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  • Linq to SQL Repository ~theory~ - Generic but now uses Linq to Objects?

    - by Matt Tolliday
    The project I am currently working on used Linq to SQL as an ORM data access technology. Its an MVC3 Web app. The problem I faced was primarily due to the inability to mock (for testing) the DataContext which gets autogenerated by the DBML designer. So to solve this issue (after much reading) I refactored the repository system which was in place - single repository with seperate and duplicated access methods for each table which ended up with something like 300 methods only 10 of which were unique - into a single repository with generic methods taking the table and returning more generic types to the upper reaches of the application. My question revolves more around the design I've used to get thus far and the differences I'm noticing in the structure of the app. 1) Having refactored the code from the dark ages which used classic Linq to SQL queries: public Billing GetBilling(int id) { var result = ( from bil in _bicDc.Billings where bil.BillingId == id select bil).SingleOrDefault(); return (result); } it now looks like: public T GetRecordWhere<T>(Expression<Func<T, bool>> predicate) where T : class { T result; try { result = _dataContext.GetTable<T>().Where(predicate).SingleOrDefault(); } catch (Exception ex) { throw ex; } return result; } and is used by the controller with a query along the lines of: _repository.GetRecordWhere<Billing>(x => x.BillingId == 1); which is fine, and precisely what I wanted to achieve. ...however.... I'm also having to do the following to get precisely the result set i require in the controller class (the highest point of the app in essence)... viewModel.RecentRequests = _model.GetAllRecordsWhere<Billing>(x => x.BillingId == 1) .Where(x => x.BillingId == Convert.ToInt32(BillingType.Submitted)) .OrderByDescending(x => x.DateCreated). Take(5).ToList(); This - as far as my understanding is correct - is now using Linq to Objects rather than the Linq to SQL queries I was previously? Is this okay practise? It feels wrong to me but I dont know why. Probably because the logic of the queries is in the very highest tier of the app, rather than the lowest, but... I defer to you good people for advice. One of the issues I considered was bringing the entire table into memory but I understand that using the Iqeryable return type the where clause is taken to the database and evaluated there. Thus returning only the resultset i require... i may be wrong. And if you've made it this far, well done. Thank you, and if you have any advice it is very much appreciated!!

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  • Are GUID primary keys bad in theory, or just practice?

    - by Yarin
    Whenever I design a database I automatically start with an auto-generating GUID primary key for each of my tables (excepting look-up tables) I know I'll never lose sleep over duplicate keys, merging tables, etc. To me it just makes sense philosophically that any given record should be unique across all domains, and that that uniqueness should be represented in a consistent way from table to table. I realize it will never be the most performant option, but putting performance aside, I'd like to know if there are philosophical arguments against this practice?

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  • A Guided Tour of Complexity

    - by JoshReuben
    I just re-read Complexity – A Guided Tour by Melanie Mitchell , protégé of Douglas Hofstadter ( author of “Gödel, Escher, Bach”) http://www.amazon.com/Complexity-Guided-Tour-Melanie-Mitchell/dp/0199798109/ref=sr_1_1?ie=UTF8&qid=1339744329&sr=8-1 here are some notes and links:   Evolved from Cybernetics, General Systems Theory, Synergetics some interesting transdisciplinary fields to investigate: Chaos Theory - http://en.wikipedia.org/wiki/Chaos_theory – small differences in initial conditions (such as those due to rounding errors in numerical computation) yield widely diverging outcomes for chaotic systems, rendering long-term prediction impossible. System Dynamics / Cybernetics - http://en.wikipedia.org/wiki/System_Dynamics – study of how feedback changes system behavior Network Theory - http://en.wikipedia.org/wiki/Network_theory – leverage Graph Theory to analyze symmetric  / asymmetric relations between discrete objects Algebraic Topology - http://en.wikipedia.org/wiki/Algebraic_topology – leverage abstract algebra to analyze topological spaces There are limits to deterministic systems & to computation. Chaos Theory definitely applies to training an ANN (artificial neural network) – different weights will emerge depending upon the random selection of the training set. In recursive Non-Linear systems http://en.wikipedia.org/wiki/Nonlinear_system – output is not directly inferable from input. E.g. a Logistic map: Xt+1 = R Xt(1-Xt) Different types of bifurcations, attractor states and oscillations may occur – e.g. a Lorenz Attractor http://en.wikipedia.org/wiki/Lorenz_system Feigenbaum Constants http://en.wikipedia.org/wiki/Feigenbaum_constants express ratios in a bifurcation diagram for a non-linear map – the convergent limit of R (the rate of period-doubling bifurcations) is 4.6692016 Maxwell’s Demon - http://en.wikipedia.org/wiki/Maxwell%27s_demon - the Second Law of Thermodynamics has only a statistical certainty – the universe (and thus information) tends towards entropy. While any computation can theoretically be done without expending energy, with finite memory, the act of erasing memory is permanent and increases entropy. Life & thought is a counter-example to the universe’s tendency towards entropy. Leo Szilard and later Claude Shannon came up with the Information Theory of Entropy - http://en.wikipedia.org/wiki/Entropy_(information_theory) whereby Shannon entropy quantifies the expected value of a message’s information in bits in order to determine channel capacity and leverage Coding Theory (compression analysis). Ludwig Boltzmann came up with Statistical Mechanics - http://en.wikipedia.org/wiki/Statistical_mechanics – whereby our Newtonian perception of continuous reality is a probabilistic and statistical aggregate of many discrete quantum microstates. This is relevant for Quantum Information Theory http://en.wikipedia.org/wiki/Quantum_information and the Physics of Information - http://en.wikipedia.org/wiki/Physical_information. Hilbert’s Problems http://en.wikipedia.org/wiki/Hilbert's_problems pondered whether mathematics is complete, consistent, and decidable (the Decision Problem – http://en.wikipedia.org/wiki/Entscheidungsproblem – is there always an algorithm that can determine whether a statement is true).  Godel’s Incompleteness Theorems http://en.wikipedia.org/wiki/G%C3%B6del's_incompleteness_theorems  proved that mathematics cannot be both complete and consistent (e.g. “This statement is not provable”). Turing through the use of Turing Machines (http://en.wikipedia.org/wiki/Turing_machine symbol processors that can prove mathematical statements) and Universal Turing Machines (http://en.wikipedia.org/wiki/Universal_Turing_machine Turing Machines that can emulate other any Turing Machine via accepting programs as well as data as input symbols) that computation is limited by demonstrating the Halting Problem http://en.wikipedia.org/wiki/Halting_problem (is is not possible to know when a program will complete – you cannot build an infinite loop detector). You may be used to thinking of 1 / 2 / 3 dimensional systems, but Fractal http://en.wikipedia.org/wiki/Fractal systems are defined by self-similarity & have non-integer Hausdorff Dimensions !!!  http://en.wikipedia.org/wiki/List_of_fractals_by_Hausdorff_dimension – the fractal dimension quantifies the number of copies of a self similar object at each level of detail – eg Koch Snowflake - http://en.wikipedia.org/wiki/Koch_snowflake Definitions of complexity: size, Shannon entropy, Algorithmic Information Content (http://en.wikipedia.org/wiki/Algorithmic_information_theory - size of shortest program that can generate a description of an object) Logical depth (amount of info processed), thermodynamic depth (resources required). Complexity is statistical and fractal. John Von Neumann’s other machine was the Self-Reproducing Automaton http://en.wikipedia.org/wiki/Self-replicating_machine  . Cellular Automata http://en.wikipedia.org/wiki/Cellular_automaton are alternative form of Universal Turing machine to traditional Von Neumann machines where grid cells are locally synchronized with their neighbors according to a rule. Conway’s Game of Life http://en.wikipedia.org/wiki/Conway's_Game_of_Life demonstrates various emergent constructs such as “Glider Guns” and “Spaceships”. Cellular Automatons are not practical because logical ops require a large number of cells – wasteful & inefficient. There are no compilers or general program languages available for Cellular Automatons (as far as I am aware). Random Boolean Networks http://en.wikipedia.org/wiki/Boolean_network are extensions of cellular automata where nodes are connected at random (not to spatial neighbors) and each node has its own rule –> they demonstrate the emergence of complex  & self organized behavior. Stephen Wolfram’s (creator of Mathematica, so give him the benefit of the doubt) New Kind of Science http://en.wikipedia.org/wiki/A_New_Kind_of_Science proposes the universe may be a discrete Finite State Automata http://en.wikipedia.org/wiki/Finite-state_machine whereby reality emerges from simple rules. I am 2/3 through this book. It is feasible that the universe is quantum discrete at the plank scale and that it computes itself – Digital Physics: http://en.wikipedia.org/wiki/Digital_physics – a simulated reality? Anyway, all behavior is supposedly derived from simple algorithmic rules & falls into 4 patterns: uniform , nested / cyclical, random (Rule 30 http://en.wikipedia.org/wiki/Rule_30) & mixed (Rule 110 - http://en.wikipedia.org/wiki/Rule_110 localized structures – it is this that is interesting). interaction between colliding propagating signal inputs is then information processing. Wolfram proposes the Principle of Computational Equivalence - http://mathworld.wolfram.com/PrincipleofComputationalEquivalence.html - all processes that are not obviously simple can be viewed as computations of equivalent sophistication. Meaning in information may emerge from analogy & conceptual slippages – see the CopyCat program: http://cognitrn.psych.indiana.edu/rgoldsto/courses/concepts/copycat.pdf Scale Free Networks http://en.wikipedia.org/wiki/Scale-free_network have a distribution governed by a Power Law (http://en.wikipedia.org/wiki/Power_law - much more common than Normal Distribution). They are characterized by hubs (resilience to random deletion of nodes), heterogeneity of degree values, self similarity, & small world structure. They grow via preferential attachment http://en.wikipedia.org/wiki/Preferential_attachment – tipping points triggered by positive feedback loops. 2 theories of cascading system failures in complex systems are Self-Organized Criticality http://en.wikipedia.org/wiki/Self-organized_criticality and Highly Optimized Tolerance http://en.wikipedia.org/wiki/Highly_optimized_tolerance. Computational Mechanics http://en.wikipedia.org/wiki/Computational_mechanics – use of computational methods to study phenomena governed by the principles of mechanics. This book is a great intuition pump, but does not cover the more mathematical subject of Computational Complexity Theory – http://en.wikipedia.org/wiki/Computational_complexity_theory I am currently reading this book on this subject: http://www.amazon.com/Computational-Complexity-Christos-H-Papadimitriou/dp/0201530821/ref=pd_sim_b_1   stay tuned for that review!

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  • Examples of different architecture methodologies

    - by Lane
    Is there a resource or site which illustrates building the same application (desktop or web) using several different contrasting architectures? Such as MVP versus MVVM versus MVC, etc. It would be very helpful to see how they look side-by-side using real-world code instead of comparing written theory to written theory. I've often found that something can be described well in a book, but when you go to implement it, the subtleties and weaknesses of the theory become readily apparent.

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  • Game thread, render thread, animation/inverse kinematics, and synchronization

    - by user782220
    In a multithreaded setup with a game logic thread and a render thread, with some kind of skin mesh animation with inverse kinematics plus etc how does animation work? Does the game logic thread just update a number saying time T in the animation and then the render thread infers Who owns the skin mesh animation, the game logic thread or the render thread? How is it stored in the scene graph if it is stored there at all? When the game logic updates does it do the computation of the skin mesh animation and the computation of the inverse kinematics and then store the result directly in the scene graph or is it stored indirectly and the render thread does the computation?

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  • Who could ask for more with LESS CSS? (Part 3 of 3&ndash;Clrizr)

    - by ToString(theory);
    Welcome back!  In the first two posts in this series, I covered some of the awesome features in CSS precompilers such as SASS and LESS, as well as how to get an initial project setup up and running in ASP.Net MVC 4. In this post, I will cover an actual advanced example of using LESS in a project, and show some of the great productivity features we gain from its usage. Introduction In the first post, I mentioned two subjects that I will be using in this example – constants, and color functions.  I’ve always enjoyed using online color scheme utilities such as Adobe Kuler or Color Scheme Designer to come up with a scheme based off of one primary color.  Using these tools, and requesting a complementary scheme you can get a couple of shades of your primary color, and a couple of shades of a complementary/accent color to display. Because there is no way in regular css to do color operations or store variables, there was no way to accomplish something like defining a primary color, and have a site theme cascade off of that.  However with tools such as LESS, that impossibility becomes a reality!  So, if you haven’t guessed it by now, this post is on the creation of a plugin/module/less file to drop into your project, plugin one color, and have your primary theme cascade from it.  I only went through the trouble of creating a module for getting Complementary colors.  However, it wouldn’t be too much trouble to go through other options such as Triad or Monochromatic to get a module that you could use off of that. Step 1 – Analysis I decided to mimic Adobe Kuler’s Complementary theme algorithm as I liked its simplicity and aesthetics.  Color Scheme Designer is great, but I do believe it can give you too many color options, which can lead to chaos and overload.  The first thing I had to check was if the complementary values for the color schemes were actually hues rotated by 180 degrees at all times – they aren’t.  Apparently Adobe applies some variance to the complementary colors to get colors that are actually more aesthetically appealing to users.  So, I opened up Excel and began to plot complementary hues based on rotation in increments of 10: Long story short, I completed the same calculations for Hue, Saturation, and Lightness.  For Hue, I only had to record the Complementary hue values, however for saturation and lightness, I had to record the values for ALL of the shades.  Since the functions were too complicated to put into LESS since they aren’t constant/linear, but rather interval functions, I instead opted to extrapolate the HSL values using the trendline function for each major interval, onto intervals of spacing 1. For example, using the hue extraction, I got the following values: Interval Function 0-60 60-140 140-270 270-360 Saturation and Lightness were much worse, but in the end, I finally had functions for all of the intervals, and then went the route of just grabbing each shades value in intervals of 1.  Step 2 – Mapping I declared variable names for each of these sections as something that shouldn’t ever conflict with a variable someone would define in their own file.  After I had each of the values, I extracted the values and put them into files of their own for hue variables, saturation variables, and lightness variables…  Example: /*HUE CONVERSIONS*/@clrizr-hue-source-0deg: 133.43;@clrizr-hue-source-1deg: 135.601;@clrizr-hue-source-2deg: 137.772;@clrizr-hue-source-3deg: 139.943;@clrizr-hue-source-4deg: 142.114;.../*SATURATION CONVERSIONS*/@clrizr-saturation-s2SV0px: 0;@clrizr-saturation-s2SV1px: 0;@clrizr-saturation-s2SV2px: 0;@clrizr-saturation-s2SV3px: 0;@clrizr-saturation-s2SV4px: 0;.../*LIGHTNESS CONVERSIONS*/@clrizr-lightness-s2LV0px: 30;@clrizr-lightness-s2LV1px: 31;@clrizr-lightness-s2LV2px: 32;@clrizr-lightness-s2LV3px: 33;@clrizr-lightness-s2LV4px: 34;...   In the end, I have 973 lines of mapping/conversion from source HSL to shade HSL for two extra primary shades, and two complementary shades. The last bit of the work was the file to compose each of the shades from these mappings. Step 3 – Clrizr Mapper The final step was the hardest to overcome as I was still trying to understand LESS to its fullest extent.  Imports As mentioned previously, I had separated the HSL mappings into different files, so the first necessary step is to import those for use into the Clrizr plugin: @import url("hue.less");@import url("saturation.less");@import url("lightness.less"); Extract Component Values For Each Shade Next, I extracted the necessary information for each shade HSL before shade composition: @clrizr-input-saturation: 1px+floor(saturation(@clrizr-input))-1;@clrizr-input-lightness: 1px+floor(lightness(@clrizr-input))-1; @clrizr-complementary-hue: formatstring("clrizr-hue-source-{0}", ceil(hue(@clrizr-input))); @clrizr-primary-2-saturation: formatstring("clrizr-saturation-s2SV{0}",@clrizr-input-saturation);@clrizr-primary-1-saturation: formatstring("clrizr-saturation-s1SV{0}",@clrizr-input-saturation);@clrizr-complementary-1-saturation: formatstring("clrizr-saturation-c1SV{0}",@clrizr-input-saturation); @clrizr-primary-2-lightness: formatstring("clrizr-lightness-s2LV{0}",@clrizr-input-lightness);@clrizr-primary-1-lightness: formatstring("clrizr-lightness-s1LV{0}",@clrizr-input-lightness);@clrizr-complementary-1-lightness: formatstring("clrizr-lightness-c1LV{0}",@clrizr-input-lightness); Here, you can see a couple of odd things…  On the first line, I am using operations to add units to the saturation and lightness.  This is due to some limitations in the operations that would give me saturation or lightness in %, which can’t be in a variable name.  So, I use first add 1px to it, which casts the result of the following functions as px instead of %, and then at the end, I remove that pixel.  You can also see here the formatstring method which is exactly what it sounds like – something like String.Format(string str, params object[] obj). Get Primary & Complementary Shades Now that I have components for each of the different shades, I can now compose them into each of their pieces.  For this, I use the @@ operator which will look for a variable with the name specified in a string, and then call that variable: @clrizr-primary-2: hsl(hue(@clrizr-input), @@clrizr-primary-2-saturation, @@clrizr-primary-2-lightness);@clrizr-primary-1: hsl(hue(@clrizr-input), @@clrizr-primary-1-saturation, @@clrizr-primary-1-lightness);@clrizr-primary: @clrizr-input;@clrizr-complementary-1: hsl(@@clrizr-complementary-hue, @@clrizr-complementary-1-saturation, @@clrizr-complementary-1-lightness);@clrizr-complementary-2: hsl(@@clrizr-complementary-hue, saturation(@clrizr-input), lightness(@clrizr-input)); That’s is it, for the most part.  These variables now hold the theme for the one input color – @clrizr-input.  However, I have one last addition… Perceptive Luminance Well, after I got the colors, I decided I wanted to also get the best font color that would go on top of it.  Black or white depending on light or dark color.  Now I couldn’t just go with checking the lightness, as that is half the story.  You see, the human eye doesn’t see ALL colors equally well but rather has more cells for interpreting green light compared to blue or red.  So, using the ratio, we can calculate the perceptive luminance of each of the shades, and get the font color that best matches it! @clrizr-perceptive-luminance-ps2: round(1 - ( (0.299 * red(@clrizr-primary-2) ) + ( 0.587 * green(@clrizr-primary-2) ) + (0.114 * blue(@clrizr-primary-2)))/255)*255;@clrizr-perceptive-luminance-ps1: round(1 - ( (0.299 * red(@clrizr-primary-1) ) + ( 0.587 * green(@clrizr-primary-1) ) + (0.114 * blue(@clrizr-primary-1)))/255)*255;@clrizr-perceptive-luminance-ps: round(1 - ( (0.299 * red(@clrizr-primary) ) + ( 0.587 * green(@clrizr-primary) ) + (0.114 * blue(@clrizr-primary)))/255)*255;@clrizr-perceptive-luminance-pc1: round(1 - ( (0.299 * red(@clrizr-complementary-1)) + ( 0.587 * green(@clrizr-complementary-1)) + (0.114 * blue(@clrizr-complementary-1)))/255)*255;@clrizr-perceptive-luminance-pc2: round(1 - ( (0.299 * red(@clrizr-complementary-2)) + ( 0.587 * green(@clrizr-complementary-2)) + (0.114 * blue(@clrizr-complementary-2)))/255)*255; @clrizr-col-font-on-primary-2: rgb(@clrizr-perceptive-luminance-ps2, @clrizr-perceptive-luminance-ps2, @clrizr-perceptive-luminance-ps2);@clrizr-col-font-on-primary-1: rgb(@clrizr-perceptive-luminance-ps1, @clrizr-perceptive-luminance-ps1, @clrizr-perceptive-luminance-ps1);@clrizr-col-font-on-primary: rgb(@clrizr-perceptive-luminance-ps, @clrizr-perceptive-luminance-ps, @clrizr-perceptive-luminance-ps);@clrizr-col-font-on-complementary-1: rgb(@clrizr-perceptive-luminance-pc1, @clrizr-perceptive-luminance-pc1, @clrizr-perceptive-luminance-pc1);@clrizr-col-font-on-complementary-2: rgb(@clrizr-perceptive-luminance-pc2, @clrizr-perceptive-luminance-pc2, @clrizr-perceptive-luminance-pc2); Conclusion That’s it!  I have posted a project on clrizr.codePlex.com for this, and included a testing page for you to test out how it works.  Feel free to use it in your own project, and if you have any questions, comments or suggestions, please feel free to leave them here as a comment, or on the contact page!

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  • Hadoop: Iterative MapReduce Performance

    - by S.N
    Is it correct to say that the parallel computation with iterative MapReduce can be justified only when the training data size is too large for the non-parallel computation for the same logic? I am aware that the there is overhead for starting MapReduce jobs. This can be critical for overall execution time when a large number of iterations is required. I can imagine that the sequential computation is faster than the parallel computation with iterative MapReduce as long as the memory allows to hold a data set in many cases. Is it the only benefit to use the iterative MapReduce? If not, what are the other benefits could be?

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  • I suspect that my HDD is causing hardlocks, as all other components have been replaced. How can I check this theory and solve the potential cause?

    - by user867814
    I have had this problem over quite a while now, thorough multiple Linux kernel versions and distributions, as well as replacement of all components, aside from my main HDD - RAM, GPU(twice), mother board, CPU, power supply. What happens is, at one point during the operation of the PC, it will hardlock - everything stops working, external HDD is not shut down correctly and continues to spin until I plug it out and in, there are no system/kernel logs of any kind, and no otherwise nothing that would suggest a cause. Another reason for my suspicion is that the failures happen almost exclusively during HDD read/write activity - shutdown(happens nearly 1/3 of the time so far, it's only been few days though), launching programs, and once during operation of apt. I hope the post is descriptive enough, if you need any additional info, ask(and tell me how to prepare/obtain it), and I will provide. If I'm wrong, point me in the right direction. Thanks in advance.

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  • yield – Just yet another sexy c# keyword?

    - by George Mamaladze
    yield (see NSDN c# reference) operator came I guess with .NET 2.0 and I my feeling is that it’s not as wide used as it could (or should) be.   I am not going to talk here about necessarity and advantages of using iterator pattern when accessing custom sequences (just google it).   Let’s look at it from the clean code point of view. Let's see if it really helps us to keep our code understandable, reusable and testable.   Let’s say we want to iterate a tree and do something with it’s nodes, for instance calculate a sum of their values. So the most elegant way would be to build a recursive method performing a classic depth traversal returning the sum.           private int CalculateTreeSum(Node top)         {             int sumOfChildNodes = 0;             foreach (Node childNode in top.ChildNodes)             {                 sumOfChildNodes += CalculateTreeSum(childNode);             }             return top.Value + sumOfChildNodes;         }     “Do One Thing” Nevertheless it violates one of the most important rules “Do One Thing”. Our  method CalculateTreeSum does two things at the same time. It travels inside the tree and performs some computation – in this case calculates sum. Doing two things in one method is definitely a bad thing because of several reasons: ·          Understandability: Readability / refactoring ·          Reuseability: when overriding - no chance to override computation without copying iteration code and vice versa. ·          Testability: you are not able to test computation without constructing the tree and you are not able to test correctness of tree iteration.   I want to spend some more words on this last issue. How do you test the method CalculateTreeSum when it contains two in one: computation & iteration? The only chance is to construct a test tree and assert the result of the method call, in our case the sum against our expectation. And if the test fails you do not know wether was the computation algorithm wrong or was that the iteration? At the end to top it all off I tell you: according to Murphy’s Law the iteration will have a bug as well as the calculation. Both bugs in a combination will cause the sum to be accidentally exactly the same you expect and the test will PASS. J   Ok let’s use yield! That’s why it is generally a very good idea not to mix but isolate “things”. Ok let’s use yield!           private int CalculateTreeSumClean(Node top)         {             IEnumerable<Node> treeNodes = GetTreeNodes(top);             return CalculateSum(treeNodes);         }             private int CalculateSum(IEnumerable<Node> nodes)         {             int sumOfNodes = 0;             foreach (Node node in nodes)             {                 sumOfNodes += node.Value;             }             return sumOfNodes;         }           private IEnumerable<Node> GetTreeNodes(Node top)         {             yield return top;             foreach (Node childNode in top.ChildNodes)             {                 foreach (Node currentNode in GetTreeNodes(childNode))                 {                     yield return currentNode;                 }             }         }   Two methods does not know anything about each other. One contains calculation logic another jut the iteration logic. You can relpace the tree iteration algorithm from depth traversal to breath trevaersal or use stack or visitor pattern instead of recursion. This will not influence your calculation logic. And vice versa you can relace the sum with product or do whatever you want with node values, the calculateion algorithm is not aware of beeng working on some tree or graph.  How about not using yield? Now let’s ask the question – what if we do not have yield operator? The brief look at the generated code gives us an answer. The compiler generates a 150 lines long class to implement the iteration logic.       [CompilerGenerated]     private sealed class <GetTreeNodes>d__0 : IEnumerable<Node>, IEnumerable, IEnumerator<Node>, IEnumerator, IDisposable     {         ...        150 Lines of generated code        ...     }   Often we compromise code readability, cleanness, testability, etc. – to reduce number of classes, code lines, keystrokes and mouse clicks. This is the human nature - we are lazy. Knowing and using such a sexy construct like yield, allows us to be lazy, write very few lines of code and at the same time stay clean and do one thing in a method. That's why I generally welcome using staff like that.   Note: The above used recursive depth traversal algorithm is possibly the compact one but not the best one from the performance and memory utilization point of view. It was taken to emphasize on other primary aspects of this post.

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  • Minimum team development sizes

    - by MarkPearl
    Disclaimer - these are observations that I have had, I am not sure if this follows the philosophy of scrum, agile or whatever, but most of these insights were gained while implementing a scrum scenario. Two is a partnership, three starts a team For a while I thought that a team was anything more than one and that scrum could be effective methodology with even two people. I have recently adjusted my thinking to a scrum team being a minimum of three, so what happened to two and what do you call it? For me I consider a group of two people working together a partnership - there is value in having a partnership, but some of the dynamics and value that you get from having a team is lost with a partnership. Avoidance of a one on one confrontation The first dynamic I see missing in a partnership is the team motivation to do better and how this is delivered to individuals that are not performing. Take two highly motivated individuals and put them together and you will typically see them continue to perform. Now take a situation where you have two individuals, one performing and one not and the behaviour is totally different compared to a team of three or more individuals. With two people, if one feels the other is not performing it becomes a one on one confrontation. Most people avoid confrontations and so nothing changes. Compare this to a situation where you have three people in a team, 2 performing and 1 not the dynamic is totally different, it is no longer a personal one on one confrontation but a team concern and people seem more willing to encourage the individual not performing and express their dissatisfaction as a team if they do not improve. Avoiding the effects of Tuckman’s Group Development Theory If you are not familiar with Tuckman’s group development theory give it a read (http://en.wikipedia.org/wiki/Tuckman's_stages_of_group_development) In a nutshell with Tuckman’s theory teams go through these stages of Forming, Storming, Norming & Performing. You want your team to reach and remain in the Performing stage for as long as possible - this is where you get the most value. When you have a partnership of two and you change the individuals in the partnership you basically do a hard reset on the partnership and go back to the beginning of Tuckman’s model each time. This has a major effect on the performance of a team and what they can deliver. What I have seen is that you reduce the effects of Tuckman's theory the more individuals you have in the team (until you hit the maximum team size in which other problems kick in). While you will still experience Tuckman's theory with a team of three, the impact will be greatly reduced compared to two where it is guaranteed every time a change occurs. It's not just in the numbers, it's in the people One final comment - while the actual numbers of a team do play a role, the individuals in the team are even more important - ideally you want to keep individuals working together for an extended period. That doesn't mean that you never change the individuals in a team, or that once someone joins a team they are stuck there - there is value in an individual moving from team to team and getting cross pollination, but the period of time that an individual moves should be in month's or years, not days or weeks. Why? So why is it important to know this? Why is it important to know how a team works and what motivates them? I have been asking myself this question for a while and where I am at right now is this… the aim is to achieve the stage where the sum of the total (team) is greater than the sum of the parts (team members). This is why we form teams and why understanding how they work is a challenge and also extremely stimulating.

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  • tuProlog unknow behavior

    - by Josh Guzman
    I'm using tuProlog to integrate Prolog with Java, to do so I'v been defined a .pl file wich contains this code: go:-write('hello world!'),nl. In my Java File at NetBeans i Have a Main Class that invokes this: Prolog engine = new Prolog(); Theory theory = new Theory(new FileInputStream("facultad.pl")); try { engine.setTheory(theory); } catch (InvalidTheoryException ex) { } SolveInfo solution = engine.solve("go."); if (solution.isSuccess()) { System.out.println(solution.getSolution()); } This Code must returns 'hello world', but instead of that it answer 'go', any ideas about this erratic behavior ??

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  • Embarrassingly parallel workflow creates too many output files

    - by Hooked
    On a Linux cluster I run many (N > 10^6) independent computations. Each computation takes only a few minutes and the output is a handful of lines. When N was small I was able to store each result in a separate file to be parsed later. With large N however, I find that I am wasting storage space (for the file creation) and simple commands like ls require extra care due to internal limits of bash: -bash: /bin/ls: Argument list too long. Each computation is required to run through a qsub scheduling algorithm so I am unable to create a master program which simply aggregates the output data to a single file. The simple solution of appending to a single fails when two programs finish at the same time and interleave their output. I have no admin access to the cluster, so installing a system-wide database is not an option. How can I collate the output data from embarrassingly parallel computation before it gets unmanageable?

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  • Way to kill python thread from inside thread?

    - by user859434
    I have some python code that currently performs expensive computation by performing the computation in parallel through many threads. For a given time period, many threads are created and started on the fly that share the same code which is explicitly stated within the run method of the thread. My question is how do I stop/kill a thread at the end of its run method? (the run is only called once) I need to do this in order to create more threads for the next batch of computation. #Example class someThread(threading.Thread): def __init__(self): #some init code def run(self): #Explicitly Stated Code without constant loops #Something performed to stop/kill this thread

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  • SQLAuthority News – Technical Review of Learning at Koenig Solutions

    - by pinaldave
    Yesterday I finished my 3 days fast track in person learning of course End to End SQL Server Business Intelligence at Koenig Solutions. You can read my previous article over here regarding why am I learning SQL Server. Yesterday I blogged about my experience of arriving to Training Center and my induction with the center. The Training Days I had enrolled for three days training so my routine each of the three days was very much same. However, the content every day was different as I was learning something new every day. Let me describe a few of the interesting details of my daily routine. A Single Student Batch The best part of my training was that in my training batch, I am single student. Koenig is known to smaller batches and often they have single student batches as well. I was very much delighted to know that I will have dedicated access and attention from my trainer in my batch as I will be single student in my batch. In most of the labs I have observed there are no more than 4 students at any time. Prakash and Pinal 7:30 AM Breakfast Talk We all students gather at 7:30 in breakfast area. The best time of the day. I was the only Indian student in the group. The other students were from USA, Canada, Nigeria, Bhutan, Tanzania, and a few others from other countries. I immediately become the source of information and reference manual. Though the distance between Delhi and Bangalore is 2000+ KM I was considered as a local guy. 8:30 AMHeading to Training Center Every day without fail at 8:30 the van started from our accommodation to the training center. As mentioned in an earlier blog post the distance is about 5 minutes and we were able to reach at the location before 8:45. This gave us some time settle in before our class starts at 9:00 AM. 9:00 AM Order Lunch Food Well it may sound funny that we just had breakfast 30 minutes but the first thing everybody has to do is to order lunch as soon as the class starts. There is an online training portal to order food for the day. Everybody has to place their order early during the day so the food arrives on time during lunch time. Everybody can order whatever they want to order using an online ordering system. The options are plenty and everybody can order what they like. 9:05 AM Learning Starts After deciding the lunch we started the learning. I was very fortunate to have a very experienced trainer - Prakash Chheatry. Though I have never met him before I have heard a lot about Prakash. He is known as the top most SQL Server Trainer in India. His student list contains some of the very well known SQL Server Experts of the world and few of SQL Server “best seller” book authors. Learning continues till 1:00 PM with one tea-coffee break in between. 1:00 PM Lunch The lunch time is again the fun time. We all students get together in the afternoon and tell the stories of the world. Indeed the best part of the day beside learning new stuff. 4:55 PM Ready to Return We stop at 4:55 as at precisely 5:00 PM the van stops by the institute which takes us back to our accommodation. Trust me seriously long long day always but the amount of the learning is the win of the day. 7:30 PM Dinner Time After coming back to the accommodation I study till 7:30 and then rush for dinner. Dinner is world cuisine and deserts are really delicious. After dinner every day I have written a blog and retired early as the next day is always going to be busier than the present day. What did I learn As I mentioned earlier I know SQL Server fairly well. I had expressed the same in my conversation as well. This is the reason I was assigned a fairly senior trainer and we learned everything quite quickly. As I know quite a few things we went pretty fast in many topics. There were a few things, I wanted to learn in detail as well practice on the labs. We slowed down where we wanted and rush through the concepts where I was very comfortable. Here is the list of the things which we covered in action pack three days. Introduction to Business Intelligence (Intro) SQL Server Analysis Service (Theory and Lab) SQL Server Integration Service  (Theory and Lab) SQL Server Reporting Service  (Theory and Lab) SQL Server PowerPivot (Lab) UDM (Theory) SharePoint Concepts (Theory) Power View (Demo) Business Intelligence and Security (Discussion) Well, I was delighted that I was able to refresh lots of concepts during these three days. Thanks to my trainer and my friend who helped me to have a good learning experience. I believe all the learning  will help me in my growth and future career. With this I end my this experience. I am planning to have another online learning experience later this month. I will blog about my experience as I begin it. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Training, T SQL, Technology

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  • How do I replace a modal view controller?

    - by Theory
    I'm using a modal view controller to allow a user to select an address book entry and email address. The ABPeoplePickerNavigationController object is displayed via presentModalViewController:animated: [self presentModalViewController:picker animated:YES]; What I want to do is keep the modal dialog up, but when the user selects the email address, it should cross-fade to a different controller that displays a message composition window. I've tried various approaches in peoplePickerNavigationController:shouldContinueAfterSelectingPerson:property:identifier: to dismiss the picker and set my custom composition controller as the modal view. I can do it any number of ways, but never does it fade smoothly from the picker to the composition controller -- unless I make the composition controller a modal dialog of the picker, in which case the picker re-appears when I dismiss the composition controller. I don't want that, either. There must be some way to smoothly replace one controller and its view with another controller and its view, all within the context of a modal dialog, and preferably with a cross fade. Suggestions greatly appreciated.

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  • How do I use a modalViewController Identically in Two Controllers?

    - by Theory
    I'm using the Three20 TTMessageController in my app. I've figured out how to use it, adding on a bunch of other stuff (including TTMessageControllerDelegate methods and ABPeoplePickerNavigationControllerDelegate methods). It works great for me, after a bit of a struggle to figure it out. The trouble I'm having now is a design issue: I want to use it identically in two different places, including with the same delegate methods. My current approach is that I've put all the code into a single class inheriting from NSObject, called ComposerProxy, and I'm just having the two controllers that use it use the proxy, like so: ComposerProxy *proxy = [[ComposerProxy alloc] initWithController:this]; [proxy go]; The go method constructs the TTMessageController, configures it, adds it to a UINavigationController, and presents it: [self.controller presentModalViewController: navController animated: YES]; This works great, as I have all my code nicely encapsulated in ComposerProxy and I need only the above two lines anywhere I want to use it. The downside, though, is that I can't dealloc the proxy variable without getting crashes. I can't autorelease it, either: same problem. So I'm wondering if my proxy approach is a poor one. How does one normally encapsulate a bunch of behaviors like this without requiring a lot of duplicate code in the classes that use it? Do I need to add a delegate class to my ComposerProxy and make the controller responsible for dismissing the modal view controller in a hypothetical composerDidFinish method or some such? Many TIA!

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  • Why Doesn't UIWebView release all of its memory?

    - by Theory
    I have a graphic-intensive iPad app that features a UIWebView. Using the simulator (iOS 4.2.1), I can see Real Mem increase quite a lot as I browse. The more I browse, the more RAM it uses. When I close the UIWebView and release it, some of the memory it used is freed, but not all of it. This is annoying. Okay, so maybe it's because it isn't deallocated right away. Fine. But then I would expect the system to do some cleanup when there's a memory warning. However, if I browse around, then close the UIWebView (and release it), then trigger a memory warning in the simulator, Real Mem does not change! WTF? So why is this? Why isn't UIWebView better at releasing memory back to the system? And why doesn't it appear to respond to memory warnings? Am I missing something?

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  • When i run rake db:create ,Error rake aborted! uninitialized constant Cucumber

    - by Big Bang Theory
    Hi I am trying to experiment on an open source application application . when i run $ rake db:create Following is the stacktrace rake aborted! uninitialized constant Cucumber /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/active_support/dependencies.rb:443:in `load_missing_constant' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/active_support/dependencies.rb:80:in `const_missing' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/active_support/dependencies.rb:92:in `const_missing' /home/BigBangTheory/Desktop/spot-us/lib/tasks/cucumber.rake:13 /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:1882:in `in_namespace' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:910:in `namespace' /home/BigBangTheory/Desktop/spot-us/lib/tasks/cucumber.rake:12 /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/active_support/dependencies.rb:145:in `load_without_new_constant_marking' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/active_support/dependencies.rb:145:in `load' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/active_support/dependencies.rb:521:in `new_constants_in' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/active_support/dependencies.rb:145:in `load' /usr/lib/ruby/gems/1.8/gems/rails-2.3.2/lib/tasks/rails.rb:8 /usr/lib/ruby/gems/1.8/gems/rails-2.3.2/lib/tasks/rails.rb:8:in `each' /usr/lib/ruby/gems/1.8/gems/rails-2.3.2/lib/tasks/rails.rb:8 /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require' /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' /home/BigBangTheory/Desktop/spot-us/Rakefile:9 /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2383:in `load' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2383:in `raw_load_rakefile' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2017:in `load_rakefile' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2016:in `load_rakefile' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2000:in `run' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:1998:in `run' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/bin/rake:31 /usr/bin/rake:19:in `load' /usr/bin/rake:19 Any help ?

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  • How to Iterate in ruby ?

    - by Big Bang Theory
    Hi I would like to iterate @some_value outputs the following result {"Meta"=>{"Query"=>"java", "ResultOffset"=>"1", "NumResults"=>"1", "TotalResults"=>"21931"}} i need to retrieve the Value of each individual value for example java 1 1 21931

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  • As a PHP developer thinking of making Perl a secondary strong suit, what do I need to know?

    - by Hexagon Theory
    I consider myself quite fluent in PHP and am rather familiar with nearly all of the important aspects and uses, as well as its pratfalls. This in mind, I think the major problem in taking on Perl is going to be with the syntax. Aside from this (a minor hindrance, really, as I'm rather sold on the fact that Perl's is far more readable), what are some key differences you think I should make myself aware of prior to taking on the language?

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  • Imperative Programming v/s Declarative Programming v/s Functional Programming

    - by kaleidoscope
    Imperative Programming :: Imperative programming is a programming paradigm that describes computation in terms of statements that change a program state. In much the same way as the imperative mood in natural languages expresses commands to take action, imperative programs define sequences of commands for the computer to perform. The focus is on what steps the computer should take rather than what the computer will do (ex. C, C++, Java). Declarative Programming :: Declarative programming is a programming paradigm that expresses the logic of a computation without describing its control flow. It attempts to minimize or eliminate side effects by describing what the program should accomplish, rather than describing how to go about accomplishing it. The focus is on what the computer should do rather than how it should do it (ex. SQL). A  C# example of declarative v/s. imperative programming is LINQ. With imperative programming, you tell the compiler what you want to happen, step by step. For example, let's start with this collection, and choose the odd numbers: List<int> collection = new List<int> { 1, 2, 3, 4, 5 }; With imperative programming, we'd step through this, and decide what we want: List<int> results = new List<int>(); foreach(var num in collection) {     if (num % 2 != 0)           results.Add(num); } Here’s what we are doing: *Create a result collection *Step through each number in the collection *Check the number, if it's odd, add it to the results With declarative programming, on the other hand, we write the code that describes what you want, but not necessarily how to get it var results = collection.Where( num => num % 2 != 0); Here, we're saying "Give us everything where it's odd", not "Step through the collection. Check this item, if it's odd, add it to a result collection." Functional Programming :: Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. It emphasizes the application of functions.Functional programming has its roots in the lambda calculus. It is a subset of declarative languages that has heavy focus on recursion. Functional programming can be a mind-bender, which is one reason why Lisp, Scheme, and Haskell have never really surpassed C, C++, Java and COBOL in commercial popularity. But there are benefits to the functional way. For one, if you can get the logic correct, functional programming requires orders of magnitude less code than imperative programming. That means fewer points of failure, less code to test, and a more productive (and, many would say, happier) programming life. As systems get bigger, this has become more and more important. To know more : http://stackoverflow.com/questions/602444/what-is-functional-declarative-and-imperative-programming http://msdn.microsoft.com/en-us/library/bb669144.aspx http://en.wikipedia.org/wiki/Imperative_programming   Technorati Tags: Ranjit,Imperative Programming,Declarative programming,Functional Programming

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