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  • How should I change my Graph structure (very slow insertion)?

    - by Nazgulled
    Hi, This program I'm doing is about a social network, which means there are users and their profiles. The profiles structure is UserProfile. Now, there are various possible Graph implementations and I don't think I'm using the best one. I have a Graph structure and inside, there's a pointer to a linked list of type Vertex. Each Vertex element has a value, a pointer to the next Vertex and a pointer to a linked list of type Edge. Each Edge element has a value (so I can define weights and whatever it's needed), a pointer to the next Edge and a pointer to the Vertex owner. I have a 2 sample files with data to process (in CSV style) and insert into the Graph. The first one is the user data (one user per line); the second one is the user relations (for the graph). The first file is quickly inserted into the graph cause I always insert at the head and there's like ~18000 users. The second file takes ages but I still insert the edges at the head. The file has about ~520000 lines of user relations and takes between 13-15mins to insert into the Graph. I made a quick test and reading the data is pretty quickly, instantaneously really. The problem is in the insertion. This problem exists because I have a Graph implemented with linked lists for the vertices. Every time I need to insert a relation, I need to lookup for 2 vertices, so I can link them together. This is the problem... Doing this for ~520000 relations, takes a while. How should I solve this? Solution 1) Some people recommended me to implement the Graph (the vertices part) as an array instead of a linked list. This way I have direct access to every vertex and the insertion is probably going to drop considerably. But, I don't like the idea of allocating an array with [18000] elements. How practically is this? My sample data has ~18000, but what if I need much less or much more? The linked list approach has that flexibility, I can have whatever size I want as long as there's memory for it. But the array doesn't, how am I going to handle such situation? What are your suggestions? Using linked lists is good for space complexity but bad for time complexity. And using an array is good for time complexity but bad for space complexity. Any thoughts about this solution? Solution 2) This project also demands that I have some sort of data structures that allows quick lookup based on a name index and an ID index. For this I decided to use Hash Tables. My tables are implemented with separate chaining as collision resolution and when a load factor of 0.70 is reach, I normally recreate the table. I base the next table size on this http://planetmath.org/encyclopedia/GoodHashTablePrimes.html. Currently, both Hash Tables hold a pointer to the UserProfile instead of duplication the user profile itself. That would be stupid, changing data would require 3 changes and it's really dumb to do it that way. So I just save the pointer to the UserProfile. The same user profile pointer is also saved as value in each Graph Vertex. So, I have 3 data structures, one Graph and two Hash Tables and every single one of them point to the same exact UserProfile. The Graph structure will serve the purpose of finding the shortest path and stuff like that while the Hash Tables serve as quick index by name and ID. What I'm thinking to solve my Graph problem is to, instead of having the Hash Tables value point to the UserProfile, I point it to the corresponding Vertex. It's still a pointer, no more and no less space is used, I just change what I point to. Like this, I can easily and quickly lookup for each Vertex I need and link them together. This will insert the ~520000 relations pretty quickly. I thought of this solution because I already have the Hash Tables and I need to have them, then, why not take advantage of them for indexing the Graph vertices instead of the user profile? It's basically the same thing, I can still access the UserProfile pretty quickly, just go to the Vertex and then to the UserProfile. But, do you see any cons on this second solution against the first one? Or only pros that overpower the pros and cons on the first solution? Other Solution) If you have any other solution, I'm all ears. But please explain the pros and cons of that solution over the previous 2. I really don't have much time to be wasting with this right now, I need to move on with this project, so, if I'm doing to do such a change, I need to understand exactly what to change and if that's really the way to go. Hopefully no one fell asleep reading this and closed the browser, sorry for the big testament. But I really need to decide what to do about this and I really need to make a change. P.S: When answering my proposed solutions, please enumerate them as I did so I know exactly what are you talking about and don't confuse my self more than I already am.

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  • Can anyone tell me what the authors mean on this line?

    - by Anirudh Goel
    i was going through this link: FAT16 Basics to Assemble Clusters. I have read the structures involved in defining a directory entry in FAT. Now when giving the example for a FAT16 File, it says the data cluster is 0x03 for the example file MyFile.txt. Which means if we logically compute the Data Cluster we will be able to reach to the first node which happens to be cluster no 3. But what I fail to understand is what the author is trying to say in the next line where it says What we can see in the File Allocation Table at this moment? How suddenly we reach to the File Allocation Table? Weren't we already there when we were going through the information of Myfile.txt? I couldn't find any reason how suddenly the author jumped to an offset location of 00000200 and is identifying the emptiness of the clusters. It will be great if someone can help me understand. Thanks

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  • How to think in data stores instead of databases?

    - by Jim
    As an example, Google App Engine uses data stores, not a database, to store data. Does anybody have any tips for using data stores instead of databases? It seems I've trained my mind to think 100% in object relationships that map directly to table structures, and now it's hard to see anything differently. I can understand some of the benefits of data stores (e.g. performance and the ability to distribute data), but some good database functionality is sacrificed (e.g. joins). Does anybody who has worked with data stores like BigTable have any good advice to working with them?

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  • Is there a distributed VCS that can manage large files?

    - by joelhardi
    Is there a distributed version control system (git, bazaar, mercurial, darcs etc.) that can handle files larger than available RAM? I need to be able to commit large binary files (i.e. datasets, source video/images, archives), but I don't need to be able to diff them, just be able to commit and then update when the file changes. I last looked at this about a year ago, and none of the obvious candidates allowed this, since they're all designed to diff in memory for speed. That left me with a VCS for managing code and something else ("asset management" software or just rsync and scripts) for large files, which is pretty ugly when the directory structures of the two overlap.

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  • I like to learn computer science and programming, but i have no understanding.

    - by Josiah
    Hi all, I like to learn computer science and programming, but i don't know where and how to start. For the past two months, i have been researching on types of programming, i found my interest in desktop programming, and also found this subjects (discrete maths, logic, algorithms, data structures, artificial intelligence, simulation) said to be a most known (subjects). Well as a beginner, i have no understanding on what type of language or books that can cover all these subjects, or even how to write any code. Secondly, am as young as you can guess and i need a language to start with that will be easy for me to understand, and books to read. Thank you.

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  • Which build tool to teach?

    - by Helper Method
    While similiar questions have been asked, this one's focused on which is best/easiest to teach. I'm giving a weekly tutorial at my university focusing on data structures and algorithms. Fromn time to time I introduce tools which may prove helpful in future projects like JUnit, Mercurial, Eclipse etc.. I plan to show them some kind of build tool but I'm not sure which one to choose. I by myself have very little knowledge about build tools, except a little experience in using make. It's more the concept of a build tool I want to show them, not a special tool per se. Which would be the most easiest/future proof/whatever tool to show them? I've read a little bit about Gradle, which looks nice, but so far I think Ant could be a good choice (it's a Java course I'm giving).

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  • Performance of fopen vs stat

    - by Alex Marshall
    Hello, I'm writing several C programs for an embedded system where every bit of performance we can squeeze out will matter. Part of that is accessing log files. When determining if a file exists, is there any performance difference between using open / fopen, and stat ? I've been using stat on the assumption that it only has to do a quick check against the file system, whereas fopen would have to actually gain access to a file and manipulate internal data structures before returning. Is there any merit to this ?

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  • Is it considered bad form to execute a function within a conditional statement?

    - by michael
    Consider a situation in which you need to call successive routines and stop as soon as one returns a value that could be evaluated as positive (true, object, 1, str(1)). It's very tempting to do this: if (fruit = getOrange()) elseif (fruit = getApple()) elseif (fruit = getMango()) else fruit = new Banana(); return fruit; I like it, but this isn't a very recurrent style in what can be considered professional production code. One is likely to rather see more elaborate code like: fruit = getOrange(); if(!fruit){ fruit = getApple(); if(!fruit){ fruit = getMango(); if(!fruit){ fruit = new Banana(); } } } return fruit; According to the dogma on basic structures, is the previous form acceptable? Would you recommend it?

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  • how to compare between Doctrine & Propel in symfony

    - by Patrick
    I am in the early stages of rearchitecting my company's application. The app is currently running on symfony 1.2, and I used the default ORM at the time, Propel. Symfony has since updated to 1.4 and switched default ORM to Doctrine. From my understanding, each ORM excels at particular types of database structures. Is this true or is one far and away better than the other? Are there any good methods to test which ORM would be best in my situation in a test environment using my schema (i.e.- set up dual, identical sites and run tests)?

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  • Database table copying

    - by vbNewbie
    I am trying to rectify a previous database creation with tables that contains data that needs to be saved. Instead of recreating a completely new database since some of the tables are still reusable, I need to split a table that exists into 2 new tables which I have done. Now I am trying to insert the data into the 2 new tables and because of duplicate data in the old table I am having a hard time doing this. Old table structure: ClientProjects clientId PK clientName clientProj hashkey MD5 (clientname and clientProj) new table structures: client clientId PK clientName projects queryId PK clientId PK projectName I hope this makes sense. The problem is that in the old table for example you have clients with multiple clientIds.

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  • Can we represent bit fields in JSON/BSON?

    - by zubair
    We have a dozen simulators talking to each other on UDP. The interface definition is managed in a database. The simulators are written using different languages; mostly C++, some in Java and C#. Currently, when systems engineer makes changes in the interface definition database, simulator developers manually update the communication data structures in their code. The data is mostly 2-5 bytes with bit fields for each signal. What I want to do is to generate one file from interface definition database describing byte and bit field definitions and let each developer add it to his simulator code with minimal fuss. I looked at JSON/BSON but couldn't find a way to represent bit fields in it. Thanks Zubair

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  • Use LINQ and C# to make a new List from an old List

    - by Addie
    This should be pretty simple, but I am new at LINQ. I have a List of FillList structs. I'd like to use LINQ to create a new List where instead of having the number of buys and sells, I would have one variable containing the sum. For example, if the FillStruct structure has buy = 4 and sell = 2 then the NewFillStruct structure will have numlong = 2. If the FillStruct structure has buy = 2 and sell = 4 then the NewFillStruct structure will have numlong = -2. Here are the structures. struct FillStruct { int buy; int sell; string date; } struct NewFillStruct { int numlong; string date; }

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  • Are there any widely-agreed upon guidelines for rating your language knowledge on a scale?

    - by DVK
    The question was imagined after a co-worker was complaining for an hour about some guy who could not answer basic Java questions on an interview after self-identifying himself as "8 out of 10" on Java. While that was an obvious fib, I personally always had major trouble defining my specific language skills on a sliding scale unless I'm given specific guidelines (remember 40 standard libraries by heart? Able to solve 10 random Project Euler problems in <30 mins each? Can write implementation of A, B and C data-structures from scratch in 30 mins? Know 30% of standard? Can answer 50% of questions on StackOverflow pertaining to the language?) So, I was wondering - is there some sort of commonly accepted methodology for translating such tangible benchmarks into "rate yourself on a language between 1-10"? "Kernighan gets an A, God gets a B, everyone else gets C and less" type jokes are not helpful :)

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  • Should one use PHP to print all of a page's HTML?

    - by Mala
    Hi So I've always developed PHP pages like this: <?php goes at the top, ?> goes at the bottom, and all the HTML gets either print()ed or echo()ed out. Is that slower than having non-dynamic html outputted outside of <?php ?> tags? I can't seem to find any info about this. Thanks! --Mala UPDATE: the consesus seems to be on doing it my old way being hard to read. This is not the case if you break your strings up line by line as in: print("\n". "first line goes here\n". "second line goes here\n". "third line"); etc. It actually makes it a lot easier to read than having html outside of php structures, as this way everything is properly indented. That being said, it involves a lot of string concatenation.

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  • ZendFramework integration with other frameworks

    - by St.Woland
    I want to make this question a guide for those interested in ZendFramework integration with other libraries/frameworks. Searching over StackOverflow doesn't give a broad view on the subject. The question is: which libraries/frameworks do you use in your current ZF-based project? what are the best practices for ZF-based project architecture? I don't mean any components that are already a part of ZF. Please give a description of aditional frameworks you have integrated (like RuckUsing, Smarty, or Doctrine). It also applies to any GUI frameworks (perhaps you use a CSS framework), as well as JS frameworks (not just jQuery or prototype, but rather some advanced structures). The main requirement: it has to be a ZendFramework project. Additional bonus will be given to answers that describe performance optimization.

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  • Executing certain code for every method call in C++

    - by Luís Guilherme
    I have a C++ class I want to inspect. So, I would like to all methods print their parameters and the return, just before getting out. The latter looks somewhat easy. If I do return() for everything, a macro #define return(a) cout << (a) << endl; return (a) would do it (might be wrong) if I padronize all returns to parenthesized (or whatever this may be called). If I want to take this out, just comment out the define. However, printing inputs seems more difficult. Is there a way I can do it, using C++ structures or with a workaroud hack?

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  • Why isn't Hadoop implemented using MPI?

    - by artif
    Correct me if I'm wrong, but my understanding is that Hadoop does not use MPI for communication between different nodes. What are the technical reasons for this? I could hazard a few guesses, but I do not know enough of how MPI is implemented "under the hood" to know whether or not I'm right. Come to think of it, I'm not entirely familiar with Hadoop's internals either. I understand the framework at a conceptual level (map/combine/shuffle/reduce and how that works at a high level) but I don't know the nitty gritty implementation details. I've always assumed Hadoop was transmitting serialized data structures (perhaps GPBs) over a TCP connection, eg during the shuffle phase. Let me know if that's not true.

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  • Reducing time in C# Forms Control.set_Text(string) function

    - by awshepard
    Hoping for a quick answer (which SO seems to be pretty good for)... I just ran a performance analysis with VS2010 on my app, and it turns out that I'm spending about 20% of my time in the Control.set_Text(string) function, as I'm updating labels in quite a few places in my app. The window has a timer object (Forms timer, not Threading timer) that has a timer1_Tick callback, which updates one label every tick (to give a stop-watch sort of effect), and updates about 15 labels once each second. Does anyone have quick suggestions for how to reduce the amount of time spent updating text on a form, other than increasing the update interval? Are there other structures or functions I should be using?

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  • T-SQL: Build Nested Set From Parent-Child Relationship

    - by Peder Rice
    I have a table that stores my Customer hierarchy with a nested set (due to the specific design of the application, I wasn't able to leverage just a Customer/Parent Customer mapping table). To simplify maintenance of this table, I've built a couple of stored procedures to handle moving nodes around and creating new nodes, but it's significantly more work than maintaining a Customer/Parent Customer table. Further, these structures are very fragile. So I'm looking for a way to have a Customer/Parent Customer table and then convert that table to a nested set on demand. Does anyone have a link to such an implementation?

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  • How can the Kindle be used as a source code reading tool?

    - by Homer6
    I'm a programmer. I want to be a better programmer. I want to read more source code written by other people (especially open source projects). Also, I'd like to be able to have a on-hand searchable reference to all of that source code so that I can pull up reference to structures and snippets. Does anyone know of a way to use the Kindle for this? Has anyone tried? What were your findings? Additionally, does anyone know of a website that indexes all open source source code?

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  • Import Error when use templatetags in Django

    - by zmfantasy
    Well, when I'm trying to use 'inclusion' in Django, I met some confused problems that I can't solve it by myself. There is the structures for my project. MyProject--- App1--- __init__.py models.py test.py urls.py views.py App2--- ... template--- App1--- some htmls App2--- ... templatetags--- __init__.py inclusion_test.py manage.py urls.py __init__.py settings.py I have registered templatetags folder in the settings.py (Both in Installed APPS & TEMPLATE_DIRS). But when I want to use {% load inclusion_test %} in my html, it raise an exception like this: 'inclusion_cld_tags' is not a valid tag library: Could not load template library from django.templatetags.inclusion_cld_tags, No module named inclusion_cld_tags I think there is nothing wrong with my import work, how can I do with that? Thanks for help! My django version: 1.0+ My Python version: 2.6.4

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  • Rtti for Variant Records

    - by Coco
    I try to write a kind of object/record serializer with Delphi 2010 and wonder if there is a way to detect, if a record is a variant record. E.g. the TRect record as defined in Types.pas: TRect = record case Integer of 0: (Left, Top, Right, Bottom: Longint); 1: (TopLeft, BottomRight: TPoint); end; As my serializer should work recursively on my data structures, it will descent on the TPoint records and generate redundant information in my serialized file. Is there a way to avoid this, by getting detailed information on the record?

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  • Add an existing ASP.NET Website to Subversion using AnkhSVN/Tortoise

    - by EasyDot
    How do you add a existing ASP.NET website to Subversion dealing with the problems that Subversion dosent support multiple folder structures in the repository: An default ASP.NET Website Solution folder structure look like this: C:\Documents and Settings\UserName\My Documents\Visual Studio 2008\Projects\WebSite1\ WebSite1.sln WebSite1.suo C:\Documents and Settings\UserName\My Documents\Visual Studio 2008\WebSites\WebSite1\ App_Data Default.aspx web.config How do i import the website to the repository? How do i get working copys of the website from the repository? How do i branch the website? How do i merge the websitebranch into the trunk?

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  • Interpreters: How much simplification?

    - by Ray
    In my interpreter, code like the following x=(y+4)*z echo x parses and "optimizes" down to four single operations performed by the interpreter, pretty much assembly-like: add 4 to y multiply <last operation result> with z set x to <last operation result> echo x In modern interpreters (for example: CPython, Ruby, PHP), how simplified are the "opcodes" for which are in end-effect run by the interpreter? Could I achieve better performance when trying to keep the structures and commands for the interpreter more complex and high-level? That would be surely a lot harder, or?

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  • Why do people still use C these days? [closed]

    - by Joshua
    C++ is clearly a far superior language than C, since it has many features that C lacks (although, C++'s object model isn't as ideal as say C#'s). With the coming off the new C++0x standard, why hasn't C been phased out to obscurity? C++ has been around for so long, since the '80s. The Linux kernel has already been ported to C++ with negligible performance differences. I believe, with no evidence, that larger program structures benefit in performance if written in C++ than in C, if only because of object interaction. Don't get me started on "objects-in-C!" libraries, which are all a terrible hack. (Not that C++'s object model is the most ideal, but it is almost up to snuff with C# using common ad-hoc techniques.)

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