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  • C++11 support for higher-order list functions

    - by Giorgio
    Most functional programming languages (e.g. Common Lisp, Scheme / Racket, Clojure, Haskell, Scala, Ocaml, SML) support some common higher-order functions on lists, such as map, filter, takeWhile, dropWhile, foldl, foldr (see e.g. Common Lisp, Scheme / Racket, Clojure side-by-side reference sheet, the Haskell, Scala, OCaml, and the SML documentation.) Does C++11 have equivalent standard methods or functions on lists? For example, consider the following Haskell snippet: let xs = [1, 2, 3, 4, 5] let ys = map (\x -> x * x) xs How can I express the second expression in modern standard C++? std::list<int> xs = ... // Initialize the list in some way. std::list<int> ys = ??? // How to translate the Haskell expression? What about the other higher-order functions mentioned above? Can they be directly expressed in C++?

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  • How do I set up a .emacs initialization file? [migrated]

    - by Harry Weston
    I am using Linux Fedora 13 (Constantine) and emacs 23.1.1. I am trying to set up a .emacs file for initialization, by using emacs itself to edit and save a file .emacs in my home directory. However, although the file is there, emacs does not seem to recognize it. What might I be doing wrong, and is there a simple text for .emacs that will show me if it is being used, one that will display a message on emacs start up?

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  • How to make inner UL list not inherit from outer UL List in CSS

    - by Minghui Yu
    For the HTML List below, I need to add a background image only to the LI of the outer list. (aka the one with class "menu-mlid-594 dhtml-menu expanded start-collapsed") HTML codes are: <li class="menu-mlid-594 dhtml-menu expanded start-collapsed ">About the Collection<ul class="menu"><li class="leaf first dhtml-menu ">By Theme</li><li class="leaf last dhtml-menu ">By Individual</li></ul></li> How can I do that? Thanks.

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  • Join a list of lists together into 1 list in Python

    - by dotty
    Hay All. I have a list which consists of many lists, here is an example [ [Obj, Obj, Obj, Obj], [Obj], [Obj], [ [Obj,Obj], [Obj,Obj,Obj] ] ] Is there a way to join all these items together as 1 list, so the output will be something like [Obj,Obj,Obj,Obj,Obj,Obj,Obj,Obj,Obj,Obj,Obj] Thanks

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  • Splitting a list based on another list values in Mathematica

    - by Max
    In Mathematica I have a list of point coordinates size = 50; points = Table[{RandomInteger[{0, size}], RandomInteger[{0, size}]}, {i, 1, n}]; and a list of cluster indices these points belong to clusterIndices = {1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 2, 1, 2, 1, 1, 1, 1, 1, 1, 1}; what is the easiest way to split the points into two separate lists based on the clusterIndices values?

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  • Thread Safety of C# List<T> for readers

    - by ILIA BROUDNO
    I am planning to create the list once in a static constructor and then have multiple instances of that class read it (and enumerate through it) concurrently without doing any locking. In this article http://msdn.microsoft.com/en-us/library/6sh2ey19.aspx MS describes the issue of thread safety as follows: Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe. A List can support multiple readers concurrently, as long as the collection is not modified. Enumerating through a collection is intrinsically not a thread-safe procedure. In the rare case where an enumeration contends with one or more write accesses, the only way to ensure thread safety is to lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization. The "Enumerating through a collection is intrinsically not a thread-safe procedure." Statement is what worries me. Does this mean that it is thread safe for readers only scenario, but as long as you do not use enumeration? Or is it safe for my scenario?

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  • Parent and siblings inherits a child list items styles

    - by elvista
    I have a simple menu <ul id="menu"> <li class="leaf"><a href="#">Menu Item 1</a></li> <li class="leaf"><a href="#">Menu Item 2</a></li> <li class="expanded"><a href="#">Menu Item 3</a> <ul> <li class="leaf"><a href="#">Menu Item a</a></li> <li class="leaf"><a href="#">Menu Item b</a></li> <li class="leaf"><a href="#">Menu Item c</a></li> </ul> </li> <li class="leaf"><a href="#">Menu Item 4</a></li> </ul> and ul#menu li:hover {font-weight:bold;} The problem I am facing is when I hover above a ul li li, the parent as well as all its siblings gets the hover effect. I only want the list item I hovered above to get the effect. I tried ul#menu li.leaf:hover {..}, ul#menu li.expanded:hover {..} , but even in that case, when I hover above li.expanded, it's child inherits the style. It is important for me to style the list items, not a (the style is more complicated than the one I posted) How do I fix this?

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  • List comprehension from multiple sources in Python?

    - by Noah
    Is it possible to replace the following with a list comprehension? res = [] for a, _, c in myList: for i in c: res.append((a, i)) For example: # Input myList = [("Foo", None, [1, 2, 3]), ("Bar", None, ["i", "j"])] # Output res = [("Foo", 1), ("Foo", 2), ("Foo", 3), ("Bar", "i"), ("Bar", "j")]

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  • C++ - Constructor or Initialize Method to Startup

    - by Bob Fincheimer
    I want to determine when to do non-trivial initialization of a class. I see two times to do initialization: constructor and other method. I want to figure out when to use each. Choice 1: Constructor does initialization MyClass::MyClass(Data const& data) : m_data() { // does non-trivial initialization here } MyClass::~MyClass() { // cleans up here } Choice 2: Defer initialization to an initialize method MyClass::MyClass() : m_data() {} MyClass::Initialize(Data const& data) { // does non-trivial initialization here } MyClass::~MyClass() { // cleans up here } So to try and remove any subjectivity I want to figure out which is better in a couple of situations: Class that encapsulates a resource (window/font/some sort of handle) Class that composites resources to do something (a control/domain object) Data structure classes (tree/list/etc.) [Anything else you can think of] Things to analyze: Performance Ease of use by other developers How error-prone/opportunities for bugs [Anything else you can think of]

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  • How do I process a nested list?

    - by ddbeck
    Suppose I have a bulleted list like this: * list item 1 * list item 2 (a parent) ** list item 3 (a child of list item 2) ** list item 4 (a child of list item 2 as well) *** list item 5 (a child of list item 4 and a grand-child of list item 2) * list item 6 I'd like to parse that into a nested list or some other data structure which makes the parent-child relationship between elements explicit (rather than depending on their contents and relative position). For example, here's a list of tuples containing an item and a list of its children (and so forth): [('list item 1',), ('list item 2', [('list item 3',), [('list item 4', [('list item 5'),]] ('list item 6',)] I've attempted to do this with plain Python and some experimentation with Pyparsing, but I'm not making progress. I'm left with two major questions: What's the strategy I need to employ to make this work? I know recursion is part of the solution, but I'm having a hard time making the connection between this and, say, a Fibonacci sequence. I'm certain I'm not the first person to have done this, but I don't know the terminology of the problem to make fruitful searches for more information on this topic. What problems are related to this so that I can learn more about solving these kinds of problems in general?

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  • Is there any reason lazy initialization couldn't be built into Java?

    - by Renesis
    Since I'm working on a server with absolutely no non-persisted state for users, every User-related object we have is rolled out on every request. Consequently I often find myself doing lazy initialization of properties of objects that may go unused. protected EventDispatcher dispatcher = new EventDispatcher(); Becomes... protected EventDispatcher<EventMessage> dispatcher; public EventDispatcher<EventMessage> getEventDispatcher() { if (dispatcher == null) { dispatcher = new EventDispatcher<EventMessage>(); } return dispatcher; } Is there any reason this couldn't be built into Java? protected lazy EventDispatcher dispatcher = new EventDispatcher();

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  • How to solve lazy initialization exception using JPA and Hibernate as provider

    - by rupertin
    I am working on a project for a customer who wants to use lazy initialization. They always get "lazy initialization exception" when mapping classes with the default lazy loading mode. @JoinTable(name = "join_profilo_funzionalita", joinColumns = {@JoinColumn(name = "profilo_id", referencedColumnName = "profilo_id")}, inverseJoinColumns = {@JoinColumn(name = "funzionalita_id", referencedColumnName = "funzionalita_id")}) //@ManyToMany(fetch=FetchType.EAGER) - no exceptions if uncommented @ManyToMany private Collection<Funzionalita> funzionalitaIdCollection; Is there a standard pattern using JPA classes to avoid this error? Snippets are welcome, thanks a lot for your time.

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  • initialization of objects in c++

    - by Happy Mittal
    I want to know, in c++, when does the initialization of objects take place? Is it at the compile time or link time? For ex: //file1.cpp extern int i; int j=5; //file2.cpp ( link with file1.cpp) extern j; int i=10; Now, what does compiler do : according to me, it allocates storage for variables. Now I want to know : does it also put initialization value in that storage or is it done at link time?

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  • List<element> initialization fires "Process is terminated due to StackOverflowException"

    - by netmajor
    I have structs like below and when I do that initialization: ArrayList nodesMatrix = null; List<vertex> vertexMatrix = null; List<bool> odwiedzone = null; List<element> priorityQueue = null; vertexMatrix = new List<vertex>(nodesNr + 1); nodesMatrix = new ArrayList(nodesNr + 1); odwiedzone = new List<bool>(nodesNr + 1); priorityQueue = new List<element>(); arr.NodesMatrix = nodesMatrix; arr.VertexMatrix = vertexMatrix; arr.Odwiedzone = odwiedzone; arr.PriorityQueue = priorityQueue; //only here i have exception debuger fires Process is terminated due to StackOverflowException :/ Some idea why this collection fires this exception ? private struct arrays { ArrayList nodesMatrix; public ArrayList NodesMatrix { get { return nodesMatrix; } set { nodesMatrix = value; } } List<vertex> vertexMatrix; public List<vertex> VertexMatrix { get { return vertexMatrix; } set { vertexMatrix = value; } } List<bool> odwiedzone; public List<bool> Odwiedzone { get { return odwiedzone; } set { odwiedzone = value; } } public List<element> PriorityQueue { get { return PriorityQueue; } set { PriorityQueue = value; } } } public struct element : IComparable { public double priority { get { return priority; } set { priority = value; } } public int node { get { return node; } set { node = value; } } public element(double _prio, int _node) { priority = _prio; node = _node; } #region IComparable Members public int CompareTo(object obj) { element elem = (element)obj; return priority.CompareTo(elem.priority); } #endregion

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  • Haskell - function (that returns a list) on each element in a list

    - by Ben
    The assignment is to create a multiples function and I essentially want todo the following code: map (\t -> scanl (\x y -> x+y) t (repeat t)) listofnumbers The problem is that the scanl function returns a list of results rather than the one which the map function requires. So is there a function that will allow the return of lists?

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  • Release Candidates of Application Initialization and Dynamic IP Restrictions Released

    - by The Official Microsoft IIS Site
    Two new Release Candidates for the following IIS Extensions have been released today: Application Initialization for IIS 7.5 (the replacement for the previously released Application Warmup beta extension) Dynamic IP Restrictions for IIS7/7.5 Application Initialization for IIS 7.5 Application Initialization is a feature which is coming in IIS 8.0 and is now also available for IIS 7.5 (please note this feature is not available for IIS 7.0).   This module helps to eliminate the lack of feedback...(read more)

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  • Random List of numbers in C

    - by Ant
    I have just started a C programming course and so far have only done the basics like printf, read a little on variables etc on the course book. The teacher has tasked us with writing a program that will take a value entered by the user, this will be the number of students in the class (25 at the moment but can be variable). It will then list the number of students randomly and place them in 3 columns. The purpose is to sort students into groups of 3 randomly, then display on the screen in columns. Now my question is not for the code that defeats the object of me attempting the exercise, but how to structure it. I can see that using an array can be used to display the list, but really after some pointers on how best to approach the problem in blocks, then I can attempt to program each block.

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  • trying to append a list, but something breaks

    - by romunov
    I'm trying to create an empty list which will have as many elements as there are num.of.walkers. I then try to append, to each created element, a new sub-list (length of new sub-list corresponds to a value in a. When I fiddle around in R everything goes smooth: list.of.dist[[1]] <- vector("list", a[1]) list.of.dist[[2]] <- vector("list", a[2]) list.of.dist[[3]] <- vector("list", a[3]) list.of.dist[[4]] <- vector("list", a[4]) I then try to write a function. Here is my feeble attempt that results in an error. Can someone chip in what am I doing wrong? countNumberOfWalks <- function(walk.df) { list.of.walkers <- sort(unique(walk.df$label)) num.of.walkers <- length(unique(walk.df$label)) #Pre-allocate objects for further manipulation list.of.dist <- vector("list", num.of.walkers) a <- c() # Count the number of walks per walker. for (i in list.of.walkers) { a[i] <- nrow(walk.df[walk.df$label == i,]) } a <- as.vector(a) # Add a sublist (length = number of walks) for each walker. for (i in i:num.of.walkers) { list.of.dist[[i]] <- vector("list", a[i]) } return(list.of.dist) } > num.of.walks.per.walker <- countNumberOfWalks(walk.df) Error in vector("list", a[i]) : vector size cannot be NA

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  • Using FindAll on a List<List<T>> type

    - by Ken Foster
    Assuming public class MyClass { public int ID {get; set; } public string Name {get; set; } } and List<MyClass> classList = //populate with MyClass instances of various IDs I can do List<MyClass> result = classList.FindAll(class => class.ID == 123); and that will give me a list of just classes with ID = 123. Works great, looks elegant. Now, if I had List<List<MyClass>> listOfClassLists = //populate with Lists of MyClass instances How do I get a filtered list where the lists themselves are filtered. I tried List<List<MyClass>> result = listOfClassLists.FindAll (list => list.FindAll(class => class.ID == 123).Count > 0); it looks elegant, but doesn't work. It only includes Lists of classes where at least one class has an ID of 123, but it includes ALL MyClass instances in that list, not just the ones that match. I ended up having to do List<List<MyClass>> result = Results(listOfClassLists, 123); private List<List<MyClass>> Results(List<List<MyClass>> myListOfLists, int id) { List<List<MyClass>> results = new List<List<MyClass>>(); foreach (List<MyClass> myClassList in myListOfLists) { List<MyClass> subList = myClassList.FindAll(myClass => myClass.ID == id); if (subList.Count > 0) results.Add(subList); } return results; } which gets the job done, but isn't that elegant. Just looking for better ways to do a FindAll on a List of Lists. Ken

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  • Unique elements of list within list in python

    - by user2901061
    We are given a list of animals in different zoos and need to find which zoos have animals that are not in any others. The animals of each zoo are separated by spaces, and each zoo is originally separated by a comma. I am currently enumerating over all of the zoos to split each animal and create lists within lists for different zoos as such: for i, zoo in enumerate(zoos): zoos[i] = zoo.split() However, I then do not know how to tell and count how many of the zoos have unique animals. I figure it is something else with enumerate and possibly sets, but cannot get it down exactly. Any help is greatly appreciated. Thanks

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  • Optimizing list comprehension to find pairs of co-prime numbers

    - by user3685422
    Given A,B print the number of pairs (a,b) such that GCD(a,b)=1 and 1<=a<=A and 1<=b<=B. Here is my answer: return len([(x,y) for x in range(1,A+1) for y in range(1,B+1) if gcd(x,y) == 1]) My answer works fine for small ranges but takes enough time if the range is increased. such as 1 <= A <= 10^5 1 <= B <= 10^5 is there a better way to write this or can this be optimized?

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