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• Avoid an "out of memory error" in Java(eclipse), when using large data structure?

  - by gnomed

  OK, so I am writing a program that unfortunately needs to use a huge data structure to complete its work, but it is failing with a "out of memory error" during its initialization. While I understand entirely what that means and why it is a problem, I am having trouble overcoming it, since my program needs to use this large structure and I don't know any other way to store it. The program first indexes a large corpus of text files that I provide. This works fine. Then it uses this index to initialize a large 2D array. This array will have nXn entries, where "n" is the number of unique words in the corpus of text. For the relatively small chunk I am testing it on(about 60 files) it needs to make approximately 30,000x30,000 entries. this will probably be bigger once I run it on my full intended corpus too. It consistently fails every time, after it indexes, while it is initializing the data structure(to be worked on later). Things I have done include: revamp my code to use a primitive "int[]" instead of a "TreeMap" eliminate redundant structures, etc... Also, I have run eclipse with "eclipse -vmargs -Xmx2g" to max out my allocated memory I am fairly confident this is not going to be a simple line of code solution, but is most likely going to require a very new approach. I am looking for what that approach is, any ideas? Thanks, B.

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• Most elegant way to break CSV columns into separate data structures using Python?

  - by Nick L

  I'm trying to pick up Python. As part of the learning process I'm porting a project I wrote in Java to Python. I'm at a section now where I have a list of CSV headers of the form: headers = [a, b, c, d, e, .....] and separate lists of groups that these headers should be broken up into, e.g.: headers_for_list_a = [b, c, e, ...] headers_for_list_b = [a, d, k, ...] . . . I want to take the CSV data and turn it into dict's based on these groups, e.g.: list_a = [ {b:val_1b, c:val_1c, e:val_1e, ... }, {b:val_2b, c:val_2c, e:val_2e, ... }, {b:val_3b, c:val_3c, e:val_3e, ... }, . . . ] where for example, val_1b is the first row of the 'b' column, val_3c is the third row of the 'c' column, etc. My first "Java instinct" is to do something like: for row in data: for col_num, val in enumerate(row): col_name = headers[col_num] if col_name in group_a: dict_a[col_name] = val elif headers[col_cum] in group_b: dict_b[col_name] = val ... list_a.append(dict_a) list_b.append(dict_b) ... However, this method seems inefficient/unwieldy and doesn't posses the elegance that Python programmers are constantly talking about. Is there a more "Zen-like" way I should try- keeping with the philosophy of Python?

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• confusion about using types instead of gtts in oracle

  - by Omnipresent

  I am trying to convert queries like below to types so that I won't have to use GTT: insert into my_gtt_table_1 (house, lname, fname, MI, fullname, dob) (select house, lname, fname, MI, fullname, dob from (select 'REG' house, mbr_last_name lname, mbr_first_name fname, mbr_mi MI, mbr_first_name || mbr_mi || mbr_last_name fullname, mbr_dob dob from table_1 a, table_b where a.head = b.head and mbr_number = '01' and mbr_last_name = v_last_name) c above is just a sample but complex queries are bigger than this. the above is inside a stored procedure. So to avoid the gtt (my_gtt_table_1). I did the following: create or replace type lname_row as object ( house varchar2(30) lname varchar2(30), fname varchar2(30), MI char(1), fullname VARCHAR2(63), dob DATE ) create or replace type lname_exact as table of lname_row Now in the SP: type lname_exact is table of <what_table_should_i_put_here>%rowtype; tab_a_recs lname_exact; In the above I am not sure what table to put as my query has nested subqueries. query in the SP: (I am trying this for sample purpose to see if it works) select lname_row('', '', '', '', '', '', sysdate) bulk collect into tab_a_recs from table_1; I am getting errors like : ORA-00913: too many values I am really confused and stuck with this :(

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• Linq and returning types

  - by cdotlister

  My GUI is calling a service project that does some linq work, and returns data to my GUI. However, I am battling with the return type of the method. After some reading, I have this as my method: public static IEnumerable GetDetailedAccounts() { IEnumerable accounts = (from a in Db.accounts join i in Db.financial_institution on a.financial_institution.financial_institution_id equals i.financial_institution_id join acct in Db.z_account_type on a.z_account_type.account_type_id equals acct.account_type_id orderby i.name select new {account_id = a.account_id, name = i.name, description = acct.description}); return accounts; } However, my caller is battling a bit. I think I am screwing up the return type, or not handling the caller well, but it's not working as I'd hoped. This is how I am attempting to call the method from my GUI. IEnumerable accounts = Data.AccountService.GetDetailedAccounts(); Console.ForegroundColor = ConsoleColor.Green; Console.WriteLine("Accounts:"); Console.ForegroundColor = ConsoleColor.White; foreach (var acc in accounts) { Console.WriteLine(string.Format("{0:00} {1}", acc.account_id, acc.name + " " + acc.description)); } int accountid = WaitForKey(); However, my foreach, and the acc - isn't working. acc doesn't know about the name, description and id that I setup in the method. Am I at least close to being right?

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• Types in Haskell

  - by Linda Cohen

  I'm kind of new in Haskell and I have difficulty understanding how inferred types and such works. map :: (a -> b) -> [a] -> [b] (.) :: (a -> b) -> (c -> a) -> c -> b What EXACTLY does that mean? foldr :: (a -> b -> b) -> b -> [a] -> b foldl :: (a -> b -> a) -> a -> [b] -> a foldl1 :: (a -> a -> a) -> [a] -> a What are the differences between these? And how would I define the inferred type of something like foldr map THANKS!

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• Using different numeric variable types

  - by DataPimp

  Im still pretty new so bear with me on this one, my question(s) are not meant to be argumentative or petty but during some reading something struck me as odd. Im under the assumption that when computers were slow and memory was expensive using the correct variable type was much more of a necessity than it is today. Now that memory is a bit easier to come by people seem to have relaxed a bit. For example, you see this sample code everywhere: for (int i = 0; i < length; i++) int? (-2,147,483,648 to 2,147,483,648) for length? Isnt byte (0-255) a better choice? So Im curious of your opinion and what you believe to be best practice, I hate to think this would be used only because the acronym "int" is more intuitive for a beginner...or has memory just become so cheap that we really dont need to concern ourselves with such petty things and therefore we should just use long so we can be sure any other numbers/types(within reason) used can be cast automagically? ...or am Im just being silly by concerning myself with such things?

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• Multiple generic types in one container

  - by Lirik

  I was looking at the answer of this question regarding multiple generic types in one container and I can't really get it to work: the properties of the Metadata class are not visible, since the abstract class doesn't have them. Here is a slightly modified version of the code in the original question: public abstract class Metadata { } public class Metadata<T> : Metadata { // ... some other meta data public T Function{ get; set; } } List<Metadata> metadataObjects; metadataObjects.Add(new Metadata<Func<double,double>>()); metadataObjects.Add(new Metadata<Func<int,double>>()); metadataObjects.Add(new Metadata<Func<double,int>>()); foreach( Metadata md in metadataObjects) { var tmp = md.Function; // <-- Error: does not contain a definition for Function } The exact error is: error CS1061: 'Metadata' does not contain a definition for 'Function' and no extension method 'Function' accepting a first argument of type 'Metadata' could be found (are you missing a using directive or an assembly reference?) I believe it's because the abstract class does not define the property Function, thus the whole effort is completely useless. Is there a way that we can get the properties?

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• Generics in return types of static methods and inheritance

  - by Axel

  Generics in return types of static methods do not seem to get along well with inheritance. Please take a look at the following code: class ClassInfo<C> { public ClassInfo(Class<C> clazz) { this(clazz,null); } public ClassInfo(Class<C> clazz, ClassInfo<? super C> superClassInfo) { } } class A { public static ClassInfo<A> getClassInfo() { return new ClassInfo<A>(A.class); } } class B extends A { // Error: The return type is incompatible with A.getClassInfo() public static ClassInfo<B> getClassInfo() { return new ClassInfo<B>(B.class, A.getClassInfo()); } } I tried to circumvent this by changing the return type for A.getClassInfo(), and now the error pops up at another location: class ClassInfo<C> { public ClassInfo(Class<C> clazz) { this(clazz,null); } public ClassInfo(Class<C> clazz, ClassInfo<? super C> superClassInfo) { } } class A { public static ClassInfo<? extends A> getClassInfo() { return new ClassInfo<A>(A.class); } } class B extends A { public static ClassInfo<? extends B> getClassInfo() { // Error: The constructor ClassInfo<B>(Class<B>, ClassInfo<capture#1-of ? extends A>) is undefined return new ClassInfo<B>(B.class, A.getClassInfo()); } } What is the reason for this strict checking on static methods? And how can I get along? Changing the method name seems awkward.

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• Handling Apache Thrift list/map Return Types in C++

  - by initzero

  First off, I'll say I'm not the most competent C++ programmer, but I'm learning, and enjoying the power of Thrift. I've implemented a Thrift Service with some basic functions that return void, i32, and list. I'm using a Python client controlled by a Django web app to make RPC calls and it works pretty well. The generated code is pretty straight forward, except for list returns: namespace cpp Remote enum N_PROTO { N_TCP, N_UDP, N_ANY } service Rcon { i32 ping() i32 KillFlows() i32 RestartDispatch() i32 PrintActiveFlows() i32 PrintActiveListeners(1:i32 proto) list<string> ListAllFlows() } The generated signatures from Rcon.h: int32_t ping(); int32_t KillFlows(); int32_t RestartDispatch(); int32_t PrintActiveFlows(); int32_t PrintActiveListeners(const int32_t proto); int64_t ListenerBytesReceived(const int32_t id); void ListAllFlows(std::vector<std::string> & _return); As you see, the ListAllFlows() function generated takes a reference to a vector of strings. I guess I expect it to return a vector of strings as laid out in the .thrift description. I'm wondering if I am meant to provide the function a vector of strings to modify and then Thrift will handle returning it to my client despite the function returning void. I can find absolutely no resources or example usages of Thrift list< types in C++. Any guidance would be appreciated.

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• How to store and locate multiple interface types within a Delphi TInterfaceList

  - by Brian Frost

  Hi, I'm storing small interfaces from a range of objects into a single TInterfaceList 'store' with the intention of offering list of specific interface types to the end user, so each interface will expose a 'GetName' function but all other methods are unique to that interface type. For example here are two interfaces: IBase = interface //---------------------------------------- function GetName : string; //---------------------------------------- end; IMeasureTemperature = interface(IBase) //------------------------------------ function MeasureTemperature : double; //---------------------------------------- end; IMeasureHumidity = interface(IBase) //---------------------------------------- function MeasureHumidity: double; //---------------------------------------- end; I put several of these interfaces into a single TInterfaceList and then I'd like to scan the list for a specific interface type (e.g. 'IMeasureTemperature') building another list of pointers to the objects exporting those interfaces. I wish to make no assumptions about the locations of those objects, some may export more than one type of interface. I know I could do this with a class hierarchy using something like: If FList[I] is TMeasureTemperature then .. but I'd like to do something simliar with an interface type, Is this possible?

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• Java constructor using generic types

  - by Beer Me

  I'm having a hard time wrapping my head around Java generic types. Here's a simple piece of code that in my mind should work, but I'm obviously doing something wrong. Eclipse reports this error in BreweryList.java: The method breweryMethod() is undefined for the type <T> The idea is to fill a Vector with instances of objects that are a subclass of the Brewery class, so the invocation would be something like: BreweryList breweryList = new BreweryList(BrewerySubClass.class, list); BreweryList.java package com.beerme.test; import java.util.Vector; public class BreweryList<T extends Brewery> extends Vector<T> { public BreweryList(Class<T> c, Object[] j) { super(); for (int i = 0; i < j.length; i++) { T item = c.newInstance(); // breweryMethod() is an instance method // of Brewery, of which <T> is a subclass (right?) c.breweryMethod(); // "The method breweryMethod() is undefined // for the type <T>" } } } Brewery.java package com.beerme.test; public class Brewery { public Brewery() { super(); } protected void breweryMethod() { } } BrewerySubClass.java package com.beerme.test; public class BrewerySubClass extends Brewery { public BrewerySubClass() { super(); } public void brewerySubClassMethod() { } } I'm sure this is a complete-generics-noob question, but I'm stuck. Thanks for any tips!

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• C++ private inheritance and static members/types

  - by WearyMonkey

  I am trying to stop a class from being able to convert its 'this' pointer into a pointer of one of its interfaces. I do this by using private inheritance via a middle proxy class. The problem is that I find private inheritance makes all public static members and types of the base class inaccessible to all classes under the inheriting class in the hierarchy. class Base { public: enum Enum { value }; }; class Middle : private Base { }; class Child : public Middle { public: void Method() { Base::Enum e = Base::value; // doesn't compile BAD! Base* base = this; // doesn't compile GOOD! } }; I've tried this in both VS2008 (the required version) and VS2010, neither work. Can anyone think of a workaround? Or a different approach to stopping the conversion? Also I am curios of the behavior, is it just a side effect of the compiler implementation, or is it by design? If by design, then why? I always thought of private inheritance to mean that nobody knows Middle inherits from Base. However, the exhibited behavior implies private inheritance means a lot more than that, in-fact Child has less access to Base than any namespace not in the class hierarchy!

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• Java constructor using generic types

  - by user37903

  I'm having a hard time wrapping my head around Java generic types. Here's a simple piece of code that in my mind should work, but I'm obviously doing something wrong. Eclipse reports this error in BreweryList.java: The method initBreweryFromObject() is undefined for the type <T> The idea is to fill a Vector with instances of objects that are a subclass of the Brewery class, so the invocation would be something like: BreweryList breweryList = new BreweryList(BrewerySubClass.class, list); BreweryList.java package com.beerme.test; import java.util.Vector; public class BreweryList<T extends Brewery> extends Vector<T> { public BreweryList(Class<T> c, Object[] j) { super(); for (int i = 0; i < j.length; i++) { T item = c.newInstance(); // initBreweryFromObject() is an instance method // of Brewery, of which <T> is a subclass (right?) c.initBreweryFromObject(); // "The method initBreweryFromObject() is undefined // for the type <T>" } } } Brewery.java package com.beerme.test; public class Brewery { public Brewery() { super(); } protected void breweryMethod() { } } BrewerySubClass.java package com.beerme.test; public class BrewerySubClass extends Brewery { public BrewerySubClass() { super(); } public void androidMethod() { } } I'm sure this is a complete-generics-noob question, but I'm stuck. Thanks for any tips!

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• stdio data from write not making it into a file

  - by user1551209

  I'm having a problem with using stdio commands for manipulating data in a file. I short, when I write data into a file, write returns an int indicating that it was successful, but when I read it back out I only get the old data. Here's a stripped down version of the code: fd = open(filename,O_RDWR|O_APPEND); struct dE *cDE = malloc(sizeof(struct dE)); //Read present data printf("\nreading values at %d\n",off); printf("SeekStatus <%d>\n",lseek(fd,off,SEEK_SET)); printf("ReadStatus <%d>\n",read(fd,cDE,deSize)); printf("current Key/Data <%d/%s>\n",cDE->key,cDE->data); printf("\nwriting new values\n"); //Change the values locally cDE->key = //something new cDE->data = //something new //Write them back printf("SeekStatus <%d>\n",lseek(fd,off,SEEK_SET)); printf("WriteStatus <%d>\n",write(fd,cDE,deSize)); //Re-read to make sure that it got written back printf("\nre-reading values at %d\n",off); printf("SeekStatus <%d>\n",lseek(fd,off,SEEK_SET)); printf("ReadStatus <%d>\n",read(fd,cDE,deSize)); printf("current Key/Data <%d/%s>\n",cDE->key,cDE->data); Furthermore, here's the dE struct in case you're wondering: struct dE { int key; char data[DataSize]; }; This prints: reading values at 1072 SeekStatus <1072> ReadStatus <32> current Key/Data <27/old> writing new values SeekStatus <1072> WriteStatus <32> re-reading values at 1072 SeekStatus <1072> ReadStatus <32> current Key/Data <27/old>

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• Design pattern for loading multiple message types

  - by lukem00

  As I was looking through SO I came across a question about handling multiple message types. My concern is - how do I load such a message in a neat way? I decided to have a separate class with a method which loads one message each time it's invoked. This method should create a new instance of a concrete message type (say AlphaMessage, BetaMessage, GammaMessage, etc.) and return it as a Message. class MessageLoader { public Message Load() { // ... } } The code inside the method is something which looks really awful to me and I would very much like to refactor it/get rid of it: Message msg = Message.Load(...); // load yourself from whatever source if (msg.Type == MessageType.Alpha) return new AlphaMessage(msg); if (msg.Type == MessageType.Beta) return new BetaMessage(msg); // ... In fact, if the whole design looks just too messy and you guys have a better solution, I'm ready to restructure the whole thing. If my description is too chaotic, please let me know what it's missing and I shall edit the question. Thank you all.

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• Passing XML data and user from coldfusion page to .NET page

  - by Mark Rullo

  I'd appreciate some input on this situation, I can't figure out the best way to do this. I have some data that's being prepared for me in a ColdFusion app and in an IFrame within the CF app we want to display some graphs (not strictly an image, it's an entire page) being generated on the .NET side of things. I'd like to pass XML data from the CF side to .NET as well as the user. On the .NET side I'm putting the data in a session so the user can sift through it without the need to have it re-queried and re-passed from CF. What I've tried: Generating XML with CF, putting it in a hidden form field, auto-submitting (with JS) a the form to the .NET side. The issue I'm having with this approach is the encoding being done on the form post. The data has entries like <entry data="hello &amp; goodbye">. It's an issue because it's being URL encdeded, Posted, and when I get it on the .NET side I get <entry data="hello & goodbye"> which isn't properly formed XML. What I'd like to avoid: An intermediary DB approach (dropping the data in a DB on CF, picking it up with .NET) I'd like to only display what is passed to the page. I have security concerns with the data, it's very sensitive. Passing the data to a webservice, returning a GUID, forwarding the user with a URL Parameter to access the passed in data. I think that'd be risky if someone happened on a link to that data. I can't take that risk. I was thinking of passing the data with JSON, but I'm very unfamiliar with it. Thoughts? Thanks for your time folks.

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• A data structure based on the R-Tree: creating new child nodes when a node is full, but what if I ha

  - by Tom

  I realize my title is not very clear, but I am having trouble thinking of a better one. If anyone wants to correct it, please do. I'm developing a data structure for my 2 dimensional game with an infinite universe. The data structure is based on a simple (!) node/leaf system, like the R-Tree. This is the basic concept: you set howmany childs you want a node (a container) to have maximum. If you want to add a leaf, but the node the leaf should be in is full, then it will create a new set of nodes within this node and move all current leafs to their new (more exact) node. This way, very populated areas will have a lot more subdivisions than a very big but rarely visited area. This works for normal objects. The only problem arises when I have more than maxChildsPerNode objects with the exact same X,Y location: because the node is full, it will create more exact subnodes, but the old leafs will all be put in the exact same node again because they have the exact same position -- resulting in an infinite loop of creating more nodes and more nodes. So, what should I do when I want to add more leafs than maxChildsPerNode with the exact same position to my tree? PS. if I failed to explain my problem, please tell me, so I can try to improve the explanation.

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• How can I read and parse chunks of data into a Perl hash of arrays?

  - by neversaint

  I have data that looks like this: #info #info2 1:SRX004541 Submitter: UT-MGS, UT-MGS Study: Glossina morsitans transcript sequencing project(SRP000741) Sample: Glossina morsitans(SRS002835) Instrument: Illumina Genome Analyzer Total: 1 run, 8.3M spots, 299.9M bases Run #1: SRR016086, 8330172 spots, 299886192 bases 2:SRX004540 Submitter: UT-MGS Study: Anopheles stephensi transcript sequencing project(SRP000747) Sample: Anopheles stephensi(SRS002864) Instrument: Solexa 1G Genome Analyzer Total: 1 run, 8.4M spots, 401M bases Run #1: SRR017875, 8354743 spots, 401027664 bases 3:SRX002521 Submitter: UT-MGS Study: Massive transcriptional start site mapping of human cells under hypoxic conditions.(SRP000403) Sample: Human DLD-1 tissue culture cell line(SRS001843) Instrument: Solexa 1G Genome Analyzer Total: 6 runs, 27.1M spots, 977M bases Run #1: SRR013356, 4801519 spots, 172854684 bases Run #2: SRR013357, 3603355 spots, 129720780 bases Run #3: SRR013358, 3459692 spots, 124548912 bases Run #4: SRR013360, 5219342 spots, 187896312 bases Run #5: SRR013361, 5140152 spots, 185045472 bases Run #6: SRR013370, 4916054 spots, 176977944 bases What I want to do is to create a hash of array with first line of each chunk as keys and SR## part of lines with "^Run" as its array member: $VAR = { 'SRX004541' => ['SRR016086'], # etc } But why my construct doesn't work. And it must be a better way to do it. use Data::Dumper; my %bighash; my $head = ""; my @temp = (); while ( <> ) { chomp; next if (/^\#/); if ( /^\d{1,2}:(\w+)/ ) { print "$1\n"; $head = $1; } elsif (/^Run \#\d+: (\w+),.*/){ print "\t$1\n"; push @temp, $1; } elsif (/^$/) { push @{$bighash{$head}}, [@temp]; @temp =(); } } print Dumper \%bighash ;

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• C++: Trouble with dependent types in templates

  - by Rosarch

  I'm having trouble with templates and dependent types: namespace Utils { void PrintLine(const string& line, int tabLevel = 0); string getTabs(int tabLevel); template<class result_t, class Predicate> set<result_t> findAll_if(typename set<result_t>::iterator begin, set<result_t>::iterator end, Predicate pred) // warning C4346 { set<result_t> result; return findAll_if_rec(begin, end, pred, result); } } namespace detail { template<class result_t, class Predicate> set<result_t> findAll_if_rec(set<result_t>::iterator begin, set<result_t>::iterator end, Predicate pred, set<result_t> result) { typename set<result_t>::iterator nextResultElem = find_if(begin, end, pred); if (nextResultElem == end) { return result; } result.add(*nextResultElem); return findAll_if_rec(++nextResultElem, end, pred, result); } } Compiler complaints, from the location noted above: warning C4346: 'std::set<result_t>::iterator' : dependent name is not a type. prefix with 'typename' to indicate a type error C2061: syntax error : identifier 'iterator' What am I doing wrong?

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• What are your suggestions for best practises for regular data updates in a website database?

  - by bboyle1234

  My shared-hosting asp.net website must automatically run data update routines at regular times of day. Once it has finished running certain update routines, it can run update routines that are dependent on the previous updates. I have done this type of work before, using quite complicated setups. Some features of the framework I created are: A cron job from another server makes a request which starts a data update routine on the main server Each updater is loaded from web.config Each updater overrides a "canRunUpdate" method that determines whether its dependencies have finished updating Each updater overrides a "hasFinishedUpdate" method Each updater overrides a "runUpdate" method Updaters start and run in parallel threads The initial request from the cron job server started each updater in its own thread and then ended. As a result, the threads containing the updaters would be terminated before the updaters were finished. Therefore I had to give the updaters the ability to save partial results and continue the update job next time they are started up. As a result, the cron server had to call the updater many times to ensure the job is done. Sometimes the cron server would continue making update requests long after all the updates were completed. Sometimes the cron server would finish calling the update requests and leave some updates uncompleted. It's not the best system. I'm looking for inspiration. Any ideas please? Thank you :)

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• How do I display core data on second view controller?

  - by jon

  I am working on my first core data iPhone application. I am using a navigation controller, and the root view controller displays 4 rows. Clicking the first row takes me to a second table view controller. However, when I click the back button, repeat the row tap, click the back button again, and tap the row a third time, I get an error. I have been researching this for a week with no success. I can reproduce the error easily: Create a new Navigation-based Application, use Core Data for storage, call it MyTest which creates MyTestAppDelegate and RootViewController. Add new UIViewController subclass, with UITableViewController and xib, call it ListViewController. Copy code from RootViewController.h and .m to ListViewController.h and .m., changing the file names appropriately. To simplify the code, I removed the trailing “_” from all variables. In RootViewController, I added #import ListViewController.h, set up an array to display 4 rows and navigate to ListViewController when clicking the first row. In ListViewController.m, I added #import MyTestAppDelegate.h” and the following code: - (void)viewDidLoad { [super viewDidLoad]; if (managedObjectContext == nil) { managedObjectContext = [(MyTestAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; } .. } The sequence that causes the error is tap row, return, tap row, return, tap row - error. managedObjectContext is synthesized for the third time. I appreciate your patience and your help, as this makes no sense to me. ADDENDUM: I may have a partial solution. http://www.iphonedevsdk.com/forum/iphone-sdk-development/41688-accessing-app-delegates-managed-object-context.html If I do not release the managedObjectContext in the .m file, the error goes away. Is that ok or will that cause me issues? - (void)dealloc { [fetchedResultsController release]; // [managedObjectContext release]; [super dealloc]; } ADDENDUM 2: See solution below. Sorry for the formatting issues - this was my first post.

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• Separating code logic from the actual data structures. Best practices?

  - by Patrick

  I have an application that loads lots of data into memory (this is because it needs to perform some mathematical simulation on big data sets). This data comes from several database tables, that all refer to each other. The consistency rules on the data are rather complex, and looking up all the relevant data requires quite some hashes and other additional data structures on the data. Problem is that this data may also be changed interactively by the user in a dialog. When the user presses the OK button, I want to perform all the checks to see that he didn't introduce inconsistencies in the data. In practice all the data needs to be checked at once, so I cannot update my data set incrementally and perform the checks one by one. However, all the checking code work on the actual data set loaded in memory, and use the hashing and other data structures. This means I have to do the following: Take the user's changes from the dialog Apply them to the big data set Perform the checks on the big data set Undo all the changes if the checks fail I don't like this solution since other threads are also continuously using the data set, and I don't want to halt them while performing the checks. Also, the undo means that the old situation needs to be put aside, which is also not possible. An alternative is to separate the checking code from the data set (and let it work on explicitly given data, e.g. coming from the dialog) but this means that the checking code cannot use hashing and other additional data structures, because they only work on the big data set, making the checks much slower. What is a good practice to check user's changes on complex data before applying them to the 'application's' data set?

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• Value types of variable size

  - by YellPika

  I'm trying to code a small math library in C#. I wanted to create a generic vector structure where the user could define the element type (int, long, float, double, etc.) and dimensions. My first attempt was something like this... public struct Vector<T> { public readonly int Dimensions; public readonly T[] Elements; // etc... } Unfortunately, Elements, being an array, is also a reference type. Thus, doing this, Vector<int> a = ...; Vector<int> b = a; a[0] = 1; b[0] = 2; would result in both a[0] and b[0] equaling 2. My second attempt was to define an interface IVector<T>, and then use Reflection.Emit to automatically generate the appropriate type at runtime. The resulting classes would look roughly like this: public struct Int32Vector3 : IVector<T> { public int Element0; public int Element1; public int Element2; public int Dimensions { get { return 3; } } // etc... } This seemed fine until I found out that interfaces seem to act like references to the underlying object. If I passed an IVector to a function, and changes to the elements in the function would be reflected in the original vector. What I think is my problem here is that I need to be able to create classes that have a user specified number of fields. I can't use arrays, and I can't use inheritance. Does anyone have a solution? EDIT: This library is going to be used in performance critical situations, so reference types are not an option.

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• Fastest way to read/store lots of multidimensional data? (Java)

  - by RemiX

  I have three questions about three nested loops: for (int x=0; x<400; x++) { for (int y=0; y<300; y++) { for (int z=0; z<400; z++) { // compute and store value } } } And I need to store all computed values. My standard approach would be to use a 3D-array: values[x][y][z] = 1; // test value but this turns out to be slow: it takes 192 ms to complete this loop, where a single int-assignment int value = 1; // test value takes only 66 ms. 1) Why is an array so relatively slow? 2) And why does it get even slower when I put this in the inner loop: values[z][y][x] = 1; // (notice x and z switched) This takes more than 4 seconds! 3) Most importantly: Can I use a data structure that is as quick as the assignment of a single integer, but can store as much data as the 3D-array?

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• Java: Incompatible Types

  - by user2922081

  import java.text.*; import java.util.*; public class Proj3 { public static void main(String[]args){ // DecimalFormat df = new DecimalFormat("#0.00”); Scanner s = new Scanner(System.in); int TotalHours = 0; int TotalGrade = 0; System.out.print("How many courses did you take? "); int Courses = Integer.parseInt(s.nextLine()); System.out.println(""); int CourseNumber = Courses - (Courses - 1); while (Courses > 0){ System.out.print("Course (" + CourseNumber +"): How many hours? "); int Hours = Integer.parseInt(s.nextLine()); TotalHours = TotalHours + Hours; System.out.print("Course (" + CourseNumber +"): Letter grade? "); char Grade = s.nextLine().charAt(0); if (Grade == 'A'){ TotalGrade = TotalGrade + (4 * Hours); } if (Grade == 'B'){ TotalGrade = TotalGrade + (3 * Hours); } if (Grade == 'C'){ TotalGrade = TotalGrade + (2 * Hours); } if (Grade == 'D'){ TotalGrade = TotalGrade + (1 * Hours); } Courses = Courses - 1; CourseNumber = CourseNumber + 1; } Double GPA = TotalGrade / TotalHours; System.out.println(df.format(GPA)); } } This is for an assignment and I don't know how to fix my problem. The Double GPA = TotalGrade / ToutalHours; line is coming up with the Incompatible Types error. Also I'm supposed to include the DecimalFormat df = new DecimalFormat("#0.00”);line at the beginning of the main but its not working. Anything is very helpful. Thanks

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