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• rails: has_many :through + polymorphism validation?

  - by ramonrails

  I am trying to achieve this. Any hints? A project has many users through join model A user has many projects through join model Admin class inherits User class. It also has some Admin specific stuff. Admin like inheritance for Supervisor and Operator Project has one Admin, One supervisor and many operators. Now I want to 1. submit data for project, admin, supervisor and operator in a single project form 2. validate all and show errors on the project form. Project has_many :users, :through = :projects_users User has_many :projects, :through = :projects_users ProjectsUser = :id integer, :user_id :integer, :project_id :integer, :user_type :string ProjectUser belongs_to :project, belongs_to :user, :polymorphic = true Admin < User Supervisor < User Operator < User Is the approach correct? Any and all suggestions are welcome.

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• Distance between hyperplanes

  - by michael dillard

  I'm trying to teach myself some machine learning, and have been using the MNIST database (http://yann.lecun.com/exdb/mnist/) do so. The author of that site wrote a paper in '98 on all different kinds of handwriting recognition techniques, available at http://yann.lecun.com/exdb/publis/pdf/lecun-98.pdf. The 10th method mentioned is a "Tangent Distance Classifier". The idea being that if you place each image in a (NxM)-dimensional vector space, you can compute the distance between two images as the distance between the hyperplanes formed by each where the hyperplane is given by taking the point, and rotating the image, rescaling the image, translating the image, etc. I can't figure out enough to fill in the missing details. I understand that most of these are indeed linear operators, so how does one use that fact to then create the hyperplane? And once we have a hyperplane, how do we take its distance with other hyperplanes?

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• User Defined Class as a Template Parameter

  - by isurulucky

  Hi, I' m implementing a custom STL map. I need to make sure that any data type (basic or user defined) key will work with it. I declared the Map class as a template which has two parameters for the key and the value. My question is if I need to use a string as the key type, how can I overload the < and operators for string type keys only?? In template specialization we have to specialize the whole class with the type we need as I understand it. Is there any way I can do this in a better way?? What if I add a separate Key class and use it as the template type for Key? Thank You!!

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• Nonstatic conversion functions; Casting different types, e.g. DirectX vector to OpenGL vector

  - by Markus

  I am currently working on a game "engine" that needs to move values between a 3D engine, a physics engine and a scripting language. Since I need to apply vectors from the physics engine to 3D objects very often and want to be able to control both the 3D, as well as the physics objects through the scripting system, I need a mechanism to convert a vector of one type (e.g. vector3d<float>) to a vector of the other type (e.g. btVector3). Unfortunately I can make no assumptions on how the classes/structs are laid out, so a simple reinterpret_cast probably won't do. So the question is: Is there some sort of 'static'/non-member casting method to achieve basically this: vector3d<float> operator vector3d<float>(btVector3 vector) { // convert and return } btVector3 operator btVector3(vector3d<float> vector) { // convert and return } Right now this won't compile since casting operators need to be member methods. (error C2801: 'operator foo' must be a non-static member)

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• ASP.Net navigation tabs like windows tab control

  - by devphil

  I would like to have a webpage something like windows tab control. Each webpage does not lose the contents and data while moving between pages, postbacks, etc. Here is the website design and my idea: [Master Page] "Fruits" "Cars" "Animals" "Operators" clicking on "Fruits" will forwards to "Fruits" page, and the same for other links (tabs) The user works on "Fruits" page searching fruits, fill up some fields, etc. The user then moves to "Cars" page and then builds up his own car by filling some fields, etc and then the user goes back to "Fruits" page again - the user sees the same page where she/he left on "Fruits" page. Please suggest some good ways other than using javascript:history.go(-1). Is this possible to implement?

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• how to structure code that uses std::rel_ops

  - by R Samuel Klatchko

  I was working on some code and wanted to make use of std::rel_ops. From what I can tell, you need to do using std::rel_ops to your source code to make use of them. But I'm not sure where the best place to put that is. Let's say I have a header file with a class that only defines the minimal operator== and operator<: // foo.h class foo { public: bool operator==(const foo &other) const; bool operator<(const foo &other) const; }; I'm not sure where to put using std::rel_ops. If I leave it out of the foo.h, then every user of foo.h needs to know the implementation detail that foo is not defining all the operators itself. But putting using std::rel_ops inside foo.h breaks the rule of thumb about not having a using in a header file. How do other people resolve this issue?

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• Creating LINQ to SQL for counting a parameter

  - by Matt

  I'm trying to translate a sql query into LINQ to SQL. I keep getting an error "sequence operators not supported for type 'system.string'" If I take out the distinct count part, it works. Is it not because I'm using the GROUP BY? SELECT COUNT(EpaValue) AS [Leak Count], Location, EpaValue AS [Leak Desc.] FROM ChartMes.dbo.RecourceActualEPA_Report WHERE (EpaName = N'LEAK1') AND (Timestamp) '20100429030000' GROUP BY EpaValue, Location ORDER BY Location, [Leak Count] DESC Dim temp = (From p In db2.RecourceActualEPA_Reports _ Where (p.Timestamp = str1stShiftStart) And (p.Timestamp < str2ndShiftCutoff) _ And (p.EpaName = "Leak1") _ Select p.EpaName.Distinct.Count(), p.Location, p.EpaValue)

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• Is there a way to serialize automatically enums as int?

  - by FireAphis

  Hello, Is there a way to serialize enums automatically as int? Every time I define a new enum and write std::stringstream stream; stream << myenum1; stream >> myenum2; the compiler complains that the operators << and are not defined. Do you know a way to tell the compiler to treat enums as plain int's? What makes the problem harder is that, actually, the serialization is inside a template. Something like this: template <typename T> void serialize(const T& value) { std::stringstream stream; stream << value; } So I cannot add any casts :( Maybe I can specialize it somehow? Thank you.

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• Semantic errors

  - by gautam kumar

  Can semantic errors be detected by the compiler or not? If not when do the errors get detected? As far as I know semantic errors are those errors which result from the expressions involving operators with incorrect number/type of operands. For example: n3=n1*n2;//n1 is integer, n2 is a string, n3 is an integer The above statement is semantically incorrect. But while reading C Primer Plus by Stephen Prata I found the following statement The compiler does not detect semantic errors, because they don't violate C rules. The compiler has no way of divining your true intentions. That leaves it to you to find these kinds of errors. One way is to compare what a program does to what you expected it to do. If not the compiler, who detects those errors? Am I missing something?

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• How to create a valid schema in a WSDL that restrict to <|<=|>|>=

  - by wsxedc

  This is what I have in my schema section of my WSDL to specify the field has to be comparison operators <xsd:simpleType> <xsd:restriction base="xsd:string"> <xsd:pattern value="&lt;|&gt;|&lt;=|&gt;=|="/> </xsd:restriction> </xsd:simpleType> SoapUI complains about this part of the WSDL, I tried to set the value to something with non special characters and the WSDL is valid. So I tried to replace that whole long string to be value=">gt;" and it valid but value="<lt;" is not valid, and value=">" is also not valid. My question is, why does the WSDL validation need > to be double escaped? The main question is, how to provide a valid less than side within the pattern value.

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• using NEWSEQUENTIALID() with UPDATE Trigger

  - by Ram

  I am adding a new GUID/Uniqueidentifier column to my table. ALTER TABLE table_name ADD VersionNumber UNIQUEIDENTIFIER UNIQUE NOT NULL DEFAULT NEWSEQUENTIALID() GO And when ever a record is updated in the table, I would want to update this column "VersionNumber". So I create a new trigger CREATE TRIGGER [DBO].[TR_TABLE_NAMWE] ON [DBO].[TABLE_NAME] AFTER UPDATE AS BEGIN UPDATE TABLE_NAME SET VERSIONNUMBER=NEWSEQUENTIALID() FROM TABLE_NAME D JOIN INSERTED I ON D.ID=I.ID/* some ID which is used to join*/ END GO But just realized that NEWSEQUENTIALID() can only be used with CREATE TABLE or ALTER TABLE. I got this error The newsequentialid() built-in function can only be used in a DEFAULT expression for a column of type 'uniqueidentifier' in a CREATE TABLE or ALTER TABLE statement. It cannot be combined with other operators to form a complex scalar expression. Is there a workaround for this ? Edit1: Changing NEWSEQUENTIALID() to NEWID() in the trigger solves this, but I am indexing this column and using NEWID() would be sub-optimal

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• Mixing LINQ to SQL with properties of objects in a generic list

  - by BPotocki

  I am trying to accomplish something like this query: var query = from a in DatabaseTable where listOfObjects.Any(x => x.Id == a.Id) select a; Basically, I want to filter the results where a.Id equals a property of one of the objects in the generic list "listOfObjects". I'm getting the error "Local sequence cannot be used in LINQ to SQL implementation of query operators except the Contains() operator." Any ideas on how to filter this in an easily readable way using "contains" or another method? Thanks in advance.

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• Can a variable like 'int' be considered a primitive/fundamental data structure?

  - by Ravi Gupta

  A rough definition of a data structure is that it allows you to store data and apply a set of operations on that data while preserving consistency of data before and after the operation. However some people insist that a primitive variable like 'int' can also be considered as a data structure. I get that part where it allows you to store data but I guess the operation part is missing. Primitive variables don't have operations attached to them. So I feel that unless you have a set of operations defined and attached to it you cannot call it a data structure. 'int' doesn't have any operation attached to it, it can be operated upon with a set of generic operators. Please advise if I got something wrong here.

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• What does $this generally mean in PHP?

  - by xczzhh

  I am really new to PHP, so I am kind of confused seeing these different operators all day. Here is some code I came across when watching a video tutorail, I'd appreciate it if some could explain a little bit: function index() { $config = Array( 'protocol' => 'smtp', 'smtp_host' => 'ssl://smtp.googlemail.com', 'smtp_port' => 465, 'smtp_user' => '[email protected]', 'smtp_pass' =>'password', ); $this->load->library('email', $config); $this->email->set_newline("\r\n"); $this->email->from('[email protected]', 'Jerry'); $this->email->to('[email protected]'); $this->email->subject('this is an email test'); $this->email->message('this is test message!'); if($this->email->send()) { echo 'Your email was sent'; } else { show_error($this->email->print_debugger()); } } ...

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• How to create and Expression tree to do the same as "StartsWith"

  - by Jonathan

  Hi to all. Currently, I have this method to compare two numbers Private Function ETForGreaterThan(ByVal query As IQueryable(Of T), ByVal propertyValue As Object, ByVal propertyInfo As PropertyInfo) As IQueryable(Of T) Dim e As ParameterExpression = Expression.Parameter(GetType(T), "e") Dim m As MemberExpression = Expression.MakeMemberAccess(e, propertyInfo) Dim c As ConstantExpression = Expression.Constant(propertyValue, propertyValue.GetType()) Dim b As BinaryExpression = Expression.GreaterThan(m, c) Dim lambda As Expression(Of Func(Of T, Boolean)) = Expression.Lambda(Of Func(Of T, Boolean))(b, e) Return query.Where(lambda) End Function It works fine and is consumed in this way query = ETForGreaterThan(query, Value, propertyInfo) As you can see, I give it an IQueryable collection and it add a where clause to it, base on a property and a value. Y can construct Lessthan, LessOrEqualThan etc equivalents as Expression has this operators predefined. ¿How can I transform this code to do the same with strings? Expression don't give me a predefined operator like "contains" or "startwith" and I'm really noob with Expression trees. Thanks, and please Post your answer in C#/VB. Choose the one that make you feel more confortable.

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• What is the best solution to replace a new memory allocator in an existing code?

  - by O. Askari

  During the last few days I've gained some information about memory allocators other than the standard malloc(). There are some implementations that seem to be much better than malloc() for applications with many threads. For example it seems that tcmalloc and ptmalloc have better performance. I have a C++ application that uses both malloc and new operators in many places. I thought replacing them with something like ptmalloc may improve its performance. But I wonder how does the new operator act when used in C++ application that runs on Linux? Does it use the standard behavior of malloc or something else? What is the best way to replace the new memory allocator with the old one in the code? Is there any way to override the behavior or new and malloc or do I need to replace all the calls to them one by one?

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• how to convert big-endian numbers to native numbers delphi

  - by steve0

  hi all i want to know how to convert big endian numbers to native numbers in delphi i am porting some c++ code in that i came accross this part unsigned long blockLength = *blockLengthPtr++ << 24; blockLength |= *blockLengthPtr++ << 16; blockLength |= *blockLengthPtr++ << 8; blockLength |= *blockLengthPtr; unsigned long dataLength = *dataLengthPtr++ << 24; dataLength |= *dataLengthPtr++ << 16; dataLength |= *dataLengthPtr++ << 8; dataLength |= *dataLengthPtr; i am not familiar with c++ ,so i didnt understand what those operators doing can any one help ? regards

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• How to call operator<< on "this" in a descendant of std::stringstream?

  - by romkyns

  class mystream : public std::stringstream { public: void write_something() { this << "something"; } }; This results in the following two compile errors on VC++10: error C2297: '<<' : illegal, right operand has type 'const char [10]' error C2296: '<<' : illegal, left operand has type 'mystream *const ' Judging from the second one, this is because what this points at can't be changed, but the << operator does (or at least is declared as if it does). Correct? Is there some other way I can still use the << and >> operators on this?

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• algorithm to combine data for linear fit?

  - by BoldlyBold

  I'm not sure if this is the best place to ask this, but you guys have been helpful with plenty of my CS homework in the past so I figure I'll give it a shot. I'm looking for an algorithm to blindly combine several dependent variables into an index that produces the best linear fit with an external variable. Basically, it would combine the dependent variables using different mathematical operators, include or not include each one, etc. until an index is developed that best correlates with my external variable. Has anyone seen/heard of something like this before? Even if you could point me in the right direction or to the right place to ask, I would appreciate it. Thanks.

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• What features can I use during log in/out

  - by thecoshman

  I know that this question is going to be painfully vague, but here it is any way. I have made an small console application designed to be run on Windows XP Pro computers. It will be run at log in and log out. The command to run this program will be set via GPO and will include command line operators to control what data the program sends. I have used a few built in C# classes to find out information about the computer, which is then sent of to a server as a web request. I need to know which of the following will have issues on a restricted user account on a domain. Enviroment ManagementObjectSearcher ManagmentObjectCollection System.Diagnostics.PerformanceCounter <-- side note, this class dosent seem to accept be saying using System.Diagnostics ComputerInfo WebRequest

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• Sorting and displaying a custom QVariant type.

  - by Kranar

  Hello, I have a custom type I'd like to use with QVariant but I don't know how to get the QVariant to display in a table or have it sort in a QSortFilterProxyModel. I register the type with Q_DECLARE_METATYPE and wrote streaming operators registered via qRegisterMetaTypeStreamOperators but for whatever reason when I use the type with a table model, it doesn't display anything and it doesn't sort. I should specify that this custom type can not be modified. It has a copy and default constructor, but I can not go in and modify the source code to get it to work with QVariant. Is there a way of non-intrusively getting the behaviour I'd like?

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• Encrypt/ Decrypt text file in Delphi?

  - by Hemant Kothiyal

  Hi i would like to know best encryption technique for text file encryption and ecryption. My Scenario: I have software having two type of users Administartor and Operators. Our requirement is to encrypt text file when Administrator enter data using GUI and save it. That encrypted file would be input for Operator and they just need to select it and use that file. Here file should be automatically decrypt data for further calculation when Operator select those files. Please help me which encryption/ decryption technique should i use?

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• Is tertiary operator possible here?

  - by silow

  I'm trying to set $value1, $value2, $value3 entirely using tertiary operators. This is what it looks like without tertiary if ($chk1 == 20) { $value1 = true; if ($chk2 == 40) { $value2 = 100 ; $value3 = 300; } else { $value2 = 200 ; $value3 = 400; } } else { $value1 = false; } I can set $value2 and $value3, but not sure how to set $value1. Can it be done? if ($chk1 == 20) { $value1 = true; $value2 = ($chk2 == 40) ? 100 : 200; $value3 = ($chk2 == 40) ? 300 : 400; } else { $value1 = false; }

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• can we write this in C++ switch ?

  - by jellly

  #include <iostream> using namespace std; int main(){ char i; cin >>i; switch (i){ case ('e'||'i'||'o'||'u'||'a'): cout<<"Vowel"; break; case ('+'||'-'||'/'||'*'||'%'): cout<<"Op"; break; } return 0; } if not than how can we use comparison or logical operators in switch ? & why cant we declare and initialize variable in single case without using scope ?

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• Why the streams in C++?

  - by oh boy

  As you all know there are libraries using streams such as iostream and fstream. My question is: Why streams? Why didn't they stick with functions similar to print, fgets and so on (for example)? They require their own operators << and >> but all they do could be implemented in simple functions like above, also the function printf("Hello World!"); is a lot more readable and logical to me than cout << "Hello World"; I also think that all of those string abstractions in C++ all compile down to (less efficient) standard function calls in binary.

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