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• Secondary keys in a B-tree

  - by Phenom

  Let's say that there is a file that contains an unsorted list of student information, which includes a student ID number as well as other information. I want to make a program that retrieves student information based on student ID number. In order to make it efficient, I store the student IDs in a B-tree. So when I enter a student ID number, it searches the B-tree to see if its there or not. It also does one more thing. If it finds the student ID number, then it also returns where in the file that student's information is. This is the secondary key. The program uses this information to locate the rest of the student's information and prints it to screen. Can this be done? Is this how a b-tree works?

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• Objects instead of global variables in Perl

  - by Gaurav Dadhania

  I don't know if this is the right thing to do. But I'm lookig for tutorials/articles on using objects instead of global variables to store state. For eg. package something # some code here... # that generates errors and uses # something::errors to track errors. package something::errors sub new { my ($this) = @_; bless $this; return $this; } sub setErrors{ my ($this, @errors) = @_; $this->{errors} = \@errors; } sub getErrors{ my ($this) = @_; return $this->{errors}; } Is this better than using global varibles? Any down-sides to this? Any approach which might be better? Thanks.

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• Need help specifying a ending while condition

  - by johnthexiii

  I have written a Python script to download all of the xkcd comic images. The only problem is I can't tell it to stop when it gets to the last one... Here is what I have so far. import re, mechanize from urllib import urlretrieve from BeautifulSoup import BeautifulSoup as bs baseUrl = "http://xkcd.com/1/" #Specify the first comic page br = mechanize.Browser() #Create a browser response = br.open(baseUrl) #Create an initial response x = 1 #Assign an initial file name while (SomeCondition): soup = bs(response.get_data()) #Create an instance of bs that contains the response data img = soup.findAll('img')[1] #Get the online file path of the image localFile = "C:\\Comics\\xkcd\\" + str(x) + ".jpg" #Come up with a local file name urlretrieve(img["src"], localFile) #Download the image file response = br.follow_link(text = "Next >") #Store the response of the next button x += 1 #Increase x by 1 print "All xkcd comics downloaded" #Let the user know the images have been downloaded Initially what I had was something like while br.follow_link(text = "Next >") != br.follow_link(text = ">|"): but by doing this I actually send skip to the last page before the script has a chance to perform the intended purpose.

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• Enumerable.Range in and Expression and Entity Framework

  - by eka808

  I'm currently developping an expression method (used in linq to entity queries) who has to give me a daycount for a given period (start date and end date) decrementing this daycount if specials days are in the period. My idea was the following : Generate an enumerable with all the dates (and with Enumerable.Range) Make a .Where on this enumerable to remove the specials dates Like a MyEnumerable.Where(a = a != "20120101") After that, return a MyEnumerable.Count() I come with this code : return (p) => Enumerable .Range(1, 4) .Where(a => a != 20120101) .AsQueryable() .Count() I tried to cast as a list, as a queryable, both (like the example) and no way ! it doesn't work ! I always get this error : LINQ to Entities does not recognize the method 'System.Collections.Generic.IEnumerable`1[System.Int32] Range(Int32, Int32)' method, and this method cannot be translated into a store expression. Have you got an idea about that ? Using an enumerable is of course not mandatory, any working solutions is good ^^ Thank's by advance !

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• In ASP.NET, can too many CacheDependency instances affect scalability?

  - by frankadelic

  I am building an ASP.NET application. Within each ASPX page, we are outputting inline snippets of HTML that are pulled from static text files. Similar to the example shown here: http://www.dotnetcurry.com/ShowArticle.aspx?ID=331 As in the article, we store the contents of the files in HttpRuntime.Cache with a CacheDependency pointing to the included file. For each cached file, the operating system needs to monitor a file for changes. Is this going to be a potential scalability problem? Does Windows 2008 have a maximum number of file change monitors?

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• C++ containers on classes, returning pointers

  - by otneil

  Hello, I'm having some trouble to find the best way to accomplish what I have in mind due to my inexperience. I have a class where I need to a vector of objects. So my first question will be: is there any problem having this: vector< AnyType container* and then on the constructor initialize it with new (and deleting it on the destructor)? Another question is: if this vector is going to store objects, shouldn't it be more like vector< AnyTipe* so they could be dynamically created? In that case how would I return an object from a method and how to avoid memory leaks (trying to use only STL)?

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• Cookies ignored on Apache/Magento installation

  - by Laizer

  I'm running a Magento based website store on Linux/Apache. In order that user logins are maintained, I've set my cookie lifetime to be close to two years. The cookies are sent out with the right times, I can see them in my browsers. When I visit the site from a previously logged-in browser after about a day, the user is logged out. I can still see the cookies, with their extended life, present in the browser. Where should I start looking to get to the bottom of this issue?

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• Indexed key vs indexed separate columns, which one is faster ?

  - by Jerry

  In MYSQL, from a pure performance perspective, if I have a table with large amount of data with 10/1 read/write ratio. is it faster in read/write performance to have 4 search criteria in separate columns and all indexed or have them combined in to one single string acting as a key and store in one indexed column ? e.g. say this table with 5 columns, first name, last name, sex, country and file where the first four columns will ALWAYS be given as a part of search parameters in a search or have a table with two columns, key and file. where the value of key can be john-smith-male-australia ?? I don't quite get the pros and cons. the point I try to stress is the fact that all parameters will be given.in a search.

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• Result of Long Positive Integers & Search and element in array..

  - by AGeek

  Hi, I have two Questions for which I cannot find answers by googling, but I find these questions very important for preparation.. Kindly explain only the logic, I will be able to code. In Search of Efficient Logic..... in terms of Memory and Time. WAP to add two long positive integers. What Data structure / data type we can use to store the numbers and result. What is the best way to search an element from an array in shortest time. Size of the array could be large enough, and any elements could be stored in the array(i.e. no range). Thanks.

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• A 4-byte Unsigned Int for Sql Server 2008?

  - by Jeff Meatball Yang

  I understand there are multiple questions about this on SO, but I have yet to find a definitive answer of "yes, here's how..." So here it is again: What are the possible ways to store an unsigned integer value (32-bit value or 32-bit bitmap) into a 4-byte field in SQL Server? Here are ideas I have seen: 1) Use a -1*2^31 offset for all values Disadvantages: need to perform math on the values before reading/writing/aggregating. 2) Use 4 tinyint fields Disadvantages: need to concatenate values to perform any operations 3) Use binary(4) Disadvantages: actually uses 4 + 2 bytes of space

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• Using the same CArchive object for archive and un-archive

  - by bdhar

  Following is a sample code: CFile serFile; serFile.Open(_T("Person.ser"), CFile::modeCreate | CFile::modeWrite); CArchive writer(&serFile, CArchive::store); me.Serialize(writer); writer.Close(); serFile.Close(); serFile.Open(_T("Person.ser"), CFile::modeRead); CArchive reader(&serFile, CArchive::load); CPerson clone; clone.Serialize(reader); reader.Close(); serFile.Close(); Here, I have a writer which archives the object me. Then, I use another CArchive object reader to un-archive it. Is it possible to re-construct or set any property of writer to make it, the reader instead of declaring another CArchive object reader? Thanks.

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• Can you use MongoDB map/reduce to migrate data?

  - by Brian Armstrong

  I have a large collection where I want to modify all the documents by populating a field. A simple example might be caching the comment count on each post: class Post field :comment_count, type: Integer has_many :comments end class Comment belongs_to :post end I can run it in serial with something like: Post.all.each do |p| p.udpate_attribute :comment_count, p.comments.count end But it's taking 24 hours to run (large collection). I was wondering if mongo's map/reduce could be used for this? But I haven't seen a great example yet. I imagine you would map off the comments collection and then store the reduced results in the posts collection. Am I on the right track?

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• How does Core Data determine if an NSObjects data can be dropped?

  - by Kevin

  In the app I am working on now I was storing about 500 images in Core Data. I have since pulled those images out and store them in the file system now, but in the process I found that the app would crash on the device if I had an array of 500 objects with image data in them. An array with 500 object ids with the image data in those objects worked fine. The 500 objects without the image data also worked fine. I found that I got the best performance with both an array of object ids and image data stored on the filesystem instead of in core data. The conclusion I came to was that if I had an object in an array that told Core Data I was "using" that object and Core Data would hold on to the data. Is this correct?

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• Basic Hibernate question using and sql query

  - by Aerosteak

  Hello Sorry if this is basic but I cannot find the solution anywhere. I have an java Object ‘Person’ with 3 properties firstname,lastname and username. I have an Oracle Store procedure returning a Resultset with the 3 column. All works fine for that. Now I have another StoreProcedure that will only return firstname and lastname but not username. I get the following error : « could not read column value from result set username. » Hibernate tries to fetch the username property from the resultset. If I remove the property username, then it works. Do I have to Create a Special Pojo for Each type of resultset or can I tell Hibernate what to map for each result set? Please help.

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• Javascript eval limits

  - by user117701

  Is there a limit to javascript's eval, like in lenght? I'm trying to build an app where you can store JS code in the DB, which you can later load and eval in order to execute it, but i'm reaching a limit. First of all, the code has to all be in one line. Any multiline statements are not executed. Next, i'm reaching a limit in length (i guess). If i execute the code manually, it works, but put that same code in the db, load it via ajax, and try to execute it, and it fails. Any ideas why?

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• Using CouchDB to serve HTML.

  - by alxross

  I'm trying to use CouchDB with HTML/standalone REST architecture. That is, no other app server other than CouchDB and ajax style javascript calling CouchDB. It looks like cross scripting is a problem. I was using Cloudkit/Tokyo Cabinet before and it seems like the needed callback function was screwing it up in the URL. Now I'm trying CouchDB and getting the same problem. Here are my questions: 1) Are these problems because the REST/JSON store like CouchDB or CloudKit is running on a different port from my web page? They're both run locally and called from "localhost". 2) Should I let CouchDB host my page and serve the HTML? 3) How do I do this? The documentation didnt seem so clear... Thanks, Alex

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• Human readable URL causes a problem in Ruby on Rails

  - by TK

  I have a basic CRUD with "Company" model. To make the company name show up, I did def to_param name.parameterize end Then I accessed http://localhost:3000/companies/american-express which runs show action in the companies controller. Obviously this doesn't work because the show method is as following: def show @company = Company.find_by_id(params[:id]) end The params[:id] is american-express. This string is not stored anywhere. Do I need to store the short string (i.e., "american-express") in the database when I save the record? Or is there any way to retrieve the company data without saving the string in the database?

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• ODBC Storage Size

  - by dcp3450

  I'm pulling a lot of text from a MS SQL Server database. I'm not getting all the text (which includes some html. The text is stored perfectly on the database. However, when I run the query to get the data It will only pull part of the text. I pull the data using odbc_exec and store using $variable = odbc_result($runquery,"body"). if i display the content with odbc_result_all($runquery) i get part of the content. if I use echo $body; i get part of the content then some garbage and part of the text from the begining. very strange response. Is there a size limit? Any ideas what I'm missing here?

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• why Observable snapshot observer vector

  - by han14466

  In Observable's notifyObservers method, why does the coder use arrLocal = obs.toArray();? Why does not coder iterate vector directly? Thanks public void notifyObservers(Object arg) { Object[] arrLocal; synchronized (this) { /* We don't want the Observer doing callbacks into * arbitrary code while holding its own Monitor. * The code where we extract each Observable from * the Vector and store the state of the Observer * needs synchronization, but notifying observers * does not (should not). The worst result of any * potential race-condition here is that: * 1) a newly-added Observer will miss a * notification in progress * 2) a recently unregistered Observer will be * wrongly notified when it doesn't care */ if (!changed) return; arrLocal = obs.toArray(); clearChanged(); } for (int i = arrLocal.length-1; i>=0; i--) ((Observer)arrLocal[i]).update(this, arg); }

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• Are there any Objective-C / Cocoa naming conventions for properties that are acronyms?

  - by t6d

  I have an object that models an online resource. Therefore, my object has to store the URL of the resource it belongs to. How would I name the getter and setter? MyObject *myObject = [[MyObject alloc] init]; // Set values [myObject setURL:url]; myObject.URL = url; // Get values [myObject URL]; myObject.URL; or would the following be better: MyObject *myObject = [[MyObject alloc] init]; // Set values [myObject setUrl:url]; myObject.url = url; // Get values [myObject url]; myObject.url; The former example would of course require to define the property in the following way: @property (retain, getter = URL, setter = setURL:) NSURL *url;

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• R: how to make a unique set of names from a vector of strings?

  - by Mike Dewar

  Hi, I have a vector of strings. Check out my vector, it's awesome: > awesome [1] "a" "b" "c" "d" "d" "e" "f" "f" I'd like to make a new vector that is the same length as awesome but where, if necessary, the strings have been uniqueified. For example, a valid output of my desired function would be > awesome.uniqueified [1] "a" "b" "c" "d.1" "d.2" "e" "f.1" "f.2" Is there an easy, R-thonic and beautiful way to do this? I should say my list in real life (it's not called awesome) contains 25000ish mircoarray probeset identifiers. I'm always nervous when I embark on writing little generic functions (which I'm sure I could do) as I'm sure some R guru has come across this problem in the past, nailed it with some incredible algorithm that doesn't even have to store more than half an element in the vector. I'm just not sure what they might have called it. Probably not uniqueify.

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• JDO Exception in google app engine transaction

  - by Mariselvam

  I am getting the following exception while trying to use transation in app engine datastore. javax.jdo.JDOUserException: Transaction is still active. You should always close your transactions correctly using commit() or rollback(). FailedObject:org.datanucleus.store.appengine.jdo.DatastoreJDOPersistenceManager@12bbe6b at org.datanucleus.jdo.JDOPersistenceManager.close(JDOPersistenceManager.java:277) The following is the code snippet I used : List<String> friendIds = getFriends(userId); Date currentDate = new Date(); PersistenceManager manager = pmfInstance.getPersistenceManager(); try { Transaction trans = manager.currentTransaction(); trans.begin(); for(String friendId : friendIds) { User user = manager.getObjectById(User.class, friendId); if(user != null) { user.setRecoCount(user.getRecoCount() + 1); user.setUpdatedDate(currentDate); manager.makePersistent(user); } } trans.commit(); } finally { manager.close(); }

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• django modeling

  - by SledgehammerPL

  Concept: Drinks are made of components. E.g. 10ml of Vodka. In some receipt the component is very particular (10ml of Finlandia Vodka), some not (10 ml of ANY Vodka). I wonder how to model a component to solve this problem - on stock I have particular product, which can satisfy more requirements. The model for now is: class Receipt(models.Model): name = models.CharField(max_length=128) (...) components = models.ManyToManyField(Product, through='ReceiptComponent') def __unicode__(self): return self.name class ReceiptComponent(models.Model): product = models.ForeignKey(Product) receipt = models.ForeignKey(Receipt) quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) class Admin: pass def __unicode__(self): return unicode(self.quantity!=0 and self.quantity or '') + ' ' + unicode(self.unit) + ' ' + self.product.genitive class Product(models.Model): name = models.CharField(max_length = 128) (...) class Admin: pass def __unicode__(self): return self.name class Stock(Store): products = models.ManyToManyField(Product) class Admin: pass def __unicode__(self): return self.name I think about making some table which joins real product (on stock) with abstract product (receiptcomponent). But maybe there's easy solution?

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• Relational databases are not suited for my application - what's the alternative?

  - by waitinforatrain

  Hi, I'm writing a CMS in PHP that allows the user to define different fields (e.g. a Blog page could have fields for Title (string), Content (rich text), Picture (file)). I need the user to be able to add and remove fields dynamically, and the only way I can think of to do it with relational DBs is to serialise all these values and store them in one cell. This seems like a slow approach and like I'm trying to fit something dynamic within a static structure. Could someone recommend anything that is PHP-compatible that would make this easier?

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• Invoking a superclass's class methods in Python

  - by LeafStorm

  I am working on a Flask extension that adds CouchDB support to Flask. To make it easier, I have subclassed couchdb.mapping.Document so the store and load methods can use the current thread-local database. Right now, my code looks like this: class Document(mapping.Document): # rest of the methods omitted for brevity @classmethod def load(cls, id, db=None): return mapping.Document.load(cls, db or g.couch, id) I left out some for brevity, but that's the important part. However, due to the way classmethod works, when I try to call this method, I receive the error message File "flaskext/couchdb.py", line 187, in load return mapping.Document.load(cls, db or g.couch, id) TypeError: load() takes exactly 3 arguments (4 given) I tested replacing the call with mapping.Document.load.im_func(cls, db or g.couch, id), and it works, but I'm not particularly happy about accessing the internal im_ attributes (even though they are documented). Does anyone have a more elegant way to handle this?

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