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  • tidy/efficient function writing in R

    - by romunov
    Excuse my ignorance, as I'm not a computer engineer but with roots in biology. I have become a great fan of pre-allocating objects (kudos to SO and R inferno by Patrick Burns) and would like to improve my coding habits. In lieu of this fact, I've been thinking about writing more efficient functions and have the following question. Is there any benefits in removing variables that will be overwritten at the start of the next loop, or is this just a waste of time? For the sake of argument, let's assume that the size of old and new variables is very similar or identical.

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  • Heap corruption detected error when attempting to free pointer

    - by AndyGeek
    Hi, I'm pretty new to C++ and have run into a problem which I have not been able to solve. I'm trying to convert a System::String to a wchar_t pointer that I can keep for longer than the scope of the function. Once I'm finished with it, I want to clean it up properly. Here is my code: static wchar_t* g_msg; int TestConvert() { pin_ptr<const wchar_t> wchptr = PtrToStringChars("Test"); g_msg = (wchar_t*)realloc(g_msg, wcslen(wchptr) + 1); wcscpy(g_msg, wchptr); free (g_msg); // Will be called from a different method } When the free is called, I'm getting "HEAP CORRUPTION DETECTED: after Normal block (#137) at 0x02198F90." Why would I be getting this error? Andrew L

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  • Dynamically add items to Tkinter Canvas

    - by nick369
    I'm attempting to learn Tkinter with the goal of being able to create a 'real-time' scope to plot data. As a test, I'm trying to draw a polygon on the canvas every time the 'draw' button is pressed. The triangle position is randomized. I have two problems: There is a triangle on the canvas as soon as the program starts, why and how do I fix this? It doesn't draw any triangles when I press the button, at least none that I can see. CODE from Tkinter import * from random import randint class App: def __init__(self,master): #frame = Frame(master) #frame.pack(side = LEFT) self.plotspc = Canvas(master,height = 100, width = 200, bg = "white") self.plotspc.grid(row=0,column = 2, rowspan = 5) self.button = Button(master, text = "Quit", fg = "red", \ command = master.quit) self.button.grid(row=0,column=0) self.drawbutton = Button(master, text = "Draw", command = \ self.pt([50,50])) self.drawbutton.grid(row = 0, column = 1) def pt(self, coords): coords[0] = coords[0] + randint(-20,20) coords[1] = coords[1] + randint(-20,20) x = (0,5,10) y = (0,10,0) xp = [coords[0] + xv for xv in x] yp = [coords[1] + yv for yv in y] ptf = zip(xp,yp) self.plotspc.create_polygon(*ptf) if _name_ == "_main_": root = Tk() app = App(root) root.mainloop() The code is formatting strangely within the code tags, I have no idea how to fix this.

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  • How to make the value of one select box drive the options of a second select box

    - by Ben McCormack
    I want to make an HTML form with 2 select boxes. The selected option in the first select box should drive the options in the second select box. I would like to solve this dynamically on the client (using javascript or jQuery) rather than having to submit data to the server. For example, let's say I have the following Menu Categories and Menu Items: Sandwiches Turkey Ham Bacon Sides Mac 'n Cheese Mashed Potatoes Drinks Coca Cola Sprite Sweetwater 420 I would have two select boxes, named Menu Category and Items, respectively. When the user selects Sandwiches in the Menu Category box, the options in the Items box will only show Sandwich options. I'm stuck as how I might approach this. Once I filter out the 2nd list one time, how do I "find" the list options once I change my menu category in the 1st list? Also, if I'm thinking in SQL, I would have a key in the 1st box that would be used to link to the data in the 2nd box. However, I can't see where I have room for a "key" element in the 2nd box. How could this problem be solved with a combination of jQuery or plain javascript?

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  • Longest Common Subsequence

    - by tsudot
    Consider 2 sequences X[1..m] and Y[1..n]. The memoization algorithm would compute the LCS in time O(m*n). Is there any better algorithm to find out LCS wrt time? I guess memoization done diagonally can give us O(min(m,n)) time complexity.

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  • iPhone NSCFString leaks in fetchRequest

    - by camilo
    In the following code: - (NSMutableArray *) fetchNotesForGroup: (NSString *)groupName { // Variables declaration NSMutableArray *result; NSFetchRequest *fetchRequest; NSEntityDescription *entity; NSSortDescriptor *sortDescriptor; NSPredicate *searchPredicate; NSError *error = nil; // Creates the fetchRequest and executes it fetchRequest = [[[NSFetchRequest alloc] init] autorelease]; entity = [NSEntityDescription entityForName:@"Note" inManagedObjectContext:managedObjectContext]; [fetchRequest setEntity:entity]; sortDescriptor = [[[NSSortDescriptor alloc] initWithKey:@"noteName" ascending:YES] autorelease]; [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]]; [fetchRequest setReturnsDistinctResults:YES]; searchPredicate = [NSPredicate predicateWithFormat:@"categoryName like %@", groupName]; [fetchRequest setPredicate:searchPredicate]; [fetchRequest setPropertiesToFetch:[NSArray arrayWithObject:@"noteName"]]; result = [[managedObjectContext executeFetchRequest:fetchRequest error:&error] mutableCopy]; // Variables release return result; } ... I Fetch notes for a given categoryName. When I'm running Instruments, it says that a NSCFString is leaking. I know leaks are mean for iPhone developers... but I don't have any idea on how to plug this one. Any clues? All help is welcome. Thanks a lot!

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  • NSString potencial leak

    - by VansFannel
    Hello. When I build and analyze my project on XCode, I obtain a 'warning' on the following line: NSString *contactEmail = (NSString *)ABMultiValueCopyValueAtIndex(emailInfo, 0); The message is: Potencial leak on object allocated on line ... and stored into contactEmail. Is there any error on that line?

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  • Template and Themes in WPF through Custom Xaml Files

    - by AKRamkumar
    I have an application where I give my user Widgets. Suppose my user wants to customize the layout of the widgets. For example, I have a clock that is green. In Xaml, to add an animation around the clock would be easy. How could i make it such that at runtime, my application reads a layout.xaml file. Loads it and parses all the gradients and xaml. But still be able to use my widget in there. EG <Layout> <Grid> <!-- Grid Definitions or Animations or Whatever--> <Clock/> <!-- They need to be able to simply use this and my applications needs to read this--> </Grid> </Layout>

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  • Django: How to dynamically add tag field to third party apps without touching app's source code

    - by Chris Lawlor
    Scenario: large project with many third party apps. Want to add tagging to those apps without having to modify the apps' source. My first thought was to first specify a list of models in settings.py (like ['appname.modelname',], and call django-tagging's register function on each of them. The register function adds a TagField and a custom manager to the specified model. The problem with that approach is that the function needs to run BEFORE the DB schema is generated. I tried running the register function directly in settings.py, but I need django.db.models.get_model to get the actual model reference from only a string, and I can't seem to import that from settings.py - no matter what I try I get an ImportError. The tagging.register function imports OK however. So I changed tactics and wrote a custom management command in an otherwise empty app. The problem there is that the only signal which hooks into syncdb is post_syncdb which is useless to me since it fires after the DB schema has been generated. The only other approach I can think of at the moment is to generate and run a 'south' like database schema migration. This seems more like a hack than a solution. This seems like it should be a pretty common need, but I haven't been able to find a clean solution. So my question is: Is it possible to dynamically add fields to a model BEFORE the schema is generated, but more specifically, is it possible to add tagging to a third party model without editing it's source. To clarify, I know it is possible to create and store Tags without having a TagField on the model, but there is a major flaw in that approach in that it is difficult to simultaneously create and tag a new model.

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  • -(void)dealloc - How ? Objective - C

    - by sagar
    Please Note that - this is not similar than this question. OK. To understand my question, First of all please see both of these destructors. - (void)dealloc { [Marketdetails release]; Marketdetails=nil; [parsedarray release]; parsedarray=nil; [Marketid release]; Marketid=nil; [marketname release]; marketname=nil; [super dealloc]; } - (void)dealloc { [super dealloc]; [Marketdetails release]; Marketdetails=nil; [parsedarray release]; parsedarray=nil; [Marketid release]; Marketid=nil; [marketname release]; marketname=nil; } See, Both destructors have different code. In First Destructor first current class objects are released & then [super dealloc] is called. In second Desctructor first [super dealloc] is called. My question is as follows. Where should we write [super dealloc] ? first or last ? or it doesn't matter ?

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  • Returning object from function

    - by brainydexter
    I am really confused now on how and which method to use to return object from a function. I want some feedback on the solutions for the given requirements. Scenario A: The returned object is to be stored in a variable which need not be modified during its lifetime. Thus, const Foo SomeClass::GetFoo() { return Foo(); } invoked as: someMethod() { const Foo& l_Foo = someClassPInstance->GetFoo(); //... } Scneraio B: The returned object is to be stored in a variable which will be modified during its lifetime. Thus, void SomeClass::GetFoo(Foo& a_Foo_ref) { a_Foo_ref = Foo(); } invoked as: someMethod() { Foo l_Foo; someClassPInstance-GetFoo(l_Foo); //... } I have one question here: Lets say that Foo cannot have a default constructor. Then how would you deal with that in this situation, since we cant write this anymore: Foo l_Foo Scenario C: Foo SomeClass::GetFoo() { return Foo(); } invoked as: someMethod() { Foo l_Foo = someClassPInstance->GetFoo(); //... } I think this is not the recommended approach since it would incur constructing extra temporaries. What do you think ? Also, do you recommend a better way to handle this instead ?

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  • What is happening in this T-SQL code? (Concatenting the results of a SELECT statement)

    - by Ben McCormack
    I'm just starting to learn T-SQL and could use some help in understanding what's going on in a particular block of code. I modified some code in an answer I received in a previous question, and here is the code in question: DECLARE @column_list AS varchar(max) SELECT @column_list = COALESCE(@column_list, ',') + 'SUM(Case When Sku2=' + CONVERT(varchar, Sku2) + ' Then Quantity Else 0 End) As [' + CONVERT(varchar, Sku2) + ' - ' + Convert(varchar,Description) +'],' FROM OrderDetailDeliveryReview Inner Join InvMast on SKU2 = SKU and LocationTypeID=4 GROUP BY Sku2 , Description ORDER BY Sku2 Set @column_list = Left(@column_list,Len(@column_list)-1) Select @column_list ---------------------------------------- 1 row is returned: ,SUM(Case When Sku2=157 Then Quantity Else 0 End) As [157 -..., SUM(Case ... The T-SQL code does exactly what I want, which is to make a single result based on the results of a query, which will then be used in another query. However, I can't figure out how the SELECT @column_list =... statement is putting multiple values into a single string of characters by being inside a SELECT statement. Without the assignment to @column_list, the SELECT statement would simply return multiple rows. How is it that by having the variable within the SELECT statement that the results get "flattened" down into one value? How should I read this T-SQL to properly understand what's going on?

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  • dealloc on Background Thread

    - by Mark Brackett
    Is it an error to call dealloc on a UIViewController from a background thread? It seems that UITextView (can?) eventually call _WebTryThreadLock which results in: bool _WebTryThreadLock(bool): Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Background: I have a subclassed NSOperation that takes a selector and a target object to notify. -(id)initWithTarget:(id)target { if (self = [super init]) { _target = [target retain]; } return self; } -(void)dealloc { [_target release]; [super dealloc]; } If the UIViewController has already been dismissed when the NSOperation gets around to running, then the call to release triggers it's dealloc on a background thread.

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  • Select row data as ColumnName and Value

    - by Bobcat1506
    I have a history table and I need to select the values from this table in ColumnName, ColumnValue form. I am using SQL Server 2008 and I wasn’t sure if I could use the PIVOT function to accomplish this. Below is a simplified example of what I need to accomplish: This is what I have: The table’s schema is CREATE TABLE TABLE1 (ID INT PRIMARY KEY, NAME VARCHAR(50)) The “history” table’s schema is CREATE TABLE TABLE1_HISTORY( ID INT, NAME VARCHAR(50), TYPE VARCHAR(50), TRANSACTION_ID VARCHAR(50)) Here is the data from TABLE1_HISTORY ID NAME TYPE TRANSACTION_ID 1 Joe INSERT a 1 Bill UPDATE b 1 Bill DELETE c I need to extract the data from TABLE1_HISTORY into this format: TransactionId Type ColumnName ColumnValue a INSERT ID 1 a INSERT NAME Joe b UPDATE ID 1 b UPDATE NAME Bill c DELETE ID 1 c DELETE NAME Bill Other than upgrading to Enterprise Edition and leveraging the built in change tracking functionality, what is your suggestion for accomplishing this task?

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  • Optimizing a shared buffer in a producer/consumer multithreaded environment

    - by Etan
    I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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  • Nested mysql select statements

    - by Jimmy Kamau
    I have a query as below: $sult = mysql_query("select * from stories where `categ` = 'businessnews' and `stryid`='".mysql_query("SELECT * FROM comments WHERE `comto`='".mysql_query("select * from stories where `categ` ='businessnews'")." ORDER BY COUNT(comto) DESC")."' LIMIT 3") or die(mysql_error()); while($ow=mysql_fetch_array($sult)){ The code above should return the top 3 'stories' with the most comments {count(comto)}. The comments are stored in a different table from the stories. The code above does not return any values and doesn't show any errors. Could someone please help?

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  • UIWebView in multithread ViewController

    - by Tao
    I have a UIWebView in a viewcontroller, which has two methods as below. The question is if I pop out(tap back on navigation bar) this controller before the second thread is done, the app will crash after [super dealloc], because "Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread.". Any help would be really appreciated. -(void)viewDidAppear:(BOOL)animated { [super viewWillAppear:animated]; NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(load) object:nil]; [operationQueue addOperation:operation]; [operation release]; } -(void)load { [NSThread sleepForTimeInterval:5]; [self performSelectorOnMainThread:@selector(done) withObject:nil waitUntilDone:NO]; }

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  • In .NET, how do I prevent, or handle, tampering with form data of disabled fields before submission?

    - by David
    Hi, If a disabled drop-down list is dynamically rendered to the page, it is still possible to use Firebug, or another tool, to tamper with the submitted value, and to remove the "disabled" HTML attribute. This code: protected override void OnLoad(EventArgs e) { var ddlTest = new DropDownList() {ID="ddlTest", Enabled = false}; ddlTest.Items.AddRange(new [] { new ListItem("Please select", ""), new ListItem("test 1", "1"), new ListItem("test 2", "2") }); Controls.Add(ddlTest); } results in this HTML being rendered: <select disabled="disabled" id="Properties_ddlTest" name="Properties$ddlTest"> <option value="" selected="selected">Please select</option> <option value="1">test 1</option> <option value="2">test 2</option> </select> The problem occurs when I use Firebug to remove the "disabled" attribute, and to change the selected option. On submission of the form, and re-creation of the field, the newly generated control has the correct value by the end of OnLoad, but by OnPreRender, it has assumed the identity of the submitted control and has been given the submitted form value. .NET seems to have no way of detecting the fact that the field was originally created in a disabled state and that the submitted value was faked. This is understandable, as there could be legitimate, client-side functionality that would allow the disabled attribute to be removed. Is there some way, other than a brute force approach, of detecting that this field's value should not have been changed? I see the brute force approach as being something crap, like saving the correct value somewhere while still in OnLoad, and restoring the value in the OnPreRender. As some fields have dependencies on others, that would be unacceptable to me.

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  • Re-binding an ajaxForm after content re-loads with ajax (jQuery 1.4.2)

    - by Cristian
    I'm trying to figure out why this is a problem when using jQuery 1.4.2 and not 1.3.2. This is my function: function prepare_logo_upload() { $("#logo-upload-form").ajaxForm({ //alert(responseText); success: function(responseText) { //alert(responseText); $('#profile .wrapper').html(responseText); prepare_logo_upload(); } }); } Every other live event works but can't use the .live() method because ajaxForm is a plugin. I have noticed this also for other types of binding (clicks) using the old form (re-binding after callback) Can you tell me if it is a way of solving this? This is a similar question, but due to my newbie reputation here, can't comment or ask a question there, so I'll ask a new one here. - http://stackoverflow.com/questions/2208880/jquery-bind-ajaxform-to-a-form-on-a-page-loaded-via-load Thank you!

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  • Ext JS 4.2.1 loading controller - best practice

    - by Hown_
    I am currently developing a Ext JS application with many views/controlers/... I am wondering myself what the best practice is for loading the JS controllers/views/and so on... currently i have my application defined like this: // enable javascript cache for debugging, otherwise Chrome breakpoints are lost Ext.Loader.setConfig({ disableCaching: false }); Ext.require('Ext.util.History'); Ext.require('app.Sitemap'); Ext.require('app.Error'); Ext.define('app.Application', { name: 'app', extend: 'Ext.app.Application', views: [ // TODO: add views here 'app.view.Viewport', 'app.view.BaseMain', 'app.view.Main', 'app.view.ApplicationHeader', //administration 'app.view.administration.User' ... ], controllers: [ 'app.controller.Viewport', 'app.controller.Main', 'app.controller.ApplicationHeader', //administration 'app.controller.administration.User', ... ], stores: [ // stores in there.. ] }); somehow this forces the client to load all my views and controllers at startup and is calling all init methods of all controllers of course.. i need to load data everytime i chnage my view.. and now i cant load it in my controllers init function. I would have to do something like this i assume: init: function () { this.control({ '#administration_User': { afterrender: this.onAfterRender } }); }, Is there a better way to do this? Or just an other event? Though the main thing i am questioning myself is if it is the best practice to load all the javascript at startup. Wouldnt it be better to only load the controllers/views/... which the client does need right now? Or should i load all the JS at startup? If i do want to load the controllers dynamicly how could i do this? I assume a would have to remove them from my application arrays (views, controllers, stores) and create an instance if i do need it and mby set the view in the controllers init?! What's best practice??

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  • jQuery-AJAX to rebind dropdown list to results from stored procedure

    - by webworm
    I have a dropdown list of peoples names that is quite long. As many as 2,000 names. I would like to make it easier to find the name the user is interested in by limiting the dropdown list to a subset of names at a time. I have done this by creating a series of 26 links (A, B, C ... Z) that call a method in the code behind that populates the dropdown list with only those names starting with the letter the user clicked. This all works well but I would like to be able to use AJAX to accomplish this update of the dropdown list without a page refresh. I would like to use jQuery for the AJAX functionality rather than ASP.NET AJAX. My problem is I am not sure how to execute the stored procedure and then "rebind" the dropdown list with the new dataset via jQuery AJAX. Any suggestions or resources that might provide and example or walk-through? Thank you.

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