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• Agile and Scrum burning me down please help me figuring out the truth

  - by jadook

  hi all, in the last while I installed MS-TFS 2008 then started to get myself prepared to use Agile Process Guidance template shipped with the TFS. with little googling I passed through Mike Cohn materials: I watched his conference in youtube "sponsored by google: http://www.youtube.com/watch?v=fb9Rzyi8b90 http://www.youtube.com/watch?v=jeT0pOVg0EI Read his book "Agile Estimating and Planning" Watching the video series in his website: http://www.mountaingoatsoftware.com/presentations-tag/video-recorded I was very happy while absorbing and eating the techniques he is using with the teams and how agile and scrum is such a great software process/methodology until I saw Mike answering a question regarding an architect role and talking about the requirements document... at that point everything start falling apart due to the following: Last year I had been assigned to make full analysis "including requirements gathering" for big project "very high priority project". within 2 months of hardwork, dedication and commitment I delivered the whole analysis with full satisfaction of the customer and my BOSS and ZERO amendments. Later on, the project entered the architecting, development ... phases. due to the fact that the system included many competitive and exciting features I requested patenting it and its going in the process... so imagine you are the kind of person who used to love facing all kind of challenges and returning with excellent experience and results for the stakeholders and yourself, How fairly agile and scrum processes will credit and admit your talent and passion while the scrum master/coach treat the team as one unit that accomplish user stories and converge through trial and error approach??!!!! with that dark thoughts about agile and scrum I found many people "anti agile" and on top of them is "Crispin Rogers Johnson": http://agile-crispin.blogspot.com/ that guy made anti statement for everything Mike Cohn used to talk about. I really don't know what to do next! so any guidance will be appreciated. Thanks,

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• Where can I find clear examples of MVC?

  - by Tom

  I've read a couple of things about MVCs but I still don't understand when they should be used and when they shouldn't be used. I am looking for clear examples that say things like "if you're developing this then you should use MVC, like this" and "if you're developing this, you shouldn't use MVC." Most of the examples I've seen rely on complex frameworks which have already implemented everything and you have to learn the framework and use it a lot to understand what's really happening. To many programmers, phrasings such as "UI business logic" sound like marketing terms — for example, the words "Instead the View binds directly to a Presentation Model" are used in this post. I am aware of the dangers that may lurk in the shadows as MVC is a concept and everyone feels like they know it best, yet nobody really knows exactly how to use it because there may be a lot of variables involved and everyone is allowed to have a different perspective on how to dissect a project into the Model, the View and the Controller. There is a lot of theory out there but very few clear examples. What I'm looking for are not "the best" ways of doing it so this should not be considered as subjective; I'm looking for different simple implementations that would allow me to decide on my own which are the best approaches. Succinctly: What are good on-line resources that present pro and con arguments to using MVC in various situations and provide clear examples to help the reader understand the concept?

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• structured vs. unstructured data in db

  - by Igor

  the question is one of design. i'm gathering a big chunk of performance data with lots of key-value pairs. pretty much everything in /proc/cpuinfo, /proc/meminfo/, /proc/loadavg, plus a bunch of other stuff, from several hundred hosts. right now, i just need to display the latest chunk of data in my UI. i will probably end up doing some analysis of the data gathered to figure out performance problems down the road, but this is a new application so i'm not sure what exactly i'm looking for performance-wise just yet. i could structure the data in the db -- have a column for each key i'm gathering. the table would end up being O(100) columns wide, it would be a pain to put into the db, i would have to add new columns if i start gathering a new stat. but it would be easy to sort/analyze the data just using SQL. or i could just dump my unstructured data blob into the table. maybe three columns -- host id, timestamp, and a serialized version of my array, probably using JSON in a TEXT field. which should I do? am i going to be sorry if i go with the unstructured approach? when doing analysis, should i just convert the fields i'm interested in and create a new, more structured table? what are the trade-offs i'm missing here?

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• rails + compass: advantages vs using haml + blueprint directly

  - by egarcia

  I've got some experience using haml (+sass) on rails projects. I recently started using them with blueprintcss - the only thing I did was transform blueprint.css into a sass file, and started coding from there. I even have a rails generator that includes all this by default. It seems that Compass does what I do, and other things. I'm trying to understand what those other things are - but the documentation/tutorials weren't very clear. These are my conclusions: Compass comes with built-in sass mixins that implement common CSS idioms, such as links with icons or horizontal lists. My solution doesn't provide anything like that. (1 point for Compass). Compass has several command-line options: you can create a rails project, but you can also "install" it on an existing rails project. A rails generator could be personalized to do the same thing, I guess. (Tie). Compass has two modes of working with blueprint: "basic" and "semantic" usage. I'm not clear about the differences between those. With my rails generator I only have one mode, but it seems enough. (Tie) Apparently, Compass is prepared to use other frameworks, besides blueprint (e.g. YUI). I could not find much documentation about this, and I'm not interested on it anyway - blueprint is ok for me (Tie). Compass' learning curve seems a bit stiff and the documentation seems sparse. Learning could be a bit difficult. On the other hand, I know the ins and outs of my own system and can use it right away. (1 point for my system). With this analysis, I'm hesitant to give Compass a try. Is my analysis correct? Are Am I missing any key points, or have I evaluated any of these points wrongly?

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• In Ruby, how to implement global behaviour?

  - by Gordon McAllister

  Hi all, I want to implement the concept of a Workspace. This is a global concept - all other code will interact with one instance of this Workspace. The Workspace will be responsible for maintaining the current system state (i.e. interacting with the system model, persisting the system state etc) So what's the best design strategy for my Workspace, bearing in mind this will have to be testable (using RSpec now, but happy to look at alternatives). Having read thru some open source projects out there and I've seen 3 strategies. None of which I can identify as "the best practice". They are: Include the singleton class. But how testable is this? Will the global state of Workspace change between tests? Implemented all behaviour as class methods. Again how do you test this? Implemented all behaviour as module methods. Not sure about this one at all! Which is best? Or is there another way? Thanks, Gordon

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• using Autofac in a multi-layered architecture

  - by Kamyar

  I'm fairly new to the DI/IoC concept and would like to use Autofac in a 3-layered ASP.NET Webforms application. UI layer: An ASP.NET webforms website. BLL: Business logic layer which calls the repositories on DAL. DAL: .EDMX file (Entity Model) and ObjectContext with Repository classes which abstract the CRUD operations for each entity. Entities: The POCO Entities. Persistence Ignorant. Generated by Microsoft's ADO.Net POCO Entity Generator. I have asked a more general question here. Basically, I'd like to create an obejctcontext per HttpContext in my DAL. But i don't want to add a reference to DAL in UI or access to HttpContext in DAL directly. I guess this is where IoC tools come to play. The answer to my previous question is a very good example of using Windsor Castle. I'd like to use Autofac as my IoC tool and Don't know how to achieve this. (How to access DAL in application_start to register the component while I don't want to reference it in my UI, what are the proper references to be able to use DAL component in BLL with Autofac, Should I register BLL as a component with Autofac too) Sorry folks for not providing an explicit question and requesting a kind of working example, But I'm very unfamiliar to the whole IoC concept and I don't think I can achieve it to use in my current time-limited project.

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• What should every developer know about databases?

  - by Aaronaught

  Whether we like it or not, many if not most of us developers either regularly work with databases or may have to work with one someday. And considering the amount of misuse and abuse in the wild, and the volume of database-related questions that come up every day, it's fair to say that there are certain concepts that developers should know - even if they don't design or work with databases today. So: What are the important concepts that developers and other software professionals ought to know about databases? Guidelines for Responses: Keep your list short. One concept per answer is best. Be specific. "Data modelling" may be an important skill, but what does that mean precisely? Explain your rationale. Why is your concept important? Don't just say "use indexes." Don't fall into "best practices." Convince your audience to go learn more. Upvote answers you agree with. Read other people's answers first. One high-ranked answer is a more effective statement than two low-ranked ones. If you have more to add, either add a comment or reference the original. Don't downvote something just because it doesn't apply to you personally. We all work in different domains. The objective here is to provide direction for database novices to gain a well-founded, well-rounded understanding of database design and database-driven development, not to compete for the title of most-important.

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• What is the difference between cubes and the Unified Dimensional Model (if any)?

  - by ngm

  I'm currently researching SQL Server 2008 as a business intelligence solution, and currently looking at Analysis Services (and I'm pretty new to business intelligence as a whole...) I'm a bit confused by some of the terms in SSAS, particularly the conceptual differences between cubes and MS's Unified Dimensional Model. I believe that a cube in SSAS is basically an OLAP cube -- dimensions, measures, something that sits between the underlying data source and a business user. But then that's kind of what I understand UDM to be as well. The docs for SQL Server 2005 seem to suggest as much: "A cube is essentially synonymous with a Unified Dimensional Model (UDM)". But then the SQL Server 2008 pages sort of suggest that UDM is a wrapper for both multidimensional data (cubes) and relational data: "Use the Unified Dimensional Model to provide one consolidated business view for relational and multidimensional data that includes business entities, business logic, calculations, and metrics." This blog post suggests similarly: "UDM provides a single dimensional model for all OLAP analysis and relational reporting needs. So you can use either MDX or SQL" Is UDM something that sits above cubes? Or are they the same thing? I presume I would develop cubes with the Cube Designer application; what would I develop a UDM with?

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• Scripts to parse and download iTunes Connect and AppStore data

  - by bradhouse

  I'm looking for recommendations of a script or series of scripts that download and parse iTunes Connect sales data and AppStore comments, ratings and rankings data for a defined app. I'm also aware of solutions like: AppViz appsales-mobile iphone-stats Heartbeat.app I'm sure I'll find a few more with more searching. I can't help but feel there must be a really decent set of open source scripts out there to do this, given how many developers are now writing apps for the AppStore. Would be interested to hear any commercial offerings as well (although my personal preference is for open source, so I can at least see what it is doing with my iTunes Connect login credentials). To be clear, I'm really looking for something that hits all of the areas mentioned: App Store (per store) Comments Ratings Category/store rankings iTunes Connect The contents of the sales reports Analysis/graphs of the data is not necessary (but would be a nice to have I guess). I'm not really looking for something like AppSales Mobile above, I would like the raw data so I can do my own analysis and formatting. So far it looks like AppViz (listed above) is the best out there. Any suggestions on what is good/available or should I just go roll my own?

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• Exponential regression : p-value and F significance

  - by Saravanan K

  I am new to statistics. I have a set of independent data and dependent data (X,Y), where I would like to do an exponential regression to obtain its p-value and significant F (already obtained R2 and also the coefficients through mathematical calculation). What is the natural evolution from the (X,Y) data to mathematically calculate those variables. Spent a week on the internet to study this but unable to find the right answer. Often an exponential data, y=be^(mx) will be converted first to a linear data, ln y = mx + ln b . Then a linear regression will done on the converted data, obtaining its p-value etc. Assume we use a statistical tool such as Excel's Analysis ToolPak: Data Analysis : Regression, it will produce a result such as below, I believe the p-value and Significant F value is representing the converted linear data and not the original exponential data. Questions: What is the approach/steps used by Excel to get the p-value and Significant F value for the converted linear data as shown in the statistic output in the image above? It is not clear in their help page or website. Can the p-value and Significant F could be mathematically calculated for exponential regression without using a statistical tool? Can you assist to point me to the right link if this has been answered before.

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• Is there a disassembler + debugger for java (ala OllyDbg / SoftICE for assembler)?

  - by Ran Biron

  Is there a utility similar to OllyDbg / SoftICE for java? I.e. execute class (from jar / with class path) and, without source code, show the disassembly of the intermediate code with ability to step through / step over / search for references / edit specific intermediate code in memory / apply edit to file... If not, is it even possible to write something like this (assuming we're willing to live without hotspot for the debug duration)? Edit: I'm not talking about JAD or JD or Cavaj. These are fine decompilers, but I don't want a decompiler for several reasons, most notable is that their output is incorrect (at best, sometimes just plain wrong). I'm not looking for a magical "compiled bytes to java code" - I want to see the actual bytes that are about to be executed. Also, I'd like the ability to change those bytes (just like in an assembly debugger) and, hopefully, write the changed part back to the class file. Edit2: I know javap exists - but it does only one way (and without any sort of analysis). Example (code taken from the vmspec documentation): From java code, we use "javac" to compile this: void setIt(int value) { i = value; } int getIt() { return i; } to a java .class file. Using javap -c I can get this output: Method void setIt(int) 0 aload_0 1 iload_1 2 putfield #4 5 return Method int getIt() 0 aload_0 1 getfield #4 4 ireturn This is OK for the disassembly part (not really good without analysis - "field #4 is Example.i"), but I can't find the two other "tools": A debugger that goes over the instructions themselves (with stack, memory dumps, etc), allowing me to examine the actual code and environment. A way to reverse the process - edit the disassembled code and recreate the .class file (with the edited code).

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• deadlock because of foreign key?

  - by George2

  Hello everyone, I am using SQL Server 2008 Enterprise. I met with deadlock in the following store procedure, but because of my fault, I did not record the deadlock graph. But now I can not reproduce deadlock issue. I want to have a postmortem to find the root cause of deadlock to avoid deadlock in the future. The deadlock happens on delete statement. For the delete statement, Param1 is a column of table FooTable, Param1 is a foreign key of another table (refers to another primary key clustered index column of the other table). There is no index on Param1 itself for table FooTable. FooTable has another column which is used as clustered primary key, but not Param1 column. Here is my guess why there is deadlock, and I want to let people review whether my analysis is correct? Since Param1 column has no index, there will be a table scan, and will acquire table level lock, because of foreign key, the delete operation will also need to check master table (e.g. to acquire lock on master table); Some operation on master table acquires master table lock, but want to acquire lock on FooTable; (1) and (2) cause cycle lock which makes deadlock happen. My analysis correct? Any reproduce scenario? create PROCEDURE [dbo].[FooProc] ( @Param1 int ,@Param2 int ,@Param3 int ) AS DELETE FooTable WHERE Param1 = @Param1 INSERT INTO FooTable ( Param1 ,Param2 ,Param3 ) VALUES ( @Param1 ,@Param2 ,@Param3 ) DECLARE @ID bigint SET @ID = ISNULL(@@Identity,-1) IF @ID > 0 BEGIN SELECT IdentityStr FROM FooTable WHERE ID = @ID END thanks in advance, George

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• Getting started with massive data

  - by Max

  I'm a math guy and occasionally do some statistics/machine learning analysis consulting projects on the side. The data I have access to are usually on the smaller side, at most a couple hundred of megabytes (and almost always far less), but I want to learn more about handling and analyzing data on the gigabyte/terabyte scale. What do I need to know and what are some good resources to learn from? Hadoop/MapReduce is one obvious start. Is there a particular programming language I should pick up? (I primarily work now in Python, Ruby, R, and occasionally Java, but it seems like C and Clojure are often used for large-scale data analysis?) I'm not really familiar with the whole NoSQL movement, except that it's associated with big data. What's a good place to learn about it, and is there a particular implementation (Cassandra, CouchDB, etc.) I should get familiar with? Where can I learn about applying machine learning algorithms to huge amounts of data? My math background is mostly on the theory side, definitely not on the numerical or approximation side, and I'm guessing most of the standard ML algorithms don't really scale. Any other suggestions on things to learn would be great!

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• Is this a good job description? What title would you give this position?

  - by Zack Peterson

  Department: Information Technology Reports To: Chief Information Officer Purpose: Company's ________________ is specifically engaged in the development of World Wide Web applications and distributed network applications. This person is concerned with all facets of the software development process and specializes in software product management. He or she contributes to projects in an application architect role and also performs individual programming tasks. Essential Duties & Responsibilities: This person is involved in all aspects of the software development process such as: Participation in software product definitions, including requirements analysis and specification Development and refinement of simulations or prototypes to confirm requirements Feasibility and cost-benefit analysis, including the choice of architecture and framework Application and database design Implementation (e.g. installation, configuration, customization, integration, data migration) Authoring of documentation needed by users and partners Testing, including defining/supporting acceptance testing and gathering feedback from pre-release testers Participation in software release and post-release activities, including support for product launch evangelism (e.g. developing demonstrations and/or samples) and subsequent product build/release cycles Maintenance Qualifications: Bachelor's degree in computer science or software engineering Several years of professional programming experience Proficiency in the general technology of the World Wide Web: Hypertext Transfer Protocol (HTTP) Hypertext Markup Language (HTML) JavaScript Cascading Style Sheets (CSS) Proficiency in the following principles, practices, and techniques: Accessibility Interoperability Usability Security (especially prevention of SQL injection and cross-site scripting (XSS) attacks) Object-oriented programming (e.g. encapsulation, inheritance, modularity, polymorphism, etc.) Relational database design (e.g. normalization, orthogonality) Search engine optimization (SEO) Asynchronous JavaScript and XML (AJAX) Proficiency in the following specific technologies utilized by Company: C# or Visual Basic .NET ADO.NET (including ADO.NET Entity Framework) ASP.NET (including ASP.NET MVC Framework) Windows Presentation Foundation (WPF) Language Integrated Query (LINQ) Extensible Application Markup Language (XAML) jQuery Transact-SQL (T-SQL) Microsoft Visual Studio Microsoft Internet Information Services (IIS) Microsoft SQL Server Adobe Photoshop

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• How would the 'Model' in a Rails-type webapp be implemented in a functional programming langauge?

  - by ceptorial

  In MVC web development frameworks such as Ruby on Rails, Django, and CakePHP, HTTP requests are routed to controllers, which fetch objects which are usually persisted to a backend database store. These objects represent things like users, blog posts, etc., and often contain logic within their methods for permissions, fetching and/or mutating other objects, validation, etc. These frameworks are all very much object oriented. I've been reading up recently on functional programming and it seems to tout tremendous benefits such as testability, conciseness, modularity, etc. However most of the examples I've seen for functional programming implement trivial functionality like quicksort or the fibonnacci sequence, not complex webapps. I've looked at a few 'functional' web frameworks, and they all seem to implement the view and controller just fine, but largely skip over the whole 'model' and 'persistence' part. (I'm talking more about frameworks like Compojure which are supposed to be purely functional, versus something Lift which conveniently seems to use the OO part of Scala for the model -- but correct me if I'm wrong here.) I haven't seen a good explanation of how functional programming can be used to provide the metaphor that OO programming provides, i.e. tables map to objects, and objects can have methods which provide powerful, encapsulated logic such as permissioning and validation. Also the whole concept of using SQL queries to persist data seems to violate the whole 'side effects' concept. Could someone provide an explanation of how the 'model' layer would be implemented in a functionally programmed web framework?

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• Why is this attempt at a binary search crashing?

  - by Ian Campbell

  I am fairly new to the concept of a binary search, and am trying to write a program that does this in Java for personal practice. I understand the concept of this well, but my code is not working. There is a run-time exception happening in my code that just caused Eclipse, and then my computer, to crash... there are no compile-time errors here though. Here is what I have so far: public class BinarySearch { // instance variables int[] arr; int iterations; // constructor public BinarySearch(int[] arr) { this.arr = arr; iterations = 0; } // instance method public int findTarget(int targ, int[] sorted) { int firstIndex = 1; int lastIndex = sorted.length; int middleIndex = (firstIndex + lastIndex) / 2; int result = sorted[middleIndex - 1]; while(result != targ) { if(result > targ) { firstIndex = middleIndex + 1; middleIndex = (firstIndex + lastIndex) / 2; result = sorted[middleIndex - 1]; iterations++; } else { lastIndex = middleIndex + 1; middleIndex = (firstIndex + lastIndex) / 2; result = sorted[middleIndex - 1]; iterations++; } } return result; } // main method public static void main(String[] args) { int[] sortedArr = new int[] { 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29 }; BinarySearch obj = new BinarySearch(sortedArr); int target = sortedArr[8]; int result = obj.findTarget(target, sortedArr); System.out.println("The original target was -- " + target + ".\n" + "The result found was -- " + result + ".\n" + "This took " + obj.iterations + " iterations to find."); } // end of main method } // end of class BinarySearch

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• Simplest way to automatically alter "const" value in Java during compile time

  - by Michael Mao

  Hi all: This is a question corresponds to my uni assignment so I am very sorry to say I cannot adopt any one of the following best practices in a short time -- you know -- assignment is due tomorrow :( link to Best way to alter const in Java on StackOverflow Basically the only task (I hope so) left for me is the performance tuning. I've got a bunch of predefined "const" values in my single-class agent source code like this: //static final values private static final long FT_THRESHOLD = 400; private static final long FT_THRESHOLD_MARGIN = 50; private static final long FT_SMOOTH_PRICE_IDICATOR = 20; private static final long FT_BUY_PRICE_MODIFIER = 0; private static final long FT_LAST_ROUNDS_STARTTIME = 90; private static final long FT_AMOUNT_ADJUST_MODIFIER = 5; private static final long FT_HISTORY_PIRCES_LENGTH = 10; private static final long FT_TRACK_DURATION = 5; private static final int MAX_BED_BID_NUM_PER_AUC = 12; I can definitely alter the values manually and then compile the code to give it another go around. But the execution time for a thorough "statistic analysis" usually requires over 2000 times of execution, which will typically lasts more than half an hour on my own laptop... So I hope there is a way to alter values using other ways than dig into the source code to change the "const" values there, so I can automatically distributed compiled code to other people's PC and let them run the statistic analysis instead. One other reason for a automatically value adjustment is that I can try using my own agent to defeat itself by choosing different "const" values. Although my values are derived from previous history and statistical results, they are far from the most optimized values. I hope there is a easy way so I can quickly adopt that so to have a good sleep tonight while the computer does everything for me... :) Any hints on this sort of stuff? Any suggestion is welcomed and much appreciated.

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• Understanding sql queries formulation methodoloy. How do you think while formulating Sql Queries

  - by Shantanu Gupta

  I have been working on sql server and front end coding and have usually faced problem formulating queries. I do understand most of the concepts of sql that are needed in formulating queries but whenever some new functionality comes into the picture that can be dont using sql query, i do usually fails resolving them. I am very comfortable with select queries using joins and all such things but when it comes to DML operation i usually fails For every query that i never done before I usually finds uncomfortable with that while creating them. Whenever I goes for an interview I usually faces this problem. Is it their some concept behind approaching on formulating sql queries. Eg. I need to create an sql query such that A table contain single column having duplicate record. I need to remove duplicate records. I know i can find the solution to this query very easily on Googling, but I want to know how everyone comes to the desired result. Is it something like Practice Makes Man Perfect i.e. once you did it, next time you will be able to formulate or their is some logic or concept behind.

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• How to get a Class literal from a generically specific Class

  - by h2g2java

  There are methods like these which require Class literals as argument. Collection<EmpInfo> emps = SomeSqlUtil.select( EmpInfo.class, "select * from emps"); or GWT.create(Razmataz.class); The problem presents itself when I need to supply generic specific classes like EmpInfo<String> Razmataz<Integer> The following would be wrong syntax Collection<EmpInfo<String>> emps = SomeSqlUtil.select( EmpInfo<String>.class, "select * from emps"); or GWT.create(Razmataz<Integer>.class); Because you cannot do syntax like Razmataz<Integer>.class So, how would I be able to squeeze a class literal out of EmpInfo<String> Razmataz<Integer> so that I could feed them as arguments to methods requiring Class literals? Further info Okay, I confess that I am asking this primarily for GWT. I have a pair of GWT RPC interface Razmataz. (FYI, GWT RPC interface has to be defined in server-client pairs). I plan to use the same interface pair for communicating whether it be String, Integer, Boolean, etc. GWT.create(Razmataz) for Razmataz<T> complains that, since I did not specify T, GWT compiler treated it as Object. Then GWT compiler would not accept Object class. It needs to be more specific than being an Object. So, it seems there is no way for me to tell GWT.create what T is because a Class literal is a runtime concept while generics is a compile time concept, Right?

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• Java: How to workaround the lack of Equatable interface?

  - by java.is.for.desktop

  Hello, everyone! As far as I know, things such as SortedMap or SortedSet, use compareTo (rather than equals) on Comparable<?> types for checking equality (contains, containsKey). But what if certain types are equatable by concept, but not comparable? I have to declare a Comparator<?> and override the method int compareTo(T o1, To2). OK, I can return 0 for instances which are considered equal. But, for unqeual instances, what do I return when an order is not evident? Is the approach of using SortedMap or SortedSet on equatable but (by concept) not comparable types good anyway? Thank you! EDIT: I don't want to store things sorted, but would I use "usual" Map and Set, I couldn't "override" the equality-behavior. EDIT 2: Why I can't just override equals(...): I need to alter the equality-behavior of a foreign class. Can't edit it. EDIT 3: Just think of .NET: They have IEquatable interface which cat alter the equality-behavior without touching the comparable behavior.

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• What does it mean for an OS to "execute within user processes"? Do any modern OS's use that approach

  - by Chris Cooper

  I have recently become interested in operating system, and a friend of mine lent me a book called Operating Systems: Internals and Design Principles (I have the third edition), published in 1998. It's been a very interesting book so far, but I have come to the part dealing with process control, and it's using UNIX System V as one of its examples of an operating system that executes within user processes. This concept has struck me as a little strange. First of all, does this mean that OS instructions and data are stored in each user of the processes? Probably not, because that would be an absurdly redundant scheme. But if not, then what does it mean to "execute within" a user process? Do any modern operating systems use this approach? It seems much more logical to have the operating system execute as its own process, or even independently of all processes, if you're short on memory. All the inter-accessiblilty of process data required for this layout seems to greatly complicate things. (But maybe that's just because I don't quite get the concept ;D) Here is what the book says: "Execution within User Processes: An alternative that is common with operation systems on smaller machines is to execute virtually all operating system software in the context of a user process. ... "

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• R: Are there any alternatives to loops for subsetting from an optimization standpoint?

  - by Adam

  A recurring analysis paradigm I encounter in my research is the need to subset based on all different group id values, performing statistical analysis on each group in turn, and putting the results in an output matrix for further processing/summarizing. How I typically do this in R is something like the following: data.mat <- read.csv("...") groupids <- unique(data.mat$ID) #Assume there are then 100 unique groups results <- matrix(rep("NA",300),ncol=3,nrow=100) for(i in 1:100) { tempmat <- subset(data.mat,ID==groupids[i]) #Run various stats on tempmat (correlations, regressions, etc), checking to #make sure this specific group doesn't have NAs in the variables I'm using #and assign results to x, y, and z, for example. results[i,1] <- x results[i,2] <- y results[i,3] <- z } This ends up working for me, but depending on the size of the data and the number of groups I'm working with, this can take up to three days. Besides branching out into parallel processing, is there any "trick" for making something like this run faster? For instance, converting the loops into something else (something like an apply with a function containing the stats I want to run inside the loop), or eliminating the need to actually assign the subset of data to a variable?

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• Using an element against an entire list in Haskell

  - by Snick

  I have an assignment and am currently caught in one section of what I'm trying to do. Without going in to specific detail here is the basic layout: I'm given a data element, f, that holds four different types inside (each with their own purpose): data F = F Float Int, Int a function: func :: F -> F-> Q Which takes two data elements and (by simple calculations) returns a type that is now an updated version of one of the types in the first f. I now have an entire list of these elements and need to run the given function using one data element and return the type's value (not the data element). My first analysis was to use a foldl function: myfunc :: F -> [F] -> Q myfunc y [] = func y y -- func deals with the same data element calls myfunc y (x:xs) = foldl func y (x:xs) however I keep getting the same error: "Couldn't match expected type 'F' against inferred type 'Q'. In the first argument of 'foldl', namely 'myfunc' In the expression: foldl func y (x:xs) I apologise for such an abstract analysis on my problem but could anyone give me an idea as to what I should do? Should I even use a fold function or is there recursion I'm not thinking about?

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• Can ScalaCheck/Specs warnings safely be ignored when using SBT with ScalaTest?

  - by pdbartlett

  I have a simple FunSuite-based ScalaTest: package pdbartlett.hello_sbt import org.scalatest.FunSuite class SanityTest extends FunSuite { test("a simple test") { assert(true) } test("a very slightly more complicated test - purposely fails") { assert(42 === (6 * 9)) } } Which I'm running with the following SBT project config: import sbt._ class HelloSbtProject(info: ProjectInfo) extends DefaultProject(info) { // Dummy action, just to show config working OK. lazy val solveQ = task { println("42"); None } // Managed dependencies val scalatest = "org.scalatest" % "scalatest" % "1.0" % "test" } However, when I runsbt test I get the following warnings: ... [info] == test-compile == [info] Source analysis: 0 new/modified, 0 indirectly invalidated, 0 removed. [info] Compiling test sources... [info] Nothing to compile. [warn] Could not load superclass 'org.scalacheck.Properties' : java.lang.ClassNotFoundException: org.scalacheck.Properties [warn] Could not load superclass 'org.specs.Specification' : java.lang.ClassNotFoundException: org.specs.Specification [warn] Could not load superclass 'org.specs.Specification' : java.lang.ClassNotFoundException: org.specs.Specification [info] Post-analysis: 3 classes. [info] == test-compile == For the moment I'm assuming these are just "noise" (caused by the unified test interface?) and that I can safely ignore them. But it is slightly annoying to some inner OCD part of me (though not so annoying that I'm prepared to add dependencies for the other frameworks). Is this a correct assumption, or are there subtle errors in my test/config code? If it is safe to ignore, is there any other way to suppress these errors, or do people routinely include all three frameworks so they can pick and choose the best approach for different tests? TIA, Paul. (ADDED: scala v2.7.7 and sbt v0.7.4)

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• SPSS - sum of squares change radically with slight model changes in ANOVA??

  - by Pat

  I have noticed that the sum of squares in my models can change fairly radically with even the slightest adjustment to my models???? Is this normal???? I'm using SPSS 16, and both models presented below used the same data and variables with only one small change - categorizing one of the variables as either a 2 level or 3 level variable. Details - using a 2 x 2 x 6 mixed model ANOVA with the 6 being the repeated measure i get the following in the between group analysis ------------------------------------------------------------ Source | Type III SS | df | MS | F | Sig ------------------------------------------------------------ intercept | 4086.46 | 1 | 4086.46 | 104.93 | .000 X | 224.61 | 1 | 224.61 | 5.77 | .019 Y | 2.60 | 1 | 2.60 | .07 | .80 X by Y | 19.25 | 1 | 19.25 | .49 | .49 Error | 2570.40 | 66 | 38.95 | Then, when I use the exact same data but a slightly different model in which variable Y has 3 levels instead of 2 levels I get the following ------------------------------------------------------------ Source | Type III SS | df | MS | F | Sig ------------------------------------------------------------ intercept | 3603.88 | 1 | 3603.88 | 90.89 | .000 X | 171.89 | 1 | 171.89 | 4.34 | .041 Y | 19.23 | 2 | 9.62 | .24 | .79 X by Y | 17.90 | 2 | 17.90 | .80 | .80 Error | 2537.76 | 64 | 39.65 | I don't understand why variable X would have a different sum of squares simply because variable Y gets devided up into 3 levels instead of 2. This is also the case in the within groups analysis too. Please help me understand :D Thank you in advance Pat

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