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• Webapp: safetly update a shared List/Map in the AppContext

  - by al nik

  I've Lists and Maps in my WebAppContext. Most of the time these are only read by multiple Threads but sometimes there's the need to update or add some data. I'm wondering what's the best way to do this without incurring in a ConcurrentModificationException. I think that using CopyOnWriteArrayList I can achieve what I want in terms of - I do not have to sync on every read operation- I can safety update the list while other threads are reading it. Is this the best solution? What about Maps?

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• Use LINQ and C# to make a new List from an old List

  - by Addie

  This should be pretty simple, but I am new at LINQ. I have a List of FillList structs. I'd like to use LINQ to create a new List where instead of having the number of buys and sells, I would have one variable containing the sum. For example, if the FillStruct structure has buy = 4 and sell = 2 then the NewFillStruct structure will have numlong = 2. If the FillStruct structure has buy = 2 and sell = 4 then the NewFillStruct structure will have numlong = -2. Here are the structures. struct FillStruct { int buy; int sell; string date; } struct NewFillStruct { int numlong; string date; }

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• split a result list from mysql into separate lists based on list length

  - by liz

  i have a list of returned rows from mysql that i am outputting using php: echo '<ul class="mylist">'; foreach ($rows as $row) { echo '<li><a href="'.$row->url.'" target="_blank">' . $row->title . '</a></li>'; } echo "</ul>"; works fine, but its a long list and i would like to split it into ul chunks so that i can make columns. maybe like 5 results per ul. instead of one ul... i tried wrapping in a for statement but then just wound up outputting the results 5 times...oops...

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• mysql - filtering a list against keywords, both list and keywords > 20 million records

  - by threecheeseopera

  I have two tables, both having more than 20 million records; table1 is a list of terms, and table2 is a list of keywords that may or may not appear in those terms. I need to identify the terms that contain a keyword. My current strategy is: SELECT table1.term, table2.keyword FROM table1 INNER JOIN table2 ON table1.term LIKE CONCAT('%', table2.keyword, '%'); This is not working, it takes f o r e v e r. It's not the server (see notes). How might I rewrite this so that it runs in under a day? Notes: As for server optimization: both tables are myisam and have unique indexes on the matching fields; the myisam key buffer is greater than the sum of both index file sizes, and it is not even being fully taxed (key_blocks_unused is ... large); the server is a dual-xeon 2U beast with fast sas drives and 8G of ram, fine-tuned for the mysql workload.

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• WCF: generic list serialized to array

  - by OpticalDelusion

  So I am working with WCF and my services return types that contain generic lists. WCF is currently converting these to arrays over the wire. Is there a way I configure WCF to convert them back to lists afterwards? I know there is a way by clicking advanced when you add a service reference but I am looking for a solution in configuration files or something similar. [DataContract(IsReference = true)] public class SampleObject { [DataMember] public long ID { get; private set; } [DataMember] public ICollection<AnotherObject> Objects { get; set; } } It is very odd, also, because one service returns it as a list and the other as an array and I am pretty sure they are configured identically.

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• C++ Memory Allocation & Linked List Implementation

  - by pws5068

  I'm writing software to simulate the "first-fit" memory allocation schema. Basically, I allocate a large X megabyte chunk of memory and subdivide it into blocks when chunks are requested according to the schema. I'm using a linked list called "node" as a header for each block of memory (so that we can find the next block without tediously looping through every address value. head_ptr = (char*) malloc(total_size + sizeof(node)); if(head_ptr == NULL) return -1; // Malloc Error .. :-( node* head_node = new node; // Build block header head_node->next = NULL; head_node->previous = NULL; // Header points to next block (which doesn't exist yet) memset(head_ptr,head_node, sizeof(node)); ` But this last line returns: error: invalid conversion from 'node*' to 'int' I understand why this is invalid.. but how can I place my node into the pointer location of my newly allocated memory?

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• Javascript - Determine if String Is In List

  - by Emtucifor

  In SQL we can see if a string is in a list like so: Column IN ('a', 'b', 'c') What's a good way to do this in javascript? I realize one can use the switch function: var str = 'a' var flag = false; switch (str) { case 'a': case 'b': case 'c': flag = true; default: } if (thisthing || thatthing || flag === true) { // do something } But this is a horrible mess. It's also clunky to do this: if (thisthing || thatthing || str === 'a' || str === 'b' || str = 'c') { // do something } And I'm not sure about the performance or clarity of this: if (thisthing || thatthing || {a:1, b:1, c:1}[str]) { // do something } Any ideas?

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• C++ Linked List - Reading data from a file with a sentinel

  - by Nick

  So I've done quite a bit of research on this and can't get my output to work correctly. I need to read in data from a file and have it stored into a Linked List. The while loop used should stop once it hits the $$$$$ sentinel. Then I am to display the data (by searching by ID Number[user input]) I am not that far yet I just want to properly display the data and get it read in for right now. My problem is when it displays the data is isn't stopping at the $$$$$ (even if I do "inFile.peek() != EOF and omit the $$$$$) I am still getting an extra garbage record. I know it has something to do with my while loop and how I am creating a new Node but I can't get it to work any other way. Any help would be appreciated. students.txt Nick J Cooley 324123 60 70 80 90 Jay M Hill 412254 70 80 90 100 $$$$$ assign6.h file #pragma once #include <iostream> #include <string> using namespace std; class assign6 { public: assign6(); // constructor void displayStudents(); private: struct Node { string firstName; string midIni; string lastName; int idNum; int sco1; //Test score 1 int sco2; //Test score 2 int sco3; //Test score 3 int sco4; //Test score 4 Node *next; }; Node *head; Node *headPtr; }; assign6Imp.cpp // Implementation File #include "assign6.h" #include <fstream> #include <iostream> #include <string> using namespace std; assign6::assign6() //constructor { ifstream inFile; inFile.open("students.txt"); head = NULL; head = new Node; headPtr = head; while (inFile.peek() != EOF) //reading in from file and storing in linked list { inFile >> head->firstName >> head->midIni >> head->lastName; inFile >> head->idNum; inFile >> head->sco1; inFile >> head->sco2; inFile >> head->sco3; inFile >> head->sco4; if (inFile != "$$$$$") { head->next = NULL; head->next = new Node; head = head->next; } } head->next = NULL; inFile.close(); } void assign6::displayStudents() { int average = 0; for (Node *cur = headPtr; cur != NULL; cur = cur->next) { cout << cur->firstName << " " << cur->midIni << " " << cur->lastName << endl; cout << cur->idNum << endl; average = (cur->sco1 + cur->sco2 + cur->sco3 + cur->sco4)/4; cout << cur->sco1 << " " << cur->sco2 << " " << cur->sco3 << " " << cur->sco4 << " " << "average: " << average << endl; } }

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• Removing a node from a linked list

  - by lost_with_coding

  I would like to create a delete_node function that deletes the node at the location in the list as a count from the first node. So far this is the code I have: class node: def __init__(self): self.data = None # contains the data self.next = None # contains the reference to the next node class linked_list: def __init__(self): self.cur_node = None def add_node(self, data): new_node = node() # create a new node new_node.data = data new_node.next = self.cur_node # link the new node to the 'previous' node. self.cur_node = new_node # set the current node to the new one. def list_print(self): node = ll.cur_node while node: print node.data node = node.next def delete_node(self,location): node = ll.cur_node count = 0 while count != location: node = node.next count+=1 delete node ll = linked_list() ll.add_node(1) ll.add_node(2) ll.add_node(3) ll.list_print()

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• C++ Constructor Initializer List - using member functions of initialized members

  - by Andy

  I've run into the following a few times with initializer lists and I've never been able to explain it well. Can anyone explain why exactly the following fails (I don't have a compiler to catch typos, so bear with me): class Foo { public: Foo( int i ) : m_i( i ) {} //works with no problem int getInt() {return m_i;} ~Foo {} private: int m_i; }; class Bar { public: Bar() : m_foo( 5 ), //this is ok m_myInt( m_foo.getInt() ) //runtime error, seg 11 {} ~Bar() {} private: Foo m_foo; int m_myInt; }; When trying to call member functions of members initialized higher up the initializer list, I get seg faults. I seem to recall this is a known problem (or perhaps somehow by design) but I've never seen it well described. The attached example is contrived with plain old data types, but substitute the Bar::m_myInt with another object lacking a default (empty) constructor and the issue is more real. Can anyone enlighten me? Thanks!

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• R: Converting a list of data frames into one data frame

  - by JD Long

  I have code that at one place ends up with a list of data frames which I really want to convert to a single big data frame. I got some pointers from an earlier question which was trying to do something similar but more complex. Here's an example of what I am starting with (this is grossly simplified for illustration): listOfDataFrames <- NULL for (i in 1:100) { listOfDataFrames[[i]] <- data.frame(a=sample(letters, 500, rep=T), b=rnorm(500), c=rnorm(500)) } I am currently using this: df <- do.call("rbind", listOfDataFrames) *EDIT* whoops. In my haste to implement what I had "learned" in a previous question I totally screwed up. Yes, the unlist() is just plain wrong. I'm editing that out of the question above.

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• List<Object> as a JRBeanCollectionDataSource to a Subreport

  - by Kiran

  am passing a List as a JRBeanCollectionDataSource to a Subreport. here Object is of Type A and B. A is having properties 'name' and 'address' and B is having property 'location'. if Object is of type A then i have display 'name' and 'address' in subreport. and if is of type B then i have to diaplay 'location' in subreport. i have to access a type of Object in a subreport, means is of which type (A or B)?. i have tried a lot but not found any solution. can anyone help me please. thanks in advance.

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• How to initialize List<E> in empty class constructor?

  - by Nazgulled

  Hi, The following code obviously doesn't work because List<E> is abstract: public class MyList { private List<E> list; public MyList() { this.list = new List<E>(); } } How can I initialize MyList class with an empty constructor if I need the list variable to be a LinkedList or a ArrayList depending on my needs?

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• Apply function to one element of a list in Python

  - by user189637

  I'm looking for a concise and functional style way to apply a function to one element of a tuple and return the new tuple, in Python. For example, for the following input: inp = ("hello", "my", "friend") I would like to be able to get the following output: out = ("hello", "MY", "friend") I came up with two solutions which I'm not satisfied with. One uses a higher-order function. def apply_at(arr, func, i): return arr[0:i] + [func(arr[i])] + arr[i+1:] apply_at(inp, lambda x: x.upper(), 1) One uses list comprehensions (this one assumes the length of the tuple is known). [(a,b.upper(),c) for a,b,c in [inp]][0] Is there a better way? Thanks!

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• Rails select list reverts to top?

  - by Danny McClelland

  Hi Everyone, I have number of select lists in my rails application like this: <li>Company<span><%= f.select :company_id, Company.all.collect {|m| [m.companyname, m.id]} %></span></li> They all work well, except - sometimes if you go to the edit view, the select list reverts to the top item, not the item that was chosen when creating. So if you go to an edit view and then click update without actually making any changes, the lists default to the top item - even though you didn't touch them. Is there a way around this? Thanks, Danny

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• Why will this for loop not return one field from list rather than the list?

  - by Dick Eshelman

  import csv """sample row = 10/6/2010,73.42,74.43,72.9,74.15,2993500""" filename_in = 'c:/python27/scripts/fiverows.csv' reader = csv.reader(open(filename_in, "rb"), dialect="excel", delimiter="\t", quoting =csv.QUOTE_MINIMAL) for row in reader: for item in row: print 'row = ',row print 'item = ', item When you run this script and print the row you get the sample row returned in [] as a list. When you print the item you get the sample row as an unquoted string. Why do I not get each field ie, (10/6/2010), (73.42), etc. returned as an item? How do I return a single item?

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• Python list comprehension overriding value

  - by Joschua

  Hi, folks have a look at the following piece of code, which shows a list comprehension.. >>> i = 6 >>> s = [i * i for i in range(100)] >>> print(i) When you execute the code example in Python 2.6 it prints 99, but when you execute it in Python 3.x it prints 6. What were the reason for changing the behaviour and why is the output 6 in Python 3.x? Thank you in advance!

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• list permutations in haskell

  - by turingcomplete

  So I'm new to haskell and I've been playing with it for a while now. I want to get my function that outputs all list permutations to work. I have written 2 implementations, one works well, the other is giving me an error. Any help would be awesome. This is the first (working) implementation: permute [] = [[]] permute xs = [y| x <- xs, y <- map (x:) $ permute $ delete x xs] This one is giving me an error: permute [] = [[]] permute xs = map (\x -> map (x:) $ permute $ delete x xs) xs and here's the error message: Occurs check: cannot construct the infinite type: t0 = [t0] Expected type: [t0] Actual type: [[t0]] In the expression: map (x :) $ permute $ delete x xs In the first argument of `map', namely `(\ x -> map (x :) $ permute $ delete x xs)' I'd appreciate if someone could explain why I'm getting this error. Thanks

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• recursively reverse linked list.

  - by Amanda

  I am implementing a function to recursively reverse a linked-list, but getting seg-fault. typedef struct _node { int data; struct _node *next; } Node, *NodeP; NodeP recursiveReverseList(NodeP first){ if(first == NULL) return NULL; if(first->next == NULL) return head; NodeP rest = recursiveReverseList(head->next); rest->next = first; first->next = NULL; return first; } Can you please help. P.S. The iterative version is working fine though. Its not homework. Just practicing C.

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• How to keep a Generic list unmodified when its copy is modified?

  - by user1801934

  When I create a copy of the original list lstStudent in lstCopy and send the lstCopy to modification function, the lstStudent also gets modified. I want to keep this list unmodified. List<Student> lstStudent = new List<Student>(); Student s = new Student(); s.Name = "Akash"; s.ID = "1"; lstStudent.Add(s); List<Student> lstCopy = new List<Student>(lstStudent); Logic.ModifyList(lstCopy); // "Want to use lstStudent(original list) for rest part of the code" public static void ModifyList(List<Student> lstIntegers) { foreach (Student s in lstIntegers) { if (s.ID.Equals("1")) { s.ID = "4"; s.Name = "APS"; } } }

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• Linked List. Insert integers in order

  - by user69514

  I have a linked list of integers. When I insert a new Node I need to insert it not at the end, but in oder... i.e. 2, 4, 5, 8, 11, 12, 33, 55, 58, 102, etc. I don't think I am inserting it in the correct position. Do see what Im doing wrong? Node newNode = new Node(someInt); Node current = head; for(int i=0; i<count; i++){ if(current == tail && tail.data < someInt){ tail.next = newNode; } if(current.data < someInt && current.next.data >= someInt){ newNode.next = current.next; current.next = newNode; } }

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• How to get a list of users for all instance's databases

  - by stee1rat

  I guess the procedure should be something like this: declare @db varchar(100) declare @user varchar(100) declare c cursor for select name from sys.sysdatabases open c fetch next from c into @db while @@fetch_status = 0 begin print @db exec ('use ' + @db) declare u cursor for select name from sys.sysusers where issqlrole <> 1 and hasdbaccess <> 0 and isntname <> 1 open u fetch next from u into @user while @@fetch_status = 0 begin print @user fetch next from u into @user end print '--------------------------------------------------' close u deallocate u fetch next from c into @db end close c deallocate c But the problem is that exec ('use ' + @db) doesn't work. And i always get user list of currently chosen database. How should i fix that? P.S.: I want this code to work on both 2000 and 2005 sql servers.

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• Conditional jump or move depends on uninitialised value - freeing a linked list

  - by user720491

  I want to free a linked list in C. All is working fine, but Valgrind is telling me Conditional jump or move depends on uninitialised value(s) at 0x401400: mtf_destroy Here's the code: list_elt *head; void mtf_init() { list_elt *current; head = malloc(sizeof(list_elt)); current = head; for (int i = 0; i < LIST_SIZE-1; i++) { current->value = (BYTE) i; current->next = malloc(sizeof(list_elt)); current = current->next; } current->value = LIST_SIZE-1; } void mtf_destroy(list_elt *elt) { if (elt->next != NULL) mtf_destroy(elt->next); free(elt); } How can I solve this? Thanks!

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• Display a list of all attributes in opencart

  - by Catalin Dragos Vladulescu

  I want to display a list of all attributes that are added into database but every time I try something it doesn't work. I want to show this inside a div from the from the front page. I tried to insert this into featured.tpl: <?php foreach ($attribute_groups as $attribute_group) { echo $attribute_group['name']; print_r($attribute_group); echo '<select name="listaGrupe">'; foreach ($attribute_groups['attribute'] as $attribute) { echo '<option value="'.$attribute.'">'.$attribute.'</option>'; } echo '</select>'; } ?>

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• C# Add class instance with internal timer to a static List, is it safe?

  - by CodeMongo

  My program has a static list of type classA. ClassA implements a threading timer that executes a task. The list may contain as many instances of classA as desired. Is this technique causing threading issues where the class instances can block each other? It that is the case how can I solve the that problem. ex: static List<MyClassType> list=null; void static Main() { list = new List<MyClassType>(); var a = new MyClassType(); var b = new MyClassType(); list.Add(a); list.Add(b); Console.ReadKey(); } a and b will execute theire internal task based on the timer.Is it s bsd technique? Why?

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