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• What is the algorithm used by the memberwise equality test in .NET structs?

  - by Damian Powell

  What is the algorithm used by the memberwise equality test in .NET structs? I would like to know this so that I can use it as the basis for my own algorithm. I am trying to write a recursive memberwise equality test for arbitrary objects (in C#) for testing the logical equality of DTOs. This is considerably easier if the DTOs are structs (since ValueType.Equals does mostly the right thing) but that is not always appropriate. I would also like to override comparison of any IEnumerable objects (but not strings!) so that their contents are compared rather than their properties. This has proven to be harder than I would expect. Any hints will be greatly appreciated. I'll accept the answer that proves most useful or supplies a link to the most useful information. Thanks.

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• I want to get 2 values returned by my query. How to do, using linq-to-entity

  - by Shantanu Gupta

  var dept_list = (from map in DtMapGuestDepartment.AsEnumerable() where map.Field<Nullable<long>>("GUEST_ID") == DRowGuestPI.Field<Nullable<long>>("PK_GUEST_ID") join dept in DtDepartment.AsEnumerable() on map.Field<Nullable<long>>("DEPARTMENT_ID") equals dept.Field<Nullable<long>>("DEPARTMENT_ID") select new { dept_id=dept.Field<long>("DEPARTMENT_ID") ,dept_name=dept.Field<long>("DEPARTMENT_NAME") }).Distinct(); DataTable dt = new DataTable(); dt.Columns.Add("DEPARTMENT_ID"); dt.Columns.Add("DEPARTMENT_NAME"); foreach (long? dept_ in dept_list) { dt.Rows.Add(dept_[0], dept_[1]); } EDIT In the previous question asked by me. I got an answer like this for single value. What is the difference between the two ? foreach (long? dept in dept_list) { dt.Rows.Add(dept); }

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• Wrong image dimensions when it's dynamically loaded on a page the 1st time

  - by Nikita Barsukov

  I have the following piece of Javascript code on my web-page var central_image = document.createElement("img") central_image.setAttribute("src", imgs[curr_image_no - 1]); central_image.setAttribute("name", "jpeg"); document.getElementById("photo").appendChild(central_image); central_image.onload = getDimensions(); //function that alerts image dimensions Now, when the central_image is loaded for the 1st time in Firefox, its height always equals to 0. In IE its dimensions are 28 x 30 pixels. When I reload image, its dimensions are OK in both browsers. I guess the problem is that function getDimensions() starts before image was loaded completely. How to change that?

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• Inserting into an Associative array?

  - by RedShft

  I'm playing around with associative arrays right now and I can't seem to figure out how to add additional objects to the array. I tried insert but it doesn't recognize both arguments. Also, if I do this it produces an error: Node[bool] test; Node node; Node[bool] temp = [ false:node ]; test ~= temp; //Error 1 Error: cannot append type Node[bool] to type //Node[bool] C:\Users\CP\Documents\Visual Studio //2010\Projects\D\STDS\NPC.d 256 Does this mean you can't use the append operator on associative arrays ?

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• How to find duplicate values in SQL Server

  - by hgulyan

  Hi, I'm using SQL Server 2008. I have a table Customers customer_number int field1 varchar field2 varchar field3 varchar field4 varchar ... and a lot more columns, that doesn't matter for my queries. Column *customer_number* is pk. I'm trying to find duplicate values and some differences between them. Please, help me to find all rows that have same 1) field1, field2, field3, field4 2) only 3 columns are equal and one of them isn't (except rows from list 1) 3) only 2 columns equal and two of them aren't (except rows from list 1 and list 2) In the end, I'll have 3 tables with this results and additional groupId, which will be same for a group of similars (For example, for 3 column equals, rows that have 3 same columns equal will be a seperate group) Thank you.

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• Problem of using cin twice.

  - by gc

  Here is the code: string str; cinstr; cout<<"first input:"<<str<<endl; getline(cin, str); cout<<"line input:"<<str<<endl; The result is that getline never pauses for user input, therefore the second output is always empty. After spending some time on it, I realized after the first call "cinstr", it seems '\n' is still stored in cin (using cin.peek() to check), which ends getline immediately. The solution will be adding one more line between the first usage and the second one: cin.ignore(numeric_limits::max(), '\n'); However, I still don't understand, why is '\n' left there after the first call? What does istream& operator really do?

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• Rails: unexpected behavior updating a shared instance

  - by Pascal Lindelauf

  I have a User object, that is related to a Post object via two different association paths: Post --(has_many)-- comments --(belongs to)-- writer (of type User) Post --(belongs to)-- writer (of type User) Say the following hold: user1.name == "Bill" post1.comments[1].writer == user1 post1.writer == user1 Now when I retrieve the post1 and its comments from the database and I update post1.comments[1].writer like so: post1.comments[1].writer.name = "John" I would expect post1.writer to equal "John" too. But it doesn't! It still equals "Bill". So there seems to be some caching going on, but the kind I would not expect. I would expect Rails to be clever enough to load exactly one instance of the user with name "Bill"; instead is appears to load two individual ones: one for each association path. Can someone explain how this works exactly and how I am to handle these types of situations the "Rails way"?

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• Aggregate functions in ANSI SQL

  - by morpheous

  I want to use multiple aggregate functions in a query. All the examples i have seem on aggregate functions however, are trivial. Typically, they are of the form: SELECT field1,agg_func1, agg_func2 GROUP BY SOME_COLUMNS HAVING agg_func1 OP SOME_SCALAR Where: OP: is a boolean operator (e.g. <, = etc) SOME_SCALAR: is a scalar (i.e. a constant number) What I want to know is if it is possible to write (IN ANSI SQL) queries like: SELECT field1,agg_func1, agg_func2, agg_func3 GROUP BY SOME_COLUMNS HAVING (agg_func1 OP1 agg_func2) OP2 (agg_func2 OP3 agg_func3) Where: OP[N] are boolean operators or ANSI SQL clause operators like 'BETWEEN', 'LIKE', 'IN' etc. Also, assuming this is possible (I have not seen any documentation saying otherwise) are there any efficiency/performance considerations (i.e. penalties) when the HAVING clause consists of a boolean expression combining the output of the aggregate functions - instead of the normal comparison of the output of the aggregate with a constant number (e.g. min('salary') 100 ) - which is often used in the most banal examples involving aggregate functions?

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• alternative to check, whether a value is in a set

  - by stanleyxu2005

  Hi All, I have the following code. It looks ugly, if the value equals to one of the following value then do something. var Value: Word; begin Value := 30000; if (Value = 30000) or (Value = 40000) or (Value = 1) then do_something; end; I want to refactor the code as follows: var Value: Word; begin Value := 30000; if (Value in [1, 30000, 40000]) then // Does not work do_something; end; However, the refactored code does not work. I assume that a valid set in Delphi accepts only elements with type byte. If there any good alternative to refactor my original code (besides using case)?

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• Use LINQ to count the number of combinations existing in two lists

  - by Ben McCormack

  I'm trying to create a LINQ query (or queries) that count the total number of occurences of a combinations of items in one list that exist in a different list. For example, take the following lists: CartItems DiscountItems ========= ============= AAA AAA AAA BBB AAA BBB BBB CCC CCC DDD The result of the query operation should be 2 since I can find two combinations of AAA and BBB (from DiscountItems) within the contents of CartItems. My thinking in approaching the query is to join the lists together to shorten CartItems to only include items from DiscountItems. The solution would be to find the CartItem in the resulting query that occurs the least amount of times, thus indicating how many combinations of items exist in CartItems. How can this be done? Here's the query I already have, but it's not working. query results in an enumeration with 100 items, far more than I expected. Dim query = From cartItem In Cart.CartItems Group Join discountItem In DiscountGroup.DiscountItems On cartItem.SKU Equals discountItem.SKU Into Group Select SKU = cartItem.SKU, CartItems = Group Return query.Min(Function(x) x.CartItems.Sum(Function(y) y.Quantity))

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• How to keep the popup menu of a JComboBox open on populating it ?

  - by Stormshadow

  I have a JComboBox on my Panel. One of the popup menu items is 'More' and when I click that I fetch more menu items and add them to the existing list. After this, I wish to keep the popup menu open so that the user realizes that more items have been fetched however, the popup closes. The event handler code I am using is as follows public void actionPerformed(ActionEvent e) { if (e.getSource() == myCombo) { JComboBox selectedBox = (JComboBox) e.getSource(); String item = (String) selectedBox.getSelectedItem(); if (item.toLowerCase().equals("more")) { fetchItems(selectedBox); } selectedBox.showPopup(); selectedBox.setPopupVisible(true); } } private void fetchItems(JComboBox box) { box.removeAllItems(); /* code to fetch items and store them in the Set<String> items */ for (String s : items) { box.addItem(s); } } I do not understand why the showPopup() and setPopupVisible() methods are not functioning as expected.

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• Template type deduction with a non-copyable class

  - by Evan Teran

  Suppose I have an autolocker class which looks something like this: template <T> class autolocker { public: autolocker(T *l) : lock(l) { lock->lock(); } ~autolocker() { lock->unlock(); } private: autolocker(const autolocker&); autolocker& operator=(const autolocker&); private: T *lock; } Obviously the goal is to be able to use this autolocker with anything that has a lock/unlock method without resorting to virtual functions. Currently, it's simple enough to use like this: autolocker<some_lock_t> lock(&my_lock); // my_lock is of type "some_lock_t" but it is illegal to do: autolocker lock(&my_lock); // this would be ideal Is there anyway to get template type deduction to play nice with this (keep in my autolocker is non-copyable). Or is it just easiest to just specify the type?

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• Linq To Sql Left outer join - filtering null results

  - by Harry

  I'd like to reproduce the following SQL into C# LinqToSql SELECT TOP(10) Keywords.* FROM Keywords LEFT OUTER JOIN IgnoreWords ON Keywords.WordID = IgnoreWords.ID WHERE (DomainID = 16673) AND (IgnoreWords.Name IS NULL) ORDER BY [Score] DESC The following C# Linq gives the right answer. But I can't help think I'm missing something (a better way of doing it?) var query = (from keyword in context.Keywords join ignore in context.IgnoreWords on keyword.WordID equals ignore.ID into ignored from i in ignored.DefaultIfEmpty() where i == null where keyword.DomainID == ID orderby keyword.Score descending select keyword).Take(10); the SQL produced looks something like this: SELECT TOP (10) [t0].[DomainID], [t0].[WordID], [t0].[Score], [t0].[Count] FROM [dbo].[Keywords] AS [t0] LEFT OUTER JOIN (SELECT 1 AS [test], [t1].[ID] FROM [dbo].[IgnoreWords] AS [t1]) AS [t2] ON [t0].[WordID] = [t2].[ID] WHERE ([t0].[DomainID] = 16673) AND ([t2].[test] IS NULL) ORDER BY [t0].[Score] DESC How can I get rid of this redundant inner selection? It's only slightly more expensive but every bit helps!

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• VS 2008 linking error

  - by AvatarBlue

  I'm using Visual Studio 2008 C++ and working on a dll project. Debug compiled and linked perfectly but when I compile the release version, it shows this: VImgPtr.obj : error LNK2001: unresolved external symbol @__security_check_cookie@4 VLibraryPtr.obj : error LNK2001: unresolved external symbol "void __cdecl operator delete[](void *)" (??_V@YAXPAX@Z) D:\Source Code\VImgLib\Release-vc9u\VImgLib-vc9u.dll : fatal error LNK1120: 2 unresolved externals If I selected Multi-threaded (/MT) in "C/C++-Code Generation tab), it linked ok. The problem is only when I choose Multi-threaded DLL (/MD). I'm releasing a dll, so should be /MD right?

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• Django: text fixture fails to load

  - by Esteban Feldman

  Hi all, Did a dumpdata of my project, then in my new test I added it to fixtures. from django.test import TestCase class TestGoal(TestCase): fixtures = ['test_data.json'] def test_goal(self): """ Tests that 1 + 1 always equals 2. """ self.failUnlessEqual(1 + 1, 2) When running the test I get: Problem installing fixture 'XXX/fixtures/test_data.json': DoesNotExist: XXX matching query does not exist. But manually doing loaddata works fine does not when the db is empty. I do a dropdb, createdb a simple syncdb the try loaddata and it fails, same error. Any clue? Python version 2.6.5, Django 1.1.1

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• passing values to pages

  - by Indranil Mutsuddy

  Hello friends, What i am trying here is to pass values to other pages. When i include the following code private void Button1_Click(object sender, System.EventArgs e) { // Value sent using HttpResponse Response.Redirect("WebForm5.aspx?Name="+txtName.Text); } if (Request.QueryString["Name"]!= null) Response.write( Request.QueryString["Name"]); everything works fine the name gets displayed. Now if use MemberId instead, though i can see the Id in the Url, but while checking for Null in other page, its true. Whats wrong?? Now I tried the same thing using session i.e. Session["MemberId"] = this.TxtEnterMemberId.Text; if (MemberSex.Equals("M")) Response.Redirect("PatientDetailsMale.aspx",false ); Page_load event of the other page if (Session["MemberId"] != null) mid = Session["MemberId"].ToString(); IT Works..Could u guys explain the behaviour please? P.S. Can anyone give a breif in layman words about SessionId and its usage. Thanking you, Indranil

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• How can I combine result and subquery for IN comparison (mysql)

  - by user325804

  In order for a school project i need to create the following situation within one mysql query. The situation is as such, that a child's tags and a parent's tags need to be combined into one, and compared to a site's tags, depending on a few extra simple equals to lines. For this to happen I only see the option that the result of a subquery is combined with a sub query within that query, as such: SELECT tag.*, (SELECT group_concat(t1.id, ',', (SELECT group_concat(tag.id) FROM adcampaign INNER JOIN adcampaign_tag ON adcampaign.id = adcampaign_tag.adcampaign_id INNER JOIN tag ON adcampaign_tag.tag_id = tag.id WHERE adcampaign.id = 1)) FROM ad, ad_tag, tag AS t1 WHERE ad.id = ad_tag.ad_id AND ad_tag.tag_id = t1.id AND ad.adcampaign_id = 1 AND ad.agecategory_id = 1 AND ad.adsize_id = 1 AND ad.adtype_id = 1) as tags FROM tag WHERE tag.id IN tags But the IN comparison only returns the first result because now the tags aren't a list but a concanated string. Anyone got any suggestion on this? I really need a way to combine it into one array

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• Best datastructure for frequently queried list of objects

  - by panzerschreck

  Hello, I have a list of objects say, List. The Entity class has an equals method,on few attributes ( business rule ) to differentiate one Entity object from the other. The task that we usually carry out on this list is to remove all the duplicates something like this : List<Entity> noDuplicates = new ArrayList<Entity>(); for(Entity entity: lstEntities) { int indexOf = noDuplicates.indexOf(entity); if(indexOf >= 0 ) { noDuplicates.get(indexOf).merge(entity); } else { noDuplicates.add(entity); } } Now, the problem that I have been observing is that this part of the code, is slowing down considerably as soon as the list has objects more than 10000.I understand arraylist is doing a o(N) search. Is there a faster alternative, using HashMap is not an option, because the entity's uniqueness is built upon 4 of its attributes together, it would be tedious to put in the key itself into the map ? will sorted set help in faster querying ? Thanks

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• How can I pull data from a SQL Database that spans an academic year?

  - by Eric Reynolds

  Basically, I want to pull data from August to May for a given set of dates. Using the between operator works as long as I do not cross the year marker (i.e. BETWEEN 8 AND 12 works -- BETWEEN 8 AND 5 does not). Is there any way to pull this data? Here is the SQL Query I wrote: SELECT count(*), MONTH(DateTime) FROM Downloads WHERE YEAR(DateTime) BETWEEN 2009 AND 2010 AND MONTH(DateTime) BETWEEN 8 AND 5 GROUP BY MONTH(DateTime) ORDER BY MONTH(DateTime)" Any help is appreciated. Thanks, Eric R.

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• Is there alternative way to write this query?

  - by Kugel

  I have tables A, B, C, where A represents items which can have zero or more sub-items stored in C. B table only has 2 foreign keys to connect A and C. I have this sql query: select * from A where not exists (select * from B natural join C where B.id = A.id and C.value > 10); Which says: "Give me every item from table A where all sub-items have value less than 10. Is there a way to optimize this? And is there a way to write this not using exists operator?

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• Returning the index number of an Arraylist in Java

  - by Daniel

  I would like my method public void showClassRoomDetails(String teacherName) to return the Arraylist index number using the teacherName. Thanks import java.util.ArrayList; public class School { private ArrayList<Classroom> classrooms; private String classRoomName; private String teacherName; public School() { classrooms = new ArrayList<Classroom>(); } public void addClassRoom(Classroom newClassRoom, String theClassRoomName) { classrooms.add(newClassRoom); classRoomName = theClassRoomName; } public void addTeacherToClassRoom(int classroomId, String TeacherName) { if (classroomId < classrooms.size() ) { classrooms.get(classroomId).setTeacherName(TeacherName); } } public void showClassRoomDetails(String teacherName) { for (Classroom classroom : this.classrooms) { if (classroom.returnTeacherName().equals(teacherName)) { System.out.println(classroom.returnClassRoomName()); System.out.println(classroom.returnTeacherName()); break; } } } }

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• Lazy evaluation with ostream C++ operators

  - by SavinG

  I am looking for a portable way to implement lazy evaluation in C++ for logging class. Let's say that I have a simple logging function like void syslog(int priority, const char *format, ...); then in syslog() function we can do: if (priority < current_priority) return; so we never actually call the formatting function (sprintf). On the other hand, if we use logging stream like log << LOG_NOTICE << "test " << 123; all the formating is always executed, which may take a lot of time. Is there any possibility to actually use all the goodies of ostream (like custom << operator for classes, type safety, elegant syntax...) in a way that the formating is executed AFTER the logging level is checked ?

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• Multiplying complex with constant in C++

  - by Atilla Filiz

  The following code fails to compile #include <iostream> #include <cmath> #include <complex> using namespace std; int main(void) { const double b=3; complex <double> i(0, 1), comp; comp = b*i; comp=3*i; return 0; } with error: no match for ‘operator*’ in ‘3 * i’ What is wrong here, why cannot I multiply with immediate constants?

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• doubt in sizeof implementation

  - by aks

  Below is the program to find the size of a structure without using sizeof operator: struct MyStruct { int i; int j; }; int main() { struct MyStruct *p=0; int size = ((char*)(p+1))-((char*)p); printf("\nSIZE : [%d]\nSIZE : [%d]\n", size); return 0; } My doubt is: Why is typecasting to char * required? If I don't use the char* pointer, the output is 1 - WHY?

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• Can I use foreach to return only a certain type from a collection?

  - by RoboShop

  If I enter the code below, I get an error. Basically, the foreach will break when it comes across a Control that isn't a label. foreach (Label currControl in this.Controls()) { ... } I have to do something like this. foreach (Control currControl in this.Controls()) { if(typeof(Label).Equals(currControl.GetType())){ ... } } can anyone think of a better way of doing it without me needing to check the type? Can I somehow get foreach to skip the objects that aren't Labels?

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