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• Data frame linear fit in R

  - by user1247384

  This is perhaps a simple question, but I am n00b.Say I have a data frame with a bunch of columns. I need to call lm function over the column 1 and 2, 1 and 3, and so on. So basically I need to loop over all columns and store the results of the fit as I build the model. The problem I am running into is that lm(df[1]~df[2], data = df) doesnt work. In this case df is the data frame object and df[1] is the first column. What is a good way to do this in a loop, as in access the columns of df in an iterative fashion. Thanks.

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• How to use Region Time Zone with a .Net application?

  - by davitz38

  I'm working on an asp.net mvc application. Each user have his own time zone. Right now, I'm using "TimeZoneInfo.GetSystemTimeZones" to generate a drop down list in order for the user to select a timezone and this is what I store in my db They are like that: Morocco Standard Time (00:00:00) UTC (00:00:00) GMT Standard Time (00:00:00) ... I know that php use a different timezone set, they are "region timezone", for example: Europe/Paris Europe/London ... My question is: is there a way to play with the region timezone (like php) in an .NET application? The only way I can think of is to bind each php region timezone to the .net timezone. Also, the "TimeZoneInfo.GetSystemTimeZones" list all of the timezone on the machine. Is the list different between windows server, windows vista, windows xp? Hope this make sense, thanks guys

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• A B+tree simple implementation in C

  - by initpy

  Hi guys, I'm working on a fun project where I need a simple key/value store that uses B+Trees. I studied them some years ago, and to be honest, I don't want to reinvent the wheel, so I'm looking for a simple implementation in C of b+tree that I can just include in my project. I know of sqlite's, dbm's and tokyocabinet's ones but they're a little too "complicated" for my needs. Is there any (even pedagogical) work on this you can refer me to? Do you have some code to share? Thanks a lot!

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• How to save, retrieve and draw an image using postgresql an java (no path saving)?

  - by spderosso

  Hi, Given an object X; I want this object to have an image. The image must be stored in the database. I can't store the path, the actual image must be in the database. My question can be answered by answering the following subquestions: a) What type of field should I put in the database? (e.g VARCHAR) b) What type of object should I use for storing and manipulating the image (at an object layer)? (e.g java.awt.Image) c) How do I create an object of the type selected (answer of question b) from the data obtained from the database? d) How do I save an object of the type selected (answer of question b) to the database? e) How do I draw the image on a web page? I am using postgresql, java and it is a web application. Thanks!

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• Can I use PayPal to charge a Credit Card automatically?

  - by Mark

  If I have a Visa card number saved in my database, is there a way I can charge that Visa automatically through the PayPal API without the user having to enter anything? We want to keep this site as easy and hassle-free to use as possible. It would be a variable amount, based on how they use the site. (Don't worry, proper disclaimers will be in place, and the user will be notified) What about these "recurring payments"? That way I don't have to store the CC info on my website, but do they allow variable amounts that I could periodically send to PayPal?

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• how do you organize your programming work

  - by dole

  Hi there, I'm a newbie in the field, but in the near future I have to develop an application for a friend(I've already did some work of the app and the friend is happy). I assume that I need 3 places to store my work, but I'm not sure if this is the best approach. I need your advice, opinion, link,book, blog about this subject. I plan to have: a place where I develop the application a place where I keep a back-up of the application a place with the application ready for use I'll use git in the development stage, but for the later I don't know what tools to use, or which are the good practices. Can you give me an advice?

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• Translate to MIPS

  - by user2334400

  HELP Translate A[i] = B[i-1] + B[i] + B[i+1] to MIPS the address of array A is $s1 the address of array B is $s2 the value of i is $s3 lb $s1,0($s3) # $s1=A[i] lb $s2,0($s3) # $s2=B[i] sb $s2,0($s3) # store s2 add $t0, $zero, $s2 #t0=B[i] addi $s3,$s3,-1 #i=i-1 lb $s2 0($s3) #$s2=B[i-1] add $t1,$zero,$s2 #t1=B[i-1] add $s1,$t0,$t1 #A[i]=B[i-1]+B[i] addi $s3,$s3,2 #i+1 lb $s2,0($s3) #s2=B[i+1] add $t2,$zero,$s2 #t2=B[i+1] add $s1,$s1,$t2 #A[i] = t1 + B[i+1] sb $s1 I know this is kind of mess, but it's the best i can write

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• how to specify which child class this object belong to after retrieving from a hashmap?

  - by chandra wibowo

  hi everyone, i have a parent class called Course, and two child class PostgradCourse and UndergradCourse. i have a hashmap HashMap courses; i store all the postgradCourse and undergradCourse objects in the hashmap. i want to retrieve an undergradCourse object from the hashmap using the key. Course course = courses.get(courseCode); then i want to call a method in the UndergradCourse class, setUnits() method course.setUnits(); but the compiler say cannot find symbol- method setUnit() im pretty sure the problem is the compiler is looking for a method setUnit() in the Course class instead of UndergradCourse class i did this but its not working UndergradCourse course = courses.get(courseCode); results in incompatible type so how can i retrieve undergradCourse object from the hashmap as an undergradCourse object instead of course object? so then i can call a method inside the child class thanks in advance

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• facebook extended access token login

  - by Pota Onasys

  I have the following code: $facebook = new Facebook(array( 'appId' => ID, 'secret' => SECRET, 'cookie' => true)); $fb_uid = $facebook->getUser(); if($fb_uid) { // check if person with fb_uid as facebook id in database, // if so log them in. If not, register them. $fb_user = $facebook->api('/' . $fb_uid); I then get their email address using $fb_user['email'] and facebook_id and store in the database as a means to log them in the future Sometimes $fb_uid returns false even though the person is logged in using facebook ... I think it is because the access token expires. how can I change this code to incorporate the extended access token to log in the user to my site? offline access token is deprecated, so I need to use the extended access token.

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• What Database to distribute as part of a C# app backend

  - by jez

  I am planning on writing and commercialising a C# app which will store data in an underlying database I use MySQL on my environment for my own development and this is what I would have used to write the application for myself (no need to use FK - MyISAM engine would be fine). I am concerned about how easy it will be to distribute the app together with the database engine. Would using MySQL allow me for easy packaging of the app for a "one-click" install on the client side? (ie I do not want them to have to install MySQL by themselves) and also is it feasible from a licensing point of view? Are there other Database systems which would make the process more straight-forward

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• Python and database

  - by axl456

  hello.. Am working on a personal project, where i need to manipulate values in a database-like format.. Up until now, am using dictionaries, tuples, and list to store and consult those values. Am thinking about starting to use SQL to manipulate those values, but I dont know if its worth the effort, because I dont know anything about SQL, and I dont want to use something that wont bring me any benefits (if I can do it in a simpler way, i dont want to complicate things) if am only storing and consulting values, what would be the benefit of using SQL? PS: the numbers of row goes between 3 and 100 and the number of columns is around 10 (some may have 5 some may have 10 etc)

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• How to design this simple database?

  - by Vafello

  I have 2 tables - one storing user information (id, username, password) and the second one storing information about events (id, name, description, date, username(represents the user who created the event)). I would like to implement 'favourite events' functionality. This would allow the user to store his favourite events and later display them in a list. I am not sure how to implement this in terms of design. I need a simple solution. Something like storing the IDs of favourite events in a field in the user table. I am using mysql and php. Can anyone point me to the right direction?

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• HTTP headers: Last-Modified - how can it mimimize server load?

  - by gotts

  Imagine the following use case: I use an AJAX request for getting some info about Item and use this URL: http://domain/items/show/1 In my database all items have a field called modified_at where we store the moment when this item was previously modified. How can Last-Modified server HTTP header in response can minimize load/reduce requests/increase responsiveness if we need to process this request every time on the server side? It looks like we don't reduce the number of HTTP requests with that response and we don't reduce the load on server. Who needs this anyway?

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• How can i localize asp.net mvc application using a external assembly

  - by allrast

  i want to create a external dll to store my .resx files. i want to do this because i need to access this files from both presentation and business layers. I have created a external project that contains the default and the es-Es resx files. i have mark it as PublicResXFileCodeGenerator to be able to access it from another dll. on my view i have this test <%=localization.Common.title.ToString() % when i'm run the application i always get this error "Could not find any resources appropriate for the specified culture or the neutral culture. Make sure "localization.Common.resources" was correctly embedded or linked into assembly "localization" at compile time, or that all the satellite assemblies required are loadable and fully signed." i have read some this related to ddl signing... but i don't now if this is the problem.

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• Storing Object Types in Variable then Initializing

  - by Jon Mattingly

  Is there a way in Objective-C to store an object/class in a variable to be passed to alloc/init somewhere else? For example: UIViewController = foo foo *bar = [[foo alloc] init] I'm trying to create a system to dynamically create navigation buttons in a separate class based on the current view controller. I can pass 'self' to the method, but the variable that results does not allow me to alloc/init. I could always import the .h file directly, but ideally I would like to make reusing the code as simple as possible. Maybe I'm going about this the wrong way?

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• Core Data data type for just the date - not including time

  - by Jason

  I am new at Core Data, and it seems like it is a great way to manage the data store. However I am also very memory-conscious due to the fact that the iPhone doesn't have that much of it. I was a little surprised to see that the data types are so limited - eg. there is a Date type which includes also the time, but no Date type for just the date! All the time information takes up precious bytes of memory, if I just wanted an attribute with the date (e.g. 2/15/2010 rather than 2/15/2010 02:34:48), how could I do this? Is it possible?

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• Can getAttribute() method of Tomcat ServletContext implementation be called without synchronization?

  - by oo_olo_oo

  I would like to read some parameters during servlet initializtion (in init() method), and store them among servlet context attributes (using getServletContext().setAttribute()). I would like to read these parameters later - during some request processing (using getServletContext().getAttribute()). So, the multiple threads could do this simultaneously. My question is if such an attempt is safe? Could I be sure that multi threaded calls to the getAttribute() don't mess up any internal state of the servlet context? Please take into account that I'm not going to call the setAttribute() anywhere besides the initialization. So, only calls to the getAttribute() are going to be done from multiple threads. But depending on the internal implementation, this also could be dangerous. So, any information about Tomcat's implementation would be appreciated.

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• Whats the best data-structure for storing 2-tuple (a, b) which support adding, deleting tuples and c

  - by bhups

  Hi So here is my problem. I want to store 2-tuple (key, val) and want to perform following operations: - keys are strings and values are Integers - multiple keys can have same value - adding new tuples - updating any key with new value (any new value or updated value is greater than the previous one, like timestamps) - fetching all the keys with values less than or greater than given value - deleting tuples. Hash seems to be the obvious choice for updating the key's value but then lookups via values will be going to take longer (O(n)). The other option is balanced binary search tree with key and value switched. So now lookups via values will be fast (O(lg(n))) but updating a key will take (O(n)). So is there any data-structure which can be used to address these issues? Thanks.

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• .NET TreeView causes application to crash when trying to check Parent node

  - by alexD

  I have a TreeView with check boxes, and when a user checks a child node, I want to go up the tree and check each parent. However, for some reason my application blows up whenever I touch the parent node. For the nodes in my tree, I've extended TreeNode to create my own objects with some data that I need to store in them, but I still reference them as TreeNodes when checking/unchecking. My code looks like this: //checkBox checked event handler if (node.Parent != null) { checkAllParents(node.Parent); } // private void checkAllParents(TreeNode node) { node.Checked = true; if (node.Parent != null) { checkAllParents(node.Parent); } }

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• Which is the most supported programming language for the iPhone?

  - by Shervin

  Hi. I have decided to start programming some apps for the iPhone that eventually will get submitted to App Store. So I have to use a language the Apple supports. However, from what I understand, there are some variety of languages I can choose from. Ansi C Objective C C C++ I started learning C++ in school back in 2001, so maybe I should use that. However, I would like to use the language that is most supported API and community wize. Which one is that?

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• Extra characters Extracted with XPath and Python (html)

  - by Nacari

  I have been using XPath with scrapy to extract text from html tags online, but when I do I get extra characters attached. An example is trying to extract a number, like "204" from a <td> tag and getting [u'204']. In some cases its much worse. For instance trying to extract "1 - Mathoverflow" and instead getting [u'\r\n\t\t 1 \u2013 MathOverflow\r\n\t\t ']. Is there a way to prevent this, or trim the strings so that the extra characters arent a part of the string? (using items to store the data). It looks like it has something to do with formatting, so how do I get xpath to not pick up that stuff?

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• shell scripting: nested subshell ++

  - by jhon

  Hi guys, more than a problem, this is a request for "another way to do this" actually, if a want to use the result from a previous command I into another one, I use: R1=$("cat somefile | awk '{ print $1 }'" ) myScript -c $R1 -h123 then, a "better way"is: myScript -c $("cat somefile | awk '{ print $1 }'" ) -h123 but, what if I have to use several times the result, let's say: using several times $R1, well the 2 options: option 1 R1=$("cat somefile | awk '{ print $1}'") myScript -c $R1 -h123 -x$R1 option 2 myScript -c $("cat somefile | awk '{ print $1 }'" ) -h123 -x $("cat somefile | awk '{ print $1 }'" ) do you know another way to "store" the result of a previous command/script and use it as a argument into another command/script? thanks

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• PHP/MySQL: Storing and retrieving UUIDS

  - by Greg

  I'm trying to add UUIDs to a couple of tables, but I'm not sure what the best way to store/retrieve these would be. I understand it's far more efficient to use BINARY(16) instead of VARCHAR(36). After doing a bit of research, I also found that you can convert a UUID string to binary with: UNHEX(REPLACE(UUID(),'-','')) Pardon my ignorance, but is there an easy way to this with PHP and then turn it back to a string, when needed, for readability? Also, would it make much difference if I used this as a primary key instead of auto_increment? EDIT: Found part of the answer: $bin = pack("h*", str_replace('-', '', $guid)); How would you unpack it?

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• Need help in translating code from C to Java.

  - by Vuntic

  From this article. Here's the code: float InvSqrt(float x){ // line 0 float xhalf = 0.5f * x; int i = *(int*)&x; // store floating-point bits in integer i = 0x5f3759d5 - (i >> 1); // initial guess for Newton's method x = *(float*)&i; // convert new bits into float x = x*(1.5f - xhalf*x*x); // One round of Newton's method return x; } ...I can't even tell if that's C or C++. [okay apparently it's C, thanks] Could someone translate it to Java for me, please? It's (only, I hope) lines 2 and 4 that are confusing me.

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• Either .each do or .all isn't working how I think it should

  - by user1299656

  So whenever someone rates a shop, I want the Shop model to calculate its new average rating and store that in the database (instead of calculating the average every time someone looks at it). So I wrote the segment of code that follows, and it doesn't work. The loop always iterates exactly once, no matter how many shop_ratings in the database exist that have the shop's id as their shop_id. I played around with it a bit and found that every time a new rating is submitted the function is called successfully, but it only runs the loop once and sets the average to what the first rating was. I don't know if the "query" that sets the ratings variable is wrong or if it's the loop that's wrong. class Shop < ActiveRecord::Base has_many :shop_ratings attr_accessible :name, :latitude, :longitude validates_presence_of :name validates_presence_of :latitude validates_presence_of :longitude def distance_to(lat, long) return (self.longitude - long) + (self.latitude - lat) end def find_average total = 0 count = 0 ratings = ShopRating.all(:conditions => {:shop_id => id}) ratings.each do |submission| total = total + submission.rating count = count + 1 end update_attribute :average_rating, total/count end end

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