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  • Haskell Add Function Return to List Until Certain Length

    - by kienjakenobi
    I want to write a function which takes a list and constructs a subset of that list of a certain length based on the output of a function. If I were simply interested in the first 50 elements of the sorted list xs, then I would use fst (splitAt 50 (sort xs)). However, the problem is that elements in my list rely on other elements in the same list. If I choose element p, then I MUST also choose elements q and r, even if they are not in the first 50 elements of my list. I am using a function finderFunc which takes an element a from the list xs and returns a list with the element a and all of its required elements. finderFunc works fine. Now, the challenge is to write a function which builds a list whose total length is 50 based on multiple outputs of finderFunc. Here is my attempt at this: finish :: [a] -> [a] -> [a] --This is the base case, which adds nothing to the final list finish [] fs = [] --The function is recursive, so the fs variable is necessary so that finish -- can forward the incomplete list to itself. finish ps fs -- If the final list fs is too small, add elements to it | length fs < 50 && length (fs ++ newrs) <= 50 = fs ++ finish newps newrs -- If the length is met, then add nothing to the list and quit | length fs >= 50 = finish [] fs -- These guard statements are currently lacking, not the main problem | otherwise = finish [] fs where --Sort the candidate list sortedps = sort ps --(finderFunc a) returns a list of type [a] containing a and all the -- elements which are required to go with it. This is the interesting -- bit. rs is also a subset of the candidate list ps. rs = finderFunc (head sortedps) --Remove those elements which are already in the final list, because -- there can be overlap newrs = filter (`notElem` fs) rs --Remove the elements we will add to the list from the new list -- of candidates newps = filter (`notElem` rs) ps I realize that the above if statements will, in some cases, not give me a list of exactly 50 elements. This is not the main problem, right now. The problem is that my function finish does not work at all as I would expect it to. Not only does it produce duplicate elements in the output list, but it sometimes goes far above the total number of elements I want to have in the list. The way this is written, I usually call it with an empty list, such as: finish xs [], so that the list it builds on starts as an empty list.

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  • Splitting list into a list of possible tuples

    - by user1742646
    I need to split a list into a list of all possible tuples, but I'm unsure of how to do so. For example pairs ["cat","dog","mouse"] should result in [("cat","dog"), ("cat","mouse"), ("dog","cat"), ("dog","mouse"), ("mouse","cat"), ("mouse","dog")] I was able to form the first two, but am unsure of how to get the rest. Here's what I have so far: pairs :: [a] -> [(a,a)] pairs (x:xs) = [(m,n) | m <- [x], n <- xs]

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  • find if list 1 is a sequence of list 2 in haskell

    - by Isaak Wahb
    im trying to check if a given list is a subsequence of another list: here are example of lists which gives true: subseq "" "w" subseq "w" "w" subseq "ab" "cab" subseq "cb" "cab" subseq "aa" "xaxa" not (subseq "aa" "xax") not (subseq "ab" "ba") i just come to this but in some cases it gives a wrong result subseq :: Eq a => [a] -> [a] -> Bool subseq [] [] = True subseq [] ys = True subseq xs [] = False subseq (x:xs) (y:ys) = x == y || subseq xs ( 1 `drop` ys )

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  • troubles creating a List of doubles from a list of objects

    - by Michel
    Hi, i have a list with objects. The object has a property 'Sales' which is a string. Now i want to create a list of doubles with the values of all objects' 'Sales' properties. I tried this: var tmp = from n in e.Result select new{ Convert.ToDouble ( n.Sales) }; but this gives me this error: Error 106 Invalid anonymous type member declarator. Anonymous type members must be declared with a member assignment, simple name or member access.

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  • django convert list of objects to list of primary keys

    - by John
    Hi, As the title says I have a list of Django objects and I want to get a list of primary keys. What is the best way of doing this? I know I could do my_list = [] for item in object_list: my_list.append(item.pk) but was wondering if there is Django or Python specific way of doing this better. Thanks

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  • Could not determine metatable error binding list to asp.net datagridview

    - by Scott Vercuski
    I am working with the following block of code ... List<ThemeObject> themeList = (from theme in database.Themes join image in database.DBImages on theme.imageID equals image.imageID into resultSet from item in resultSet select new ThemeObject { Name = theme.Name, ImageID = item.imageID}).ToList(); dgvGridView.DataSource = themeList; dgvGridView.DataBind(); The list object populates fine. The datagrid is setup with 2 columns. A textbox column for the "Name" which is bound to "Name" An image column which is bound to the "ImageID" field When I execute the code I receive the following error on the DataBind() Could not determine a MetaTable. A MetaTable could not be determined for the data source '' and one could not be inferred from the request URL. Make sure that the table is mapped to the dats source, or that the data source is configured with a valid context type and table name, or that the request is part of a registered DynamicDataRoute. I'm not using any dynamicdataroutes as far as I can tell. Has anyone experienced this error before?

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  • Big problem with Dijkstra algorithm in a linked list graph implementation

    - by Nazgulled
    Hi, I have my graph implemented with linked lists, for both vertices and edges and that is becoming an issue for the Dijkstra algorithm. As I said on a previous question, I'm converting this code that uses an adjacency matrix to work with my graph implementation. The problem is that when I find the minimum value I get an array index. This index would have match the vertex index if the graph vertexes were stored in an array instead. And the access to the vertex would be constant. I don't have time to change my graph implementation, but I do have an hash table, indexed by a unique number (but one that does not start at 0, it's like 100090000) which is the problem I'm having. Whenever I need, I use the modulo operator to get a number between 0 and the total number of vertices. This works fine for when I need an array index from the number, but when I need the number from the array index (to access the calculated minimum distance vertex in constant time), not so much. I tried to search for how to inverse the modulo operation, like, 100090000 mod 18000 = 10000 and, 10000 invmod 18000 = 100090000 but couldn't find a way to do it. My next alternative is to build some sort of reference array where, in the example above, arr[10000] = 100090000. That would fix the problem, but would require to loop the whole graph one more time. Do I have any better/easier solution with my current graph implementation?

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  • [WPF Datagrid] Binding to a List<>

    - by Tr?n Qu?c Bình
    I have a datagrid like this: <dg:DataGrid Name="dg" AutoGenerateColumns="False" CanUserDeleteRows="True"> <dg:DataGrid.Columns> <dg:DataGridTextColumn Header="Product Code" x:Name="columnProductCode" Binding="{Binding Path=Product.ProductCode}" IsReadOnly="True" ></dg:DataGridTextColumn> <dg:DataGridTextColumn Header="Product Name" x:Name="columnProductName" Binding="{Binding Path=Product.Name}" IsReadOnly="True" ></dg:DataGridTextColumn> <dg:DataGridTextColumn Header="ProductMeasure" x:Name="columnDonViTinh" Binding="{Binding Path=Product.Measure IsReadOnly="True"></dg:DataGridTextColumn> <dg:DataGridTextColumn Header="Quantity" x:Name="ColumnQuantity" Binding="{Binding Path=Quantity IsReadOnly="False"></dg:DataGridTextColumn> </dg:DataGrid.Columns> </dg:DataGrid> In the behind code, I have a struct like this: private struct ProductDetail { public TProduct Product { get; set ; } // TProduct is a class provied by a web service public int Quantity { get; set; } } and a List like this: private IList<ProductDetail> bs = new List<ProductDetail>(); I had tried to fill data to "bs". And binding like this: this.dg.ItemsSource = this.bs; Everything is ok. I can insert a new row, delete row, but when I try to modified the column Quantity then click on the header of the datagrid (to resort) -- the Quantity column change to it is before. How can I fix this problem. Thanks advanced.

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  • select & print multiple value from dropdown list

    - by sandy
    hi , in this code how can selected multiple value from dropdown list <?php include ("connect.php"); $member_id = intval($_POST['sector_list']); if($member_id == 0) { // Default choice was selected } else { $res = mysql_query("SELECT * FROM members WHERE MemberID = $member_id LIMIT 1"); if(mysql_num_rows($res) == 0) { // Not a valid member } else { // The member is in the database } } ?> <form method="post" action=""> <input type="hidden" name="sector" value="sector_list"> <select name="sector_list" class="inputstandard" multiple="multiple"> <option value="0">send to</option> <?php $result = mysql_query('SELECT * from members') or die(mysql_error()); while ($row = mysql_fetch_assoc($result)) { echo '<option value="' . $row['MemberID'] . '">' . $row['MemberName']. '</option>'; } ?> </select> </form> assume the drop down list contain on (a,s,d,f,g,h,j,) users selects multiple value ( a,s,j) output = a,s,j not only j ???

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  • Presentation Issue in an Unordered List

    - by phreeskier
    I'm having an issue with correctly presenting items in an unordered list. The labels are floating left and the related spans that are long in length are wrapping and showing below the label. I need a solution that keeps the related spans in their respective columns. In other words, I don't want long spans to show under the labels. What property can I take advantage of so that I get the desired layout in all of the popular browsers, including IE6? Thanks in advance for the help. My code is as follows: <ul> <li> <label>Name</label> <span><%= Html.Encode(Model.Name) %></span> </li> <li> <label>Entity</label> <span><%= Html.Encode(Model.Entity) %></span> </li> <li> <label>Phone</label> <span><%= Html.Encode(Model.Phone) %></span> </li> </ul> My CSS styling is as follows: ul { display:block; list-style-type:none; margin:0; padding:0; } ul li label { float:left; width:100px; }

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  • How to create a list/structure? in JAVA

    - by lox
    i have to create a list of ,let's say 50 people, (in JAVA) and display the list, and i don't really know how to do that. so this is what i have tried to do so far . please correct and complete some of my code . public class Person { String name; String stuff; } public class CreatePerson { public static void ang() { ArrayList<Person> thing=new ArrayList<Person>(); Scanner diskScanner = new Scanner(in); for(int i=0; i<50; i++){ Person pers = new Person(); out.print("name: "); pers.name=diskScanner.nextLine(); out.print("stuff: "); pers.stuff=diskScanner.nextLine(); thing.add(pers); break; } // Display people for (int i=0; i<50; i++) { out.println(??);{ } } }}

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  • Linked List push()

    - by JKid314159
    The stack is initialized with a int MaxSize =3. Then I push one int onto the list. " Pushed:" is returned to the console. Program crashes here. I think my logic is flawed but unsure. Maybe an infinite loop or unmet condition? Thanks for your help. I'm trying to traverse the list to the last node in the second part of the full() method. I implemented this stack as array based so must implement this method full() as this method is inside of main class. while(!stacker.full()) { cout << "Enter number = "; cin >> intIn; stacker.push(intIn); cout << "Pushed: " << intIn << endl; }//while Call to LinkListStack.cpp to class LinkList full(). int LinkList::full() { if(head == NULL) { top = 0; } else { LinkNode * tmp1; LinkNode * tmp2; tmp1 = head; while(top != MaxSize) { if(tmp1->next != NULL){ tmp2 = tmp1->next; tmp1 = tmp2; ++top; }//if }//while }//else return (top + 1 == MaxSize); }

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  • Adding items to a generic list (novice)

    - by Crash893
    I'm some what embarrassed to even ask this but I know there is a better way to do this I just don't know how List<int> numbers = new List<int>(22); numbers.Add(3); numbers.Add(4); numbers.Add(9); numbers.Add(14); numbers.Add(15); numbers.Add(19); numbers.Add(28); numbers.Add(37); numbers.Add(47); numbers.Add(50); numbers.Add(54); numbers.Add(56); numbers.Add(59); numbers.Add(61); numbers.Add(70); numbers.Add(73); numbers.Add(78); numbers.Add(81); numbers.Add(92); numbers.Add(95); numbers.Add(97); numbers.Add(99);

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  • linked list sort function only loops once

    - by Tristan Pearce
    i have a singly linked list that i am trying to sort from least to greatest by price. here is what i have so far struct part { char* name; float price; int quantity; struct part *next; }; typedef struct part partType; partType *sort_price(partType **item) { partType *temp1 = *item; partType *temp2 = (*item)->next; if ( *item == NULL || (*item)->next == NULL ) return *item; else { while ( temp2 != NULL && temp2->next != NULL ){ if (temp2->price > temp2->next->price){ temp1->next = temp2->next; temp2->next = temp2->next->next; temp1->next->next = temp2; } temp1 = temp2; temp2 = temp2->next; } } return *item; } the list is already populated but when i call the sort function it only swaps the first two nodes that satisfy the condition in the if statement. I dont understand why it doesnt do the check again after the two temp pointers are incremented.

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  • Adding and sorting a linked list in C

    - by user1202963
    In my assignment, I have to write a function that takes as arguments a pointer to a "LNode" structure and an integer argument. Then, I have to not only add that integer into the linked list, but also put place it so that the list is in proper ascending order. I've tried several various attempts at this, and this is my code as of posting. LNode* AddItem(LNode *headPtr, int newItem) { auto LNode *ptr = headPtr; ptr = malloc(sizeof(LNode)); if (headPtr == NULL) { ptr->value = newItem; ptr->next = headPtr; return ptr; } else { while (headPtr->value > newItem || ptr->next != NULL) { printf("While\n"); // This is simply to let me know how many times the loop runs headPtr = headPtr->next; } ptr->value = newItem; ptr->next = headPtr; return ptr; } } // end of "AddItem" When I run it, and try to insert say a 5 and then a 3, the 5 gets inserted, but then the while loop runs once and I get a segmentation fault. Also I cannot change the arguments as it's part of a skeletal code for this project. Thanks to anyone who can help. If it helps this is what the structure looks like typedef struct LNode { int value; struct LNode *next; } LNode;

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  • What is a better, cleaner way of using List<T>

    - by Tim Meers
    I'm looking to implement a few nicer ways to use List in a couple of apps I'm working on. My current implementation looks like this. MyPage.aspx.cs protected void Page_Load(object sender, EventArgs e) { BLL.PostCollection oPost = new BLL.PostCollection(); oPost.OpenRecent(); rptPosts.DataSource = oArt; rptPosts.DataBind(); } BLL Class(s) public class Post { public int PostId { get; set; } public string PostTitle { get; set; } public string PostContent { get; set; } public string PostCreatedDate { get; set; } public void OpenRecentInitFromRow(DataRow row) { this.PostId = (int) row["id"]; this.PostTitle = (string) row["title"]; this.PostContent = (string) row["content"]; this.PostCreatedDate = (DateTime) row["createddate"]; } } public class PostCollection : List<Post> { public void OpenRecent() { DataSet ds = DbProvider.Instance().Post_ListRecent(); foreach (DataRow row in ds.Tables[0].Rows) { Post oPost = new Post(); oPost.OpenRecentInitFromRow(row); Add(oPost); } } } Now while this is working all well and good, I'm just wondering if there is any way to improve it, and just make it cleaner that having to use the two different classes do to something I think can happen in just one class or using an interface.

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  • C++ Bubble Sorting for Singly Linked List [closed]

    - by user1119900
    I have implemented a simple word frequency program in C++. Everything but the sorting is OK, but the sorting in the following script does not work. Any emergent help will be great.. #include <stdio.h> #include <string.h> #include <stdlib.h> #include <ctype.h> #include <iostream> #include <fstream> #include <cstdio> using namespace std; #include "ProcessLines.h" struct WordCounter { char *word; int word_count; struct WordCounter *pNext; // pointer to the next word counter in the list }; /* pointer to first word counter in the list */ struct WordCounter *pStart = NULL; /* pointer to a word counter */ struct WordCounter *pCounter = NULL; /* Print statistics and words */ void PrintWords() { ... pCounter = pStart; bubbleSort(pCounter); ... } //end-PrintWords void bubbleSort(struct WordCounter *ptr) { WordCounter *temp = ptr; WordCounter *curr; for (bool didSwap = true; didSwap;) { didSwap = false; for (curr = ptr; curr->pNext != NULL; curr = curr->pNext) { if (curr->word > curr->pNext->word) { temp->word = curr->word; curr->word = curr->pNext->word; curr->pNext->word = temp->word; didSwap = true; } } } }

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  • Java How to find a value in a linked list iteratively and recursively

    - by Roxy
    Hi I have a method that has a reference to a linked list and a int value. So, this method would count and return how often the value happens in the linked list. So, I decided to make a class, public class ListNode{ public ListNode (int v, ListNode n) {value = v; next = n;) public int value; public ListNode next; } Then, the method would start with a public static int findValue(ListNode x, int valueToCount){ // so would I do it like this?? I don't know how to find the value, // like do I check it? for (int i =0; i< x.length ;i++){ valueToCount += valueToCount; } So, I CHANGED this part, If I did this recursively, then I would have public static int findValue(ListNode x, int valueToCount) { if (x.next != null && x.value == valueToCount { return 1 + findValue(x, valueToCount);} else return new findvalue(x, valueToCount); SO, is the recursive part correct now?

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  • Rails how to return a list of answers with a specific question_id

    - by mytwocentsisworthtwocents
    Let's say I have two Models, Answers and Questions (there are others, but irrelevant to the question). The models are as follows: Answer.rb class Answer < ActiveRecord::Base attr_accessible :description, :question_id has_one :question, :through => :user, :dependent => :destroy validates :description, :presence => true end Question.rb class Question < ActiveRecord::Base attr_accessible :budget, :description, :headline, :user_id, :updated_at, :created_at belongs_to :user has_many :answers validates :headline, :description, :user_id, :presence => true end I'd like to display on a page a list of all answers associated with a question, and only those questions. I got this far. I believe this variable finds all the questions in the database by the question_id (foreign key): @findanswers = Answer.all(params[:question_id]) And this one grabs the the id of the current question (this code will reside as an ERB on the page where the current question is located): @questionshow = Question.find(params[:id]) And now I'm stuck. How do I put the two together so that I list all the answers with the current question id?

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  • Sorting a Singly Linked List With Pointers

    - by Mark Simson
    I am trying to sort a singly linked list using bubble sort by manipulating ONLY the pointers, no keys. The following gets stuck in the for loop and loops infinitely. I don't understand why this is. Can anybody explain to me why the end of the list is not being found? Node* sort_list(Node* head) { Node * temp; Node * curr; for(bool didSwap = true; didSwap; ) { didSwap = false; for(curr = head; curr->next != NULL; curr = curr->next) { if(curr->key > curr->next->key) { temp = curr; curr = curr->next; curr->next = temp; didSwap = true; } cout << curr->next->key << endl; } } return head; } If I change the code so that the keys (data) are swapped, then the function works properly but for some reason I am not able make it work by manipulating only pointers.

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  • Having trouble deleting a node from a linked list

    - by Requiem
    I've been working on this code for my shell that I'm creating and for some reason it isn't working. I'm implementing a watchuser function that watch's a user when an argument is given (args[1]). However, when a second argument (args[2]) of "off" is given, the user should be deleted from the linked list and should no longer be watched. struct userList * goList; goList = userInventory; do{ if (strcmp(userInventory->username, args[1]) == 0){ printf("%s\n", args[1]); printf("%s\n",userInventory->username); struct userList * temp2; temp2 = userInventory->next; if (userInventory->next != NULL){ userInventory->next = temp2->next; userInventory->next->prev = userInventory; } free(temp2); } goList = goList->next; }while (goList != userInventory); My global struct is also as follows: struct userList{ char * username; struct userList * prev; struct userList * next; } For reason, this code won't delete the user node from my linked list. The adding works, but this remove function won't and I'm not sure why. The print statements are there just to make sure it's executing the condition, which it is. If anyone could help me find the reasoning behind my error, I'd greatly appreciate it. Till then, I'll be trying to debug this. Thanks.

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  • Access Denied

    - by Tony Davis
    When Microsoft executives wake up in the night screaming, I suspect they are having a nightmare about their own version of Frankenstein's monster. Created with the best of intentions, without thinking too hard of the long-term strategy, and having long outlived its usefulness, the monster still lives on, occasionally wreaking vengeance on the innocent. Its name is Access; a living synthesis of disparate body parts that is resistant to all attempts at a mercy-killing. In 1986, Microsoft had no database products, and needed one for their new OS/2 operating system, the successor to MSDOS. In 1986, they bought exclusive rights to Sybase DataServer, and were also intent on developing a desktop database to capture Ashton-Tate's dominance of that market, with dbase. This project, first called 'Omega' and later 'Cirrus', eventually spawned two products: Visual Basic in 1991 and Access in late 1992. Whereas Visual Basic battled with PowerBuilder for dominance in the client-server market, Access easily won the desktop database battle, with Dbase III and DataEase falling away. Access did an excellent job of abstracting and simplifying the task of building small database applications in a short amount of time, for a small number of departmental users, and often for a transient requirement. There is an excellent front end and forms generator. We not only see it in Access but parts of it also reappear in SSMS. It's good. A business user can pull together useful reports, without relying on extensive technical support. A skilled Access programmer can deliver a fairly sophisticated application, whilst the traditional client-server programmer is still sharpening his pencil. Even for the SQL Server programmer, the forms generator of Access is useful for sketching out application designs. So far, so good, but here's where the problems start; Access ties together two different products and the backend of Access is the bugbear. The limitations of Jet/ACE are well-known and documented. They range from MDB files that are prone to corruption, especially as they grow in size, pathetic security, and "copy and paste" Backups. The biggest problem though, was an infamous lack of scalability. Because Microsoft never realized how long the product would last, they put little energy into improving the beast. Microsoft 'ate their own dog food' by using Access for Microsoft Exchange and Outlook. They choked on it. For years, scalability and performance problems with Exchange Server have been laid at the door of the Jet Blue engine on which it relies. Substantial development work in Exchange 2010 was required, just in order to improve the engine and storage schema so that it more efficiently handled the reading and writing of mails. The alternative of using SQL Server just never panned out. The Jet engine was designed to limit concurrent users to a small number (10-20). When Access applications outgrew this, bitter experience proved that there really is no easy upgrade path from Access to SQL Server, beyond rewriting the whole lot from scratch. The various initiatives to do this never quite bridged the cultural gulf between Access and a true relational database So, what are the obvious alternatives for small, strategic database applications? I know many users who, for simple 'list maintenance' requirements are very happy using Excel databases. Surely, now that PowerPivot has led the way, it is time for Microsoft to offer a new RAD package for database application development; namely an Excel-based front end for SQL Server Express. In that way, we'll have a powerful and familiar front end, to a scalable database, and a clear upgrade path when an app takes off and needs to go enterprise. Cheers, Tony.

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