here: determining the position of interception between the projectile and a (moving) target, and then calculating the trajectory of the projectile. Any help would be greatly appreciated.

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• C#: When should I use TryParse?

  - by zxcvbnm

  I understand it doesn't throw an Exception and because of that it might be sightly faster, but also, you're most likely using it to convert input to data you can use, so I don't think it's used so often to make that much of difference in terms of performance. Anyway, the examples I saw are all along the lines of an if/else block with TryParse, the else returning an error message. And to me, that's basically the same thing as using a try/catch block with the catch returning an error message. So, am I missing something? Is there a situation when this is actually useful?

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• How to insert multiple check-box values inside database when one or more will be left unchecked?

  - by Sally

  I have a form that contains 5 check boxes. The user may select one or more of these check boxes. The user may select 2 and leave 3 unchecked or select 4 and leave one unchecked and so on, in that case how can I write the php/mysql code that will insert the form data into the database. With just one selection it's easy, I would do: $checkbox_value = $_POST['i_agree']; mysql_query("INSERT INTO terms (user, pass, conditions) VALUES ('$user','$pass','$checkbox_value')"); But how can I write this when there are multiple check box options and only one or more of them will be checked? I want to insert them all in one column called "tags" separated by commas.

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• How, exactly, does the double-stringize trick work?

  - by Peter Hosey

  At least some C preprocessors let you stringize the value of a macro, rather than its name, by passing it through one function-like macro to another that stringizes it: #define STR1(x) #x #define STR2(x) STR1(x) #define THE_ANSWER 42 #define THE_ANSWER_STR STR2(THE_ANSWER) /* "42" */ Example use cases here. This does work, at least in GCC and Clang (both with -std=c99), but I'm not sure how it works in C-standard terms. Is this behavior guaranteed by C99? If so, how does C99 guarantee it? If not, at what point does the behavior go from C-defined to GCC-defined?

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• Color space - RGB and YCbCr question

  - by HardCoder1986

  Hello! I am now trying to understand how JPEG encoding works and everything seems fine except the color transformation part. Before attempting to do a DCT in JPEG algorithm, the image is transformed into YCbCr color space. To me this essentially means that we just (comparing to initial RGB image) take a chunk of color information and dispose it while applying the RGB -> YCbCr transformation. So, our encoding steps look generally like RGB -> YCbCr -> DCT -> Huffman. The decoding means inversing this process. And my question is - why does the image (for example, created and exported to JPEG) remain the same in terms of color, although we have to make inverse YCbCr -> RGB transform. Where does the disposed part of color information comes from or how is it handled?

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• Database indexes and their Big-O notation

  - by miket2e

  I'm trying to understand the performance of database indexes in terms of Big-O notation. Without knowing much about it, I would guess that: Querying on a primary key or unique index will give you a O(1) lookup time. Querying on a non-unique index will also give a O(1) time, albeit maybe the '1' is slower than for the unique index (?) Querying on a column without an index will give a O(N) lookup time (full table scan). Is this generally correct ? Will querying on a primary key ever give worse performance than O(1) ? My specific concern is for SQLite, but I'd be interested in knowing to what extent this varies between different databases too.

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• Rails gems and plugins usage in Netbeans

  - by LearnRails

  Hi, I am working with rails 2.3 with netbeans 6.5.1 on vista. I want to install more plugins from Git in netbeans like shoulda, cucumber etc. I have these questions: 1) I do not have much knowledge of Git. Is it necessary to install Git to make use of the Git plugins in netbeans? Are gems and plugins dependant on each other? 2) In case Git is needed and I do install msysgit , for example I can use the command ruby script/plugin install http://github.com/thoughtbot/shoulda.git/ to install shoulda plugin. How to make netbeans use this plugin or how to include this plugin in netbeans? 3) Is RubyMine a better IDE for Rails than Netbeans in terms of more gems and plugins availability? Thanks

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• Visual Studio 2008 resolving wrong reference

  - by e28Makaveli

  In my project file, I have the following entry: <Reference Include="Microsoft.Practices.Unity, Version=1.2.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL"> <HintPath>..\..\..\..\Libraries\Microsoft.Practices.Unity.dll</HintPath> </Reference> which in absolute terms translates to: C:\dev\LUT600 2.1.1\OCC600\Libraries Somehow, when I try to compile the project, Visual Studio loads a reference from a totally different path: /reference:"C:\Program Files\Microsoft Enterprise Library 4.1 - October 2008\Bin\Microsoft.Practices.Unity.dll. How it resolves to this location is a complete mystery as this DLL is not referenced anywhere in this project. I have set Specific Verion to true but it still resolves the reference from this location. Any ideas? TIA. Klaus

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• can QuickGraph support these requirements? (includes database persistence support)

  - by Greg

  Hi, Would QuickGraph be able to help me out with my requirements below? (a) want to model a graph of nodes and directional relationships between nodes - for example to model web pages/files linked under a URL, or modeling IT infrastructure and dependencies between hardware/software. The library would include methods such as * Node.GetDirectParents() //i.e. there could be more than one direct parent for a node * Node.GetRootParents() //i.e. traverse the tree to the top root parent(s) for the given node * Node.GetDirectChildren() * Node.GetAllChildren() (b) have to persist the data to a database - so it should support SQL Server and ideally SQLite as well. If it does support these requirement then I'd love to hear: any pointers to any parts of QuickGraph to dig into? what is the best concept re it's usage in terms of how to use database persistence - is it a simpler design to assume every search/method works directly on the database, or does QuickGraph support smarts to be able to work in memory and the "save" to database all changes at an appropriate point in time (e.g. like ADO.net does with DataTable etc) Thanks in advance

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• Java hashcode based on identity

  - by hjfreyer

  The default behavior of Object.hashCode() is to return essentially the "address" of the object so that a.hashCode() == b.hashCode() if and only if a == b. How can I get this behavior in a user-defined class if a superclass already defines hashCode()? For instance: class A { public int hashCode() { return 0; } } class B extends A { public int hashCode() { // Now I want to return a unique hashcode for each object. // In pythonic terms, it'd look something like: return Object.hashCode(this); } } Ideas?

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• Open source C compiler in C#?

  - by Dinah

  I've been getting into compiler creation. I've found some terrific beginner stuff and advanced stuff but nothing in the middle. I've created 3 different simple proof-of-concept compilers for toy languages but I want to expose myself to something real. The most straight forward real language in terms of syntax seems to be C. Since the language I'm most comfortable with right now is C#, I'd love to study the source code of a real non-tutorial C compiler written in C#. Does one (with source code available) exist?

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• Levenshtein: MySQL + PHP

  - by user317005

  $word = strtolower($_GET['term']); $lev = 0; $q = mysql_uqery("SELECT `term` FROM `words`"); while($r = mysql_fetch_assoc($q)) { $r['term'] = strtolower($r['term']); $lev = levenshtein($word, $r['term']); if($lev >= 0 && $lev < 5) { $word = $r['term']; } } how can I move all that into just one query? don't want to have to query through all terms and do the filtering in php.

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• What's the most "death-resistant" component on Android?

  - by Arhimed

  I'm looking for the most suitable class to be a dispatcher for AsyncTasks invoked from my Activities. I think it could be one of these: subclass of Application; subclass of Service; my own static stuff. As for me - it's simlier to implement the 3rd choice. But the question is will it be more "death-resistant" than Service or Application? Also it's very interesting what will live longer - Application or Service? My guess is the Application lives as long as the app (task in terms of Android) process lives. So basically I need to range those options by their "death-resistant" quality, because I'd like to rely on the most "static" thing.

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• Hardware-specific questions

  - by overflow

  I'm good at programming yet I feel like I don't know enough about the architecture of the hardware I'm working on. What does the Northbridge on the mainboard do? What does the L2 cache of my processor do? Can Windows XP use multiple processors? Not in terms of concrete multitasking in all programs but using the capacity of all cores if needed instead of always only one core. How can my processor/mainboard interact with multiple kinds of graphics/sound cards?

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• Storage for large gridded datasets

  - by nullglob

  I am looking for a good storage format for large, gridded datasets. The application is meteorology, and we would prefer a format that is common within this field (to help exchange data with others). I don't need to deal with special data structures, and there should be a Fortran API. I am currently considering HDF5, GRIB2 and NetCDF4. How do these formats compare in terms of data compression? What are their main limitations? How steep is the learning curve? Are there any other storage formats worth investigating? I have not found a great deal of material outlining the differences and pros/cons of these formats (there is one relevant SO thread, and a presentation comparing GRIB and NetCDF).

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• Why are difference lists more efficient than regular concatenation?

  - by Craig Innes

  I am currently working my way through the Learn you a haskell book online, and have come to a chapter where the author is explaining that some list concatenations can be ineffiecient: For example ((((a ++ b) ++ c) ++ d) ++ e) ++ f Is supposedly inefficient. The solution the author comes up with is to use 'difference lists' defined as newtype DiffList a = DiffList {getDiffList :: [a] -> [a] } instance Monoid (DiffList a) where mempty = DiffList (\xs -> [] ++ xs) (DiffList f) `mappend` (DiffList g) = DiffList (\xs -> f (g xs)) I am struggling to understand why DiffList is more computationally efficient than a simple concatenation in some cases. Could someone explain to me in simple terms why the above example is so inefficient, and in what way the DiffList solves this problem?

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• what is the pattern for modifying a collection in C#

  - by macias

  What is the pattern (best practice) for such problem -- modifying elements (values) in collection? Conditions: size of the collection is not changed (no element is deleted or added) modification is in-place In C++ it was easy and nice, I just iterated trough a collection and changed the elements. But in C# iterating (using enumerator) is read-only operation (speaking in terms of C++, only const_iterator is available). So, how to do this in C#? Example: having sequence of "1,2,3,4" modification is changing it to "1, 2, 8, 9" but not "1, 2, 3" or "1, 2, 3, 4, 5".

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• What mail storage should I choose for our web application; IMAP, key-valud store, rdbms, ...

  - by tvrtko

  I have to store e-mail messages for use with our application. I have "metadata" for all messages inside a relational database, but I don't feel comfortable keeping message content (gigabytes and terabytes of email data) inside a database. I'm currently using IMAP as a storage, but I have my doubts if I choose correctly. First of all there is a problem of uidvalidity and how to keep a permanent reference to message inside IMAP. Second, I'm not sure if this is the most robust solution in terms of backup/restore strategies, corruption of store, replication ... Positive side is that I can query IMAP using the headers because the data is mostly indexed. I don't know if key-value stores are a better approach (Casandra, Tokyo cabinet, redis). How they handle storing 1KB and 50MB of data. How they prevent corruption and when corruption or device failure happens how can I repair the store.

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• How do I measure distances in an image?

  - by Ram Bhat

  Let's say we have an image like so Let's say we've already used filters and an edge detection algorithm in this pic. Now my goal is to measure distances (NOT actual distances, distance can be in any arbitrary unit) . eg: How do I find the length of the hall? (until the window) Or the height of the bookshelves? How exactly do you place the "scale" and measure. I'm looking for ideas. However it would help if the answers were in terms of OpenCV.

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• Count of memory copies in *nix systems between packet at NIC and user application?

  - by Michael_73

  Hi there, This is just a general question relating to some high-performance computing I've been wondering about. A certain low-latency messaging vendor speaks in its supporting documentation about using raw sockets to transfer the data directly from the network device to the user application and in so doing it speaks about reducing the messaging latency even further than it does anyway (in other admittedly carefully thought-out design decisions). My question is therefore to those that grok the networking stacks on Unix or Unix-like systems. How much difference are they likely to be able to realise using this method? Feel free to answer in terms of memory copies, numbers of whales rescued or areas the size of Wales ;) Their messaging is UDP-based, as I understand it, so there's no problem with establishing TCP connections etc. Any other points of interest on this topic would be gratefully thought about! Best wishes, Mike

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• Efficiently retrieve objects with one to many references in Grails using GORM

  - by bebeastie

  I'm trying to determine how to find/retrieve/load objects efficiently in terms of a.) minimizing calls to database and b.) keeping the code as elegant/simple as possible (i.e. not writing hql etc.). Assume you have two objects: public class Foo { Bar bar String badge } public class Bar { String name } Each Foo has a bar and a badge. Also assume that all badges are unique within a bar. So if a Foo has a badge "4565" there are no other Foos that have the same badge # AND the same bar. If I have a bar ID, how can I efficiently retrive the Foo w/o first selecting Bar? I know I can do this: Foo.findByBadgeAndBar("4565", Bar.findById("1")) But that seems to cause a select on the Bar table followed by a select on the Foo table. In other words, I need to produce the Grails/Hibernate/GORM equivalent of the following: select * from foo where badge="4565" and bar_id="1"

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• How to estimate the quality of a web page?

  - by roddik

  Hello, I'm doing a university project, that must gather and combine data on a user provided topic. The problem I've encountered is that Google search results for many terms are polluted with low quality autogenerated pages and if I use them, I can end up with wrong facts. How is it possible to estimate the quality/trustworthiness of a page? You may think "nah, Google engineers are working on the problem for 10 years and he's asking for a solution", but if you think about it, SE must provide up-to-date content and if it marks a good page as a bad one, users will be dissatisfied. I don't have such limitations, so if the algorithm accidentally marks as bad some good pages, that wouldn't be a problem.

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• Should I use C++0x Features Now?

  - by svu2g

  With the official release of VS 2010, is it safe for me to start using the partially-implemented C++0x feature set in my new code? The features that are of interest to me right now are both implemented by VC++ 2010 and recent versions of GCC. These are the only two that I have to support. In terms of the "safety" mentioned in the first sentence: can I start using these features (e.g., lambda functions) and still be guaranteed that my code will compile in 10 years on a compiler that properly conforms to C++0x when it is officially released? I guess I'm asking if there is any chance that VC++ 2010 or GCC will end up like VC++ 6; it was released before the language was officially standardized and consequently allowed grossly ill-formed code to compile. After all, Microsoft does say that "10 is the new 6". ;)

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