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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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• 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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• car and cdr in Scheme are driving me crazy ...

  - by kristian Roger

  Hi Im facing a problem with the car and cdr functions for example: first I defined a list called it x (define x (a (bc) d ( (ef) g ) )) so x now is equal to (a (bc) d ( (ef) g ) ) now for example I need to get the g from this list using only car and cdr (!! noshortcuts as caddr cddr !!) the correct answer is: (car(cdr(car(cdr(cdr(cdr x)))))) BUT how ? :-( I work according to the rules (the car gives the head of list and cdr gives the tail) and instead of getting the answer above I keep reaching wrong answers. Can any one help me in understanding this ... give me step or a way to solve it step by step Thanks in advance. I'm really sick of Scheme.

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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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• 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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• 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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• 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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• 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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• linux's fork and system resources

  - by Dmitry Bespalov

  Suppose I have following code in linux: int main() { FILE* f = fopen("file.txt", "w"); fork(); fwrite("A", 1, 1, f); fclose(f); return 0; } What I know about fork from documentation, is that it makes the copy of current process. It copies state of the memory as well, so *f should be equal in both instances. But what happens with system resources, such as a file handle? In this example I open the file with write intentions, so only one instance can write into file, right? Which of the instances will actually write into file? Who should care further about the file handle, and call fclose() ?

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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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• Why does a C# System.Decimal remember trailing zeros?

  - by Rob Davey

  Is there a reason that a C# System.Decimal remembers the number of trailing zeros it was entered with? See the following example: public void DoSomething() { decimal dec1 = 0.5M; decimal dec2 = 0.50M; Console.WriteLine(dec1); //Output: 0.5 Console.WriteLine(dec2); //Output: 0.50 Console.WriteLine(dec1 == dec2); //Output: True } The decimals are classed as equal, yet dec2 remembers that it was entered with an additional zero. What is the reason/purpose for this?

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• Java M4A atom tagging free space issue

  - by Brett

  Hey, I've been trying to be able to read and write iTunes style M4A atoms and while I've successfully done the reading part, I've come to a bit of a halt in regards to the free space atoms. I figured that I should be able edit and shift the padding around to accommodate writing an atom with more data than it originally had. I've been stuck on this for about a day now, and I've been trying to figure out how to determine the closest free space atom with enough size to accommodate the new data. so far I have: private freeAtom acquireFreeSpaceAtom( long position ) { long atomStart = Long.MAX_VALUE; freeAtom atom = null; for( freeAtom a : freeSpace ) { if( Math.abs( position - atomStart ) > Math.abs( position - a.getAtomStart() ) ) atomStart = ( atom = a ).getAtomStart(); } return atom; } That code only takes into account the closest free space atom and completely disregards the fact that it should be greater than or equal to a certain size, but I can't quite figure out how I should check for both closeness and size efficiently.

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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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• different explanation

  - by Delirium tremens

  The following code echoes 5, not 10: $global_obj = null; class my_class { var $value; function my_class() { global $global_obj; $global_obj = &$this; } } $a = new my_class; $a->my_value = 5; $global_obj->my_value = 10; echo $a->my_value; "Upon first examination, it would seem that the constructor of my_class stores a reference to itself inside the $global_obj variable. Therefore, one would expect that, when we later change the value of $global_obj-my_value to 10, the corresponding value in $a would change as well. Unfortunately, the new operator does not return a reference, but a copy of the newly created object." Please, give me a different explanation.

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• UIScrollView Does not Scroll

  - by paul simmons

  I have added a long info screen to my iPhone app. The info is a long UIImageView, and it is contained inside a UIScrollView. They are both defined in .xib file. At run-time, initially I set scrollview's position outside window, and when user clicks a button, set its position inside window. This part is OK. But scrollview displays the image but does not scroll. Isn't it enough to place in MainViewContoller.xib, set the contained content, and (at code) set its contentSize equal to the content's size? BTW: I try it at simulator currently.

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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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• 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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• 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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• Using the .where method in Rails3

  - by Elliot

  Hey Guys, I've just started using the .where method, and I'm a little bit confused about how to fully utilize it. I'd like to do something like: @books = Book.where(:author_id => 1 || 2) clearly I know that doesn't work, but I'm trying to demonstrate that I want some extra logic here. some "or" "and" "does not equal" etc. Any ideas for where I can research this? I was looking in the rails API but I didnt see anything that was that helpful. Thanks!

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• hibernate not throwing stale state exception nor it is overwriting data

  - by Reddy

  Our application do the following. 1. Start the transaction. 2. Execute a query using prepared statement 3. Check a condition to see the number of rows updated are equal to the required number. 4. It commits on success of above condition otherwise it will roll back However the problem is that when two threads are simultaneously enter this code. Thread-1 is updating a row in step 2. It checked the condition and committed successfully since the condition is successful. Thread-2 started execution somewhere between steps 1 & 4, and it is failing on at condition checking at step 3 (as it is getting number of updated rows as 0). I expected second thread to throw an exception but it is not. What could be the problem?

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• I need to do a BASICE For Loop algorithm for a java Pyramid

  - by user1665119

  Question 2. USE THE FOR LOOP. Design and write an algorithm that will read a single positive number from the keyboard and will then print a pyramid out on the screen. The pyramid will need to be of a height equal in lines to the number inputted by the operator. Your program is not to test for negative numbers, nor is it to cater for them. For your test, use the number 7. If you would like to take the problem further, try 18 and watch what happens. Example input: 4 Example output: 1 121 12321 1234321

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• How can I rotate an image using Java/Swing and then set its origin to 0,0?

  - by JT

  I'm able to rotate an image that has been added to a JLabel. The only problem is that if the height and width are not equal, the rotated image will no longer appear at the JLabel's origin (0,0). Here's what I'm doing. I've also tried using AffineTransform and rotating the image itself, but with the same results. Graphics2D g2d = (Graphics2D)g; g2d.rotate(Math.toRadians(90), image.getWidth()/2, image.getHeight()/2); super.paintComponent(g2d); If I have an image whose width is greater than its height, rotating that image using this method and then painting it will result in the image being painted vertically above the point 0,0, and horizontally to the right of the point 0,0.

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• JAVA: 500 Worker Threads, what kind of thread pool?

  - by Submerged

  I am wondering if this is the best way to do this. I have about 500 threads that run indefinitely, but Thread.sleep for a minute when done one cycle of processing. ExecutorService es = Executors.newFixedThreadPool(list.size()+1); for (int i = 0; i < list.size(); i++) { es.execute(coreAppVector.elementAt(i)); //coreAppVector is a vector of extends thread objects } I do need a separate threads for each running task, so changing the architecture isn't an option. I tried making my threadPool size equal to Runtime.getRuntime().availableProcessors() which attempted to run all 500 threads, but only let 8 (4xhyperthreading) of them execute. The other threads wouldn't surrender and let other threads have their turn. I tried putting in a wait() and notify(), but still no luck. If anyone has a simple example or some tips, I would be grateful!

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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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• Problem with literal arguments in the PATTERN string for a python 2to3 fixer

  - by Zxaos

  Hi folks. I'm writing a fixer for the 2to3 tool in python. In my pattern string, I have a section where I'd like to match an empty string as an argument, or an empty unicode string. The relevant chunk of my pattern looks like: (args='""' | args='u""') My issue is the second option never matches. Even if it's alone, it won't match. However, if I simply say args=any and then output args, I can catch cases where args is exactly equal to the second option. Is there some weird unicode handling thing going on? Why won't the second literal option ever match?

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