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  • Best practices for upgrading user data when updating versions of software

    - by Javy
    In my code I check the current version of the software on launch and compare it to the version stored in the user's data file(s). If the version is newer, then I call different methods to update the old data to the newer data version, if necessary. I usually have to make a new method to convert the data with each update that changes user data in some way, and cannot remove the old ones in case there was someone who missed an update. So the app must be able to go through each method call and update their data until they get their data current. With larger data sets, this could be a problem. In addition, I recently had a brief discussion with another StackOverflow user this and he indicated he always appended a date stamp to the filename to manage data versions, although his reasoning as to why this was better than storing the version data in the file itself was unclear. Since I've rarely seen management of user data versions in books I've read, I'm curious what are the best practices for naming user data files and procedures for updating older data to newer versions.

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  • How to tackle archived who-is personal data with opt-out?

    - by defaye
    As far as I understand it, it is possible to opt-out (in the UK at least) of having your address details displayed on who-is information of a domain for non-trading individuals. What I want to know is, after opt-out, how do individuals combat archived data? Is there any enforcement of this? How many who-is websites are there which archive data and what rights do we have to force them to remove that data without paying absurd fees? In the case of capitulating to these scoundrels, what point is it in paying for the removal of archived data if that data can presumably resurface on another who-is repository? In other words, what strategy is one supposed to take, besides being wiser after the fact?

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  • What is the rationale to not allow overloading of C++ conversions operator with non-member function

    - by Vicente Botet Escriba
    C++0x has added explicit conversion operators, but they must always be defined as members of the Source class. The same applies to the assignment operator, it must be defined on the Target class. When the Source and Target classes of the needed conversion are independent of each other, neither the Source can define a conversion operator, neither the Target can define a constructor from a Source. Usually we get it by defining a specific function such as Target ConvertToTarget(Source& v); If C++0x allowed to overload conversion operator by non member functions we could for example define the conversion implicitly or explicitly between unrelated types. template < typename To, typename From > operator To(const From& val); For example we could specialize the conversion from chrono::time_point to posix_time::ptime as follows template < class Clock, class Duration> operator boost::posix_time::ptime( const boost::chrono::time_point<Clock, Duration>& from) { using namespace boost; typedef chrono::time_point<Clock, Duration> time_point_t; typedef chrono::nanoseconds duration_t; typedef duration_t::rep rep_t; rep_t d = chrono::duration_cast<duration_t>( from.time_since_epoch()).count(); rep_t sec = d/1000000000; rep_t nsec = d%1000000000; return posix_time::from_time_t(0)+ posix_time::seconds(static_cast<long>(sec))+ posix_time::nanoseconds(nsec); } And use the conversion as any other conversion. For a more complete description of the problem, see here or on my Boost.Conversion library.. So the question is: What is the rationale to non allow overloading of C++ conversions operator with non-member functions?

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  • pure-ftpd debian, can't get www-data user working

    - by lynks
    I'm trying to add FTP access to the apache web files, in the past I have done this with an ftpuser and group arrangement. This time I would like to make it possible to login directly as www-data (the default apache user on debian) to make things a bit cleaner. I have checked and re-checked all the common issues; MinUID is set to 1 (www-data has uid 33) www-data has shell set to /bin/bash in /etc/passwd PAMAuthentication is off UnixAuthentication is on I have restarted pure-ftpd using /etc/init.d/pure-ftpd restart My resulting pure-ftpd run is; /usr/sbin/pure-ftpd -l unix -A -Y 1 -u 1 -E -O clf:/var/log/pure-ftpd/transfer.log -8 UTF-8 -B My syslog contains; Oct 7 19:46:40 Debian-60-squeeze-64 pure-ftpd: ([email protected]) [WARNING] Can't login as [www-data]: account disabled And my ftp client is giving me; 530 Sorry, but I can't trust you Am I missing something obvious?

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  • Chef: nested data bag data to template file returns "can't convert String into Integer"

    - by Dalho Park
    I'm creating simple test recipe with a template and data bag. What I'm trying to do is creating a config file from data bag that has simple nested information, but I receive error "can't convert String into Integer" Here are my setting file 1) recipe/default.rb data1 = data_bag_item( 'mytest', 'qa' )['test'] data2 = data_bag_item( 'mytest', 'qa' ) template "/opt/env/test.cfg" do source "test.erb" action :create_if_missing mode 0664 owner "root" group "root" variables({ :pepe1 = data1['part.name'], :pepe2 = data2['transport.tcp.ip2'] }) end 2)my data bag named "mytest" $knife data bag show mytest qa id: qa test: part.name: L12 transport.tcp.ip: 111.111.111.111 transport.tcp.port: 9199 transport.tcp.ip2: 222.222.222.222 3)template file test.erb part.name=<%= @pepe1 % transport.tcp.binding=<%= @pepe2 % Error reurns when I run chef-client on my server, [2013-06-24T19:50:38+00:00] DEBUG: filtered backtrace of compile error: /var/chef/cache/cookbooks/config_test/recipes/default.rb:19:in []',/var/chef/cache/cookbooks/config_test/recipes/default.rb:19:inblock in from_file',/var/chef/cache/cookbooks/config_test/recipes/default.rb:12:in from_file' [2013-06-24T19:50:38+00:00] DEBUG: filtered backtrace of compile error: /var/chef/cache/cookbooks/config_test/recipes/default.rb:19:in[]',/var/chef/cache/cookbooks/config_test/recipes/default.rb:19:in block in from_file',/var/chef/cache/cookbooks/config_test/recipes/default.rb:12:infrom_file' [2013-06-24T19:50:38+00:00] DEBUG: backtrace entry for compile error: '/var/chef/cache/cookbooks/config_test/recipes/default.rb:19:in `[]'' [2013-06-24T19:50:38+00:00] DEBUG: Line number of compile error: '19' Recipe Compile Error in /var/chef/cache/cookbooks/config_test/recipes/default.rb TypeError can't convert String into Integer Cookbook Trace: /var/chef/cache/cookbooks/config_test/recipes/default.rb:19:in []' /var/chef/cache/cookbooks/config_test/recipes/default.rb:19:inblock in from_file' /var/chef/cache/cookbooks/config_test/recipes/default.rb:12:in `from_file' Relevant File Content: /var/chef/cache/cookbooks/config_test/recipes/default.rb: 12: template "/opt/env/test.cfg" do 13: source "test.erb" 14: action :create_if_missing 15: mode 0664 16: owner "root" 17: group "root" 18: variables({ 19 :pepe1 = data1['part.name'], 20: :pepe2 = data2['transport.tcp.ip2'] 21: }) 22: end 23: I tried many things and if I comment out "pepe1 = data1['part.name'],", then :pepe2 = data2['transport.tcp.ip2'] works fine. only nested data "part.name" cannot be set to @pepe1. Does anyone knows why I receive the errors? thanks,

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  • Data recovery on a corrupted 3TB disk

    - by Mark K Cowan
    Short version I probably need software to run a deep-scan recovery (ideally on Linux) to find files on NTFS filesystem. The file data is intact, but the references are no longer present. Analogous to recovering data from a "quick-formatted" partition. Hopefully there is a smarter way available than deep-scan, one which would recover filenames and possibly paths. Long version I have a 3TB disk containing a load of backups. Windows 7 SP1 refused to detect the disk when plugged in directly via SATA, so I put it on a USB/SATA adaptor which seemed to work at first. The SATA/USB adaptor probably does not support disks over 2.2TB though. Windows first asked me if I wanted to 'format' the disk, then later showed me most of the contents but some folder were inaccessible. I stupidly decided to run a CHKDSK on my backup disk, which made the folders accessible but also left them empty. I connected this disk via SATA to my main PC (Arch Linux). I tried: testdisk ntfsundelete ntfsfix --no-action (to look for diagnostically relevant faults, disk was "OK" though) to no avail as the files references in the tables had presumably been zeroed out by CHKDSK, rather than using a typical journal'd deletion). If it is useful at all, a majority of the files that I want to recover are JPEG, Photoshop PSD, and MPEG-3/MPEG-4/AVI/MKV files. If worst comes to worst, I'll just design my own sector scanner and use some simple heuristic-driven analysis to recover raw binary blocks of data from the disk which appears to match the structures of the above file types. I am unfamiliar with the exact workings of NTFS but used to be proficient at recovering FAT32 systems with just a hex-editor, so I can provide any useful diagnostic information if you let me know how to find it! My priorities in ascending order of importance for choosing the accepted answer: Restores directory structure Recovers many filenames in addition to the file data Is free / very cheap Runs on Linux Recovers a majority of file data The last point is the most important, but the more of the higher points you match the more rep you'll probably get :)

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  • Any "Magic Tricks" For Getting Data Back After Windows 7 Install

    - by user163757
    My old man installed Windows 7 without making a proper backup, and now realizes he left behind some important data. He did a true "clean install", so there is no Windows.old folder in the root directory. However, I believe the format performed on the hard drive was only a quick format, so I am hoping there is some chance at data recovery. I took his hard drive out, and have spent a majority of the weekend researching data recovery options. I paid $70 for the GetDataBack software, but have had little success with it. I can see all of the files I want to restore, however they appear corrupt when I try to open them. With that all being said, does anyone know of a viable way to recover some of this data, or is it a lost cause all together?

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  • raid 0 data recovery?

    - by Fred
    HI All, I have two identical seagate 7200.9 500Gb drives confiured as a RAID 0 spanned disk in windows. One of the drives has lost power and wont spin up at all. I know this normally means death for the data on both drives but i have a cunning plan.. DISK 1 - NO POWER RAID 0 DISK DISK 2 - FULLY FUNCTIONAL RAID 0 DISK DISK 3 - FULLY FUNCTIONAL SPARE DISK Copy the working drive (disk 2) data to a third 500GB DISK (disk 3), remove the logic board from the working disk (disk 2) and replace it with the non working logic board on the broken drive (disk 1) , then hopefully recreate the RAID 0 with disk 1 and disk 3, just long enough to get the data off it. Hope this makes sense, here are my questions: Windows disk manager atm recognises disk 2 but wont let me access it in anyway, therefore copying the data off it (or getting a disk image) cant be done in windows. Does anyone know of any software (in linux or self booting) that would allow me to access this disk? Anyone know of any software that will recreate the spanned drive off two disk images Am i missing any key information that means i definitely shouldn't even bother starting this, i know its a long shot anyway but its worth a try unless i definitely cant do it. The irritating thing is that i am sure its a logic board failure on disk 1 as it simply wont power up at all, suddenly no signs of life, so i am sure the data is intact! Any help would be really appreciated! Thanks

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  • Data take on with Drupal 6

    - by Robert MacLean
    We are migrating our current intranet to Drupal 6 and there is a lot of data within the current system which can be classified into: List data, general lists of fields. Common use is phone list of the employees phone numbers. Document repository. Just basically a web version of a file share for documents. I can easily get the data + meta infomation out, but how do I bulk upload the two types of data into Drupal, as uploading the hundred of thousands of items manually is just not acceptable.

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  • Summing up spreadsheet data when a column contains “#N/A”

    - by Doris
    I am using Goggle Spreadsheet to work up some historical stock data and I use a Google function (=googlefinance=…) to import the historical closing prices for a stock, then I work with that data further. But, in that list of data generated from the =googlefinance=… function, one of the amounts comes up as #N/A. I don’t know why, but it happens for various symbols that I have tried. When I use a max function on the array, which includes the N/A line, the max function does not come up with anything but an N/A, so the N/A throws off any further functions. I thought I’d create a second column to the right of the imported data in which I can give it an IF function, something like, If ((A1 <0), "0", A1), with the expectation that it would return 0 if cell A1 is the N/A, and the cell value if it is not N/A. However, this still returns N/A. I also tried an IS BLANK function but that resulted in the same NA. Does anyone have any suggestions for a workaround to eliminate the N/A from an array of numbers that I am trying to work with?

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  • Cocos2d-x v3 invalid conversion from 'cocos2d::Layer* [on hold]

    - by Hammerh5
    Hello guys I'm learning cocos2d-x v3 right but most of the code that I can find is to the version 2. My specific error is this one, when I try to compile my cocos2s-x 3 project this error shows. invalid conversion from 'cocos2d::Layer to Game* [-fpermisive]* What I want to do is create a new game scene in the following code: //Game.cpp #include "Game.h" Scene* Game::scene() { scene *sc = CCScene::create(); sc->setTag(TAG_GAME_SCENE); const Game *g = Game::create(); //Here is where the conversions fails. sc->addChild(g, 0, TAG_GAME_LAYER); return sc; } Of course this is my header file //Game.h #include "cocos2d.h" #include "Mole.h" #include "AppDelegate.h" using namespace cocos2d; class Game: public cocos2d::Layer { cocos2d::CCArray *moles; float timeBetweenMoles, timeElapsed, increaseMolesAtTime, increaseElapsed, lastMoleHiTime; int molesAtOnce; cocos2d::CCSize s; bool isPaused; public: CCString *missSound, *hitSound; static cocos2d::Scene* scene(); virtual bool init(); void showMole(); void initializeGame(); void onEnterTransitionDidFinish(); void onExit(); void onTouchesBegan(const std::vector<cocos2d::Touch *> &touches, cocos2d::Event *event); void tick(float dt); cocos2d::CCArray* getMoles(bool isUp); //LAYER_CREATE_FUNC(Game); }; #endif /* GAME_H_ */ I don't know what's wrong I suppose this code works fine in Cocos2d-x v2. It's maybe some changes in the C++ version ?

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  • TDWI World Conference Features Oracle and Big Data

    - by Mandy Ho
    Oracle is a Gold Sponsor at this year's TDWI World Conference Series, held at the Manchester Grand Hyatt in San Diego, California - July 31 to Aug 1. The theme of this event is Big Data Tipping Point: BI Strategies in the Era of Big Data. The conference features an educational look at how data is now being generated so quickly that organizations across all industries need new technologies to stay ahead - to understand customer behavior, detect fraud, improve processes and accelerate performance. Attendees will hear how the internet, social media and streaming data are fundamentally changing business intelligence and data warehousing. Big data is reaching critical mass - the tipping point. Oracle will be conducting the following Evening Workshop. To reserve your space, call 1.800.820.5592 ext 10775. Title...:    Integrating Big Data into Your Data Center (or A Big Data Reference Architecture) Date.:    Wed., August 1, 2012, at 7:00 p.m Venue:: Manchester Grand Hyatt, San Diego, Room Weblogs, Social Media, smart meters, senors and other devices generate high volumes of low density information that isn't readily accessible in enterprise data warehouses and business intelligence applications today. But, this data can have relevant business value, especially when analyzed alongside traditional information sources. In this session, we will outline a reference architecture for big data that will help you maximize the value of your big data implementation. You will learn: The key technologies in a big architecture, and their specific use case The integration point of the various technologies and how they fit into your existing IT environment How effectively leverage analytical sandboxes for data discovery and agile development of data driven solutions   At the end of this session you will understand the reference architecture and have the tools to implement this architecture at your company. Presenter: Jean-Pierre Dijcks, Senior Principal Product Manager Don't miss our booth and the chance to meet with our Big data experts on the exhibition floor at booth #306. 

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  • How do you encode Algebraic Data Types in a C#- or Java-like language?

    - by Jörg W Mittag
    There are some problems which are easily solved by Algebraic Data Types, for example a List type can be very succinctly expressed as: data ConsList a = Empty | ConsCell a (ConsList a) consmap f Empty = Empty consmap f (ConsCell a b) = ConsCell (f a) (consmap f b) l = ConsCell 1 (ConsCell 2 (ConsCell 3 Empty)) consmap (+1) l This particular example is in Haskell, but it would be similar in other languages with native support for Algebraic Data Types. It turns out that there is an obvious mapping to OO-style subtyping: the datatype becomes an abstract base class and every data constructor becomes a concrete subclass. Here's an example in Scala: sealed abstract class ConsList[+T] { def map[U](f: T => U): ConsList[U] } object Empty extends ConsList[Nothing] { override def map[U](f: Nothing => U) = this } final class ConsCell[T](first: T, rest: ConsList[T]) extends ConsList[T] { override def map[U](f: T => U) = new ConsCell(f(first), rest.map(f)) } val l = (new ConsCell(1, new ConsCell(2, new ConsCell(3, Empty))) l.map(1+) The only thing needed beyond naive subclassing is a way to seal classes, i.e. a way to make it impossible to add subclasses to a hierarchy. How would you approach this problem in a language like C# or Java? The two stumbling blocks I found when trying to use Algebraic Data Types in C# were: I couldn't figure out what the bottom type is called in C# (i.e. I couldn't figure out what to put into class Empty : ConsList< ??? >) I couldn't figure out a way to seal ConsList so that no subclasses can be added to the hierarchy What would be the most idiomatic way to implement Algebraic Data Types in C# and/or Java? Or, if it isn't possible, what would be the idiomatic replacement?

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  • Why is my ServiceOperation method missing from my WCF Data Services client proxy code?

    - by Kev
    I have a simple WCF Data Services service and I want to expose a Service Operation as follows: [System.ServiceModel.ServiceBehavior(IncludeExceptionDetailInFaults = true)] public class ConfigurationData : DataService<ProductRepository> { // This method is called only once to initialize service-wide policies. public static void InitializeService(IDataServiceConfiguration config) { config.SetEntitySetAccessRule("*", EntitySetRights.ReadMultiple | EntitySetRights.ReadSingle); config.SetServiceOperationAccessRule("*", ServiceOperationRights.All); config.UseVerboseErrors = true; } // This operation isn't getting generated client side [WebGet] public IQueryable<Product> GetProducts() { // Simple example for testing return (new ProductRepository()).Product; } Why isn't the GetProducts method visible when I add the service reference on the client?

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  • How to Convert multiple sets of Data going from left to right to top to bottom the Pythonic way?

    - by ThinkCode
    Following is a sample of sets of contacts for each company going from left to right. ID Company ContactFirst1 ContactLast1 Title1 Email1 ContactFirst2 ContactLast2 Title2 Email2 1 ABC John Doe CEO [email protected] Steve Bern CIO [email protected] How do I get them to go top to bottom as shown? ID Company Contactfirst ContactLast Title Email 1 ABC John Doe CEO [email protected] 1 ABC Steve Bern CIO [email protected] I am hoping there is a Pythonic way of solving this task. Any pointers or samples are really appreciated! p.s : In the actual file, there are 10 sets of contacts going from left to right and there are few thousand such records. It is a CSV file and I loaded into MySQL to manipulate the data.

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  • How to add data manually in core data entity

    - by pankaj
    Hi I am working on core data for the first time. I have just created an entity and attributes for that entity. I want to add some data inside the entity(u can say i want to add data in a table), earlier i when i was using sqlite, i would add data using terminal. But here in core data i am not able to find a place where i can manually add data. I just want to add data in entity and display it in a UITableView. I have gone through the the documentation of core data but it does not explain how to add data manually although it explains how i can add it programmiticaly but i dont need to do it programically. I want to do it manually. Thanks in advance

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  • How can I perform a web query in C# similar to the Data > Import External Data > New Web Query in Mi

    - by TNT
    I need to pull data from a table on a website. I can easily do this in VBA using the Web Query, but I need to do this in C#. I'm just having some trouble figuring out how to properly convert the code. I got something close, but it's returning HTML with the data. I just want the data. Any help would be great. The block of code giving me issues is below: Private Function GetData(ByVal theURL As String, ByVal theRow As Integer, ByVal thePosition As Integer, ByVal theColumn As String, ByVal theTable As Integer) With ActiveSheet.QueryTables.Add(Connection:="URL;" + theURL, Destination:=Sheet2.Range(theColumn & theRow + 1)) .Name = "op?s=" + Mid(theURL, thePosition + 1) + "_1" .PreserveFormatting = True .AdjustColumnWidth = True .WebTables = theTable .Refresh BackgroundQuery:=False End With End Function

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  • How do I set default values on new properties for existing entities after light weight core data migration?

    - by Moritz
    I've successfully completed light weight migration on my core data model. My custom entity Vehicle received a new property 'tirePressure' which is an optional property of type double with the default value 0.00. When 'old' Vehicles are fetched from the store (Vehicles that were created before the migration took place) the value for their 'tirePressure' property is nil. (Is that expected behavior?) So I thought: "No problem, I'll just do this in the Vehicle class:" - (void)awakeFromFetch { [super awakeFromFetch]; if (nil == self.tirePressure) { [self willChangeValueForKey:@"tirePressure"]; self.tirePressure = [NSNumber numberWithDouble:0.0]; [self didChangeValueForKey:@"tirePressure"]; } } Since "change processing is explicitly disabled around" awakeFromFetch I thought the calls to willChangeValueForKey and didChangeValueForKey would mark 'tirePresure' as dirty. But they don't. Every time these Vehicles are fetched from the store 'tirePressure' continues to be nil despite having saved the context.

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  • How do you verify the correct data is in a data mart?

    - by blockcipher
    I'm working on a data warehouse and I'm trying to figure out how to best verify that data from our data cleansing (normalized) database makes it into our data marts correctly. I've done some searches, but the results so far talk more about ensuring things like constraints are in place and that you need to do data validation during the ETL process (E.g. dates are valid, etc.). The dimensions were pretty easy as I could easily either leverage the primary key or write a very simple and verifiable query to get the data. The fact tables are more complex. Any thoughts? We're trying to make this very easy for a subject matter export to run a couple queries, see some data from both the data cleansing database and the data marts, and visually compare the two to ensure they are correct.

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  • What is a good approach for a Data Access Layer?

    - by Adil Mughal
    Our software is a customized Human Resource Management System (HRMS) using ASP.NET with Oracle as the database and now we are actually moving to make it a product that supports multiple tenants with their own databases. Our options: Use NHibernate to support Multiple databases and use of OO. But we concern related to NHibernate learning curve and any problem we faced. Make a generalized DAL which will continue working with Oracle using stored procedures and use tools to convert it to other databases such as SQL Server or MySql. There is a risk associated with having to support multiple database-dependent versions of a single script. Provide the software as a Service (SaaS) and maintain the way we conduct business. However there can may be clients who do not want or trust the Cloud or other SaaS business models. With this in mind, what's the best Data access layer technique?

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  • Select data from three different tables with null data

    - by user3678972
    I am new in Sql. My question is how to get data from three different tables with null values. I have tried a query as below: SELECT * FROM [USER] JOIN [Location] ON ([Location].UserId = [USER].Id) JOIN [ParentChild] ON ([ParentChild].UserId = [USER].Id) WHERE ParentId=7 which I find from this link. Its working fine but, it not fetches all and each data associated with the ParentId Something like it only fetches data which are available in all tables, but also omits some data which not available in Location tables but it comes under the given ParentId. For example: UserId ParentId 1 7 8 7 For userId 8, there is data available in Location table,so it fetches all data. But there is no data for userId 1 available in Location table, so the query didn't work for this. But I want all and every data. If there is no data for userId then it can return only null columns. Is it possible ?? hope everyone can understand my problem.

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  • How can I make the output from tapply() into a data.frame

    - by James Thompson
    I have a data.frame in R that looks like this: score rms template aln_id description 1 -261.410 4.951 2f22A.pdb 2F22A_1 S_00001_0000002_0 2 -231.987 21.813 1wb9A.pdb 1WB9A_4 S_00002_0000002_0 3 -263.722 4.903 2f22A.pdb 2F22A_3 S_00003_0000002_0 4 -269.681 17.732 1wbbA.pdb 1WBBA_6 S_00004_0000002_0 5 -258.621 19.098 1rxqA.pdb 1RXQA_3 S_00005_0000002_0 6 -246.805 6.889 1rxqA.pdb 1RXQA_15 S_00006_0000002_0 7 -281.300 16.262 1wbdA.pdb 1WBDA_11 S_00007_0000002_0 8 -271.666 4.193 2f22A.pdb 2F22A_2 S_00008_0000002_0 9 -277.964 13.066 1wb9A.pdb 1WB9A_5 S_00009_0000002_0 10 -261.024 17.153 1yy9A.pdb 1YY9A_2 S_00001_0000003_0 I can calculate summary statistics on the data.frame like this: > tapply( d$score, d$template, mean ) 1rxqA.pdb 1wb9A.pdb 1wbbA.pdb 1wbdA.pdb 1yy9A.pdb 2f22A.pdb -252.7130 -254.9755 -269.6810 -281.3000 -261.0240 -265.5993 Is there an easy way that I coerce this output back into a data.frame? I'd like for it to have these two columns: d$template mean I love tapply, but right now I'm cutting and pasting the results from tapply into a text file and hacking it up a bit to get the summary statistics that I want with appropriate names. This feels very wrong, and I'd like to do something better!

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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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  • How to handle encryption key conflicts when synchronizing data?

    - by Rafael
    Assume that there is data that gets synchronized between several devices. The data is protected with a symmetric encryption algorithm and a key. The key is stored on each device and encrypted with a password. When a user changes the password only the key gets re-encrypted. Under normal circumstances, when there is a good network connection to other peers, the current key gets synchronized and all data on the new device gets encrypted with the same key. But how to handle situations where a new device doesn’t have a network connection and e.g. creates its own new, but incompatible key? How to keep the usability as high as possible under such circumstances? The application could detect that there is no network and hence refuse to start. That’s very bad usability in my opinion, because the application isn’t functional at all in this case. I don’t consider this a solution. The application could ignore the missing network connection and create a new key. But what to do when the application gains a network connection? There will be several incompatible keys and some parts of the underlying data could only be encrypted with one key and other parts with another key. The situation would get worse if there would be more keys than just two and the application would’ve to ask every time for a password when another object that should get decrypted with another key would be needed. It is very messy and time consuming to try to re-encrypt all data that is encrypted with another key with a main key. What should be the main key at all in this case? The oldest key? The key with the most encrypted objects? What if the key got synchronized but not all objects that got encrypted with this particular key? How should the user know for which particular password the application asks and why it takes probably very long to re-encrypt the data? It’s very hard to describe encryption “issues” to users. So far I didn’t find an acceptable solution, nor some kind of generic strategy. Do you have some hints about a concrete strategy or some books / papers that describe synchronization of symmetrically encrypted data with keys that could cause conflicts?

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  • What exactly are administrative redexes after CPS conversion?

    - by eljenso
    In the context of Scheme and CPS conversion, I'm having a little trouble deciding what administrative redexes (lambdas) exactly are: all the lambda expressions that are introduced by the CPS conversion only the lambda expressions that are introduced by the CPS conversion but you wouldn't have written if you did the conversion "by hand" or through a smarter CPS-converter If possible, a good reference would be welcome.

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