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• How do I do a join in ActiveRecord after records have been returned?

  - by Russ Bradberry

  I am using ActiveRecord in Rails 3 to pull data from two different tables in two different databases. These databases can not join on each other, but I have the need to do a simple join after-the-fact. I would like to preserve the relation so that I can chain it down the line. here is a simplified version of what I am doing browsers = Browser.all # <-- this is fairly small and can reside in memory events = Event.where(:row_date=>Date.today).select(:name, :browser_id) So as you can see, I want to join browsers in on the events relation, where browser_id should equal browsers.name. events is a relation and I can still add clauses to it down the line, so I dont want to run the query on the db just yet. How would I accomplish this?

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• How I can use the HTTP headers to indicate in the Response that possibility?

  - by Cris Hong Kong CRISHK

  Finally I accomplished to cache dynamic images, css, and javascript files using HTTP headers BUT I have a problem now: I have specific dynamic images that are equal but has different URL's. For example: http://example.com/image/src/the-same-image.jpg http://example.com/image/custom/src/the-same-image2.jpg 1 and 2 has the same file content but different URL. This is a problem now because the navigator assumes that the file are different and need to be cached (due to the URL), when the real cached file is only one. I have the possibility to know if the file at the URL's are the same. How I can use the headers to indicate in the Response that possibility, and the navigator will cache only one file?

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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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• Warning as Error - How to rid these

  - by coffeeaddict

  I cannot figure out how to get rid of errors that basically should not be halting my compile in VS 2010 and should not be show stoppers, or at least I will fix them later but I don't want the compile to just error and halt on these kinds of problems. For example I'm getting the following error: Error 1 Warning as Error: XML comment on 'ScrewTurn.Wiki.SearchEngine.Relevance.Finalize(float)' has a paramref tag for 'IsFinalized', but there is no parameter by that name C:\www\Wiki\Screwturn3_0_2_509\SearchEngine\Relevance.cs 60 70 SearchEngine for this code: /// /// Normalizes the relevance after finalization. /// /// The normalization factor. /// If is false ( was not called). public void NormalizeAfterFinalization(float factor) { if(factor < 0) throw new ArgumentOutOfRangeException("factor", "Factor must be greater than or equal to zero"); if(!isFinalized) throw new InvalidOperationException("Normalization can be performed only after finalization"); value = value * factor; } I looked in Tools | Options and I don't see where I can tweak the compiler and tell it not to worry about comment or XHTML based errors.

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• C++ Urban Myths

  - by Neil Butterworth

  I'm starting to write an article on what I'm calling "C++ Urban Myths" - that is, ideas and conceptions about C++ that are common but have no actual roots in reality. Some that I've come up with so far are: TR1 is part of standard C++ TR1 (technical Report #1) proposed a whole bunch of changes to C++. Unfortunately, it was never accepted. It is faster to use iterators to access a vector than operator[] Or vice versa. All tests I've carried out indicate the two are nearly identical in performance. The C++ Standard contains something called the STL It doesn't - neither "STL" nor "Standard Template Library" appear in the Standard. I'm wondering if the SO C++ community can come up with any better ones? Ideally, they should be expressible in a single sentence, and not involve any code. Edit: I guess I didn't make it clear enough that I was interested in myths believed by C++ developers, not misconceptions held by non-C++users. Oh well...

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• Using unless in rails uniqueness validation

  - by dunxd

  I am just starting out in Rails, and trying to develop a simple application. I need to validate three values submitted to the application - each must meet the same validation criteria. The validation is pretty simple: Value is valid if unqiue, null or equal to "p" or "d". The following gets me halfway there: validates_uniqueness_of :value1, :value2, :value3, :allow_nil => true I think I can use :unless to check whether the value is either "p" or "d", however I can't figure out how. I guess I am trying to combine validates_uniqueness_of with validates_inclusion_of. Any suggestions?

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• error: typedef name may not be a nested-name-specifier

  - by Autopulated

  I am trying to do something along the lines of this answer, and struggling: $ gcc --version gcc (GCC) 4.2.4 (Ubuntu 4.2.4-1ubuntu4) file.cpp:7: error: template argument 1 is invalid file.cpp:7: error: typedef name may not be a nested-name-specifier And the offending part of the file: template <class R, class C, class T0=void, class T1=void, class T2=void> struct MemberWrap; template <class R, class C, class T0> struct MemberWrap<R, C, T0>{ typedef R (C::*member_t)(T0); typedef typename boost::add_reference<typename T0>::type> TC0; // <---- offending line MemberWrap(member_t f) : m_wrapped(f){ } R operator()(C* p, TC0 p0){ GILRelease guard; return (p->*(this->m_wrapped))(p0); } member_t m_wrapped; };

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• Mutual Information / Entropy Calculation Help

  - by Fillip

  Hi, Hoping someone can give me some pointers with this entropy problem. Say X is chosen randomly from the uniform integer distribution 0-32 (inclusive). I calculate the entropy, H(X) = 32 bits, as each Xi has equal probability of occurring. Now, say the following pseudocode executes. int r = rand(0,1); // a random integer 0 or 1 r = r * 33 + X; How would I work out the mutual information between the two variables r and X? Mutual Information is defined as I(X; Y) = H(X) - H(X|Y) but I don't really understand how to apply the conditional entropy H(X|Y) to this problem. Thanks

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• How can I access variables outside of current scope in javascript?

  - by sekmet64

  I'm writing some application in javascript and cannot figure it out how to access the variables declared in my function, inside this jquery parse. Inside I can access global variables, but I don't really want to create global vars for these values. Basically I want to extract file names from an xml document in the simulationFiles variable. I check if the node attribute is equal with the simName and extract the two strings inside the xml elements, that part I think it's working. How can I extract those xml elements and append them to local variables? function CsvReader(simName) { this.initFileName = "somepath"; this.eventsFileName = "somepath"; $(simulationFiles).find('simulation').each(function() { if ($(this).attr("name") == simName) { initFileName += $(this).find("init").text(); eventsFileName += $(this).find("events").text(); } }); }

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• What's the best way to return a random line in a text file using C?

  - by jeremy Ruten

  What's the best way to return a random line in a text file using C? It has to use the standard I/O library (<stdio.h>) because it's for Nintendo DS homebrew. Clarifications: Using a header in the file to store the number of lines won't work for what I want to do. I want it to be as random as possible (the best being if each line has an equal probability of being chosen as every other line.) The file will never change while the program is being run. (It's the DS, so no multi-tasking.)

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• functor returning 0

  - by Jon

  I've recently started teaching myself the standard template library. I was curious as to why the GetTotal() method in this class is returning 0? ... class Count { public: Count() : total(0){} void operator() (int val){ total += val;} int GetTotal() { return total;} private: int total; }; void main() { set<int> s; Count c; for(int i = 0; i < 10; i++) s.inset(i); for_each(s.begin(), s.end(), c); cout << c.GetTotal() << endl; }

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• If-statement with logical OR

  - by exiter2000

  public class Test{ public static void main(String args[]){ int a = 0; int b = 1; int c = 10; if ( a == 0 || b++ == c ){ a = b + c; }else{ b = a + c; } System.out.println("a: " + a + ",b: " + b + ",c: " + c); } } Ok, this is Java code and the output is a: 11,b: 1,c: 10 And I believe the C acts same as Java in this case That is because second condition(b++ == c) would never executed if the first condition is true in 'OR' operator. There is a "NAME" for this. I just don't remember what it is. Does anyone know what this is called?? Thanks in advance

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• Delete element from array

  - by Julio Diaz

  Is there a way I can get rid of some elements in an array. for instance, if i have this array int testArray[] = {0,2,0,3,0,4,5,6} Is there a "fast" way to get rid of the elements that equal 0 int resultArray[] = {2,3,4,5,6} I tried this function but I got lost using Lists public int[] getRidOfZero(int []s){ List<> result=new ArrayList<>(); for(int i=0; i<s.length; i++){ if(s[i]<0){ int temp = s[i]; result.add(temp); } } return result.toArray(new int[]); }

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• How to change rows in a table based on other table rows in mysql?

  - by understack

  I've a table which has 3 columns: id, a_id and b_id. Suppose rows are like this: 1, a1, b1 2, a1, b2 3, a1, b3 4, a2, b4 5, a2, b5 6, a2, b6 I want to convert it to 1, a1, b1 2, a1, b1 3, a1, b1 4, a2, b4 5, a2, b4 6, a2, b4 So I want to make all the b_id corresponding to a_id same, and equal to the one which is found first. How can I do this? For simplicity, I've removed other columns from table. So please ignore row duplication here.

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• C++'s std::string pools, debug builds? std::string and valgrind problems

  - by Den.Jekk

  Hello, I have a problem with many valgrind warnings about possible memory leaks in std::string, like this one: 120 bytes in 4 blocks are possibly lost in loss record 4,192 of 4,687 at 0x4A06819: operator new(unsigned long) (vg_replace_malloc.c:230) by 0x383B89B8B0: std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.8) by 0x383B89C3B4: (within /usr/lib64/libstdc++.so.6.0.8) by 0x383B89C4A9: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.8) I'm wondering: does std::string (GCC 4.1.2) use any memory pools? if so, is there any way to disable the pools (in form of a debug build etc.)? Regards, Den

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• Prolog for beginners about logic and syntax

  - by lnotik

  Hello everybody. I have this question : I need to create a paradict "rightGuesses" which will get 3 arguments , each one of them is a list of letters : 1) The list of guessed letters 2) The word i have to guess 3) The letters that where guessed so far . for example : rightGuesses([n,o,p,q], [p,r,o,l,o,g], Ans). will give us Ans = [p, -, o, -, o, -]. i made: rightGuesses([],T2,[ANS]) rightGuesses([A|T1],T2,[ANS]):- (member(A,T2))=\=true , rightGuesses(T1,T2,[ _ |'-']). rightGuesses([A|T1],T2,[ANS]):- member(A,T2), rightGuesses(T1,T2,[ _ |A]). but i get : ERROR: c:/users/leonid/desktop/file3.pl:5:0: Syntax error: Operator expected Warning: c:/users/leonid/desktop/file3.pl:6: when i trying to compile it what is my problem , and is there is a better way to do it ? thanks in advance.

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• Add the "selected" attribute to a drop down option with jQuery

  - by gaoshan88

  How do I add the attribute "selected" to a drop down menu option based on that option matching some variable? Here is how the dropdown is populated... loginOptions = ["First", "Second", "Third]; var Login = $( '#Login' ); for ( var i = 0; i < loginOptions.length; i++ ) { Login.append('<option value="'+ loginOptions[i] +'">'+ loginOptions[i] +'</option>'); } I want to mark one option as "selected" based on whether or not its value matches another variable. so if loginOption[i] is equal to var existingLoginValue then set that option to 'selected' Something that would do if(loginOptions[i] === existingLoginValue){ print 'selected'; }; Thanks!

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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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• Setting package-wide variables during python setup.py install

  - by Morgoth

  Is there a way that when a user types python setup.py install to install a Python package, setup.py can be made to set specific variables at the base of the pacakge? A common example would be to basically set mypackage.__revision__ to be the svn revision of the checkout if one is working from svn. Another example case would be if the user can choose a global option, so that the option mypackage.__option__ be set according to a flag passed to setup.py, e.g. python setup.py install --set-flag=10 Then when using the package, mypackage.__option__ would equal 10.

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• What is Ruby's double-colon (::) all about?

  - by Meltemi

  I'd probably be able to answer this for myself if "::" wasn't so hard to Google. Didn't see anything on SO so thought I'd try my luck. What is this double-colon :: all about? I see it everywhere in Rails: class User < ActiveRecord::Base or… ActionController::Routing::Routes.draw do |map| I found a definition from this guy: The :: is a unary operator that allows: constants, instance methods and class methods defined within a class or module, to be accessed from anywhere outside the class or module. but that just leads to more questions. What good is scope (private, protected) if you can just use :: to expose anything?

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• Is there an existing algorithm for this notation translation/conversion?

  - by John

  A system has a notation that would require writing an expression like (A+B)*C as #MUL(#ADD(A,B),C). Is there already an algorithm to do this kind of notation conversion so users can enter in a more conventional way? In other words an algorithm to convert from infix - my notation. First issue is I don't know an exact name for my notation... it's similar to reverse-polish but not quite. Every operator is encoded as a function taking arguments.

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• LINQ-to-SQL: Searching against a CSV

  - by Peter Bridger

  I'm using LINQtoSQL and I want to return a list of matching records for a CSV contains a list of IDs to match. The following code is my starting point, having turned a CSV string in a string array, then into a generic list (which I thought LINQ would like) - but it doesn't: Error Error 22 Operator '==' cannot be applied to operands of type 'int' and 'System.Collections.Generic.List<int>' C:\Documents and Settings\....\Search.cs 41 42 C:\...\ Code DataContext db = new DataContext(); List<int> geographyList = new List<int>( Convert.ToInt32(geography.Split(',')) ); var geographyMatches = from cg in db.ContactGeographies where cg.GeographyId == geographyList select new { cg.ContactId }; Where do I go from here?

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• Is this a correct implementation of singleton C++?

  - by Kamal

  class A{ static boost::shared_ptr<A> getInstance(){ if(pA==NULL){ pA = new A(); } return boost::shared_ptr(pA); } //destructor ~A(){ delete pA; pA=NULL; } private: A(){ //some initialization code } //private assigment and copy constructors A(A const& copy); // Not Implemented A& operator=(A const& copy); // Not Implemented static A* pA; }; A* A::pA = NULL;

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• How do you get the logical xor of two variables in Python?

  - by Zach Hirsch

  How do you get the logical xor of two variables in Python? For example, I have two variables that I expect to be strings. I want to test that only one of them contains a True value (is not None or the empty string): str1 = raw_input("Enter string one:") str2 = raw_input("Enter string two:") if logical_xor(str1, str2): print "ok" else: print "bad" The ^ operator seems to be bitwise, and not defined on all objects: >>> 1 ^ 1 0 >>> 2 ^ 1 3 >>> "abc" ^ "" Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for ^: 'str' and 'str'

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• HASHREF in Perl

  - by Uri

  I'm trying to decrypt a Perl code which I'm not familiar with, somehow related to HashRef. I'm using Amazon::S3, but my question is a general Perl question. See the code below: use Amazon::S3; my $s3 = Amazon::S3-new( ... ); my $response = $s3-buckets; Documentation (here) sais, about s3-buckets: Returns undef on error, else HASHREF of results The following line is working for me, but I don't understand why: for $b in ( @ { $response-{buckets} } ) { print "bucket: " . $b-bucket . "\n"; } I'm buzzled by each operator on the first line. What type exactly are $response, $respone-{bucket}. Looks like the expression within the 'for' is an array, but I don't understand this syntax: @{ ... }?

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