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  • Why appending to a list in Scala should have O(n) time complexity?

    - by Jubbat
    I am learning Scala at the moment and I just read that the execution time of the append operation for a list (:+) grows linearly with the size of the list. Appending to a list seems like a pretty common operation. Why should the idiomatic way to do this be prepending the components and then reversing the list? It can't also be a design failure as implementation could be changed at any point. From my point of view, both prepending and appending should be O(1). Is there any legitimate reason for this?

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  • Serializing a list of Key/Value pairs to XML

    - by Slauma
    I have a list of key/value pairs I'd like to store in and retrieve from a XML file. So this task is similar as described here. I am trying to follow the advice in the marked answer (using a KeyValuePair and a XmlSerializer) but I don't get it working. What I have so far is a "Settings" class ... public class Settings { public int simpleValue; public List<KeyValuePair<string, int>> list; } ... an instance of this class ... Settings aSettings = new Settings(); aSettings.simpleValue = 2; aSettings.list = new List<KeyValuePair<string, int>>(); aSettings.list.Add(new KeyValuePair<string, int>("m1", 1)); aSettings.list.Add(new KeyValuePair<string, int>("m2", 2)); ... and the following code to write that instance to a XML file: XmlSerializer serializer = new XmlSerializer(typeof(Settings)); TextWriter writer = new StreamWriter("c:\\testfile.xml"); serializer.Serialize(writer, aSettings); writer.Close(); The resulting file is: <?xml version="1.0" encoding="utf-8"?> <Settings xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <simpleValue>2</simpleValue> <list> <KeyValuePairOfStringInt32 /> <KeyValuePairOfStringInt32 /> </list> </Settings> So neither key nor value of the pairs in my list are stored though the number of elements is correct. Obviously I am doing something basically wrong. My questions are: How can I store the key/value pairs of the list in the file? How can I change the default generated name "KeyValuePairOfStringInt32" of the elements in the list to some other name like "listElement" I'd like to have?

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  • Bind postback data from a strong type view of type List<T>

    - by Robert Koritnik
    I have a strong type view of type List<List<MyViewModelClass>> The outer list will always have two lists of List<MyViewModelClass>. For each of the two outer lists I want to display a group of checkboxes. Each set can have an arbitrary number of choices. My view model class looks similar to this: public class MyViewModelClass { public Area Area { get; set; } public bool IsGeneric { get; set; } public string Code { get; set; } public bool IsChecked { get; set; } } So the final view will look something like: Please select those that apply: First set of choices: x Option 1 x Option 2 x Option 3 etc. Second set of choices: x Second Option 1 x Second Option 2 x Second Option 3 x Second Option 4 etc. Checkboxes should display MyViewModelClass.Area.Name, and their value should be related to MyViewModelClass.Area.Id. Checked state is of course related to MyViewModel.IsChecked. Question I wonder how should I use Html.CheckBox() or Html.CheckBoxFor() helper to display my checkboxes? I have to get these values back to the server on a postback of course. I would like to have my controller action like one of these: public ActionResult ConsumeSelections(List<List<MyViewModelClass>> data) { // process data } public ActionResult ConsumeSelections(List<MyViewModelClass> first, List<MyViewModelClass> second) { // process data } If it makes things simpler, I could make a separate view model type like: public class Options { public List First { get; set; } public List Second { get; set; } } As well as changing my first version of controller action to: public ActionResult ConsumeSelections(Options data) { // process data }

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  • Parallel For Loop - Problems when adding to a List - Possible .Net Bugs

    - by Kevin Crowell
    I am having some issues involving Parallel for loops and adding to a List. The problem is, the same code may generate different output at different times. I have set up some test code below. In this code, I create a List of 10,000 int values. 1/10th of the values will be 0, 1/10th of the values will be 1, all the way up to 1/10th of the values being 9. After setting up this List, I setup a Parallel for loop that iterates through the list. If the current number is 0, I add a value to a new List. After the Parallel for loop completes, I output the size of the list. The size should always be 1,000. Most of the time, the correct answer is given. However, I have seen 3 possible incorrect outcomes occur: The size of the list is less than 1,000 An IndexOutOfRangeException occurs @ doubleList.Add(0.0); An ArgumentException occurs @ doubleList.Add(0.0); The message for the ArgumentException given was: Destination array was not long enough. Check destIndex and length, and the array's lower bounds. What could be causing the errors? Is this a .Net bug? Is there something I can do to prevent this from happening? Please try the code for yourself. If you do not get an error, try it a few times. Please also note that you probably will not see any errors using a single-core machine. using System; using System.Collections.Generic; using System.Threading.Tasks; namespace ParallelTest { class Program { static void Main(string[] args) { List<int> intList = new List<int>(); List<double> doubleList = new List<double>(); for (int i = 0; i < 250; i++) { intList.Clear(); doubleList.Clear(); for (int j = 0; j < 10000; j++) { intList.Add(j % 10); } Parallel.For(0, intList.Count, j => { if (intList[j] == 0) { doubleList.Add(0.0); } }); if (doubleList.Count != 1000) { Console.WriteLine("On iteration " + i + ": List size = " + doubleList.Count); } } Console.WriteLine("\nPress any key to exit."); Console.ReadKey(); } } }

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  • How to get resultset with stored procedure calls over two linked servers?

    - by räph
    I have problems filling a temporary table with the resultset from a procedure call on a linked server, in which again a procedure on another server is called. I have a Stored Procedure sproc1 with the following code, which calls another procedure sproc2 on a linked server. SET @sqlCommand = 'INSERT INTO #tblTemp ( ModuleID, ParamID) ' + '( SELECT * FROM OPENQUERY(' + @targetServer + ', ' + '''SET FMTONLY OFF; EXEC ' + @targetDB + '.usr.sproc2 ' + @param + ''' ) )' exec ( @sqlCommand ) Now in the called sproc2 I again call a third procedure sproc3 on another linked server, which returns my resultset. SET @sqlCommand = 'EXEC ' + @targetServer +'.database.usr.sproc3 ' + @param exec ( @sqlCommand ) The whole thing doen't work, as I get an SQL error 7391 The operation could not be performed because OLE DB provider "%ls" for linked server "%ls" was unable to begin a distributed transaction. I already checked the hints at this microsoft article, but without success. But maybe, I can change the code in sproc1. Would there be some alternative to the temp table and the open query? Just calling stored procedures from server A to B to C and returning the resultset is working (I do this often in the application). But this special case with the temp table and openquery doesn't work! Or is it just not possible what I am trying to do? The microsft article states: Check the object you refer on the destination server. If it is a view or a stored procedure, or causes an execution of a trigger, check whether it implicitly references another server. If so, the third server is the source of the problem. Run the query directly on the third server. If you cannot run the query directly on the third server, the problem is not actually with the linked server query. Resolve the underlying problem first. Is this my case? PS: I can't avoid the architecture with the three servers.

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  • Parallel For Loop - Problems when adding to a List

    - by Kevin Crowell
    I am having some issues involving Parallel for loops and adding to a List. The problem is, the same code may generate different output at different times. I have set up some test code below. In this code, I create a List of 10,000 int values. 1/10th of the values will be 0, 1/10th of the values will be 1, all the way up to 1/10th of the values being 9. After setting up this List, I setup a Parallel for loop that iterates through the list. If the current number is 0, I add a value to a new List. After the Parallel for loop completes, I output the size of the list. The size should always be 1,000. Most of the time, the correct answer is given. However, I have seen 3 possible incorrect outcomes occur: The size of the list is less than 1,000 An IndexOutOfRangeException occurs @ doubleList.Add(0.0); An ArgumentException occurs @ doubleList.Add(0.0); The message for the ArgumentException given was: Destination array was not long enough. Check destIndex and length, and the array's lower bounds. What could be causing the errors? Is this a .Net bug? Is there something I can do to prevent this from happening? Please try the code for yourself. If you do not get an error, try it a few times. Please also note that you probably will not see any errors using a single-core machine. using System; using System.Collections.Generic; using System.Threading.Tasks; namespace ParallelTest { class Program { static void Main(string[] args) { List<int> intList = new List<int>(); List<double> doubleList = new List<double>(); for (int i = 0; i < 250; i++) { intList.Clear(); doubleList.Clear(); for (int j = 0; j < 10000; j++) { intList.Add(j % 10); } Parallel.For(0, intList.Count, j => { if (intList[j] == 0) { doubleList.Add(0.0); } }); if (doubleList.Count != 1000) { Console.WriteLine("On iteration " + i + ": List size = " + doubleList.Count); } } Console.WriteLine("\nPress any key to exit."); Console.ReadKey(); } } }

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  • got a question about Linked-List in java code.

    - by glacier89
    Linked-List: Mirror Consider the following private class for a node of a singly-linked list of integers: private class Node{ public int value; public Node next; } A wrapper-class, called, ListImpl, contains a pointer, called start to the first node of a linked list of Node. Write an instance-method for ListImpl with the signature: public void mirror(); That makes a reversed copy of the linked-list pointed to by start and appends that copy to the end of the list. So, for example the list: start 1 2 3 after a call to mirror, becomes: start 1 2 3 3 2 1 Note: in your answer you do not need to dene the rest of the class for ListImpl just the mirror method.

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  • applying apply() to deeply embeded list elements only

    - by romunov
    I would like to apply my function to only elements that are deeper in the list structure. For example, I would like to apply a certain function to list elements of second order only. Is this feasible with apply()? > str(l) List of 3 $ :List of 2 ..$ : num 5 ..$ : num 10 $ :List of 2 ..$ : num 15 ..$ : num 20 $ :List of 2 ..$ : num 25 ..$ : num 30

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  • Finding a sequence in a List

    - by user113164
    I have a list of integers that I would like to search for a sequence. For example, if i have a master list: 1, 2, 3, 4, 9, 2, 39, 482, 19283, 19, 23, 1, 29 And I want to find sequence: 1, 2, 3, 4 I would like some easy way to fill a subset list with: 1, 2, 3, 4 + the next five integers in the master list And then remove the integers in the subset list from the master list so at the end of the operation, my lists would look like this: Master list: 19, 23, 1, 29 Subset list: 1, 2, 3, 4, 9, 2, 39, 482, 19283 Hope that makes sense. I'm guessing maybe linq would be good for something like this, but I've never used it before. Can anyone help?

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  • how to get a sub list from a list in ocaml

    - by romerun
    Hi, I'm looking at the List document. It seems the library does not provide a sublist function. I'm trying to get list of elements from i to j. Now I have to write it as: let rec sublist list i j = if i j then [] else (List.nth list i) :: (sublist list (i+1) j) which is quite concise but I'm questioning the efficiency of List.nth, because if it's O(n), I would rather have to write it in a less concise way. I'm wondering why didn't they provide List.sublist func, if List.nth is not O(1), because it's such a quite common operation..

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  • List of Hidden / Virtual Windows User Accounts

    - by Synetech inc.
    I’m trying to find a way to get a comprehensive list of user accounts on a Windows 7 system, including hidden ones. The User Accounts dialog (>control userpasswords2) only shows the normal user accounts, and even the Local User and Groups editor only shows normal user accounts and standard hidden/disabled ones like Administrator and Guest. The Select Users or Groups dialog has a Find Now button which which combines users and groups, but alas, it has the same contents as the LUG. I’m looking for a more comprehensive list that includes “super-hidden” / virtual user accounts like TrustedInstaller (or to be more accurate, NT Service\TrustedInstaller—notice the different “domain”). I checked HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList, but the SpecialAccounts key does not exist. I also checked HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList, and while it does have the SystemProfile, LocalService, and NetworkService accounts listed, it does not have others (like TrustedInstaller and its ilk). TrustedInstaller specifically is a little confusing because it is a user, a service, and an executable file. I am using it as an example because it is “super hidden” in that it does not seem to be listed in any sort of user list. (As an experiment, I tried searching the whole registry for “trustedinstaller” to see if I could find a place where it is listed as a user, but found none.) To be clear, what I am looking for is a list of all accounts that can be used in a user input-field such as in permissions dialogs or as a runas argument.

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  • Sending single emails works, but sending to the same email in a distribution list is bounced

    - by EvilChookie
    I'm running an Exchange 2003 server on a Telstra Business internet connection (in Australia). I'm routing emails through the SMTP connecter, using the host smtp.telstrabusiness.com When users send single emails to a single recipient, the emails are sent correctly. However, when users send emails to a distribution list, they bounce back with: The message could not be delivered because the recipient's destination email system is unknown or invalid. Please check the address and try again, or contact your system administrator to verify connectivity to the email system of the recipient. One of the people in the list was able to recieve a single email from us just a few minutes afterwards, but did not recieve any of the email that should have come from the distribution list. Is there a way I can throttle the number of messages that Exchange will send at a time, so as not to appear as spam to Telstra?

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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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  • How to iterate a list inside a list in java?

    - by user2142786
    Hi i have two value object classes . package org.array; import java.util.List; public class Father { private String name; private int age ; private List<Children> Childrens; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public List<Children> getChildrens() { return Childrens; } public void setChildrens(List<Children> childrens) { Childrens = childrens; } } second is for children package org.array; public class Children { private String name; private int age ; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } } and i want to print there value i nested a list inside a list here i am putting only a single value inside the objects while in real i have many values . so i am nesting list of children inside father list. how can i print or get the value of child and father both. here is my logic. package org.array; import java.util.ArrayList; import java.util.Iterator; import java.util.List; public class ArrayDemo { public static void main(String[] args) { List <Father> fatherList = new ArrayList<Father>(); Father father = new Father(); father.setName("john"); father.setAge(25); fatherList.add(father); List <Children> childrens = new ArrayList<Children>(); Children children = new Children(); children.setName("david"); children.setAge(2); childrens.add(children); father.setChildrens(childrens); fatherList.add(father); Iterator<Father> iterator = fatherList.iterator(); while (iterator.hasNext()) { System.out.println(iterator.toString()); } } }

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  • Sort List C# in arbitrary order

    - by Jasper
    I have a C# List I.E. List<Food> x = new List<Food> () ; This list is populated with this class Public class Food { public string id { get; set; } public string idUser { get; set; } public string idType { get; set; } //idType could be Fruit , Meat , Vegetable , Candy public string location { get; set; } } Now i have this unsorted List<Food> list ; which has I.E. 15 elements. There are 8 Vegetable Types , 3 Fruit Types , 1 Meat Types , 1 Candy Types I would sort this so that to have a list ordered in this way : 1° : Food.idType Fruit 2° : Food.idType Vegetables 3° : Food.idType Meat 4° : Food.idType Candy 5° : Food.idType Fruit 6° : Food.idType Vegetables 7° : Food.idType Fruit //Becouse there isnt more Meat so i insert the //next one which is Candy but also this type is empty //so i start from begin : Fruit 8° : Food.idType Vegetables 9° : Food.idType Vegetables // For the same reason of 7° 10 ° Food.idType Vegetables ...... .... .... 15 : Food.idType Vegetables I cant find a rule to do this. Is there a linq or List.Sort instruction which help me to order the list in this way? Update i changed the return value of idType and now return int type instead string so 1=Vegetable , 2=Fruit , 3=Candy 4=Meat

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  • Implementing list position locator in C++?

    - by jfrazier
    I am writing a basic Graph API in C++ (I know libraries already exist, but I am doing it for the practice/experience). The structure is basically that of an adjacency list representation. So there are Vertex objects and Edge objects, and the Graph class contains: list<Vertex *> vertexList list<Edge *> edgeList Each Edge object has two Vertex* members representing its endpoints, and each Vertex object has a list of Edge* members representing the edges incident to the Vertex. All this is quite standard, but here is my problem. I want to be able to implement deletion of Edges and Vertices in constant time, so for example each Vertex object should have a Locator member that points to the position of its Vertex* in the vertexList. The way I first implemented this was by saving a list::iterator, as follows: vertexList.push_back(v); v->locator = --vertexList.end(); Then if I need to delete this vertex later, then rather than searching the whole vertexList for its pointer, I can call: vertexList.erase(v->locator); This works fine at first, but it seems that if enough changes (deletions) are made to the list, the iterators will become out-of-date and I get all sorts of iterator errors at runtime. This seems strange for a linked list, because it doesn't seem like you should ever need to re-allocate the remaining members of the list after deletions, but maybe the STL does this to optimize by keeping memory somewhat contiguous? In any case, I would appreciate it if anyone has any insight as to why this happens. Is there a standard way in C++ to implement a locator that will keep track of an element's position in a list without becoming obsolete? Much thanks, Jeff

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  • how do I best create a set of list classes to match my business objects

    - by ken-forslund
    I'm a bit fuzzy on the best way to solve the problem of needing a list for each of my business objects that implements some overridden functions. Here's the setup: I have a baseObject that sets up database, and has its proper Dispose() method All my other business objects inherit from it, and if necessary, override Dispose() Some of these classes also contain arrays (lists) of other objects. So I create a class that holds a List of these. I'm aware I could just use the generic List, but that doesn't let me add extra features like Dispose() so it will loop through and clean up. So if I had objects called User, Project and Schedule, I would create UserList, ProjectList, ScheduleList. In the past, I have simply had these inherit from List< with the appropriate class named and then written the pile of common functions I wanted it to have, like Dispose(). this meant I would verify by hand, that each of these List classes had the same set of methods. Some of these classes had pretty simple versions of these methods that could have been inherited from a base list class. I could write an interface, to force me to ensure that each of my List classes has the same functions, but interfaces don't let me write common base functions that SOME of the lists might override. I had tried to write a baseObjectList that inherited from List, and then make my other Lists inherit from that, but there are issues with that (which is really why I came here). One of which was trying to use the Find() method with a predicate. I've simplified the problem down to just a discussion of Dispose() method on the list that loops through and disposes its contents, but in reality, I have several other common functions that I want all my lists to have. What's the best practice to solve this organizational matter?

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  • How to put data from List<string []> to dataGridView

    - by Kirill
    Try to put some data from List to dataGridView, but have some problem with it. Currently have method, that return me required List - please see picture below code public List<string[]> ReadFromFileBooks() { List<string> myIdCollection = new List<string>(); List<string[]> resultColl = new List<string[]>(); if (chooise == "all") { if (File.Exists(filePath)) { using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read)) { StreamReader sr = new StreamReader(fs); string[] line = sr.ReadToEnd().Split(new string[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries); foreach (string l in line) { string[] result = l.Split(','); foreach (string element in result) { myIdCollection.Add(element); } resultColl.Add(new string[] { myIdCollection[0], myIdCollection[1], myIdCollection[2], myIdCollection[3] }); myIdCollection.Clear(); } sr.Close(); return resultColl; } } .... this return to me required data in requred form (like list from arrays). After this, try to move it to the dataGridView, that already have 4 columns with names (because i'm sure, that no than 4 colums required) - please see pic below Try to put data in to dataGridView using next code private void radioButtonViewAll_CheckedChanged(object sender, EventArgs e) { TxtLibrary myList = new TxtLibrary(filePathBooks); myList.chooise = "all"; //myList.ReadFromFileBooks(); DataTable table = new DataTable(); foreach (var array in myList.ReadFromFileBooks()) { table.Rows.Add(array); } dataGridViewLibrary.DataSource = table; } But as result got error - "required more rows that exist in dataGridVIew", but accordint to what I'm see (pic above) q-ty of rows (4) equal q-ty of arrays element in List (4). Try to check result by putting additional temp variables - but it's ok - please see pic below Where I'm wrong? Maybe i use dataGridView not in correct way?

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  • Where to find a list of bad passwords?

    - by Steve Morgan
    I need to implement a 'stop list' to prevent users selecting common passwords in a new online service. Can anyone point me to such a list online anywhere? Edited: Note that I'm only trying to eliminate the most common passwords, not an exhaustive dictionary. And, of course, this complements a reasonably strong password policy (length, use of non-alpha characters, etc.) Thanks.

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  • Setting up a linked server to another server which isn’t in a domain without using SQL authenticatio

    - by Telos
    Server A (SQL2005) is in our primary domain, but server B (SQL2000) is just in a windows workgroup. We are not allowed to join it to the domain, or bad things happen... We also can't enable SQL authentication on server B. We've got domain accounts for A, and matching local accounts on server B. I can connect to B from my local PC or A using SSMS and a domain login, but I can't get the linked server to connect. Any ideas how to do this?

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  • jquery Ajax sortable list stops being sortable when Ajax call updates the list html

    - by Trevor
    Hi, I am using jquery 1.4.2 and trying to achieve the following: 1 - function call that sends a value to a php page to add/remove an item 2 - returns html list of the items 3 - list should still be sortable 4 - save (serialise list) onclick My full WIP is located here [http://www.chittak.co.uk/test4/index_nw3.php][1] I tried to delegate from the level above the UL but I could get this to work $("#construnctionstage").delegate('ul li', 'click', function(){ The initial list is sortable, when you click add/remove the ajax function returns a new list with the a number of items, BUT I am doing something wrong as the alert message continues to work while the list is no longer sortable. $(document).ready(function(){ $('ul').delegate('li', 'click', function(){ alert('You clicked on an li element!'); /*$("#test-list").sortable({ handle : '.handle', update : function () { var order = $('#test-list').sortable('serialize'); $("#info").load("process-sortable.php?"+order); } });*/ }).sortable({ handle : '.handle', update : function () { var order = $('#test-list').sortable('serialize'); $("#info").load("process-sortable.php?"+order); } }); }); <div id="construnctionstage"> <ul id="test-list"> <li id="listItem_1">

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  • How do I implement a remove by index method for a singly linked list in Java?

    - by Lars Flyger
    Hi, I'm a student in a programming class, and I need some help with this code I've written. So far I've written an entire linked list class (seen below), yet for some reason the "removeByIndex" method won't work. I can't seem to figure out why, the logic seems sound to me. Is there some problem I don't know about? public class List<T> { //private sub-class Link private class Link { private T value; private Link next; //constructors of Link: public Link (T val) { this.value = val; this.next = null; } public Link (T val, Link next) { this.value = val; this.next = next; } @SuppressWarnings("unused") public T getValue() { return value; } } private static final Exception NoSuchElementException = null; private static final Exception IndexOutOfBoundsException = null; private Link chain = null; //constructors of List: public List() { this.chain = null; } //methods of List: /** * Preconditions: none * Postconditions: returns true if list is empty */ public boolean isEmpty() { return this.chain == null; } /** * Preconditions: none * Postconditions: A new Link is added via add-aux * @param element */ public void add(T element) { this.add_aux(element, this.chain); } /** * Preconditions: none * Postconditions: A new Link is added to the current chain * @param element * @param chain */ private void add_aux(T element, Link chain) { if (chain == null) { //if chain is null set chain to a new Link with a value of //element this.chain = new Link(element); } else if (chain.next != null) { //if chain.next is not null, go to next item in chain and //try //to add element add_aux(element, chain.next); } else { //if chain.next is null, set chain.next equal to a new Link //with value of element. chain.next = new Link(element); } } /** * Preconditions: none * Postconditions: returns the link at the defined index via nthlink_aux * @param index * @return */ private Link nthLink (int index) { return nthLink_aux(index, this.chain); } /** * Preconditions: none * Postconditions: returns the link at the defined index in the specified *chain * @param i * @param c * @return */ private Link nthLink_aux (int i, Link c) { if (i == 0) { return c; } else return nthLink_aux(i-1, c.next); } /** * Preconditions: the specified element is present in the list * Postconditions: the specified element is removed from the list * @param element * @throws Exception */ public void removeElement(T element) throws Exception { if (chain == null) { throw NoSuchElementException; } //while chain's next is not null and the value of chain.next is not //equal to element, //set chain equal to chain.next //use this iteration to go through the linked list. else while ((chain.next != null) && !(chain.next.value.equals(element))){ Link testlink = chain.next; if (testlink.next.value.equals(element)) { //if chain.next is equal to element, bypass the //element. chain.next.next = chain.next.next.next; } else if (testlink.next == null) { throw NoSuchElementException; } } } /** * Preconditions: none * Postsconditions: the Link at the specified index is removed * @param index * @throws Exception */ public void removeByIndex(int index) throws Exception { if (index == 0) { //if index is 0, set chain equal to chain.next chain = chain.next; } else if (index > 0) { Link target = nthLink(index); while (target != null) { if (target.next != null) { target = target.next; } //if target.next is null, set target to null else { target = null; } } return; } else throw IndexOutOfBoundsException; } /** * Preconditions: none * Postconditions: the specified link's value is printed * @param link */ public void printLink (Link link) { if(link != null) { System.out.println(link.value.toString()); } } /** * Preconditions: none * Postconditions: all of the links' values in the list are printed. */ public void print() { //copy chain to a new variable Link head = this.chain; //while head is not null while (!(head == null)) { //print the current link this.printLink(head); //set head equal to the next link head = head.next; } } /** * Preconditions: none * Postconditions: The chain is set to null */ public void clear() { this.chain = null; } /** * Preconditions: none * Postconditions: Places the defined link at the defined index of the list * @param index * @param val */ public void splice(int index, T val) { //create a new link with value equal to val Link spliced = new Link(val); if (index <= 0) { //copy chain Link copy = chain; //set chain equal to spliced chain = spliced; //set chain.next equal to copy chain.next = copy; } else if (index > 0) { //create a target link equal to the link before the index Link target = nthLink(index - 1); //set the target's next equal to a new link with a next //equal to the target's old next target.next = new Link(val, target.next); } } /** * Preconditions: none * Postconditions: Check to see if element is in the list, returns true * if it is and false if it isn't * @param element * @return */ public boolean Search(T element) { if (chain == null) { //return false if chain is null return false; } //while chain's next is not null and the value of chain.next is not //equal to element, //set chain equal to chain.next //use this iteration to go through the linked list. else while ((chain.next != null) && !(chain.next.value.equals(element))) { Link testlink = chain.next; if (testlink.next.value.equals(element)) { //if chain.next is equal to element, return true return true; } else if (testlink.next == null) { return false; } } return false; } /** * Preconditions: none * Postconditions: order of the links in the list is reversed. */ public void reverse() { //copy chain Link current = chain; //set chain equal to null chain = null; while (current != null) { Link save = current; current = current.next; save.next = chain; chain = save; } } }'

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  • Passing a non-iterable to list.extend ()

    - by JS
    Hello, I am creating a public method to allow callers to write values to a device, call it write_vals() for example. Since these values will by typed live, I would like to simplify the user's life by allowing them type in either a list or a single value, depending on how many values they need to write. For example: write_to_device([1,2,3]) or write_to_device(1) My function would like to work with a flat list, so I tried to be clever and code something like this: input_list = [] input_list.extend( input_val ) This works swimmingly when the user inputs a list, but fails miserably when the user inputs a single integer: TypeError: 'int' object is not iterable Using list.append() would create a nested list when a list was passed in, which would be an additional hassle to flatten. Checking the type of the object passed in seems clumsy and non-pythonic and wishing that list.extend() would accept non-iterables has gotten me nowhere. So has trying a variety of other coding methods. Suggestions (coding-related only, please) would be greatly appreciated.

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