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  • Solving a math problem/expression, which is a string, in PHP

    - by Koning WWWWWWWWWWWWWWWWWWWWWWW
    The user can enter a math problem (expression) like 5 + 654, 6 ^ 24, 2!, sqrt(543), log(54), sin 5, sin(50). After some reformatting (e.g. change sin 5 into sin(5)), and doing an eval, PHP gives me the right result: $problem = "5 + 5324"; eval("$result = " . $problem); echo $problem . " = " . $result; However, this is quite unsafe: /* If you read this, please, plz don't be stupid and DO NOT EXECUTE this code!!!!! */ $problem = "shell_exec('rm -rf /')"; eval("$result = " . $problem); /* Nukes system */ echo $problem . " = " . $result; Can anyone point me in the right direction parsing and solving a math question like the examples above, which is safe? Thanks.

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  • Can someone recommend a resource/site/book to improve problem solving skills

    - by kjm
    I am a reasonably experienced developer (.NET, c#, asp.NET etc) but I'd like to hone my problem solving skills. I find that when I come up against a complex problem I sometimes implement a solution that I feel could have been better had I analyzed the problem in a different way. Ideally what I am looking for is a resource of some type that has 'practice problems and solutions' as I think my skills will only get better by practicing this more and adopting better practices. I hope my question is not to vague and I wont get upset with people answering with opinions etc.. thanks

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  • Abstraction: The War between solving the problem and a general solution.

    - by Bryan Harrington
    As a programmer, I find myself in the dilemma where I want make my program as abstract and as general as possible. Doing so usually would allow me to reuse my code and have a more general solution for a problem that might (or might not) come up again. Then this voice in my head says, just solve the problem dummy its that easy! Why spend more time than you have to? We all have indeed faced this question where Abstraction is on your right shoulder and Solve-it-stupid sits on the left. Which to listen to and how often? What is your strategy for this? Should you abstract everything?

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  • Pre game loading time vs. in game loading time

    - by Keeper
    I'm developing a game in which a random maze is included. There are some AI creatures, lurking the maze. And I want them to go in some path according to the mazes shape. Now there are two possibilities for me to implement that, the first way (which I used) is by calculating several wanted lurking paths once the maze is created. The second, is by calculating a path once needed to be calculated, when a creature starts lurking it. My main concern is loading times. If I calculate many paths at the creating of the maze, the pre loading time is a bit long, so I thought about calculating them when needed. At the moment the game is not 'heavy' so calculating paths in mid game is not noticeable, but I'm afraid it will once it will get more complicated. Any suggestions, comments, opinions, will be of help. Edit: As for now, let p be the number of pre-calculated paths, a creatures has the probability of 1/p to take a new path (which means a path calculation) instead of an existing one. A creature does not start its patrol until the path is fully calculated of course, so no need to worry about him getting killed in the process.

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  • Hard problem - need help for solving

    - by dada
    I don't want you to solve this problem for me, i just want to ask for some ideas. This is the input below, and it represents a map. The 'x' represents land, and the dots - water. So with the 'x' you can represent 'islands' on the map. xxx.x...xxxxx xxxx....x...x ........x.x.x ..xxxxx.x...x ..x...x.xxx.x ..x.x.x...x.. ..x...x...xxx ...xxxxxx.... x............ As you can see, there are some islands which are closed, i.e. if some boat is inside its territory, it won't be able to get out, for ex: ..xxxxx. ..x...x. ..x.x.x. ..x...x. ..xxxxx. And there are some open islands which is possible to get out of them, ex: .xxxxx .x...x .x.x.x .xxx.x The problem is this: For a given NxM map like those above, calculate howm any of the islands are open, and how many are closed. I repeat: I don't want you to solve it, just need some sugestions, ideas for solving. thanks

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  • problem solving [closed]

    - by Suresh S
    Problem Statement The Sports Associations in India (SAI) wants to choose 2 teams of 4 people each to send to Asian games. There are 13 people who want to be members of the teams. The SAI tries grouping them in various ways to see which athletes perform well together. Each grouping gets one test run on the test track and their time is recorded. Your task is to help the SAI choose two disjoint teams of 4 such that the sum of their practice times is minimal. Input There will be several input instances. The first line of each instance gives the total number of practice runs. This will be followed by n lines. Each of those lines will contain 5 numbers: p1 p2 p3 p4 t t is the time taken (in milliseconds) by the team consisting of p1, p2, p3 and p4. The time taken will not be more than 2 minutes. The end of the input will be indicated by a line with n=0. Output Output the best total and the two teams that you choose. If it is impossible to choose two disjoint teams from the test runs given, output -1. Sample Input 6 1 2 3 4 30000 10 11 12 13 15000 5 6 7 8 37800 1 5 10 12 20000 5 6 9 11 43000 1 9 12 13 11000 3 1 4 7 9 10000 3 5 7 11 17890 6 7 12 13 20000 0 Sample Output 45000 -1 Input to the problem 40 2 8 11 9 15532 1 13 11 9 57629 10 12 1 5 43406 6 10 1 2 43904 8 3 4 11 12473 6 12 5 11 19826 3 9 10 11 48347 6 12 13 1 45854 5 4 9 7 34452 9 8 12 2 5596 4 10 2 7 6778 3 6 8 5 32858 13 12 8 6 42457 12 9 2 5 49530 6 8 10 7 51453 1 3 11 9 18620 6 2 5 11 5153 4 1 9 8 37336 10 5 1 12 59524 4 5 3 2 1318 2 13 6 8 7839 12 4 9 5 30697 4 10 13 1 25249 4 2 9 13 52359 8 11 1 9 36437 7 5 11 6 58522 9 1 12 6 58837 7 6 8 5 37826 13 1 11 3 1841 11 3 5 13 50000 2 8 7 12 10137 1 4 12 5 32558 8 5 6 7 39021 1 7 10 13 5979 9 2 11 6 29661 13 12 9 7 7219 12 1 11 9 37354 5 1 10 9 47948 8 1 2 10 11071 2 11 1 8 3074 80 3 5 8 10 37873 1 2 3 5 27633 10 13 3 11 8645 13 1 9 6 2167 5 11 13 8 30862 8 7 9 6 47591 3 11 13 8 33823 2 13 7 5 36668 12 3 11 6 53711 6 13 3 7 52412 3 6 7 5 3850 1 5 11 12 35483 1 7 6 10 50943 11 3 6 8 40191 12 8 13 7 4529 4 10 5 1 43280 4 12 10 5 35142 12 4 5 10 37242 9 7 13 2 2661 3 9 2 10 453 3 8 12 9 12479 3 10 11 5 30047 9 1 11 2 40883 6 5 1 2 8774 11 7 9 1 37701 8 3 4 6 32970 4 12 7 10 55109 8 11 13 12 44713 2 10 8 5 37763 13 10 12 2 53628 7 2 5 10 53197 3 2 1 11 14916 1 2 3 10 50756 3 13 5 6 6959 10 6 1 4 2948 4 7 13 9 14146 8 13 10 2 16784 3 2 6 5 30337 1 6 7 8 14239 2 6 11 5 13749 12 1 10 5 30827 4 6 11 8 18780 9 10 8 5 6336 7 9 1 3 3101 10 3 4 13 56678 7 6 3 8 8258 11 7 12 6 19046 13 6 9 8 46356 9 5 11 13 56570 9 1 10 5 6193 8 6 9 11 16854 3 7 4 9 53573 8 12 10 1 28135 10 3 8 4 31411 11 1 3 12 34534 8 6 4 13 3527 1 6 10 9 52307 11 7 1 12 2886 12 11 1 6 17659 13 5 6 8 48834 11 2 1 10 52951 3 9 13 7 21054 1 5 11 9 14507 11 5 12 4 42040 1 6 12 7 46414 5 12 3 10 26239 6 10 7 8 40762 8 11 6 10 38538 13 1 10 7 31140 9 10 13 4 34164 13 6 7 12 49696 6 13 3 5 36003 8 9 13 6 58409 3 10 7 9 20693 2 1 11 12 22653 5 8 4 7 49888 5 3 2 11 29911 8 12 6 9 30964 8 3 13 6 23597 4 1 6 7 31657 4 6 8 7 13 33639 13 8 10 3 27863 5 2 1 12 1408 4 11 1 12 59010 63 10 11 9 8 23611 10 8 6 11 12410 4 6 7 9 44390 8 4 1 6 16543 1 2 8 10 37452 11 12 6 13 28968 11 12 2 8 59617 1 9 11 2 28631 11 6 5 1 27251 2 7 10 4 42503 7 8 10 3 13673 9 13 11 7 30308 6 1 12 9 4888 13 1 9 8 19475 8 7 3 5 34187 8 1 12 3 46266 6 10 12 5 32855 3 7 13 1 38427 2 5 13 3 59487 6 11 1 13 2098 1 4 13 6 22239 13 7 12 3 28703 12 3 7 4 32 9 8 2 13 35271 10 13 6 12 36422 12 6 9 8 44303 1 9 13 11 22962 11 13 6 12 39518 5 6 13 11 47909 4 13 1 8 10654 11 8 12 4 31956 7 12 9 13 35923 4 9 3 2 34736 13 2 10 1 22945 7 10 8 13 36947 1 4 12 13 19432 7 12 13 4 48718 9 5 13 11 18827 11 2 1 12 45444 8 12 6 13 33175 4 2 11 13 56186 2 9 3 11 33218 12 13 8 1 50727 13 1 8 2 48138 7 1 5 3 1926 6 4 10 1 40997 11 3 1 4 26033 6 10 13 1 40988 11 12 5 4 25199 4 3 1 10 23498 3 6 12 7 24306 13 10 12 3 53255 3 13 4 12 14517 7 10 9 3 29925 9 11 12 13 28333 3 5 13 6 13602 13 12 9 6 10394 8 4 12 6 57471 9 3 4 7 34723 11 9 5 3 38480 12 9 10 11 48048 4 3 6 7 31884 2 10 4 5 57654 86 1 6 5 13 56577 6 8 2 5 20429 11 13 9 3 2243 3 1 10 12 55231 9 5 7 8 29964 5 11 8 1 29624 6 9 3 1 43055 12 13 10 8 52132 10 8 4 1 5729 7 3 6 8 53097 11 12 7 1 18711 12 7 6 13 44397 10 12 5 7 53574 5 3 4 13 27078 11 2 5 10 43623 3 7 1 8 57350 10 12 4 9 19752 5 13 9 3 59380 4 7 13 6 32575 7 5 6 11 13593 13 7 12 6 38282 13 7 6 2 45430 6 2 5 10 38082 2 11 13 7 53557 10 6 7 13 40461 6 11 7 1 22007 4 7 2 3 22386 9 7 11 10 35337 2 6 11 7 4129 6 13 5 3 31813 1 11 6 9 11749 5 11 8 13 21858 5 12 9 11 2470 13 10 6 11 14503 8 4 1 3 10783 1 10 12 7 47116 11 1 8 10 25034 8 1 4 9 23350 3 10 1 9 56717 13 2 8 12 5825 12 3 13 7 35628 10 6 1 12 26901 2 13 3 5 2775 1 8 9 7 1294 7 13 12 2 48170 11 9 13 1 34311 9 6 3 13 30663 8 3 10 6 5853 1 10 2 4 19880 9 2 3 12 48990 3 7 11 4 51558 8 13 2 4 9698 9 4 5 1 6834 3 4 12 2 20941 11 3 9 7 40108 13 11 2 4 2594 8 9 10 13 12242 1 8 10 5 42413 7 1 11 3 17779 1 5 8 3 6934 4 9 8 11 10235 8 11 10 2 18879 11 4 8 2 12691 9 7 5 2 44947 3 2 5 4 30042 2 7 12 4 27185 6 5 10 1 28695 12 9 1 5 53813 8 12 9 3 24719 6 1 4 11 22716 1 13 10 8 39981 12 11 5 2 22412 6 11 2 4 14457 4 11 5 3 39658 10 11 2 1 33056 1 3 6 9 16958 6 11 12 7 50779 8 10 6 13 24824 7 10 1 13 35692 13 4 8 9 32885 7 6 4 3 10948 4 5 7 1 36875 5 10 6 7 58746 10 7 8 12 39453 8 4 12 1 46674 11 3 1 8 48103 0

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  • Solving programming problems or contributing code?

    - by nischayn22
    What are the best skills to develop for a college graduate?? Should one spend hours/days trying to solve problems on codechef or topcoder or contribute code to open source organizations? My personal experience says solving problems teaches you how to make optimal code and learn new programming techniques (which someone else has researched and made available) to solve problems, whereas contributing to open source teaches you how to organize code (so others can work on it), use coding conventions and make "real" use of what you have learnt so far, blah blah!! Also another thing to note is that many companies are hiring today based on one's problem solving skills (Is this something I should worry about?) P.S. I have done little of online problem solving and little of code contribution (via GSoC), but left confused what I should continue doing (as doing both simultaneously isn't easy).

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  • accessing values in two dimensional arrays

    - by BrainLikeADullPencil
    In some code I'm trying to learn from, the Maze string below is turned into an array (code not shown for that) and saved in the instance variable @maze. The starting point of the Maze is represented by the letter 'A' in that Maze, which can be accessed at @maze[1][13]---row 1, column 13. However, the code I'm looking at uses @maze[1][13,1] to get the A, which you can see returns the same result in my console. If I do @maze[1][13,2], it returns the letter "A " with two blank spaces next to it, and so on. [13,3] returns "A " with three blank spaces. Does the 2 in [13,2] mean, "return two values starting at [1][13]? If so, why? Is this some feature of arrays or two dimensional arrays that I don't get? [20] pry(#<Maze>):1> @maze[1][13] => "A" [17] pry(#<Maze>):1> @maze[1][13,1] => "A" [18] pry(#<Maze>):1> @maze[1][13,2] => "A " [19] pry(#<Maze>):1> @maze[1][13,3] => "A " Maze String MAZE1 = %{##################################### # # # #A # # # # # # # # # ####### # ### # ####### # # # # # # # # # # # ##### # ################# # ####### # # # # # # # # # ##### ##### ### ### # ### # # # # # # # # # # # # B# # # # # # # # ##### ##### # # ### # # ####### # # # # # # # # # # # # # # ### ### # # # # ##### # # # ##### # # # # # # # # #####################################}

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  • Is problem solving of puzzles/logic tests a skill that can be developed with practise or only someth

    - by dotnetdev
    Programming is essentially problem solving/using a lot of logic. With solving puzzles (like the ones recruiters like MS etc ask), is this a skill that can be developed with practise or is it a skill that only someone who is gifted has (I assume the former as many people can pass these tests)? Even so, I keep thinking it is a special skill for someone gifted, not for someone with a lot of practise. I guess that with practise you are perhaps more open-minded and start to think out of the box more (solving technical problems in development may also foster this mindset perhaps). Thanks

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  • Problem solving/ Algorithm Skill is a knack or can be developed with practice?

    - by KaluSingh Gabbar
    Every time I start a hard problem and if can not figure out the exact solution or can not get started, I get into this never ending discussion with myself, as below: That problem solving/mathematics/algorithms skills are gifted (not that you can learn by practicing, by practice, you only master the kind of problems that you already have solved before) only those who went to good schools can do it, as they learned it early. What are your thoughts, can one achieve awesomeness in problem solving/algorithms just by hard work or you need to have that extra-gene in you?

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  • Solve a maze using multicores?

    - by acidzombie24
    This question is messy, i dont need a working solution, i need some psuedo code. How would i solve this maze? This is a homework question. I have to get from point green to red. At every fork i need to 'spawn a thread' and go that direction. I need to figure out how to get to red but i am unsure how to avoid paths i already have taken (finishing with any path is ok, i am just not allowed to go in circles). Heres an example of my problem, i start by moving down and i see a fork so one goes right and one goes down (or this thread can take it, it doesnt matter). Now lets ignore the rest of the forks and say the one going right hits the wall, goes down, hits the wall and goes left, then goes up. The other thread goes down, hits the wall then goes all the way right. The bottom path has been taken twice, by starting at different sides. How do i mark this path has been taken? Do i need a lock? Is this the only way? Is there a lockless solution? Implementation wise i was thinking i could have the maze something like this. I dont like the solution because there is a LOT of locking (assuming i lock before each read and write of the haveTraverse member). I dont need to use the MazeSegment class below, i just wrote it up as an example. I am allowed to construct the maze however i want. I was thinking maybe the solution requires no connecting paths and thats hassling me. Maybe i could split the map up instead of using the format below (which is easy to read and understand). But if i knew how to split it up i would know how to walk it thus the problem. How do i walk this maze efficiently? The only hint i receive was dont try to conserve memory by reusing it, make copies. However that was related to a problem with ordering a list and i dont think the hint was a hint for this. class MazeSegment { enum Direction { up, down, left, right} List<Pair<Direction, MazeSegment*>> ConnectingPaths; int line_length; bool haveTraverse; } MazeSegment root; class MazeSegment { enum Direction { up, down, left, right} List<Pair<Direction, MazeSegment*>> ConnectingPaths; bool haveTraverse; } void WalkPath(MazeSegment segment) { if(segment.haveTraverse) return; segment.haveTraverse = true; foreach(var v in segment) { if(v.haveTraverse == false) spawn_thread(v); } } WalkPath(root);

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  • How I improve my problem-solving ability

    - by gcc
    How we can improve our problem-solving ability ? Every one says same thing "real programmer knows how to handle real problem.", but they forget something how they take this ability, or where ( I know in school, no one gives us any ability, of course in my opinion. ) If you have any idea except above ones, feel free when you give an advice solve more problem do more exercise, write code, search google then write more ... For me, my question is like "Use complex/known library instead of using your own." In other words, I want your experience, book recommendation, web page

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  • Fast language for problem solving? [closed]

    - by Friend of Kim
    I learned PHP to make websites. After some years I've started using programming for solving what is difficult tasks for my level. Now I want to make a program that solves equations. (I want to write it myself, not use an API. Because I'm doing this for the sake of the challenge, not for the result..) Because of this, I'm going to learn a new and faster/better language. It's going to be C++, Java, Python or C#. What are the benefits of each language, and which language is best for speed compared to speed of writing and readability? Using C would be lightning fast, but the lack of OO is making for more complex code and reduces the readability, for example..

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  • Solving Big Problems with Oracle R Enterprise, Part I

    - by dbayard
    Abstract: This blog post will show how we used Oracle R Enterprise to tackle a customer’s big calculation problem across a big data set. Overview: Databases are great for managing large amounts of data in a central place with rigorous enterprise-level controls.  R is great for doing advanced computations.  Sometimes you need to do advanced computations on large amounts of data, subject to rigorous enterprise-level concerns.  This blog post shows how Oracle R Enterprise enables R plus the Oracle Database enabled us to do some pretty sophisticated calculations across 1 million accounts (each with many detailed records) in minutes. The problem: A financial services customer of mine has a need to calculate the historical internal rate of return (IRR) for its customers’ portfolios.  This information is needed for customer statements and the online web application.  In the past, they had solved this with a home-grown application that pulled trade and account data out of their data warehouse and ran the calculations.  But this home-grown application was not able to do this fast enough, plus it was a challenge for them to write and maintain the code that did the IRR calculation. IRR – a problem that R is good at solving: Internal Rate of Return is an interesting calculation in that in most real-world scenarios it is impractical to calculate exactly.  Rather, IRR is a calculation where approximation techniques need to be used.  In this blog post, we will discuss calculating the “money weighted rate of return” but in the actual customer proof of concept we used R to calculate both money weighted rate of returns and time weighted rate of returns.  You can learn more about the money weighted rate of returns here: http://www.wikinvest.com/wiki/Money-weighted_return First Steps- Calculating IRR in R We will start with calculating the IRR in standalone/desktop R.  In our second post, we will show how to take this desktop R function, deploy it to an Oracle Database, and make it work at real-world scale.  The first step we did was to get some sample data.  For a historical IRR calculation, you have a balances and cash flows.  In our case, the customer provided us with several accounts worth of sample data in Microsoft Excel.      The above figure shows part of the spreadsheet of sample data.  The data provides balances and cash flows for a sample account (BMV=beginning market value. FLOW=cash flow in/out of account. EMV=ending market value). Once we had the sample spreadsheet, the next step we did was to read the Excel data into R.  This is something that R does well.  R offers multiple ways to work with spreadsheet data.  For instance, one could save the spreadsheet as a .csv file.  In our case, the customer provided a spreadsheet file containing multiple sheets where each sheet provided data for a different sample account.  To handle this easily, we took advantage of the RODBC package which allowed us to read the Excel data sheet-by-sheet without having to create individual .csv files.  We wrote ourselves a little helper function called getsheet() around the RODBC package.  Then we loaded all of the sample accounts into a data.frame called SimpleMWRRData. Writing the IRR function At this point, it was time to write the money weighted rate of return (MWRR) function itself.  The definition of MWRR is easily found on the internet or if you are old school you can look in an investment performance text book.  In the customer proof, we based our calculations off the ones defined in the The Handbook of Investment Performance: A User’s Guide by David Spaulding since this is the reference book used by the customer.  (One of the nice things we found during the course of this proof-of-concept is that by using R to write our IRR functions we could easily incorporate the specific variations and business rules of the customer into the calculation.) The key thing with calculating IRR is the need to solve a complex equation with a numerical approximation technique.  For IRR, you need to find the value of the rate of return (r) that sets the Net Present Value of all the flows in and out of the account to zero.  With R, we solve this by defining our NPV function: where bmv is the beginning market value, cf is a vector of cash flows, t is a vector of time (relative to the beginning), emv is the ending market value, and tend is the ending time. Since solving for r is a one-dimensional optimization problem, we decided to take advantage of R’s optimize method (http://stat.ethz.ch/R-manual/R-patched/library/stats/html/optimize.html). The optimize method can be used to find a minimum or maximum; to find the value of r where our npv function is closest to zero, we wrapped our npv function inside the abs function and asked optimize to find the minimum.  Here is an example of using optimize: where low and high are scalars that indicate the range to search for an answer.   To test this out, we need to set values for bmv, cf, t, emv, tend, low, and high.  We will set low and high to some reasonable defaults. For example, this account had a negative 2.2% money weighted rate of return. Enhancing and Packaging the IRR function With numerical approximation methods like optimize, sometimes you will not be able to find an answer with your initial set of inputs.  To account for this, our approach was to first try to find an answer for r within a narrow range, then if we did not find an answer, try calling optimize() again with a broader range.  See the R help page on optimize()  for more details about the search range and its algorithm. At this point, we can now write a simplified version of our MWRR function.  (Our real-world version is  more sophisticated in that it calculates rate of returns for 5 different time periods [since inception, last quarter, year-to-date, last year, year before last year] in a single invocation.  In our actual customer proof, we also defined time-weighted rate of return calculations.  The beauty of R is that it was very easy to add these enhancements and additional calculations to our IRR package.)To simplify code deployment, we then created a new package of our IRR functions and sample data.  For this blog post, we only need to include our SimpleMWRR function and our SimpleMWRRData sample data.  We created the shell of the package by calling: To turn this package skeleton into something usable, at a minimum you need to edit the SimpleMWRR.Rd and SimpleMWRRData.Rd files in the \man subdirectory.  In those files, you need to at least provide a value for the “title” section. Once that is done, you can change directory to the IRR directory and type at the command-line: The myIRR package for this blog post (which has both SimpleMWRR source and SimpleMWRRData sample data) is downloadable from here: myIRR package Testing the myIRR package Here is an example of testing our IRR function once it was converted to an installable package: Calculating IRR for All the Accounts So far, we have shown how to calculate IRR for a single account.  The real-world issue is how do you calculate IRR for all of the accounts?This is the kind of situation where we can leverage the “Split-Apply-Combine” approach (see http://www.cscs.umich.edu/~crshalizi/weblog/815.html).  Given that our sample data can fit in memory, one easy approach is to use R’s “by” function.  (Other approaches to Split-Apply-Combine such as plyr can also be used.  See http://4dpiecharts.com/2011/12/16/a-quick-primer-on-split-apply-combine-problems/). Here is an example showing the use of “by” to calculate the money weighted rate of return for each account in our sample data set.  Recap and Next Steps At this point, you’ve seen the power of R being used to calculate IRR.  There were several good things: R could easily work with the spreadsheets of sample data we were given R’s optimize() function provided a nice way to solve for IRR- it was both fast and allowed us to avoid having to code our own iterative approximation algorithm R was a convenient language to express the customer-specific variations, business-rules, and exceptions that often occur in real-world calculations- these could be easily added to our IRR functions The Split-Apply-Combine technique can be used to perform calculations of IRR for multiple accounts at once. However, there are several challenges yet to be conquered at this point in our story: The actual data that needs to be used lives in a database, not in a spreadsheet The actual data is much, much bigger- too big to fit into the normal R memory space and too big to want to move across the network The overall process needs to run fast- much faster than a single processor The actual data needs to be kept secured- another reason to not want to move it from the database and across the network And the process of calculating the IRR needs to be integrated together with other database ETL activities, so that IRR’s can be calculated as part of the data warehouse refresh processes In our next blog post in this series, we will show you how Oracle R Enterprise solved these challenges.

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  • Top Down bounds of vision

    - by Rorrik
    Obviously in a first person view point the player sees only what's in front of them (with the exception of radars and rearview mirrors, etc). My game has a top down perspective, but I still want to limit what the character sees based on their facing. I've already worked out having objects obstruct vision, but there are two other factors that I worry would be disorienting and want to do right. I want the player to have reduced peripheral vision and very little view behind them. The assumption is he can turn his head and so see fairly well out to the sides, but hardly at all behind without turning the whole body. How do I make it clear you are not seeing behind you? I want the map to turn so the player is always facing up. Part of the game is to experience kind of a maze and the player should be able to lose track of North. How can I turn the map rather than the player avatar without causing confusion?

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  • How to draw the "trail" in a maze solving application

    - by snow-spur
    Hello i have designed a maze and i want to draw a path between the cells as the 'person' moves from one cell to the next. So each time i move the cell a line is drawn Also i am using the graphics module The graphics module is an object oriented library Im importing from graphics import* from maze import* my circle which is my cell center = Point(15, 15) c = Circle(center, 12) c.setFill('blue') c.setOutline('yellow') c.draw(win) p1 = Point(c.getCenter().getX(), c.getCenter().getY()) this is my loop if mazez.blockedCount(cloc)> 2: mazez.addDecoration(cloc, "grey") mazez[cloc].deadend = True c.move(-25, 0) p2 = Point(getX(), getY()) line = graphics.Line(p1, p2) cloc.col = cloc.col - 1 Now it says getX not defined every time i press a key is this because of p2???

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  • Does one's native spoken language affect quality of code?

    - by Xepoch
    There is a school of thought in linguistics that problem solving is very much tied to the syntax, semantics, grammar, and flexibility of one's own native spoken language. Working with various international development teams, I can clearly see a mental culture (if you will) in the codebase. Programming language aside, the German coding is quite different from my colleagues in India. As well, code is distinctly different in Middle America as it is in Coastal America (actually, IBM noticed this years ago). Do you notice with your international colleagues (from ANY country) that coding style and problem solving are in-line with native tongues?

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  • How to get better at solving Dynamic programming problems

    - by newbie
    I recently came across this question: "You are given a boolean expression consisting of a string of the symbols 'true', 'false', 'and', 'or', and 'xor'. Count the number of ways to parenthesize the expression such that it will evaluate to true. For example, there is only 1 way to parenthesize 'true and false xor true' such that it evaluates to true." I knew it is a dynamic programming problem so i tried to come up with a solution on my own which is as follows. Suppose we have a expression as A.B.C.....D where '.' represents any of the operations and, or, xor and the capital letters represent true or false. Lets say the number of ways for this expression of size K to produce a true is N. when a new boolean value E is added to this expression there are 2 ways to parenthesize this new expression 1. ((A.B.C.....D).E) ie. with all possible parenthesizations of A.B.C.....D we add E at the end. 2. (A.B.C.(D.E)) ie. evaluate D.E first and then find the number of ways this expression of size K can produce true. suppose T[K] is the number of ways the expression with size K produces true then T[k]=val1+val2+val3 where val1,val2,val3 are calculated as follows. 1)when E is grouped with D. i)It does not change the value of D ii)it inverses the value of D in the first case val1=T[K]=N.( As this reduces to the initial A.B.C....D expression ). In the second case re-evaluate dp[K] with value of D reversed and that is val1. 2)when E is grouped with the whole expression. //val2 contains the number of 'true' E will produce with expressions which gave 'true' among all parenthesized instances of A.B.C.......D i) if true.E = true then val2 = N ii) if true.E = false then val2 = 0 //val3 contains the number of 'true' E will produce with expressions which gave 'false' among all parenthesized instances of A.B.C.......D iii) if false.E=true then val3=( 2^(K-2) - N ) = M ie. number of ways the expression with size K produces a false [ 2^(K-2) is the number of ways to parenthesize an expression of size K ]. iv) if false.E=false then val3 = 0 This is the basic idea i had in mind but when i checked for its solution http://people.csail.mit.edu/bdean/6.046/dp/dp_9.swf the approach there was completely different. Can someone tell me what am I doing wrong and how can i get better at solving DP so that I can come up with solutions like the one given above myself. Thanks in advance.

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  • Problem Solving vs. Solution Finding

    - by ryanabr
    By enlarge, most developers fall into these two camps I will try to explain what I mean by way of example. A manager gives the developer a task that is communicated like this: “Figure out why control A is not loading on this form”. Now, right there it could be argued that the manager should probably have given better direction and said something more like: “Control A is not loading on the Form, fix it”. They might sound like the same thing to most people, but the first statement will have the developer problem solving the reason why it is failing. The second statement should have the developer looking for the solution to make it work, not focus on why it is broken. In the end, they might be the same thing, but I usually see the first approach take way longer than the second approach. The Problem Solver: The problem solver’s approach to fixing something that is broken is likely to take the error or behavior that is being observed and start to research it using a tool like Google, or any other search engine. 7/10 times this will yield results for the most common of issues. The challenge is in the other 30% of issues that will take the problem solver down the rabbit hole and cause them not to surface for days on end while every avenue is explored for the cause of the problem. In the end, they will probably find the cause of the issue and resolve it, but the cost can be days, or weeks of work. The Solution Finder: The solution finder’s approach to a problem will begin the same way the Problem Solver’s approach will. The difference comes in the more difficult cases. Rather than stick to the pure “This has to work so I am going to work with it until it does” approach, the Solution Finder will look for other ways to get the requirements satisfied that may or may not be using the original approach. For example. there are two area of an application of externally equivalent features, meaning that from a user’s perspective, the behavior is the same. So, say that for whatever reason, area A is now not working, but area B is working. The Problem Solver will dig in to see why area A is broken, where the Solution Finder will investigate to see what is the difference between the two areas and solve the problem by potentially working around it. The other notable difference between the two types of developers described is what point they reach before they re-emerge from their task. The problem solver will likely emerge with a triumphant “I have found the problem” where as the Solution Finder will emerge with the more useful “I have the solution”. Conclusion At the end of the day, users are what drives features in software development. With out users there is no need for software. In todays world of software development with so many tools to use, and generally tight schedules I believe that a work around to a problem that takes 8 hours vs. the more pure solution to the problem that takes 40 hours is a more fruitful approach.

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  • Adventures in Windows 8: Solving activation errors

    - by Laurent Bugnion
    Note: I tagged this article with “MVVM” because I got a few support requests for MVVM Light regarding this exact issue. In fact it is a Windows 8 issue and has nothing to do with MVVM Light per se… Sometimes when you work on a Windows 8 app, you will get a very annoying issue when starting the app. In that case, the app doesn’t not even start past the Splash screen. Putting a breakpoint in App.xaml.cs doesn’t help because the app doesn’t even reach that point! So what exactly is happening? Well when a Windows 8 app starts, the system is performing a few check first. One of the checks, for instance, is to see if an app with the same package ID is already available. The package ID is a unique value set in the package manifest. In the Solution Explorer, double click on Package.appxmanifest. This opens the manifest in a special editor Click on the Packaging tab See the GUID under Package Name. This is the unique ID I am talking about. If there is a conflict (i.e. if an app is already installed with the exact same ID), Windows will warm the user that the app is already installed. However when you are in the process of developing an app, you install and uninstall the same app many many times (every time that you start in Visual Studio), and sometimes some issues arise, for instance failing to uninstall the app before starting the new instance of the same app. First step if you get such an error When the application fails to start past the splash screen, the first step is to identify what kind of error happened. In my experience the “already installed” is by far the most frequent (in fact I never had another such error), but it can be something else. An annoying thing is that the popup that shows the error is usually started below the Windows 8 app, and so you don’t even see it! This is especially true if you run this in the Simulator. In that case, do the following: Press on the Simulator’s home button, then press on the Desktop tile on the Start menu. The error popup should be shown on the desktop. If your applications runs on the Local machine, you also do the same and press the Windows button, and then from the Start menu press the Desktop tile. Deployment error in Studio Sometimes the same error causes Visual Studio to fail launching the application at all with a deployment error. This is a better case, because at least it is clear that there is an issue. In that case, write down the code that is shown in the Error window (for instance 0x80073D05 in the example below). Once you have the error code, go to the “Troubleshooting packaging, deployment, and query of Windows Store apps” page and look up the code in question. In my case, the error was “ERROR_DELETING_EXISTING_APPLICATIONDATA_STORE_FAILED”, “An error occurred while deleting the package's previously existing application data.” Solving the “ERROR_DELETING_EXISTING_APPLICATIONDATA_STORE_FAILED” issue Update: Before trying the below, you can also try the simple steps: Exit Visual Studio Go to the Start menu Locate your app’s tile. It should be visible in the Start menu directly, towards the far end on the right. Right click the tile and select Uninstall from the App Bar. Restart Visual Studio and try again. Sometimes it helps. If it doesn’t, then try the following: In order to solve the case where Windows, for any reason, fails to delete the existing application before starting the new instance, follow the steps: Open the Package.appxmanifest in Visual Studio Open the Packaging tab. Change the Package name. For tests you can just try to change the last character of the GUID, though I would recommend creating a brand new GUID. Press Start Type GUID Start the GUID Generator application Select Registry Format Press Copy. Paste the new GUID in place of the Package Name in Visual Studio Important: don’t forget to remove the curly brackets at the beginning and at the end of the newly pasted GUID. Then you just have to cross your fingers and start the application again… If it works, celebrate. if it doesn’t work… well at this point I am not sure so good luck with that ;) Happy coding, Laurent   Laurent Bugnion (GalaSoft) Subscribe | Twitter | Facebook | Flickr | LinkedIn

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  • Solving Big Problems with Oracle R Enterprise, Part II

    - by dbayard
    Part II – Solving Big Problems with Oracle R Enterprise In the first post in this series (see https://blogs.oracle.com/R/entry/solving_big_problems_with_oracle), we showed how you can use R to perform historical rate of return calculations against investment data sourced from a spreadsheet.  We demonstrated the calculations against sample data for a small set of accounts.  While this worked fine, in the real-world the problem is much bigger because the amount of data is much bigger.  So much bigger that our approach in the previous post won’t scale to meet the real-world needs. From our previous post, here are the challenges we need to conquer: The actual data that needs to be used lives in a database, not in a spreadsheet The actual data is much, much bigger- too big to fit into the normal R memory space and too big to want to move across the network The overall process needs to run fast- much faster than a single processor The actual data needs to be kept secured- another reason to not want to move it from the database and across the network And the process of calculating the IRR needs to be integrated together with other database ETL activities, so that IRR’s can be calculated as part of the data warehouse refresh processes In this post, we will show how we moved from sample data environment to working with full-scale data.  This post is based on actual work we did for a financial services customer during a recent proof-of-concept. Getting started with the Database At this point, we have some sample data and our IRR function.  We were at a similar point in our customer proof-of-concept exercise- we had sample data but we did not have the full customer data yet.  So our database was empty.  But, this was easily rectified by leveraging the transparency features of Oracle R Enterprise (see https://blogs.oracle.com/R/entry/analyzing_big_data_using_the).  The following code shows how we took our sample data SimpleMWRRData and easily turned it into a new Oracle database table called IRR_DATA via ore.create().  The code also shows how we can access the database table IRR_DATA as if it was a normal R data.frame named IRR_DATA. If we go to sql*plus, we can also check out our new IRR_DATA table: At this point, we now have our sample data loaded in the database as a normal Oracle table called IRR_DATA.  So, we now proceeded to test our R function working with database data. As our first test, we retrieved the data from a single account from the IRR_DATA table, pull it into local R memory, then call our IRR function.  This worked.  No SQL coding required! Going from Crawling to Walking Now that we have shown using our R code with database-resident data for a single account, we wanted to experiment with doing this for multiple accounts.  In other words, we wanted to implement the split-apply-combine technique we discussed in our first post in this series.  Fortunately, Oracle R Enterprise provides a very scalable way to do this with a function called ore.groupApply().  You can read more about ore.groupApply() here: https://blogs.oracle.com/R/entry/analyzing_big_data_using_the1 Here is an example of how we ask ORE to take our IRR_DATA table in the database, split it by the ACCOUNT column, apply a function that calls our SimpleMWRR() calculation, and then combine the results. (If you are following along at home, be sure to have installed our myIRR package on your database server via  “R CMD INSTALL myIRR”). The interesting thing about ore.groupApply is that the calculation is not actually performed in my desktop R environment from which I am running.  What actually happens is that ore.groupApply uses the Oracle database to perform the work.  And the Oracle database is what actually splits the IRR_DATA table by ACCOUNT.  Then the Oracle database takes the data for each account and sends it to an embedded R engine running on the database server to apply our R function.  Then the Oracle database combines all the individual results from the calls to the R function. This is significant because now the embedded R engine only needs to deal with the data for a single account at a time.  Regardless of whether we have 20 accounts or 1 million accounts or more, the R engine that performs the calculation does not care.  Given that normal R has a finite amount of memory to hold data, the ore.groupApply approach overcomes the R memory scalability problem since we only need to fit the data from a single account in R memory (not all of the data for all of the accounts). Additionally, the IRR_DATA does not need to be sent from the database to my desktop R program.  Even though I am invoking ore.groupApply from my desktop R program, because the actual SimpleMWRR calculation is run by the embedded R engine on the database server, the IRR_DATA does not need to leave the database server- this is both a performance benefit because network transmission of large amounts of data take time and a security benefit because it is harder to protect private data once you start shipping around your intranet. Another benefit, which we will discuss in a few paragraphs, is the ability to leverage Oracle database parallelism to run these calculations for dozens of accounts at once. From Walking to Running ore.groupApply is rather nice, but it still has the drawback that I run this from a desktop R instance.  This is not ideal for integrating into typical operational processes like nightly data warehouse refreshes or monthly statement generation.  But, this is not an issue for ORE.  Oracle R Enterprise lets us run this from the database using regular SQL, which is easily integrated into standard operations.  That is extremely exciting and the way we actually did these calculations in the customer proof. As part of Oracle R Enterprise, it provides a SQL equivalent to ore.groupApply which it refers to as “rqGroupEval”.  To use rqGroupEval via SQL, there is a bit of simple setup needed.  Basically, the Oracle Database needs to know the structure of the input table and the grouping column, which we are able to define using the database’s pipeline table function mechanisms. Here is the setup script: At this point, our initial setup of rqGroupEval is done for the IRR_DATA table.  The next step is to define our R function to the database.  We do that via a call to ORE’s rqScriptCreate. Now we can test it.  The SQL you use to run rqGroupEval uses the Oracle database pipeline table function syntax.  The first argument to irr_dataGroupEval is a cursor defining our input.  You can add additional where clauses and subqueries to this cursor as appropriate.  The second argument is any additional inputs to the R function.  The third argument is the text of a dummy select statement.  The dummy select statement is used by the database to identify the columns and datatypes to expect the R function to return.  The fourth argument is the column of the input table to split/group by.  The final argument is the name of the R function as you defined it when you called rqScriptCreate(). The Real-World Results In our real customer proof-of-concept, we had more sophisticated calculation requirements than shown in this simplified blog example.  For instance, we had to perform the rate of return calculations for 5 separate time periods, so the R code was enhanced to do so.  In addition, some accounts needed a time-weighted rate of return to be calculated, so we extended our approach and added an R function to do that.  And finally, there were also a few more real-world data irregularities that we needed to account for, so we added logic to our R functions to deal with those exceptions.  For the full-scale customer test, we loaded the customer data onto a Half-Rack Exadata X2-2 Database Machine.  As our half-rack had 48 physical cores (and 96 threads if you consider hyperthreading), we wanted to take advantage of that CPU horsepower to speed up our calculations.  To do so with ORE, it is as simple as leveraging the Oracle Database Parallel Query features.  Let’s look at the SQL used in the customer proof: Notice that we use a parallel hint on the cursor that is the input to our rqGroupEval function.  That is all we need to do to enable Oracle to use parallel R engines. Here are a few screenshots of what this SQL looked like in the Real-Time SQL Monitor when we ran this during the proof of concept (hint: you might need to right-click on these images to be able to view the images full-screen to see the entire image): From the above, you can notice a few things (numbers 1 thru 5 below correspond with highlighted numbers on the images above.  You may need to right click on the above images and view the images full-screen to see the entire image): The SQL completed in 110 seconds (1.8minutes) We calculated rate of returns for 5 time periods for each of 911k accounts (the number of actual rows returned by the IRRSTAGEGROUPEVAL operation) We accessed 103m rows of detailed cash flow/market value data (the number of actual rows returned by the IRR_STAGE2 operation) We ran with 72 degrees of parallelism spread across 4 database servers Most of our 110seconds was spent in the “External Procedure call” event On average, we performed 8,200 executions of our R function per second (110s/911k accounts) On average, each execution was passed 110 rows of data (103m detail rows/911k accounts) On average, we did 41,000 single time period rate of return calculations per second (each of the 8,200 executions of our R function did rate of return calculations for 5 time periods) On average, we processed over 900,000 rows of database data in R per second (103m detail rows/110s) R + Oracle R Enterprise: Best of R + Best of Oracle Database This blog post series started by describing a real customer problem: how to perform a lot of calculations on a lot of data in a short period of time.  While standard R proved to be a very good fit for writing the necessary calculations, the challenge of working with a lot of data in a short period of time remained. This blog post series showed how Oracle R Enterprise enables R to be used in conjunction with the Oracle Database to overcome the data volume and performance issues (as well as simplifying the operations and security issues).  It also showed that we could calculate 5 time periods of rate of returns for almost a million individual accounts in less than 2 minutes. In a future post, we will take the same R function and show how Oracle R Connector for Hadoop can be used in the Hadoop world.  In that next post, instead of having our data in an Oracle database, our data will live in Hadoop and we will how to use the Oracle R Connector for Hadoop and other Oracle Big Data Connectors to move data between Hadoop, R, and the Oracle Database easily.

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  • Solving Kaggle’s Bike Sharing Demand Machine Learning Problem

    - by Gopinath
    Kaggle.com hosts a lot of interesting machine learning problems online and thousands of its members compete to solve them for a bounty. Problems hosted on Kaggle has varying complexity to accomodate newbies to rock star developers – few problems are good enough for  newbies to learn basics of machine learning and few of them challenge the best of machine learning developers. I’m learning basics of machine learning for the past few weeks and had an opportunity to solve Kaggel’s Bike Sharing Demand problem. Bike Sharing systems allows customers to rent a bike (or a cycle as it is called in many part of the world) for several hours and return them back . The problem provides historical information about the demand for bike sharing business and we need to forecast the demand. For more information on the problem, visit Kaggle.com website. Here is the solution I written using random forests algorithm using R programming language and you can download the source code from github.  With this solution I was able to score RMSLE of 0.70117, which placed me somewhere in the mid of the leader board.  This is the best score I could get by spending 4 hours of my time. Please feel free to fork the code and improve it.   Get Kaggle Bike Sharing Demand solution code from GitHub

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  • Solving Null Entity Problems with JPA Data Controls in PS1

    - by shay.shmeltzer
    Turns out there is a slight bug that seems to prevent you from doing interactions (update, scroll) with the results of a JPA named query that you dropped on a page using ADF Binding. People are running into this when they are doing the EJB tutorial on OTN for example. The problem is that the way the binding is set up for you automatically doesn't allow you to actually access the iterator set of records to do follow up operations. When I last checked this was solved in the next release of JDeveloper, but in the meantime there is a quick simple way to resolve the issue by changing the refresh condition of the oiterator in your page binding. Here is a little demo that shows the problem and the solution:

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