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• Seeking questions about creating Microsoft Live Labs Pivot collections

  - by John Conwell

  I've spent the past 3 weeks working a lot with Pivot from Microsoft Live Labs (http://getpivot.com/).  Pivot is a tool that allows you to visually explore data. Its an interesting take on visual data mining. Anyway, I've been writing a lot of code that creates a hierarchy of Pivot collections, where one item in the collection drills down into an entirly new collection. The dev community around Pivot is still very young, so there isnt much tribal knowledge built up yet.  I've spent a lot of time trying to get things to work through trial and error, as well as digging around in Reflector.  But I've finally got a framework built for programatically creating DeepZoom images, Pivot collections, Sparse Images, etc.   If anyone has any questions, or suggestions on a post topic, leave a comment and I'll try and answer your question.

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• How would I use for_each to delete every value in an STL map?

  - by stusmith

  Suppose I have a STL map where the values are pointers, and I want to delete them all. How would I represent the following code, but making use of std::for_each? I'm happy for solutions to use Boost. for( stdext::hash_map<int, Foo *>::iterator ir = myMap.begin(); ir != myMap.end(); ++ir ) { delete ir->second; // delete all the (Foo *) values. } (I've found Boost's checked_delete, but I'm not sure how to apply that to the pair<int, Foo *> that the iterator represents). (Also, for the purposes of this question, ignore the fact that storing raw pointers that need deleting in an STL container isn't very sensible).

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• How does java.util.Collections.contains() perform faster than a linear search?

  - by The111

  I've been fooling around with a bunch of different ways of searching collections, collections of collections, etc. Doing lots of stupid little tests to verify my understanding. Here is one which boggles me (source code further below). In short, I am generating N random integers and adding them to a list. The list is NOT sorted. I then use Collections.contains() to look for a value in the list. I intentionally look for a value that I know won't be there, because I want to ensure that the entire list space is probed. I time this search. I then do another linear search manually, iterating through each element of the list and checking if it matches my target. I also time this search. On average, the second search takes 33% longer than the first one. By my logic, the first search must also be linear, because the list is unsorted. The only possibility I could think of (which I immediately discard) is that Java is making a sorted copy of my list just for the search, but (1) I did not authorize that usage of memory space and (2) I would think that would result in MUCH more significant time savings with such a large N. So if both searches are linear, they should both take the same amount of time. Somehow the Collections class has optimized this search, but I can't figure out how. So... what am I missing? import java.util.*; public class ListSearch { public static void main(String[] args) { int N = 10000000; // number of ints to add to the list int high = 100; // upper limit for random int generation List<Integer> ints; int target = -1; // target will not be found, forces search of entire list space long start; long end; ints = new ArrayList<Integer>(); start = System.currentTimeMillis(); System.out.print("Generating new list... "); for (int i = 0; i < N; i++) { ints.add(((int) (Math.random() * high)) + 1); } end = System.currentTimeMillis(); System.out.println("took " + (end-start) + "ms."); start = System.currentTimeMillis(); System.out.print("Searching list for target (method 1)... "); if (ints.contains(target)) { // nothing } end = System.currentTimeMillis(); System.out.println(" Took " + (end-start) + "ms."); System.out.println(); ints = new ArrayList<Integer>(); start = System.currentTimeMillis(); System.out.print("Generating new list... "); for (int i = 0; i < N; i++) { ints.add(((int) (Math.random() * high)) + 1); } end = System.currentTimeMillis(); System.out.println("took " + (end-start) + "ms."); start = System.currentTimeMillis(); System.out.print("Searching list for target (method 2)... "); for (Integer i : ints) { // nothing } end = System.currentTimeMillis(); System.out.println(" Took " + (end-start) + "ms."); } }

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• Caching strategies for entities and collections

  - by Rob West

  We currently have an application framework in which we automatically cache both entities and collections of entities at the business layer (using .NET cache). So the method GetWidget(int id) checks the cache using a key GetWidget_Id_{0} before hitting the database, and the method GetWidgetsByStatusId(int statusId) checks the cache using GetWidgets_Collections_ByStatusId_{0}. If the objects are not in the cache they are retrieved from the database and added to the cache. This approach is obviously quick for read scenarios, and as a blanket approach is quick for us to implement, but requires large numbers of cache keys to be purged when CRUD operations are carried out on entities. Obviously as additional methods are added this impacts performance and the benefits of caching diminish. I'm interested in alternative approaches to handling caching of collections. I know that NHibernate caches a list of the identifiers in the collection rather than the actual entities. Is this an approach other people have tried - what are the pros and cons? In particular I am looking for options that optimise performance and can be implemented automatically through boilerplate generated code (we have our own code generation tool). I know some people will say that caching needs to be done by hand each time to meet the needs of the specific situation but I am looking for something that will get us most of the way automatically.

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• Convert collections of enums to collection of strings and vice versa

  - by Michael Freidgeim

  Recently I needed to convert collections of  strings, that represent enum names, to collection of enums, and opposite,  to convert collections of   enums  to collection of  strings. I didn’t find standard LINQ extensions.However, in our big collection of helper extensions I found what I needed - just with different names: /// <summary> /// Safe conversion, ignore any unexpected strings/// Consider to name as Convert extension /// </summary> /// <typeparam name="EnumType"></typeparam> /// <param name="stringsList"></param> /// <returns></returns> public static List<EnumType> StringsListAsEnumList<EnumType>(this List<string> stringsList) where EnumType : struct, IComparable, IConvertible, IFormattable     { List<EnumType> enumsList = new List<EnumType>(); foreach (string sProvider in stringsList)     {     EnumType provider;     if (EnumHelper.TryParse<EnumType>(sProvider, out provider))     {     enumsList.Add(provider);     }     }     return enumsList;     }/// <summary> /// Convert each element of collection to string /// </summary> /// <typeparam name="T"></typeparam> /// <param name="objects"></param> /// <returns></returns> public static IEnumerable<string> ToStrings<T>(this IEnumerable<T> objects) {//from http://www.c-sharpcorner.com/Blogs/997/using-linq-to-convert-an-array-from-one-type-to-another.aspx return objects.Select(en => en.ToString()); }

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• Defining < for STL sort algorithm - operator overload, functor or standalone function?

  - by Andy

  I have a stl::list containing Widget class objects. They need to be sorted according to two members in the Widget class. For the sorting to work, I need to define a less-than comparator comparing two Widget objects. There seems to be a myriad of ways to do it. From what I can gather, one can either: a. Define a comparison operator overload in the class: bool Widget::operator< (const Widget &rhs) const b. Define a standalone function taking two Widgets: bool operator<(const Widget& lhs, const Widget& rhs); And then make the Widget class a friend of it: class Widget { // Various class definitions ... friend bool operator<(const Widget& lhs, const Widget& rhs); }; c. Define a functor and then include it as a parameter when calling the sort function: class Widget_Less : public binary_function<Widget, Widget, bool> { bool operator()(const Widget &lhs, const Widget& rhs) const; }; Does anybody know which method is better? In particular I am interested to know if I should do 1 or 2. I searched the book Effective STL by Scott Meyer but unfortunately it does not have anything to say about this. Thank you for your reply.

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• C++/STL string: How to mimic regex like function with wildcards ?

  - by Arman

  Hello, I would like to compare 4 character string using wildcards. For example: std::vector<std::string> wildcards[]= {"H? ", "RH? ", "H[0-5] "}; /*in the last one I need to check if string is "H0 ",..., and "H5 " */ Is it possible to manage to realize only by STL? Thanks, Arman.

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• Why is it bad practice to derive a class from stl containers such as std::list?

  - by WilliamKF

  I've seen it declared that it is bad practice to derive a class from stl containers such as std::list. Why is this the case? What issues does violating this cause?

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• Function templates for arbitrary STL containers containing arbitrary types.

  - by Chad Brewbaker

  I have an arbitrary STL container C, which contains elements of an arbitrary type T. I want to create an std::vector that has a copy of all the elements. What is the cleanest way to do this? template <typename C> void myfunction(C container){ /*Derive the type T of elements within the container*/ std::vector<T> mystack; /* Iterate over container and push_back() the elements into mystack*/ }

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• What is the difference between set and hashset in C++ STL?

  - by mkal

  When should I choose one over the other. Are there any pointers that you would recommend for using the right STL containers.

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• Hash Table v/s STL map in C++

  - by anon

  Hi, I am trying to learn C++ maps. Was just wondering about the implementation of STL map. I read it employs Binary search tree. Is there a implementation of hash table in STL? How exactly do STL map stores Key Value pairs?

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• Programmatically use a server as the Build Server for multiple Project Collections

  Important: With this post you create an unsupported scenario by Microsoft. It will break your support for this server with Microsoft. So handle with care. I am the administrator an a TFS environment with a lot of Project Collections. In the supported configuration of Microsoft 2010 you need one Build Controller per Project Collection, and it is not supported to have multiple Build Controllers installed. Jim Lamb created a post how you can modify your system to change this behaviour. But since I have so many Project Collections, I automated this with the API of TFS. When you install a new build server via the UI, you do the following steps Register the build service (with this you hook the windows server into the build server environment) Add a new build controller Add a new build agent So in pseudo code, the code would look like foreach (projectCollection in GetAllProjectCollections) {       CreateNewWindowsService();       RegisterService();       AddNewController();       AddNewAgent(); } The following code fragements show you the most important parts of the method implementations. Attached is the full project. CreateNewWindowsService We create a new windows service with the SC command via the Diagnostics.Process class:             var pi = new ProcessStartInfo("sc.exe")                         {                             Arguments =                                 string.Format(                                     "create \"{0}\" start= auto binpath= \"C:\\Program Files\\Microsoft Team Foundation Server 2010\\Tools\\TfsBuildServiceHost.exe              /NamedInstance:{0}\" DisplayName= \"Visual Studio Team Foundation Build Service Host ({1})\"",                                     serviceHostName, tpcName)                         };            Process.Start(pi);             pi.Arguments = string.Format("failure {0} reset= 86400 actions= restart/60000", serviceHostName);            Process.Start(pi); RegisterService The trick in this method is that we set the NamedInstance static property. This property is Internal, so we need to set it through reflection. To get information on these you need nice Microsoft friends and the .Net reflector .             // Indicate which build service host instance we are using            typeof(BuildServiceHostUtilities).Assembly.GetType("Microsoft.TeamFoundation.Build.Config.BuildServiceHostProcess").InvokeMember("NamedInstance",              System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.SetProperty | System.Reflection.BindingFlags.Static, null, null, new object[] { serviceName });             // Create the build service host            serviceHost = buildServer.CreateBuildServiceHost(serviceName, endPoint);            serviceHost.Save();             // Register the build service host            BuildServiceHostUtilities.Register(serviceHost, user, password); AddNewController and AddNewAgent Once you have the BuildServerHost, the rest is pretty straightforward. There are methods on the BuildServerHost to modify the controllers and the agents                 controller = serviceHost.CreateBuildController(controllerName);                 agent = controller.ServiceHost.CreateBuildAgent(agentName, buildDirectory, controller);                controller.AddBuildAgent(agent); You have now seen the highlights of the application. If you need it and want to have sample information when you work in this area, download the app TFS2010_RegisterBuildServerToTPCs

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• Massive Google Street View Update: 250,000 Miles of Roadways, New Special Collections, and More

  - by Jason Fitzpatrick

  If you like tooling around in Google Street View to check out attractions near and far, you just got a whole lot more to look at. Street View’s new update adds in 250,000 miles of roads, increased coverage in over a dozen countries, and a whole pile of new special collections. From Russia to Taiwan to Canada, there’s thousands of new places and tens of thousands of new roads to explore. Hit up the link below to read the full announcement at the Google Maps blog. Making Google Maps More Comprehensive with Ciggest Street View Update Ever [Google Maps] HTG Explains: What is the Windows Page File and Should You Disable It? How To Get a Better Wireless Signal and Reduce Wireless Network Interference How To Troubleshoot Internet Connection Problems

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• PowerShell One-Liners: Collections, Hashtables, Arrays and Strings

  The way to learn PowerShell is to browse and nibble, rather than to sit down to a formal five-course meal. In his continuing series on PowerShell one-liners, Michael Sorens provides Fast Food for busy professionals who want results quickly and aren't too faddy. Part 3 has as its tasty confections - Collections, Hashtables, arrays and strings. "A real time saver" Andy Doyle, Head of IT ServicesAndy and his team saved time by automating backup and restores with SQL Backup Pro. Find out how much time you could save. Download a free trial now.

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• C++ and SDL Trouble Creating a STL Vector of a Game Object

  - by Jackson Blades

  I am trying to create a Space Invaders clone using C++ and SDL. The problem I am having is in trying to create Waves of Enemies. I am trying to model this by making my Waves a vector of 8 Enemy objects. My Enemy constructor takes two arguments, an x and y offset. My Wave constructor also takes two arguments, an x and y offset. What I am trying to do is have my Wave constructor initialize a vector of Enemies, and have each enemy given a different x offset so that they are spaced out appropriately. Enemy::Enemy(int x, int y) { box.x = x; box.y = y; box.w = ENEMY_WIDTH; box.h = ENEMY_HEIGHT; xVel = ENEMY_WIDTH / 2; } Wave::Wave(int x, int y) { box.x = x; box.y = y; box.w = WAVE_WIDTH; box.y = WAVE_HEIGHT; xVel = (-1)*ENEMY_WIDTH; yVel = 0; std::vector<Enemy> enemyWave; for (int i = 0; i < enemyWave.size(); i++) { Enemy temp(box.x + ((ENEMY_WIDTH + 16) * i), box.y); enemyWave.push_back(temp); } } I guess what I am asking is if there is a cleaner, more elegant way to do this sort of initialization with vectors, or if this is right at all. Any help is greatly appreciated.

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• C++ Tutorial: 10 New STL Algorithms That Will Make You A More Productive Developer

  Unquestionably, the most effective tool for a C++ programmer's productivity is the Standard library's rich collection of algorithms. In 2008, about 20 new algorithms were voted into the C++0x draft standard. These new algorithms let you among the rest copy n elements intuitively, perform set theory operations, and handle partitions conveniently. Find out how to use these algorithms to make your code more efficient and intuitive.

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• Is there any way to limit the size of an STL Map?

  - by Nathan Fellman

  I want to implement some sort of lookup table in C++ that will act as a cache. It is meant to emulate a piece of hardware I'm simulating. The keys are non-integer, so I'm guessing a hash is in order. I have no intention of inventing the wheel so I intend to use stl::map for this (though suggestions for alternatives are welcome). The question is, is there any way to limit the size of the hash to emulate the fact that my hardware is of finite size? I'd expect the hash's insert method to return an error message or throw an exception if the limit is reached. If there is no such way, I'll simply check its size before trying to insert, but that seems like an inelegant way to do it.

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• How do I simplify this templated vector initializer loop using lambdas or some kind of STL transform

  - by Neil G

  How do I simplify this templated vector initializer loop using lambdas or some kind of STL transform? template<typename T> template<typename... Args> DotProduct<T>::DotProduct(int n, RNG& rng, Args const&... args) { myBasis.resize(n); for (auto it = myBasis.begin(); it != myBasis.end(); ++it) { typename T::CPDDist cpd(rng, args...); *it = T(cpd); } }

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• How to dump STDIN to a file, using C++ STL?

  - by Jimm Chen

  HHello all, this is a straight forward question, but not a straight forward answer can be found by just Googling today. Hope someone can show me a concise answer before I dig into those thick C++ books and finally find the solution out. Thank you. I'm writing this program so to make a workaround in this issue: Why do I get 'Bad file descriptor' when trying sys.stdin.read() in subversion pre-revprop-change py script? Note: Content from STDIN may be arbitrary binary data. Please use C++ STL functions, iostream, ifstream etc . If the file creation/writing failed, I'd like to catch the exception to know the case.

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• How to restrict the range of elements of C++ STL vector?

  - by cambr

  vector<int> l; for(int i=0;i<10;i++){ l.push_back(i); } I want the vector to only be able to store numbers from a specified range (or set). How can that be done, in general? In particular, I want to restrict the vector to beonly be able to store single digits. So, if I do a l[9]++, it should give me an error or warn me. (because 10 is not a single digit number). Similarly, l[0]-- should warn me. Is there a way to do this using C++ STL vector?

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• How do I simplify this templated vector initializer loop using lambdas or STL transform?

  - by Neil G

  How do I simplify this templated vector initializer loop using lambdas or some kind of STL transform? template<typename T> template<typename... Args> void InitToRandomValues(vector<T>* retval, int n, RNG& rng, Args const&... args) { retval->resize(n); for (auto it = retval->begin(); it != retval->end(); ++it) { typename T::CPDDist cpd(rng, args...); *it = T(cpd); } }

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• how to get stl map to construct/destruct inserted object only once.

  - by Alberto Toglia

  I have found a very prejudicial fact about stl maps. For some reason I cant get objects being inserted in the map to get constructed/destructed only once. Example: struct MyObject{ MyObject(){ cout << "constructor" << endl; } ~MyObject(){ cout << "destructor" << endl; } }; int main() { std::map<int, MyObject> myObjectsMap; myObjectsMap[0] = MyObject(); return 0; } returns: constructor destructor destructor constructor destructor If I do: typedef std::pair<int, MyObject> MyObjectPair; myObjectsMap.insert( MyObjectPair(0,MyObject())); returns: constructor destructor destructor destructor I'm inserting Objects responsible for their own memory allocation, so when destructed they'll clean themselves up, being destructed several times is causing me some trouble.

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• How to find next (by a single parameter) element in c++? (stl) [closed]

  - by user2136963

  I have n humans of THuman class Each human has scored some points in one of two rounds. (score1 and score2) Each human has its unique id. Score1 and 2 are also unique. Besides, a human has a score_t=score1+score2, which can be the same for two of them. I need to implement 6 variables to THuman which return id of a human with: bigger score1 smaller score1 bigger score2 smaller score2 bigger score_t smaller score_t (if there are many humans those satisfy theese conditions, the one with smallest difference of corresponding parameter should be chosen (like score1 for 1 and 2)) In other words, it's some kind of storing 3 human sortings. Two more functions I need should get argument x, set score1 or score 2 to x, and then refresh some of the 6 variables above. If I needed sorting by only one variable, I would simply create set and defined and < operators for my class. But what is the solution for three of parameters? Is it possible to use STL here, or I should create my own lists/treaps? __ Answer: How to update set of pointers c++?

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• Ask How-To Geek: iPad Battery Life, Batch Resizing Photos, and Syncing Massive Music Collections

  - by Jason Fitzpatrick

  Christmas was good to many of you and now you’ve got all sorts of tech questions related to your holiday spoils. Come on in and we’ll clear up how to squeeze more life out of your iPad, resize all those photos, and sync massive music collections to mobile devices. Once a week we dip into our reader mailbag and help readers solve their problems, sharing the useful solutions with you in the process. Read on to see our fixes for this week’s reader dilemmas. Latest Features How-To Geek ETC How to Use the Avira Rescue CD to Clean Your Infected PC The Complete List of iPad Tips, Tricks, and Tutorials Is Your Desktop Printer More Expensive Than Printing Services? 20 OS X Keyboard Shortcuts You Might Not Know HTG Explains: Which Linux File System Should You Choose? HTG Explains: Why Does Photo Paper Improve Print Quality? Orbiting at the Edge of the Atmosphere Wallpaper Simon’s Cat Explores the Christmas Tree! [Video] The Outdoor Lights Scene from National Lampoon’s Christmas Vacation [Video] The Famous Home Alone Pizza Delivery Scene [Classic Video] Chronicles of Narnia: The Voyage of the Dawn Treader Theme for Windows 7 Cardinal and Rabbit Sharing a Tree on a Cold Winter Morning Wallpaper

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• Get entities ids from two similar collections using one method

  - by Patryk Roszczyniala

  I've got two lists: List<Integer, ZooEntity> zoos; List<Integer, List<ZooEntity>> groupOfZoos; These operations will return collections of values: Collection<ZooEntity> cz = zoos.values(); Collection<List<ZooEntity>> czList = groupOfZoos.values(); What I want to achieve is to get list of all zoo ids. List<Integer> zooIds = cz ids + czList ids; Of course I can create two methods to do what I want: public List<Integer> getIdsFromFlatList(Collection<ZooEntity> list) { List<Integer> ids = new ArrayList<Integer>(); for (ZooEntity z : list) { ids.add(z.getId()); } return ids; } public List<Integer> getIdsFromNestedList(Collection<List<ZooEntity>> list) { List<Integer> ids = new ArrayList<Integer>(); for (List<ZooEntity> zList : list) { for (ZooEntity z : zList) { ids.add(z.getId()); } } return ids; } As you can see those two methods are very similar and here is my question: Is it good to create one method (for example using generics) which will get ids from those two lists (zoos and groupOfZoos). If yes how it should look like? If no what is the best solution? BTW. This is only the example. I've got very similar problem at job and I want to do it in preety way (I can't change enities, I can change only getIds...() methods).

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