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• In C#, is there any way to try multiple Regexes on string to see which one matches first?

  - by Matt

  Let's say I have an arbitrary list of regexes (IList<Regex> lst; for example). Is there any way to find out which one matches first? Of course there is the straightforward solution of trying each one on the string and seeing which match has the lowest index, but this could be inefficient on long strings. Of course I can go back and pull the strings back out of each regex (Regex.ToString()) and concatenate them all together ("(regex1)|(regex2)|(regex3)"), but I find this to be an ugly solution, especially since it does not even indicate which regex was matched.

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• Group MySQL Data into Arbitrarily Sized Time Buckets

  - by Eric J.

  How do I count the number of records in a MySQL table based on a timestamp column per unit of time where the unit of time is arbitrary? Specifically, I want to count how many record's timestamps fell into 15 minute buckets during a given interval. I understand how to do this in buckets of 1 second, 1 minute, 1 hour, 1 day etc. using MySQL date functions, e.g. SELECT YEAR(datefield) Y, MONTH(datefield) M, DAY(datefield) D, COUNT(*) Cnt FROM mytable GROUP BY YEAR(datefield), MONTH(datefield), DAY(datefield) but how can I group by 15 minute buckets?

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• Multiple children in single form in rails

  - by CaptnCraig

  I have a model that has an arbitrary number of children entities. For simplicity lets call the entities Orders and Items. I would like to have a create Orders form where I input the order information, as well as add as many items as I want. If I click the "Add another item" button, a new set of form elements will be added to input the new data, amounts, etc.. I could hack this out in pure javascript, but I'm pretty sure there has to be a more magical, railsish way to do it, maybe with a partial view or something. I'm just a little too new to rails to know what it is. What is the best way to dynamically add the new form elements, and then to access them in the create controller?

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• A RecursiveParentChildIterator -- like the RecursiveDirectoryIterator

  - by Stephen J. Fuhry

  There are tons of examples of using the RecursiveIterator to flatten a tree structure.. but what about using it to explode a tree structure? Is there an elegant way to use this, or some other SPL library to recursively build a tree (read: turn a flat array into array of arbitrary depth) given a table like this: SELECT id, parent_id, name FROM my_tree EDIT: You know how you can do this with Directories? $it = new RecursiveDirectoryIterator("/var/www/images"); foreach(new RecursiveIteratorIterator($it) as $file) { echo $file . PHP_EOL; } .. What if you could do something like this: $it = new RecursiveParentChildIterator($result_array); foreach(new RecursiveIteratorIterator($it) as $group) { echo $group->name . PHP_EOL; // this would contain all of the children of this group, recursively $children = $group->getChildren(); } :END EDIT

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• What is the algorithm used by the memberwise equality test in .NET structs?

  - by Damian Powell

  What is the algorithm used by the memberwise equality test in .NET structs? I would like to know this so that I can use it as the basis for my own algorithm. I am trying to write a recursive memberwise equality test for arbitrary objects (in C#) for testing the logical equality of DTOs. This is considerably easier if the DTOs are structs (since ValueType.Equals does mostly the right thing) but that is not always appropriate. I would also like to override comparison of any IEnumerable objects (but not strings!) so that their contents are compared rather than their properties. This has proven to be harder than I would expect. Any hints will be greatly appreciated. I'll accept the answer that proves most useful or supplies a link to the most useful information. Thanks.

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• Reject (Hard 404) ASP.NET MVC-style URLs

  - by James D

  Hi, ASP.NET MVC web app that exposes "friendly" URLs: http://somesite.com/friendlyurl ...which are rewritten (not redirected) to ASP.NET MVC-style URLs under the hood: http://somesite.com/Controller/Action The user never actually sees any ASP.NET MVC style URLS. If he requests one, we hard 404 it. ASP.NET MVC is (in this app) an implementation detail, not a fundamental interface. My question: how do you examine an arbitrary incoming URL and determine whether or not that URL matches a defined ASP.NET MVC path? For extra credit: how do you do it from inside an ASP.NET-style IHttpModule, where you're getting invoked upstream from the ASP.NET MVC runtime? Thanks!

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• Changing the color of a Rebol button

  - by Dave Matuszek

  I want to ask multiple choice questions in Rebol. Possible answers will be on buttons. I want to turn a button red when it is clicked and it is the wrong answer. When the correct button is pressed, I want to proceed to the next question. I can change the color of a box (mybox/color: red show mybox). I can set up a toggle with two colors (but I can't change it based on the result of an arbitrary test (is the answer correct?). It seems like there is probably a simple way to change the color of a button, without having to create my own button-like face objects. Isn't there?

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• What wording in the C++ standard allows static_cast<non-void-type*>(malloc(N)); to work?

  - by ben

  As far as I understand the wording in 5.2.9 Static cast, the only time the result of a void*-to-object-pointer conversion is allowed is when the void* was a result of the inverse conversion in the first place. Throughout the standard there is a bunch of references to the representation of a pointer, and the representation of a void pointer being the same as that of a char pointer, and so on, but it never seems to explicitly say that casting an arbitrary void pointer yields a pointer to the same location in memory, with a different type, much like type-punning is undefined where not punning back to an object's actual type. So while malloc clearly returns the address of suitable memory and so on, there does not seem to be any way to actually make use of it, portably, as far as I have seen.

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• Function Composition in C++

  - by Channel72

  There are a lot of impressive Boost libraries such as Boost.Lambda or Boost.Phoenix which go a long way towards making C++ into a truly functional language. But is there a straightforward way to create a composite function from any 2 or more arbitrary functions or functors? If I have: int f(int x) and int g(int x), I want to do something like f . g which would statically generate a new function object equivalent to f(g(x)). This seems to be possible through various techniques, such as those discussed here. Certainly, you can chain calls to boost::lambda::bind to create a composite functor. But is there anything in Boost which easily allows you to take any 2 or more functions or function objects and combine them to create a single composite functor, similar to how you would do it in a language like Haskell?

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• Revisions: algorithm and data structure

  - by SODA

  Hi, I need ideas for structuring and processing data with revisions. For example, I have a database of objects (e.g. cars). Each object has a number of properties, which can be arbitrary, so there's no a set schema to describe these objects. These objects are probably saved as key-value pairs. Now I need to change property of an object. I don't want to completely rewrite it - I want to be able to go back and see history of changes to these properties, that's why I want to add new property and keep the old one (so I guess a timestamp would do the job of telling which property is the latest). At the same time I want to be able to get info about any object in a snap, with only latest versions of each of the properties. Any ideas what would be the best approach? At least please point me in the right direction. Thanks!

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• Efficient synchronization of querying an array of resources

  - by Erel Segal Halevi

  There is a list of N resources, each of them can be queried by at most a single thread at a time. There are serveral threads that need to do the same thing at approximately the same time: query each of the resources (each thread has a different query), in arbitrary order, and collect the responses. If each thread loops over the resources in the same order, from 0 to N-1, then they will probably have to wait for each other, which is not efficient. I thought of letting the threads loop over the resources in a random permutation, but this seems too complex and also not so efficient, for example, for 2 resources and 2 threads, in half the cases they will choose the same order and wait for each other. Is there a simple and more efficient way to solve this?

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• signed angle between two 3d vectors with same origin within the same plane? recipe?

  - by Advanced Customer

  Was looking through the web for an answer but it seems like there is no clear recipe for it. What I need is a signed angle of rotation between two vectors Va and Vb lying within the same 3D plane and having the same origin knowing that: the plane contatining both vectors is an arbitrary and is not parallel to XY or any other of cardinal planes Vn - is a plane normal both vectors along with the normal have the same origin O = { 0, 0, 0 } Va - is a reference for measuring the left handed rotation at Vn The angle should be measured in such a way so if the plane would be XY plane the Va would stand for X axis unit vector of it. I guess I should perform a kind of coordinate space transformation by using the Va as the X-axis and the cross product of Vb and Vn as the Y-axis and then just using some 2d method like with atan2() or something. Any ideas? Formulas?

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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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• How to order results based on number of search term matches?

  - by Travis

  I am using the following tables in mysql to describe records that can have multiple searchtags associated with them: TABLE records ID title desc TABLE searchTags ID name TABLE recordSearchTags recordID searchTagID To SELECT records based on arbitrary search input, I have a statement that looks sort of like this: SELECT recordID FROM recordSearchTags LEFT JOIN searchTags ON recordSearchTags.searchTagID = searchTags.ID WHERE searchTags.name LIKE CONCAT('%','$search1','%') OR searchTags.name LIKE CONCAT('%','$search2','%') OR searchTags.name LIKE CONCAT('%','$search3','%') OR searchTags.name LIKE CONCAT('%','$search4','%'); I'd like to ORDER this resultset, so that rows that match with more search terms are displayed in front of rows that match with fewer search terms. For example, if a row matches all 4 search terms, it will be top of the list. A row that matches only 2 search terms will be somewhere in the middle. And a row that matches just one search term will be at the end. Any suggestions on what is the best way to do this? Thanks!

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• make mongrel_rails (localhost:3000) visible to a virtual machine

  - by Max Williams

  I develop rails in ubuntu and i just set up a virtualbox windows xp virtual machine for IE testing. I'd like to be able to run mongrel_rails in ubuntu and then jump into the vm to check it out, so i can jump back, make a change, jump into the vm again, reload the page and test it, etc. Is this possible? In this sort of situation in the past i've had to set up an apache server on my dev machine and run mongrel under that, in order to get an externally visible (ie visible to my local network) ip address that i then paste into the address bar of IE in the vm. Is this really necessary? Is there a simpler way? Can i do something with my /etc/hosts or sites-available files to just make up some arbitrary network address which points to localhost:3000 in ubuntu? Or something? thanks, max

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• Choosing a design pattern for a class that might change it's internal attributes

  - by the_drow

  I have a class that holds arbitrary state and it's defined like this: class AbstractFoo { }; template <class StatePolicy> class Foo : public StatePolicy, public AbstractFoo { }; The state policy contains only protected attributes that represent the state. The state might be the same for multiple behaviors and they can be replaced at runtime. All Foo objects have the same interface to abstract the state itself and to enable storing Foo objects in containers. I would like to find the least verbose and the most maintainable way to express this.

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• How can I limit the number of connections to an mssql server from my tomcat deployed java applicatio

  - by CJ

  Hi, I have an application that is deployed on tomcat on server A and sends queries to a huge variety of mssql databases on an server B. I am concerned that my application could overload this mssql database server and would like some way to preventing it making requests to connect to any database on that server if some arbitrary number of connections were already in existence and unclosed. I am looking at using connection pooling but am under the impression that this will only pool connections to a specific database on the mssql server, I want to control the total of these combined connections that will occur to many different databases (incidentally I can only find out the names of individual db's dynamically as they change day to day). Will connection pooling take care of this for me, are am I looking at this from the wrong perspective? I have no access to the configuration of the mssql server. Links to tutorials or working examples of your suggested solution are most welcome! Thanks, Caroline

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• Programmatic Website Screen Shots

  - by Ian

  I'm checking into the available methods for programmatically taking screenshots of an arbitrary website. For example, Facebook: http://clicktoverify.truste.com/pvr.php?page=validate&url=www.facebook.com&sealid=102 Salesforce.com: http://clicktoverify.truste.com/pvr.php?page=validate&companyName=Salesforce.com,%20Inc.&sealid=102&internal=true On that page you'll see they have a screenshot of the referenced site. What are my options for getting these kinds of screenshots in an automated fashion? I'm primarily working with PHP, but am open to all suggestions. Thanks!

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• What's void *userData exactly?

  - by mystify

  In a C function declaration, I have seen this parameter definition: void *userData so, what exactly is that? My guess: the void says it can be anything arbitrary, or even nothing. Almost similar to id of objective-c. It just allows to pass in whatever data structure you like. The star in front of userData says, that the argument must be passed in by reference. So when using this stuff in the function body, typically it must be casted and dereferenced. So if I pass in an pointer to SomeClass instance, I would get that like this: SomeClass *myObj = (SomeClass*)userData; In the case I had nothing special to pass along, I would provide NULL as argument. Are my assumptions correct? Or did I get something wrong?

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• How do I get phpMyAdmin to connect to a local mysql server?

  - by bryan

  Hi everyone, I have my config.inc.php file, and have set my host name to localhost. Unfortunately, I have no idea what my username/password should be. Is that something I need to configure on the MySql side? I tried creating an arbitrary username/password (admin/password), but when I try to log into phpMyAdmin with those credentials, I get an error: (#1045 - Access denied for user 'admin'@'localhost' (using password: YES)) Can anyone point me in the right direction? (Sorry for the dumb question; I just haven't had to install mysql before. I've always had a host name / username / password given to me.) Thanks!

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• C++ library for Coordinate Transformation Matrices (CTM)?

  - by BastiBense

  I'm looking for a C++ library which allows for easy integration of Coordinate Transformation Matrices (CTM) in my application. You might know CTMs from PDF or PostScript. For one project we are using C++/Qt4 as a framework, which offers a QTransform class, which provides methods like .translate(double x, double y) or .rotate(double degrees). After doing some transformations, it would allow me to get all 6 CTM values, which I could feed into a PDF library or use a transformation matrix in export files. Qt's API also allows for arbitrary mapping of polygons (QPolygon), rectangles (QRect) and other primitive data structures into transformed coordinate systems. So basically I'm looking for something similar to what Qt provides, but without the need of using Qt. I know I could do the matrix multiplications myself, but I'm not really interested in doing so, as I'm very sure that someone already solved this problem, so please no links to books or other guides on how to multiply matrices. Thanks!

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• is this a simple monad example?

  - by zcaudate

  This is my attempt to grok monadic functions after watching http://channel9.msdn.com/Shows/Going+Deep/Brian-Beckman-Dont-fear-the-Monads. h uses bind to compose together two arbitrary functions f and g. What is the unit operator in this case? ;; f :: int - [str] ;; g :: str = [keyword] ;; bind :: [str] - (str - [keyword]) - [keyword] ;; h :: int - [keyword] (defn f [v] (map str (range v))) (defn g [s] (map keyword (repeat 4 s))) (defn bind [l f] (flatten (map f l))) (f 8) ;; = (0 1 2 3 4 5 6 7) (g "s") ;; = (:s :s :s :s) (defn h [v] (bind (f v) g)) (h 9) ;; = (:0 :0 :0 :0 :1 :1 :1 :1 :2 :2 :2 :2 :3 :3 :3 :3 :4 :4 :4 :4 :5 :5 :5 :5)

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• filtering elements from list of lists in Python?

  - by user248237

  I want to filter elements from a list of lists, and iterate over the elements of each element using a lambda. For example, given the list: a = [[1,2,3],[4,5,6]] suppose that I want to keep only elements where the sum of the list is greater than N. I tried writing: filter(lambda x, y, z: x + y + z >= N, a) but I get the error: <lambda>() takes exactly 3 arguments (1 given) How can I iterate while assigning values of each element to x, y, and z? Something like zip, but for arbitrarily long lists. thanks, p.s. I know I can write this using: filter(lambda x: sum(x)..., a) but that's not the point, imagine that these were not numbers but arbitrary elements and I wanted to assign their values to variable names.

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• Prims vs Polys: what are the pros and cons of each?

  - by Richard Inglis

  I've noticed that most 3d gaming/rendering environments represent solids as a mesh of (usually triangular) 3d polygons. However some examples, such as Second Life, or PovRay use solids built from a set of 3d primitives (cube, sphere, cone, torus etc) on which various operations can be performed to create more complex shapes. So my question is: why choose one method over the other for representing 3d data? I can see there might be benefits for complex ray-tracing operations to be able to describe a surface as a single mathematical function (like PovRay does), but SL surely isn't attempting anything so ambitious with their rendering engine. Equally, I can imagine it might be more bandwidth-efficient to serve descriptions of generalised solids instead of arbitrary meshes, but is it really worth the downside that SL suffers from (ie modelling stuff is really hard, and usually the results are ugly) - was this just a bad decision made early in SL's development that they're now stuck with? Or is it an artefact of what's easiest to implement in OpenGL?

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• How to stream a WAV file?

  - by jonasb

  I'm writing an app where I record audio and upload the audio file over the web. In order to speed up the upload I want to start uploading before I've finished recording. The file I'm creating is a WAV file. My plan was to use multiple data chunks. So instead of the normal encoding (RIFF, fmt , data) I’m using (RIFF, fmt , data, data, ..., data). The first issue is that the RIFF header wants the total length of the whole file, but that is of course not known when streaming the audio (I’m now using an arbitrary number). The other problem is that I'm not sure if it's valid since Audacity doesn't recognise the file, and Windows Media Player opens the file but plays only a very small part. I've been reading WAV specs but haven’t found an answer. Any suggestions?

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