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  • Which algorithms/data structures should I "recognize" and know by name?

    - by Earlz
    I'd like to consider myself a fairly experienced programmer. I've been programming for over 5 years now. My weak point though is terminology. I'm self-taught, so while I know how to program, I don't know some of the more formal aspects of computer science. So, what are practical algorithms/data structures that I could recognize and know by name? Note, I'm not asking for a book recommendation about implementing algorithms. I don't care about implementing them, I just want to be able to recognize when an algorithm/data structure would be a good solution to a problem. I'm asking more for a list of algorithms/data structures that I should "recognize". For instance, I know the solution to a problem like this: You manage a set of lockers labeled 0-999. People come to you to rent the locker and then come back to return the locker key. How would you build a piece of software to manage knowing which lockers are free and which are in used? The solution, would be a queue or stack. What I'm looking for are things like "in what situation should a B-Tree be used -- What search algorithm should be used here" etc. And maybe a quick introduction of how the more complex(but commonly used) data structures/algorithms work. I tried looking at Wikipedia's list of data structures and algorithms but I think that's a bit overkill. So I'm looking more for what are the essential things I should recognize?

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  • Type classes or implicit parameters? What do you prefer and why? [closed]

    - by Petr Pudlák
    I was playing a bit with Scalaz and I realized that Haskell's type classes are very similar to Scala's implicit parameters. While Haskell passes the methods defined by a type class using hidden dictionaries, Scala allows a similar thing using implicit parameters. For example, in Haskell, one could write: incInside :: (Functor f) => f Int -> f Int incInside = fmap (+ 1) and the same function using Scalaz: import scalaz._; import Scalaz._; def incInside[F[_]](x: F[Int])(implicit fn: Functor[F]): F[Int] = fn.fmap(x, (_:Int) + 1); I wonder: If you could choose (i.e. your favorite language would offer both), what would you pick - implicits or type classes? And what are your pros/cons?

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  • Five new junior developers and lots of complex tasks. What's now?

    - by mxe
    Our company has hired five new junior developers to help me to developer our product. Unfortunately the new features and incoming bug fixes usually require deeper knowledge than a recently graduated developer usually has (threading/concurrency, debugging performance bottlenecks in a complex system, etc.) Delegating (and planning) tasks which they (probably) can solve, answering their questions, mentoring/managing them, reviewing their code use up all of my time and I often feel that I could solve the issues less time than the whole delegating process takes (counting only my time). In addition I don't have time to solve the tasks which require deeper system knowledge/more advanced skills and it does not seem that it will change in the near future. So, what's now? What should I do to use their and my time effectively?

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  • How/where to run the algorithm on large dataset?

    - by niko
    I would like to run the PageRank algorithm on graph with 4 000 000 nodes and around 45 000 000 edges. Currently I use neo4j graph databse and classic relational database (postgres) and for software projects I mostly use C# and Java. Does anyone know what would be the best way to perform a PageRank computation on such graph? Is there any way to modify the PageRank algorithm in order to run it at home computer or server (48GB RAM) or is there any useful cloud service to push the data along the algorithm and retrieve the results? At this stage the project is at the research stage so in case of using cloud service if possible, would like to use such provider that doesn't require much administration and service setup, but instead focus just on running the algorith once and get the results without much overhead administration work.

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  • Remote Data connection in iphone app

    - by Tariq- iPHONE Programmer
    Hello, i am working with Social Networking iphone app which require remote data connection. So i hired a php developer in order to provide me RESTful services. But when i start working with him, he arguing me that he will not make stored procedures and web services. Instead of he suggested me to pass query as a parameter. Suppose If I have to call Search service, he told me to send POST request with 3 parameters: Query="select * from users", username=abd and password = 123 And i thing there is no such architecture in order to use remote data. Then he is saying it is possible through socket programming. And I am 100% sure this is not an appropriate way to access remote data. This is simply illogical. Thousands of iphone application using REST/SOAP services to make remote data connection He just declined me to provide RESTful services. Please its my heartily advice to all developers that post your own views over here. So that I can show to that developers that these are the views from all developers worldwide.

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  • How to store generated eigen faces for future face recognition?

    - by user3237134
    My code works in the following manner: 1.First, it obtains several images from the training set 2.After loading these images, we find the normalized faces,mean face and perform several calculation. 3.Next, we ask for the name of an image we want to recognize 4.We then project the input image into the eigenspace, and based on the difference from the eigenfaces we make a decision. 5.Depending on eigen weight vector for each input image we make clusters using kmeans command. Source code i tried: clear all close all clc % number of images on your training set. M=1200; %Chosen std and mean. %It can be any number that it is close to the std and mean of most of the images. um=60; ustd=32; %read and show images(bmp); S=[]; %img matrix for i=1:M str=strcat(int2str(i),'.jpg'); %concatenates two strings that form the name of the image eval('img=imread(str);'); [irow icol d]=size(img); % get the number of rows (N1) and columns (N2) temp=reshape(permute(img,[2,1,3]),[irow*icol,d]); %creates a (N1*N2)x1 matrix S=[S temp]; %X is a N1*N2xM matrix after finishing the sequence %this is our S end %Here we change the mean and std of all images. We normalize all images. %This is done to reduce the error due to lighting conditions. for i=1:size(S,2) temp=double(S(:,i)); m=mean(temp); st=std(temp); S(:,i)=(temp-m)*ustd/st+um; end %show normalized images for i=1:M str=strcat(int2str(i),'.jpg'); img=reshape(S(:,i),icol,irow); img=img'; end %mean image; m=mean(S,2); %obtains the mean of each row instead of each column tmimg=uint8(m); %converts to unsigned 8-bit integer. Values range from 0 to 255 img=reshape(tmimg,icol,irow); %takes the N1*N2x1 vector and creates a N2xN1 matrix img=img'; %creates a N1xN2 matrix by transposing the image. % Change image for manipulation dbx=[]; % A matrix for i=1:M temp=double(S(:,i)); dbx=[dbx temp]; end %Covariance matrix C=A'A, L=AA' A=dbx'; L=A*A'; % vv are the eigenvector for L % dd are the eigenvalue for both L=dbx'*dbx and C=dbx*dbx'; [vv dd]=eig(L); % Sort and eliminate those whose eigenvalue is zero v=[]; d=[]; for i=1:size(vv,2) if(dd(i,i)>1e-4) v=[v vv(:,i)]; d=[d dd(i,i)]; end end %sort, will return an ascending sequence [B index]=sort(d); ind=zeros(size(index)); dtemp=zeros(size(index)); vtemp=zeros(size(v)); len=length(index); for i=1:len dtemp(i)=B(len+1-i); ind(i)=len+1-index(i); vtemp(:,ind(i))=v(:,i); end d=dtemp; v=vtemp; %Normalization of eigenvectors for i=1:size(v,2) %access each column kk=v(:,i); temp=sqrt(sum(kk.^2)); v(:,i)=v(:,i)./temp; end %Eigenvectors of C matrix u=[]; for i=1:size(v,2) temp=sqrt(d(i)); u=[u (dbx*v(:,i))./temp]; end %Normalization of eigenvectors for i=1:size(u,2) kk=u(:,i); temp=sqrt(sum(kk.^2)); u(:,i)=u(:,i)./temp; end % show eigenfaces; for i=1:size(u,2) img=reshape(u(:,i),icol,irow); img=img'; img=histeq(img,255); end % Find the weight of each face in the training set. omega = []; for h=1:size(dbx,2) WW=[]; for i=1:size(u,2) t = u(:,i)'; WeightOfImage = dot(t,dbx(:,h)'); WW = [WW; WeightOfImage]; end omega = [omega WW]; end % Acquire new image % Note: the input image must have a bmp or jpg extension. % It should have the same size as the ones in your training set. % It should be placed on your desktop ed_min=[]; srcFiles = dir('G:\newdatabase\*.jpg'); % the folder in which ur images exists for b = 1 : length(srcFiles) filename = strcat('G:\newdatabase\',srcFiles(b).name); Imgdata = imread(filename); InputImage=Imgdata; InImage=reshape(permute((double(InputImage)),[2,1,3]),[irow*icol,1]); temp=InImage; me=mean(temp); st=std(temp); temp=(temp-me)*ustd/st+um; NormImage = temp; Difference = temp-m; p = []; aa=size(u,2); for i = 1:aa pare = dot(NormImage,u(:,i)); p = [p; pare]; end InImWeight = []; for i=1:size(u,2) t = u(:,i)'; WeightOfInputImage = dot(t,Difference'); InImWeight = [InImWeight; WeightOfInputImage]; end noe=numel(InImWeight); % Find Euclidean distance e=[]; for i=1:size(omega,2) q = omega(:,i); DiffWeight = InImWeight-q; mag = norm(DiffWeight); e = [e mag]; end ed_min=[ed_min MinimumValue]; theta=6.0e+03; %disp(e) z(b,:)=InImWeight; end IDX = kmeans(z,5); clustercount=accumarray(IDX, ones(size(IDX))); disp(clustercount); QUESTIONS: 1.It is working fine for M=50(i.e Training set contains 50 images) but not for M=1200(i.e Training set contains 1200 images).It is not showing any error.There is no output.I waited for 10 min still there is no output. I think it is going infinite loop.What is the problem?Where i was wrong? 2.Instead of running the training set everytime how eigen faces generated are stored so that stored eigen faces are used for future face recoginition for a new input image.So it reduces wastage of time.

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  • How to deal with colleagues refuse to follow practices?

    - by Adrian Shum
    I was discussing with another colleague about what we should be used when an DB entity is referring to another. I don't think there is any good reason to break the practice of putting the Primary Key in the referring entity. However, one of my colleague says: "You should use a surrogate key in the entity, but it is better to put the human-readable natural key in the referring entity. As long it is unique, it is fine and it is easier when you are doing support or maintenance job" I know it will works, but obviously it is not a good practice you are putting a non-PK unique column as "foreign key", just for gaining a bit of ease in writing SQL during support as we can have less table join. Though I mentioned the his approach is conceptual incorrect, and causing problem too practically etc, he seems rather trade off correctness in data model in exchange of ease of maintenance. And he said: "I know it is not good practice, but good practice is not golden rule" Honestly I feel frustrated when dealing with something like this. I know there are always case that we should break some rule or practice, but doubtless it is not such case now. What will you when you are facing situation like this? Please assume yourself being a senior developer which is expected to contribute in misc development direction and convention.

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  • I feel stuck in the center of Python, How to get past beginner

    - by Isov5
    I really apologize if this doesn't follow the S.O rules but I need a little help, I personally still classify myself as a beginner in python, Yet I've wrote a very small and VERY SURE impractical program for my boss to use. I know I'm still a beginner because simple things still perplex me but every book I read for beginners honestly just rehashes what I do already know but every 'more advanced' book doesn't really allow me to learn, they depend on example files and I never really understand why they built 'said' function or 'said' class. So onto my question... Is there any recommendations on a book or ANYTHING that pushes me out of this stage, I've used head first and normally they are really good but my issue there is they have me back tracking just to move forward again, It worked in HTML but its confusing in Python, basically I think I need to build a program while following along, Again I like HeadFirst's style but I need something that isn't going to make me have to remember one thing just to forget it... for record, I've checked into some O'Reilly books

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  • When should I make the first commit to source control?

    - by Kendall Frey
    I'm never sure when a project is far enough along to first commit to source control. I tend to put off committing until the project is 'framework-complete' and primarily commit features from then on. (I haven't done any personal projects large enough to have a core framework too big for this.) I have a feeling this isn't best practice, though I'm not sure what all could go wrong. Let's say, for example, I have a project which consists of a single code file. It will take about 10 lines of boilerplate code, and 100 lines to get the project working with extremely basic functionality (1 or 2 features). Should I first check in: The empty file? The boilerplate code? The first features? At some other point? Also, what are the reasons to check in at a specific point?

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  • Why was Python's popularity so sudden? [closed]

    - by Eric Wilson
    Python first appeared in 1991, but it was somewhat unknown until 2004, if the TIOBE rankings quantify anything meaningful. What happened? What caused the interest in this 13 year old language to go through the roof? Is there a reason that Python wasn't considered a real competitor to Perl in its first decade of existence? Is there a reason that Python didn't continue in relative obscurity for another ten years? I personally think that Python is a very nice language, and I'm glad that I'm not the only one. But it doesn't have corporate backing or a killer feature that would explain a sudden rise to relevance. Does anyone know the story?

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  • Amazon how does their remarkable search work?

    - by JonH
    We are working on a fairly large CRM system /knowledge management system in asp.net. The db is SQL server and is growing in size based on all the various relationships. Upper management keeps asking us to implement search much like amazon does. Right from there search you can specify to search certain objects like outdoor equipment, clothing, etc. and you can even select all. I keep mentioning to upper management that we need to define the various fields to search on. Their response is all fields...they probably look at the search and assume that it is so simple. I'm the guy who has to say hold on guys we are talking about amazon here. My question is how can amazon run a search on an "all" category. Also one of the things management here likes is the dynamic filters. For instance, searching robot brings up filters specific to a robot toy. How can I put management in check and at least come up with search functionality that works like amazon. We are using asp.net, SQL server 2008 and jquery.

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  • What defines code readability?

    - by zxcdw
    It is often said that readability is perhaps the most important quality-defining measure of a given piece of code for reasons concerning maintainability, ease of understanding and use. What defines the word readable in context of program source code? What kind of definitive aspects are there to code readability? I would be grateful with code examples of readable code, along with reasoning why it is readable.

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  • Why should I use Zend_Application?

    - by Billy ONeal
    I've been working on a Zend Framework application which currently does a bunch of things through Zend Application and a few resource plugins written for it. However, looking at this codebase now, it seems to me that using Zend_Application just makes things more complicated; and a plain, more "traditional" bootstrap file would do a better job of being transparent. This is even more the case because the individual components of Zend -- Zend_Controller, Zend_Navigation, etc. -- don't reference Zend_Application at all. Therefore they do things like "Well just call setRoute and be on your way," and the user is left scratching their head as to how to implement that in terms of the application.ini configuration file. This is not to say that one can't figure out what's going on by doing spelunking through the ZF source code. My problem with that approach is that it's to easy to depend on something that's an implementation detail, rather than a contract, and that all it seems to do is add an extra layer of indirection that one must wade through to understand an application. I look at pre ZF 1.8 example code, before Zend_Application existed, and everywhere I see plain bootstrap files that setup the MVC framework and get on their way. The code is clear and easy to understand, even if it is a bit repetitive. I like the DRY concept that Application gets you, but particularly when I'm assuming first people looking at the app's code aren't really familiar with Zend at all, I'm considering blowing away any dependence I have on Zend_Application and returning to a traditional bootstrap file. Now, my concern here is that I don't have much experience doing this, and I don't want to get rid of Zend_Application if it does something particularly important of which I am unaware, or something of that nature. Is there a really good reason I should keep it around?

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  • Should I comment Tables or Columns in my database?

    - by jako
    I like to comment my code with various information, and I think most people nowadays do so while writing some code. But when it comes to database tables or columns, I have never seen anyone setting some comments, and, to be honest, I don't even think of looking for comments there. So I am wondering if some people are commenting their DB strcuture here, and if I should bother commenting, for instance when I create a new column to an existing table?

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  • Good Practices for development team in large projects

    - by Moshe Magnes
    Since I started learning C a few years ago, I have never been a part of a team that worked on a project. Im very interested to know what are the best practices for writing large projects in C. One of the things i want to know, is when (not how) do I split my project into different source files. My previous experience is with writing a header-source duo (the functions defined in the header are written in the source). I want to know what are the best practices for splitting a project, and some pointers on important things when writing a project as part of a team.

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  • Is there a solution for SugarCRM that can map roles or privileges to Active Directory groups?

    - by Cory Larson
    We're presenting SugarCRM as an option to one of our clients, but they want to drive permissions within Sugar by users' AD groups. Current LDAP integration with SugarCRM only does password management. Does anybody know of a plug-in that supports this? I've searched and have not been able to find anything. Has anybody change the LDAP module code within Sugar to accommodate these features? I'd be interested in chatting with you. I apologize if this isn't on the correct site; neither serverfault nor stackoverflow seemed like the correct place. Perhaps webapps? Thanks!

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  • Do I need to know servlets and JSP to learn spring or hibernate or any other java web frameworks?

    - by KyelJmD
    I've been asking a lot of people where to start learning java web development, I already know core java (Threading,Generics,Collections, a little experience with (JDBC)) but I do not know JSPs and servlets. I did my fair share of development with several web based applications using PHP for server-side and HTML,CSS,Javascript,HTML5 for client side. Most people that I asked told me to jump right ahead to Hibernate while some told me that I do not need to learn servlets and jsps and I should immediately study the Spring framework. Is this true? do I not need to learn servlets and JSPs to learn hibernate or Spring? All of their answers confused me and now I am completely lost what to learn or study. I feel that if I skipped learning JSP and servlets I would missed a lot of important concepts that will surely help me in the future. So the question, do I need to have foundation/know servlets and JSP to learn spring or hibernate or any other java web frameworks.?

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  • Handling Errors In PHP When Using MVC

    - by James Jeffery
    I've been using Codeigniter a lot recently, but one thing that gets on my nerves is handling errors and displaying them to the user. I've never been good at handling errors without it getting messy. My main concern is when returning errors to the user. Is it good practice to use exceptions and throw/catch exceptions rather than returning 0 or 1 from functions and then using if/else to handle the errors. Thus, making it easier to inform the user about the issue. I tend to go away from exceptions. My Java tutor at university some years ago told me "exceptions shouldn't be used in production code it's more for debugging". I get the feeling he was lying. But, an example, I have code that adds a user to a database. During the process more than 1 thing could go wrong, such as a database issue, a duplicate entry, a server issue, etc. When an issue happens during registration the user needs to know about it. What's the best way to handle errors in PHP, keeping in mind that I'm using an MVC framework.

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  • Is it ok to replace optimized code with readable code?

    - by Coder
    Sometimes you run into a situation where you have to extend/improve an existing code. You see that the old code is very lean, but it's also difficult to extend, and takes time to read. Is it a good idea to replace it with modern code? Some time ago I liked the lean approach, but now, it seems to me that it's better to sacrifice a lot of optimizations in favor of higher abstractions, better interfaces and more readable, extendable code. The compilers seem to be getting better as well, so things like struct abc = {} are silently turned into memsets, shared_ptrs are pretty much producing the same code as raw pointer twiddling, templates are working super good because they produce super lean code, and so on. But still, sometimes you see stack based arrays and old C functions with some obscure logic, and usually they are not on the critical path. Is it good idea to change such code if you have to touch a small piece of it either way?

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  • One method with many behaviours or many methods

    - by Krowar
    This question is quite general and not related to a specific language, but more to coding best practices. Recently, I've been developing a feature for my app that is requested in many cases with slightly different behaviours. This function send emails , but to different receivers, or with different texts according to the parameters. The method signature is something like public static sendMail (t_message message = null , t_user receiver = null , stream attachedPiece = null) And then there are many condition inside the method, like if(attachedPiece != null) { } I've made the choice to do it this way (with a single method) because it prevents me to rewrite the (nearly) same method 10 times, but I'm not sure that it's a good practice. What should I have done? Write 10 sendMail method with different parameters? Are there obvious pros and cons for these different ways of programming? Thanks a lot.

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  • What is the exception in java code? [closed]

    - by Karandeep Singh
    This java code is for reverse the string but it returning concat null with returned string. import java.util.*; import java.util.logging.Level; import java.util.logging.Logger; public class Practice { public static void main(String[] args) { String str = ""; try { str = reverse("Singh"); } catch (Exception ex) { Logger.getLogger(Practice.class.getName()).log(Level.SEVERE, null, ex); System.out.print(ex.getMessage()); }finally{ System.out.println(str); } } public static String reverse(String str) throws Exception{ String temp = null; if(str.length()<=0){ throw new Exception("empty"); }else{ for(int i=str.length()-1;i>=0;i--){ temp+=str.charAt(i); } } return temp.trim(); } } Output: nullhgniS

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  • Can I use silverlight for building SocialNetworking applicaiton?

    - by dimmV
    Hi all, I am wondering: how feasible it would be to start developing a social networking website entirely based on silverlight; This has been fairly discussed over the years in favor of HTML. Has something changed with silverlight improvements over the years? What about: * Performance -- active users -- technology used, MVVM + MEF (possibility of lags, server memory overflow...) * Security --- WCF Ria Services & EF What are your thoughts on this subject?

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  • Security in a private web service

    - by Oni
    I am developing a web site and a web service for a small on-line game. Technically, I'll be using Express (node.js) and MongoDB+Redis for the databases. This the structure I came up with: One Express server that will server as the Web Service. This will connect to the databases. One Express server that will provide the web site. It will connect to the Web Service to retrieve and push the information. iOS and Android application will be able to interact with the WebService. Taking into account: It is a small game. The information transferred is not critical. There will NOT be third party applications. At least for the moment. My concern is about which level of security I should use in each of the scenarios: Security of the user playing through web browser Security of the applications and the Web Server connecting to the WS. I have take a look at the different options and: OAuth and/or Https is too much for this scenario, isn't it? Will be a good option to hash the user and password with MD5(or similar) and some salt? I would like to get some directions and investigate by my own rather than getting a response like "you should you use this node.js module..." Thanks in advance,

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  • what is best book to learn optimized programming in java [closed]

    - by Abhishek Simon
    Possible Duplicate: Is there a canonical book for learning Java as an experienced developer? Let me elaborate a little: I used to be a C/C++ programmer where I used data structure concept like trees, queues stack etc and tried to optimize as much as possible, minimum no. of loops, variables and tried to make it efficient. It's been a couple of years that I started writing java codes, but it is simply not that efficient in terms of performance, memory intensive etc. To the point: I want to enter programming challenges using java so I need to improve my approach at things I program. So please suggest me some books that can help me learn to program better and have a chance in solving challenges in programming.

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  • Advice for beginner programmer

    - by user3461957
    I am beginner in software development. I noticed when I try to learn one technology let's say .NET I loose my grip over other for example Java. I thought it would be better to concentrate on one technology either Java or .NET to make significant advancement and be an expert, because they can be many details which one can ignore when keeps on changing between technologies. Is my decision right? Do experts choose this approach? Update: Should I pursue my career knowing one technology or not?

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