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• Grouping data into ranges in R

  - by Maddy

  supposing i have a data frame in R that has names of students in one column and their marks in another column. these marks range from 20 to 100. > mydata id name marks gender 1 a1 56 female 2 a2 37 male i want to divide the student into groups, based on the criteria of obtained marks, so that difference between marks in each group should be more than 10. i tried to use the function table, which gives the number of students in each range from say 20-30, 30-40, but i want it to pick those students that have marks in a given range and put all their information together in a group. any help is appreciated.

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• How to reduce the number of points in (x,y) data

  - by Gowtham

  I have a set of data points: (x1, y1) (x2, y2) (x3, y3) ... (xn, yn) The number of sample points can be thousands. I want to represent the same curve as accurately as possible with minimal (lets suppose 30) set of points. I want to capture as many inflection points as possible. However, I have a hard limit on the number of allowed points to represent the data. What is the best algorithm to achieve the same? Is there any free software library that can help? PS: I have tried to implement relative slope difference based point elimination, but this does not always result in the best possible data representation. Thanks for your time. -Gowtham

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• Does the "using" directive provide any benefit?

  - by Adam Drummond

  Is there a programmatic benefit to using a using statement? Notice the difference between this sample: using Application.Data; namespace Application.Web { public class SampleClass { public void SampleMethod() { List<Category> categories = CreateCategoriesData(); Category expected = categories[0]; ... ... } } } And this one: namespace Application.Web { public class SampleClass { public void SampleMethod() { List<Data.Category> categories = CreateCategoriesData(); Data.Category expected = categories[0]; ... ... } } }

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• Where to place the login/authentication related actions in MVC

  - by rogeriopvl

  I've searched around and found that when implementing an authentication module in MVC architecture some people opt to place the login related actions in the User controller while others place it in a controller dedicated to authentication only. In pseudo-java-like code: class UserController extends Controller { public login() { //... } } Accessed with http://mydomain.com/user/login. vs. class AuthController extends Controller { public login() { //... } } Accessed with http://mydomain.com/auth/login. I would like to know which approach is better, and why. That is, if there's really any difference at all. Thanks in advance.

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• How efficient is an if statement compared to a test that doesn't use an if? (C++)

  - by Keand64

  I need a program to get the smaller of two numbers, and I'm wondering if using a standard "if x is less than y" int a, b, low; if (a < b) low = a; else low = a; is more or less efficient than this: int a, b, low; low = b + ((a - b) & ((a - b) >> 31)); (or the variation of putting int delta = a - b at the top and rerplacing instances of a - b with that). I'm just wondering which one of these would be more efficient (or if the difference is to miniscule to be relevant), and the efficiency of if-else statements versus alternatives in general.

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• Interview Question: .Any() vs if (.Length > 0) for testing if a collection has elements

  - by Chris

  In a recent interview I was asked what the difference between .Any() and .Length > 0 was and why I would use either when testing to see if a collection had elements. This threw me a little as it seems a little obvious but feel I may be missing something. I suggested that you use .Length when you simply need to know that a collection has elements and .Any() when you wish to filter the results. Presumably .Any() takes a performance hit too as it has to do a loop / query internally.

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• Why are cookies only sent to http://www.example.com and NOT http://example.com?

  - by Axel

  I have a PHP login which sets 2 cookies once someone login. The problem is that if you login from http://www.example.com and you go to http://example.com, you will find yourself not logged in. I think that is because the browser only send the cookies to the first syntax. It is only one domain, the difference is the www. before the domain name, so how to set cookies to the whole domain whatever there is www. or not? <?php setcookie('username',$username,time()+3600); ?>

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• static, define, and const in C

  - by yCalleecharan

  Hi, I've read that static variables are used inside function when one doesn't want the variable value to change/initialize each time the function is called. But what about defining a variable static in the main program before "main" e.g. #include <stdio.h> static double m = 30000; int main(void) { value = m * 2 + 3; } Here the variable m has a constant value that won't get modified later in the main program. In the same line of thought what difference does it make to have these instead of using the static definition: const double m = 30000; or #define m 30000 //m or M and then making sure here to use double operations in the main code so as to convert m to the right data type. Thanks a lot...

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• Why does File::Find finished short of completely traversing a large directory?

  - by Stan

  A directory exists with a total of 2,153,425 items (according to Windows folder Properties). It contains .jpg and .gif image files located within a few subdirectories. The task was to move the images into a different location while querying each file's name to retrieve some relevant info and store it elsewhere. The script that used File::Find finished at 20462 files. Out of curiosity I wrote a tiny recursive function to count the items which returned a count of 1,734,802. I suppose the difference can be accounted for by the fact that it didn't count folders, only files that passed the -f test. The problem itself can be solved differently by querying for file names first instead of traversing the directory. I'm just wondering what could've caused File::Find to finish at a small fraction of all files. The data is stored on an NTFS file system.

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• Gnome screensaver

  - by BParker

  Hi, After many years of Windows development in C/C++ i've decided to make a move to linux, and see if i can put together a simple screen saver. The code is an SDL based OpenGL particle engine affair, nothing too complex. I've got the code running ok as a stand-alone app, but i have been having some trouble finding out how to build a screen saver app. I'm running ubuntu 10.04 if that makes much difference, but i was wondering if anyone can point me in the direction of a decent tutorial on building basic gnome screen savers. Thanks

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• Attaching catalog with SQL Authentication credentials attaches it as Read-Only

  - by Nissim

  Hello, As part of our product's installation process, a database is attached to the server. We use EXEC sp_attach_db in order to attach it to MSSQL. The problem occures when we try to attach it with "SQL Authentication" connection string - the database is attached to the server as read-only, thus preventing any write access from being performed This is driving us nuts... it's working just fine with Windows Authentication, and the only difference is the connection string... I tried googling for it but no mention for such a scenario is found. Any ideas anyone? It's important to mention that the MDF/LDF physical files are not set with "ReadOnly" attribute, so this is not the problem.

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• IO.Directory.Exists always returns true

  - by roygbiv

  I am executing a IO.Directory.Exists on a network share from an ASP.NET application running under a specific Application Pool with a specific user account. The call always returns true. I have tried several variations: \\server\share$\directory \\192.168.0.1\share$\directory H:\directory I have checked that directory and share permissions are available to the account. The path does have spaces in it \\server\share$\directory\name name\test test, which should make no difference, however I have read otherwise. I will continue to check permissions, as it does work from my local machine (with the built in VS web-server and I am an administrator on the network), but when deployed to the IIS 6.0 virtual directory, and run under the Application Pool, it does not work.

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• iOS get file size on disk

  - by F2_CMD

  I'm trying to get the size on disk of a file in iOS using Objective C. As of now I've been able to get the actual size of the file and other file information using NSFileManager and then getting the attributes attributesOfItemAtPath:error but not the size on disk. I also tried getting the file size from struct stat but again it doesn't give me size on disk.I tried using NSTask to make a call to du -h but iOS didn't allow me to fork other processes. Any ideas are welcome :) I know this questions is similar to many others but the difference is that I'm trying to do this in iOS and most of the methods used in other systems don't work here. Thanks

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• MySQL inner join different results

  - by Darryl at NetHosted

  I am trying to work out why the following two queries return different results: SELECT DISTINCT i.id, i.date FROM `tblinvoices` i INNER JOIN `tblinvoiceitems` it ON it.userid=i.userid INNER JOIN `tblcustomfieldsvalues` cf ON it.relid=cf.relid WHERE i.`tax` = 0 AND i.`date` BETWEEN '2012-07-01' AND '2012-09-31' and SELECT DISTINCT i.id, i.date FROM `tblinvoices` i WHERE i.`tax` = 0 AND i.`date` BETWEEN '2012-07-01' AND '2012-09-31' Obviously the difference is the inner join here, but I don't understand why the one with the inner join is returning less results than the one without it, I would have thought since I didn't do any cross table references they should return the same results. The final query I am working towards is SELECT DISTINCT i.id, i.date FROM `tblinvoices` i INNER JOIN `tblinvoiceitems` it ON it.userid=i.userid INNER JOIN `tblcustomfieldsvalues` cf ON it.relid=cf.relid WHERE cf.`fieldid` =5 AND cf.`value` REGEXP '[A-Za-z]' AND i.`tax` = 0 AND i.`date` BETWEEN '2012-07-01' AND '2012-09-31' But because of the different results that seem incorrect when I add the inner join (it removes some results that should be valid) it's not working at present, thanks.

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• java: ClassCastException - [Ljava.lang.Long; cannot be cast to java.lang.Long

  - by ufk

  Hello. well.. I use red5 and setting/getting attributes using the IConnection class but tha's really not relevant. 'L' means long in java. so 0L is 0 type Long instead of just '0' which is 0 type Integer. the following error message: stack trace: java.lang.ClassCastException: [Ljava.lang.Long; cannot be cast to java.lang.Long what's the difference between [Ljava.lang.Long and java.lang.Long ? thanks!

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• Ensuring Updated CSS/JavaScript on Client Side

  - by Alex

  I'm trying to ensure that visitors of my ASP.NET MVC website always have the most-current CSS and Javascript (and not some older cached version). I tried to realize this by generating a seed value when the application domain starts, and automatically append it to the CSS and Javascript URLs (so now instead of /Content/All.js the link is /Content/All.js?549238 etc.). Unfortunately I just found out by debugging via Firebug that this causes now a full download request every time (the new "seeded" response is no longer cached at all, but I only wanted the first check to download the 'updated' version, but then cache again/only check if there is a difference). How can I achieve my goal, is there a better way of doing this? I need the client to always request the newest version, but then cache if no change happened. Edit: This appears to be related to the fact that my page is served over SSL. I asked a follow up question here regarding enabling clientside caching with SSL.

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• HttpWebRequest giving "target machine actively refused" error

  - by user1371314

  I am trying to access a URI through HttpWebRequest and am getting the "target machine actively refused" error. I know from a machine that has no proxy this works fine and i know my corp internet uses a PAC file to determine the proxy however it doesnt seem to be picking this up for me. Here is what i know: My app.config has I presume i dont need to specify WebRequest.DefaultWebProxy but that makes no difference I can explictly set the proxy with WebProxy and NetworkCredentials which works Any ideas? Anybody have experience with PAC files and why I can access the target through IE but not through code. obviously if i hardcode the proxy it all works so it would seem that this same proxy is not being auto detected?

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• CRT not initialized

  - by jfhs

  I'm trying to compile one project with MSVC 2010, compilation is ok, but when I try to run the app, it gives me CRT not initialized error. It is a console application, so I tried to specify mainCRTStartup as Entry Point, but it didn't help. In the same solution there are other projects, and they don't have such a problem. The difference which I see between them is that one which is not working, uses boost. Boost v1.38.0 if this is important. Runtime Library is Multi-threaded DLL. Linker command line is: /OUT:"D:\temp\ghost\Release\ghost.exe" /INCREMENTAL:NO /NOLOGO /LIBPATH:"..\zlib\lib" /LIBPATH:"..\mysql\lib\opt" /LIBPATH:"..\boost\lib" "ws2_32.lib" "winmm.lib" "zdll.lib" "StormLibRAS.lib" "kernel32.lib" "user32.lib" "gdi32.lib" "winspool.lib" "comdlg32.lib" "advapi32.lib" "shell32.lib" "ole32.lib" "oleaut32.lib" "uuid.lib" "odbc32.lib" "odbccp32.lib" "D:\temp\ghost\bncsutil\vc8_build\Release\BNCSutil.lib" /MANIFEST /ManifestFile:"Release\ghost.exe.intermediate.manifest" /ALLOWISOLATION /MANIFESTUAC:"level='asInvoker' uiAccess='false'" /DEBUG /PDB:"D:\temp\ghost\Release\ghost.pdb" /SUBSYSTEM:CONSOLE /OPT:REF /OPT:ICF /PGD:"D:\temp\ghost\Release\ghost.pgd" /LTCG /TLBID:1 /ENTRY:"mainCRTStartup" /DYNAMICBASE /NXCOMPAT /MACHINE:X86 /ERRORREPORT:QUEUE

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• Why is this postgresql query so slow?

  - by user315975

  I'm no database expert, but I have enough knowledge to get myself into trouble, as is the case here. This query SELECT DISTINCT p.* FROM points p, areas a, contacts c WHERE ( p.latitude > 43.6511659465 AND p.latitude < 43.6711659465 AND p.longitude > -79.4677941889 AND p.longitude < -79.4477941889) AND p.resource_type = 'Contact' AND c.user_id = 6 is extremely slow. The points table has fewer than 2000 records, but it takes about 8 seconds to execute. There are indexes on the latitude and longitude columns. Removing the clause concering the resource_type and user_id make no difference. The latitude and longitude fields are both formatted as number(15,10) -- I need the precision for some calculations. There are many, many other queries in this project where points are compared, but no execution time problems. What's going on?

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• How can I reverse ruby's include function.

  - by Glen

  I'll explain what i'm looking for in code as thats probably the most succinct: module Mixin def method puts "Foo" end end class Whatever include Mixin end w = Whatever.new w.method => "Foo" # some magic here w2 = Whatever.new w.method => NoMethodError I had tried just undefining the Mixin module using remove_const, but this doesn't seem to make any difference to Whatever. I had assumed that #include just added a reference to the module into the class's method resolution chain - but this behaviour doesn't agree with that. Can anyone tell me what include actually does behind the scenes, and how to reverse this?

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• Objective-c pointer assignment and reassignment dilema

  - by moshe

  Hi, If I do this: 1 NSMutableArray *near = [[NSMutableArray alloc] init]; 2 NSMutableArray *all = [[NSMutableArray alloc] init]; 3 NSMutableArray *current = near; 4 current = all; What happens to near? At line 3, am I setting current to point to the same address as near so that I now have two variables pointing to the same place in memory, or am I setting current to point to the location of near in memory such that I now have this structure: current - near - NSMutableArray The obvious difference would be the value of near at line 4. If the former is happening, near is untouched and still points to its initial place in memory. If the latter is happening,

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• How to change input button image using CSS?

  - by Baltimark

  So, I can create an input button with an image using <INPUT type="image" src="/images/Btn.PNG" value=""> But, I can't get the same behavior using CSS. for instance, i've tried <INPUT type="image" class="myButton" value=""> where "myButton" is defined in the css file as .myButton{ background:url(/images/Btn.PNG) no-repeat; cursor:pointer; width: 200px; height: 100px; border: none; } If that's all I wanted to do, I could use the original style, but I want to change the button's appearance on hover (using a myButton:hover class). I know the links are good because I've been able to load them for a background image for other parts of the page (just as a check). I found examples on the web of how to do it using javascript, but I'm looking for a css solution. I'm using Firefox 3.0.3 if that makes a difference. Thanks

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• consts and other animals

  - by bks

  Hello i have a cpp code wich i'm having trouble reading. a class B is defined now, i understand the first two lines, but the rest isn't clear enough. is the line "B const * pa2 = pa1" defines a const variable of type class B? if so, what does the next line do? B a2(2); B *pa1 = new B(a2); B const * pa2 = pa1; B const * const pa3 = pa2; also, i'm having trouble figuring out the difference between these two: char const *cst = “abc”; const int ci = 15; thank you

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• Which one is better apporach comet or ajax?

  - by Rajesh Rolen- DotNet Developer

  i need to update client on any changes occurred on server. for that i found 2 approach. 1. using ajax which is also known as reverse ajax for this purpose. 2. using COMET. but i don't know exact difference in both. my site contains news content and i want that news to be automatically updates when new news is entered by my CMS application. i have got hundreds of concurrent users on my web application. please suggest me which approach should i use to get best solution. also please provide me good example's like for that so that i can implement it. NOTE: i am using .net framework 2.0 but if its not possible in 2.0 then can also move to 3.5 Thanks.

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• C static variables and intialization

  - by yCalleecharan

  Hi, If I have a global static variable x like in this code #include <stdio.h> #include <stdio.h> static int x; int main(void) { DO SOMETHING WITH x HERE x++; } What will be difference if I opted to initialize x to a value first say as in static int x = 0; before entering "main"? In my first case where I didn't assign a value to x, does the compiler implicitly know that x is to be set to zero as it's a static variable? I heard that we can do this with static variables. Thanks a lot...

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