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• LINQ How to force query to materialize?

  - by Bobb

  Say I have simple LINQ extenstion: var filtered = data.Where(i => i.Count > 0); I know that this will not evaluated unless I start to use filtered i.e. foreach(DataItem i in filtered) ... However I need to create cloned version of data and release data as soon as possible. data can be changed in other thread so I want to get immediate snapshot of it. How can I force filtered to be evaluated immediately?

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• Copy method optimization in compilers

  - by Dženan

  Hi All! I have the following code: void Stack::operator =(Stack &rhs) { //do the actual copying } Stack::Stack(Stack &rhs) //copy-constructor { top=NULL; //initialize this as an empty stack (which it is) *this=rhs; //invoke assignment operator } Stack& Stack::CopyStack() { return *this; //this statement will invoke copy contructor } It is being used like this: unsigned Stack::count() { unsigned c=0; Stack copy=CopyStack(); while (!copy.empty()) { copy.pop(); c++; } return c; } Removing reference symbol from declaration of CopyStack (returning a copy instead of reference) makes no difference in visual studio 2008 (with respect to number of times copying is invoked). I guess it gets optimized away - normally it should first make a copy for the return value, then call assignment operator once more to assign it to variable sc. What is your experience with this sort of optimization in different compilers? Regards, Dženan

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• Why is std::tr1::shared_ptr<>.reset() so expensive?

  - by Paul Oyster

  Profiling some code that heavily uses shared_ptrs, I discovered that reset() was surprisingly expensive. For example: struct Test { int i; Test() { this->i = 0; } Test(int i) { this->i = i; } } ; ... auto t = make_shared<Test>(1); ... t.reset(somePointerToATestObject); Tracing the reset() in the last line (under VC++ 2010), I discovered that it creates a new reference-counting object. Is there a cheaper way, that reuses the existing ref-count and does not bother the heap?

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• How do I search for values in a dictionary

  - by fishhead

  what would be the best way to search for a value in a dictionary. for instance I would like to search for modified objects, would going through the entire collection be the only way to do this? c#, .net 2.0 class RecA { public bool modified {get;set:} public string{get;set;} } class RecA_Dic : Dictionary<int,Rec_A> { public bool GetItemByKey(int key,out obj) { return this.TryGetValue(key, out obj); } public List<Rec_A> getModifiedItems() { List<Rec_A> li = new List<Rec_A>(); for(int i=0;i<this.count;i++) if (((Rec_A)this[i]).modified == true) li.Add((Rec_A)this[i]); return li; } }

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• Xcode automatically converts the object to NSArray

  - by Farrukh Javeid

  I have been working on an app and during the development, I am facing a very strange problem. I have a NSMutableArray tempSortedArray, which is full of objects of Store types. All the objects are valid as I can see them in my GUI, the problem arises when I iterate through the array, at index 90, which can be generally anyone, the XCode converts the Store object to NSMutableArray object. Any idea, why this is happening. This is the code to check out what I am doing: NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"cashBack" ascending:NO]; NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor]; NSArray *sortedArray = [storesArray sortedArrayUsingDescriptors:sortDescriptors]; for (int i = 0; i < [tempSortedArray count]; i++) { Store *currentStore = [tempSortedArray objectAtIndex:i]; NSLog(@"store class: %@", [currentStore.class description]); if (currentStore.cashBackTypeString != (id)[NSNull null]) { //do whatever is required to do here }

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• Stuck on solving the Minimal Spanning Tree problem.

  - by kunjaan

  I have reduced my problem to finding the minimal spanning tree in the graph. But I want to have one more constraint which is that the total degree for each vertex shouldnt exceed a certain constant factor. How do I model my problem? Is MST the wrong path? Do you know any algorithms that will help me? One more problem: My graph has duplicate edge weights so is there a way to count the number of unique MSTs? Are there algorithms that do this? Thank You. Edit: By degree, I mean the total number of edges connecting the vertex. By duplicate edge weight I mean that two edges have the same weight.

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• Improve SQL strategy - denormalize in object-children-images case

  - by fesja

  Hi, I have a Tour object which has many Place objects. For the list of tours, I want to show some info of the tour, the number of places of the tour, and three Place's images. Right one my SQL queries are (i'm using Doctrine with Symfony on MySQL) get Tour get Tour 1 places get Tour 2 places get Tour 3 places ... get Tour n places If I have a three Tour list, it's not so bad; but I'm sure it can get bad if I do a 10-20 tour-list. So, thinking on how to improve the queries I've thought of several measures: Having a place count cache Storing the urls of three images on a new tour field. The problem with 2. is that if I change the image, I have to check all the tours to update that image for another one. What solution do you think is best to scale the system in a near future? Any other suggestion. thanks!

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• Indexing affects only the WHERE clause?

  - by andre matos

  If I have something like: CREATE INDEX idx_myTable_field_x ON myTable USING btree (field_x); SELECT COUNT(field_x), field_x FROM myTable GROUP BY field_x ORDER BY field_x; Imagine myTable with around 500,000 rows and most of field_x values being unique. Since I don't use any WHERE clause, will the created index have any effect at all in my query? Edit: I'm asking this question because I don't get any relevant difference between query-times before and after creating the index; They always take about 8 seconds (which, of course is too much time!). Is this behaviour expected?

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• Simple Thread Programming

  - by mike

  I have started to play with threads in c#, but need now help, here is my code: public partial class Form1 : Form { public Form1() { InitializeComponent(); DoCount(); } public void DoCount() { for (int i = 0; i < 100; i++) { objTextBox.Text = i.ToString(); Thread.Sleep(100); } } } its a simple win forms with a textbox, i want to see the "counting", but as you see in my code, the textbox shows me 99, it count till 99 and then shows up.. i`ll think, i have to manage this in a new thread but dont know how!

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• Retrieving specific tuples using Mysql

  - by Narayanan

  Hi, I have some problems retrieving specific tuples. I am actually a student trying to build a Room management system. I have two tables: Room(roomID,hotelname,rate) and Reservation(resID,arriveDate,departDate,roomID). I am not sure how to retrieve the rooms that are available between 2 specific dates. This was the query that i used. SELECT Room.roomID,hotelname,rate FROM Room LEFT JOIN Reservation on ( Room.roomID=Reservation.resID and arriveDate >='2010-02-16' and departDate <='2010-02-20' ) GROUP BY roomID,hotelname,rate HAVING count(*)=0;' but it returns an empty set. Can any1 be kind enough to tell me what mistake i am doing??

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• Can't seem to be able to set ListViewItem.imageIndex

  - by TKL

  I have been scratching my head with this error for at least an hour, what the heck is wrong here? In a loop: if (selectedItems[x].ImageIndex == 3) { List<ListViewItem> dupes = CP.listCache.FindAll(delegate(ListViewItem item) { return item.Text == selectedItems[x].Text; }); if (dupes != null && dupes.Count == 1) dupes[0].ImageIndex = 0; } I can access the imageIndex, but not set it. ArgumentOutOfRange exception occurs.

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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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• SSRS 2008: How to do multiple values report?

  - by Shimrod

  Hi everyone, Right now I have an application which uses Reporting Services to render reports. This is working nicely, I call each report with a given value (e.g. a ClientId), and the report gets rendered correctly. However, what I'd like to do now is being able to send multiple ClientIDs to the report, and would like to get 1 pdf file with count(ClientsIDs) pages, each containing the report, according to the ClienID. How is that possible? I don't really know how to name what I want to do, so I don't really find answers on the net right now. Maybe someone has a tutorial for me? Thanks in advance !

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• Python design mistakes

  - by Andrea

  A while ago, when I was learning Javascript, I studied Javascript: the good parts, and I particularly enjoyed the chapters on the bad and the ugly parts. Of course, I did not agree with everything, as summing up the design defects of a programming language is to a certain extent subjective - although, for instance, I guess everyone would agree that the keyword with was a mistake in Javascript. Nevertheless, I find it useful to read such reviews: even if one does not agree, there is a lot to learn. Is there a blog entry or some book describing design mistakes for Python? For instance I guess some people would count the lack of tail call optimization a mistake; there may be other issues (or non-issues) which are worth learning about.

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• Sum of distinc rows after a 1-many table join

  - by Lock

  I have 2 tables that I am joining. Table 1 has 1-many relationship with table 2. That is, table 2 can return multiple rows for a single row of table 1. Because of this, the records of table 1 is duplicated for as many rows as are on table 2.. which is expected. Now, I have a sum on one of the columns from table 1, but because of the multiple rows that get returned on the join, the sum is obviously multiplying. Is there a way to get this number back to its original number? I tried dividing by the count of rows from table 2 but this didnt quite give me the expected result. Are there any analytical functions that could do this? I almost want something like "if this row has not yet been counted in the sum, add it to the sum"

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• How to get total number of potential results in Lucene

  - by Slace

  I'm using lucene on a site of mine and I want to show the total result count from a query, for example: Showing results x to y of z But I can't find any method which will return me the total number of potential results. I can only seem to find methods which you have to specify the number of results you want, and since I only want 10 per page it seems logical to pass in 10 as the number of results. Or am I doing this wrong, should I be passing in say 1000 and then just taking the 10 in the range that I require?

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• Building an array of arrays

  - by iFloh

  I am trying to get the following loop working to fill an array of arrays: while (condition) { [itemsArray fillFromDB]; if (! [checkArray containsObject:checkFlag]) { // Add existing itemsArray to myArray if (itemsArray.count) { // add the itemsArray to myArray and create a new instance of itemsArray [myArray addObject:itemsArray]; [itemsArray release]; NSMutableArray *itemsArray = [[NSMutableArray alloc] init]; } [itemsArray addObject:myObject]; [checkArray addObject:checkFlag]; } else { [itemsArray addObject:tmpEvent]; } } However I try to shape this loop it falls over the release of itemsArray when I use release (as above), the array does not re-initialise as a new instance with alloc. Whilst expecting emptyness, the next Object is added to the old array. when I use removeAllObjects, my Array is emptied and so is the array attached to myArray. Where am I going in the wrong direction?

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• How to get email from pop.gmail.com using c#?

  - by jiya gupta

  hi, i want to read email from pop.gmail.com using console application. Pop3 client = new Pop3(); client.Connect("pop.gmail.com",995); client.Login("[email protected]", "12345"); //client.IsAuthenticated = true; // get message list Pop3MessageCollection list = client.GetMessageList(); if (list.Count == 0) { Console.WriteLine("There are no messages in the mailbox."); } else { // download the first message MailMessage message = client.GetMailMessage(list[0].SequenceNumber); } client.Disconnect(); } i got error server has closed the connection. i have already disable firewall and antivirus. plz help me.

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• Query - Trying to SUM one field based on content of another field

  - by ShaneL

  Table: DayOfWeek Enrollments Monday 35 Monday 12 Saturday 25 Tuesday 15 Monday 9 Tuesday 15 Basically I'm trying to sum the total enrolments for each day. so the Output will look like: DayOfWeek Enrollments Monday 56 Saturday 25 Tuesday 30 I've spent around 4 hours trying to work this out trying many many different ways but no luck. The problem I'm having is i can count how many enrollments for each day but can't have it aligned with the correct day when i run the query e.g. I want The total to be on the same line as the day it was calculated from. (I hope that is clear enough)

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• How to create unique user key

  - by Grayson Mitchell

  Scenario: I have a fairly generic table (Data), that has an identity column. The data in this table is grouped (lets say by city). The users need an identifier in order for printing on paper forms, etc. The users can only access their cites data, so if they use the identity column for this purpose they will see odd numbers (e.g. a 'New York' user might see 1,37,2028... as the listed keys. Idealy they would see 1,2,3... (or something similar) The problem of course is concurrency, this being a web application you can't just have something like: UserId = Select Count(*)+1 from Data Where City='New York' Has anyone come up with any cunning ways around this problem?

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• Class design question (Disposable and singleton behavior)

  - by user137348

  The Repository class has singleton behavior and the _db implements the disposable pattern. As excepted the _db object gets disposed after the first call and because of the singleton behavior any other call of _db will crash. [ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)] public class Repository : IRepository { private readonly DataBase _db; public Repository(DataBase db) { _db = db; } public int GetCount() { using(_db) { return _db.Menus.Count(); } } public Item GetItem(int id) { using(_db) { return _db.Menus.FirstOrDefault(x=>x.Id == id); } } } My question is, is there any way to design this class to work properly without removing the singleton behavior? The Repositoryclass will be serving big amount of requests.

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• How can I apply indexer to Dictionary VALUES (C#3.0)

  - by Newbie

  I have done a program string[] arrExposureValues = stock.ExposureCollection[dt] .Values.ToArray(); for(int i=0;i<arrExposureValues .length;i++) Console.WriteLine(arrExposureValues[i]); Nothing wrong and works fine. But is it possible to do something like the below for(int i=0;i<stock.ExposureCollection[dt].Count;i++) Console.WriteLine(stock.ExposureCollection[dt].Values[i]); This is just for my sake of knowledge (Basically trying to accomplish the same in one line). Note: ExposureCollection is a dictionary object Dictionary<DateTime, Dictionary<string, string>> First of all I have the doubt if it is at all possible! I am using C#3.0. Thanks.

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• How can I apply indexer to Dictionary.Values (C# 3.0)

  - by Newbie

  I have done a program string[] arrExposureValues = stock.ExposureCollection[dt].Values.ToArray(); for(int i = 0; i < arrExposureValues.Length; i++) Console.WriteLine(arrExposureValues[i]); Nothing wrong and works fine. But is it possible to do something like the below for(int i = 0; i < stock.ExposureCollection[dt].Count; i++) Console.WriteLine(stock.ExposureCollection[dt].Values[i]); This is just for my sake of knowledge (Basically trying to accomplish the same in one line). Note: ExposureCollection is Dictionary<DateTime, Dictionary<string, string>> First of all I have the doubt if it is at all possible! I am using C# 3.0. Thanks.

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• how external counter get unique visitors?

  - by dnkira

  hello how do external counter track unique visitors via image i'd also like to get Referrer if possible. something like img="http://www.somecounterdomain.com/count.php?page=83599" i'm using ASP.NET, c# i'm aware of a user can "cheat" but would like to make that posibility minimal. additional difficulty is that i should trach external server and can't implement c# code there. what i can is only imlement a counter imag or smth like that. i try to use generated image. thx for answers.

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• SQL To Filter A SubSet Of Data

  - by Nick LaMarca

  I have an arraylist that holds a subset of names found in my database. I need to write a query to get a count of the people in the arraylist for certain sections i.e. There is a field "City" in my database from the people in the arraylist of names I want to know how many of them live in Chicago, how many live in New York etc. Can someone help me how I might set up an sql statement to handle this. I think somehow I have to pass the subset of names to sql somehow.

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