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• Scheme vs Haskell for an Introduction to Functional Programming?

  - by haziz

  I am comfortable with programming in C and C#, and will explore C++ in the future. I may be interested in exploring functional programming as a different programming paradigm. I am doing this for fun, my job does not involve computer programming, and am somewhat inspired by the use of functional programming, taught fairly early, in computer science courses in college. Lambda calculus is certainly beyond my mathematical abilities, but I think I can handle functional programming. Which of Haskell or Scheme would serve as a good intro to functional programming? I use emacs as my text editor and would like to be able to configure it more easily in the future which would entail learning Emacs Lisp. My understanding, however, is that Emacs Lisp is fairly different from Scheme and is also more procedural as opposed to functional. I would likely be using "The Little Schemer" book, which I have already bought, if I pursue Scheme (seems to me a little weird from my limited leafing through it). Or would use the "Learn You a Haskell for Great Good" if I pursue Haskell. I would also watch the Intro to Haskell videos by Dr Erik Meijer on Channel 9. Any suggestions, feedback or input appreciated. Thanks. P.S. BTW I also have access to F# since I have Visual Studio 2010 which I use for C# development, but I don't think that should be my main criteria for selecting a language.

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• Calculating 3d rotation around random axis

  - by mitim

  This is actually a solved problem, but I want to understand why my original method didn't work (hoping someone with more knowledge can explain). (Keep in mind, I've not very experienced in 3d programming, having only played with the very basic for a little bit...nor do I have a lot of mathematical experience in this area). I wanted to animate a point rotating around another point at a random axis, say a 45 degrees along the y axis (think of an electron around a nucleus). I know how to rotate using the transform matrix along the X, Y and Z axis, but not an arbitrary (45 degree) axis. Eventually after some research I found a suggestion: Rotate the point by -45 degrees around the Z so that it is aligned. Then rotate by some increment along the Y axis, then rotate it back +45 degrees for every frame tick. While this certainly worked, I felt that it seemed to be more work then needed (too many method calls, math, etc) and would probably be pretty slow at runtime with many points to deal with. I thought maybe it was possible to combine all the rotation matrixes involve into 1 rotation matrix and use that as a single operation. Something like: [ cos(-45) -sin(-45) 0] [ sin(-45) cos(-45) 0] rotate by -45 along Z [ 0 0 1] multiply by [ cos(2) 0 -sin(2)] [ 0 1 0 ] rotate by 2 degrees (my increment) along Y [ sin(2) 0 cos(2)] then multiply that result by (in that order) [ cos(45) -sin(45) 0] [ sin(45) cos(45) 0] rotate by 45 along Z [ 0 0 1] I get 1 mess of a matrix of numbers (since I was working with unknowns and 2 angles), but I felt like it should work. It did not and I found a solution on wiki using a different matirx, but that is something else. I'm not sure if maybe I made an error in multiplying, but my question is: this is actually a viable way to solve the problem, to take all the separate transformations, combine them via multiplying, then use that or not?

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• jQuery - I'm getting unexpected outputs from a basic math formula.

  - by OllieMcCarthy

  Hi I would like to start by saying I'd greatly appreciate anyones help on this. I have built a small caculator to calculate the amount a consumer can save annually on energy by installing a ground heat pump or solar panels. As far as I can tell the mathematical formulas are correct and my client verified this yesterday when I showed him the code. Two problems. The first is that the calculator is outputting ridiculously large numbers for the first result. The second problem is that the solar result is only working when there are no zeros in the fields. Are there some quirks as to how one would write mathematical formulas in JS or jQuery? Any help greatly appreciated. Here is the link - http://www.olliemccarthy.com/test/johncmurphy/?page_id=249 And here is the code for the entire function - $jq(document).ready(function(){ // Energy Bill Saver // Declare Variables var A = ""; // Input for Oil var B = ""; // Input for Storage Heater var C = ""; // Input for Natural Gas var D = ""; // Input for LPG var E = ""; // Input for Coal var F = ""; // Input for Wood Pellets var G = ""; // Input for Number of Occupants var J = ""; var K = ""; var H = ""; var I = ""; // Declare Constants var a = "0.0816"; // Rate for Oil var b = "0.0963"; // Rate for NightRate var c = "0.0558"; // Rate for Gas var d = "0.1579"; // Rate for LPG var e = "0.121"; // Rate for Coal var f = "0.0828"; // Rate for Pellets var g = "0.02675"; // Rate for Heat Pump var x = "1226.4"; // Splittin up I to avoid error var S1 = ""; // Splitting up the calcuation for I var S2 = ""; // Splitting up the calcuation for I var S3 = ""; // Splitting up the calcuation for I var S4 = ""; // Splitting up the calcuation for I var S5 = ""; // Splitting up the calcuation for I var S6 = ""; // Splitting up the calcuation for I // Calculate H (Ground Sourced Heat Pump) $jq(".es-calculate").click(function(){ $jq(".es-result-wrap").slideDown(300); A = $jq("input.es-oil").val(); B = $jq("input.es-storage").val(); C = $jq("input.es-gas").val(); D = $jq("input.es-lpg").val(); E = $jq("input.es-coal").val(); F = $jq("input.es-pellets").val(); G = $jq("input.es-occupants").val(); J = ( A / a ) + ( B / b ) + ( C / c ) + ( D / d ) + ( E / e ) + ( F / f ) ; H = A + B + C + D + E + F - ( J * g ) ; K = ( G * x ) ; if ( A !== "0" ) { S1 = ( ( ( A / a ) / J ) * K * a ) ; } else { S1 = "0" ; } if ( B !== "0" ) { S2 = ( ( ( B / b ) / J ) * K * b ) ; } else { S2 = "0" ; } if ( C !== "0" ) { S3 = ( ( ( C / c ) / J ) * K * c ) ; } else { S3 = "0" ; } if ( D !== "0" ) { S4 = ( ( ( D / d ) / J ) * K * d ) ; } else { S4 = "0" ; } if ( E !== "0" ) { S5 = ( ( ( E / e ) / J ) * K * e ) ; } else { S5 = "0" ; } if ( F !== "0" ) { S6 = ( ( ( F / f ) / J ) * K * f ) ; } else { S6 = "0" ; } I = S1 + S2 + S3 + S4 + S5 + S6 ; if(!isNaN(H)) {$jq("span.es-result-span-h").text(H.toFixed(2));} else{$jq("span.es-result-span-h").text('Error: Please enter numerals only');} if(!isNaN(I)) {$jq("span.es-result-span-i").text(I.toFixed(2));} else{$jq("span.es-result-span-i").text('Error: Please enter numerals only');} }); });

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• Japanese Multiplication simulation - is a program actually capable of improving calculation speed?

  - by jt0dd

  On SuperUser, I asked a (possibly silly) question about processors using mathematical shortcuts and would like to have a look at the possibility at the software application of that concept. I'd like to write a simulation of Japanese Multiplication to get benchmarks on large calculations utilizing the shortcut vs traditional CPU multiplication. I'm curious as to whether it makes sense to try this. My Question: I'd like to know whether or not a software math shortcut, as described above is actually a shortcut at all. This is a question of programming concept. By utilizing the simulation of Japanese Multiplication, is a program actually capable of improving calculation speed? Or am I doomed from the start? The answer to this question isn't required to determine whether or not the experiment will succeed, but rather whether or not it's logically possible for such a thing to occur in any program, using this concept as an example. My theory is that since addition is computed faster than multiplication, a simulation of Japanese multiplication may actually allow a program to multiply (large) numbers faster than the CPU arithmetic unit can. I think this would be a very interesting finding, if it proves to be true. If, in the multiplication of numbers of any immense size, the shortcut were to calculate the result via less instructions (or faster) than traditional ALU multiplication, I would consider the experiment a success.

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• Vector vs Scalar velocity?

  - by Serguei Fedorov

  I am revamping an engine I have been working on and off on for the last few weeks to use a directional vector to dictate direction; this way I can dictate the displacement based on a direction. However, the issue I am trying to overcome is the following problem; the speed towards X and speed towards Y are unrelated to one another. If gravity pulls the object down by an increasing velocity my velocity towards the X should not change. This is very easy to implement if my speed is broken into a Vector datatype, Vector.X dictates one direction Vector.Y dictates the other (assuming we are not concerned about the Z axis). However, this defeats the purpose of the directional vector because: SpeedX = 10 SpeedY = 15 [1, 1] normalized = ~[0.7, 0.7] [0.7, 0.7] * [10, 15] = [7, 10.5] As you can see my direction is now "scaled" to my speed which is no longer the direction that I want to be moving in. I am very new to vector math and this is a learning project for me. I looked around a little bit on the internet but I still want to figure out things on my own (not just look at an example and copy off it). Is there way around this? Using a directional vector is extremely useful but I am a little bit stumped at this problem. I am sorry if my mathematical understanding maybe completely wrong.

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• How can Agile methodologies be adapted to High Volume processing system development?

  - by luckyluke

  I am developing high volume processing systems. Like mathematical models that calculate various parameters based on millions of records, calculated derived fields over milions of records, process huge files having transactions etc... I am well aware of unit testing methodologies and if my code is in C# I have no problem in unit testing it. Problem is I often have code in T-SQL, C# code that is a SQL stored assembly, and SSIS workflow with a good amount of logic (and outcomes etc) or some SAS process. What is the approach YOu use when developing such systems. I usually develop several tests as Stored procedures in a designed schema(TEST) and then automatically run them overnight and check out the results. But this is only for T-SQL. And Continous integration IS hard. But the problem is with testing SSIS packages. How do You test it? What is Your preferred approach for stubbing data into tables (especially if You need a lot data initialization). I have some approach derived over the years but maybe I am just not reading enough articles. So Banking, Telecom, Risk developers out there. How do You test your mission critical apps that process milions of records at end day, month end etc? What frameworks do You use? How do You validate that Your ssis package is Correct (as You develop it)/ How do You achieve continous integration in such an environment (Personally I never got there)? I hope this is not to open-ended question. How do You test Your map-reduce jobs for example (i do not use hadoop but this is quite similar). luke Hope that this is not too open ended

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• Enforcing Constraints Upon Data Documents of Various Formats

  - by Christopher Berman

  This seems like the sort of problem that must have been solved elegantly long ago, but I haven't the foggiest how to google it and find it. Suppose you're maintaining a large legacy system, which has a large collection of data (tens of GB) of various formats, including XML and two different internal configuration formats. Suppose further that there are abstract rules governing the values these files may or may not contain. EXAMPLE: File A defines the raw, mathematical data pertaining to the aerodynamics of a car for consumption of the physics component of the system. File B contains certain values from File A in an easily accessible, XML hierarchy for consumption of a different component of the system. There exists, therefore, an abstract rule (or constraint) such that the values from File B must match the values from File A. This is probably the simplest constraint that can be specified, but in practice, the constraints between files can become very complicated indeed. What is the best method for managing these constraints between files of arbitrary formats, short of migrating it over to an RDBMS (which simply isn't feasible for the foreseeable future)? Has this problem been solved already? To be more specific, I would expect the solution to at least produce notifications of violated constraints; the solution need not resolve the constraints. ============================== Sample file structures File A (JeepWrangler2011.emv): MODEL JeepWrangler2011 { EsotericMathValueX 11.1 EsotericMathValueY 22.2 EsotericMathValueZ 33.3 } File B (JeepWrangler2011.xml): <model name="JeepWrangler2011"> <!--These values must correspond File A's EsotericMathValues--> <modelExtent x="11.1" y="22.2" z="33.3"/> [...] </model>

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• Generic rule parser for RPG board game rules - how to do it?

  - by burzum

  I want to build a generic rule parser for pen and paper style RPG systems. A rule can involve usually 1 to N entities 1 to N roles of a dice and calculating values based on multiple attributes of an entity. For example: Player has STR 18, his currently equipped weapon gives him a bonus of +1 STR but a malus of DEX -1. He attacks a monster entity and the game logic now is required to run a set of rules or actions: Player rolls the dice, if he gets for example 8 or more (base attack value he needs to pass is one of his base attributes!) his attack is successfully. The monster then rolls the dice to calculate if the attack goes through it's armor. If yes the damage is taken if not the attack was blocked. Besides simple math rules can also have constraints like applying only to a certain class of user (warrior vs wizzard for example) or any other attribute. So this is not just limited to mathematical operations. If you're familiar with RPG systems like Dungeon and Dragons you'll know what I'm up to. My issue is now that I have no clue how to exactly build this the best possible way. I want people to be able to set up any kind of rule and later simply do an action like selecting a player and a monster and run an action (set of rules like an attack). I'm asking less for help with the database side of things but more about how to come up with a structure and a parser for it to keep my rules flexible. The language of choice for this is php by the way.

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• What is the R Language?

  - by TATWORTH

  I encountered the R Language recently with O'Reilly books and while from the context I knew it was a language for dealing with statistics, doing a web search for the support web site was futile. However I have now located the web site and it is at http://www.r-project.org/R is a free language available for a number of platforms including windows. CRAN mirrors are available at a number of locations worldwide.Here is the official description:"R is a language and environment for statistical computing and graphics. It is a GNU project which is similar to the S language and environment which was developed at Bell Laboratories (formerly AT&T, now Lucent Technologies) by John Chambers and colleagues. R can be considered as a different implementation of S. There are some important differences, but much code written for S runs unaltered under R. R provides a wide variety of statistical (linear and nonlinear modelling, classical statistical tests, time-series analysis, classification, clustering, ...) and graphical techniques, and is highly extensible. The S language is often the vehicle of choice for research in statistical methodology, and R provides an Open Source route to participation in that activity. One of R's strengths is the ease with which well-designed publication-quality plots can be produced, including mathematical symbols and formulae where needed. Great care has been taken over the defaults for the minor design choices in graphics, but the user retains full control. R is available as Free Software under the terms of the Free Software Foundation's GNU General Public License in source code form. It compiles and runs on a wide variety of UNIX platforms and similar systems (including FreeBSD and Linux), Windows and MacOS."

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• Spherical to Cartesian Coordinates

  - by user1258455

  Well I'm reading the Frank's Luna DirectX10 book and, while I'm trying to understand the first demo, I found something that's not very clear at least for me. In the updateScene method, when I press A, S, W or D, the angles mTheta and mPhi change, but after that, there are three lines of code that I don't understand exactly what they do: // Convert Spherical to Cartesian coordinates: mPhi measured from +y // and mTheta measured counterclockwise from -z. float x = 5.0f*sinf(mPhi)*sinf(mTheta); float z = -5.0f*sinf(mPhi)*cosf(mTheta); float y = 5.0f*cosf(mPhi); I mean, this explains that they do, it says that it converts the spherical coordinates to cartesian coordinates, but, mathematically, why? why the x value is calculated by the product of the sins of both angles? And the z by the product of the sine and cosine? and why the y just uses the cosine? After that, those values (x, y and z) are used to build the view matrix. The book doesn't explain (mathematically) why those values are calculated like that (and I didn't find anything to help me to understand it at the first Part of the book: "Mathematical prerequisites"), so it would be good if someone could explain me what exactly happen in those code lines or just give me a link that helps me to understand the math part. Thanks in advance!

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• Best way to calculate unit deaths in browser game combat?

  - by MikeCruz13

  My browser game's combat system is written and mechanically functioning well. It's written in PHP and uses a SQL database. I'm happy with the unit balance in relation to one another. I am, however, a little worried about how I'm calculating unit deaths when one player attacks another because the deaths seem to pile up a little fast for my taste. For this system, a battle doesn't just trigger, calculate winner, and end. Instead, it is allowed to go for several rounds (say one round every 15 mins.) until one side passes a threshold of being too strong for the other player and allows players to send reinforcements between rounds. Each round, units pair up and attack each other. Essentially what I do is calculate the damage: AP = Attack Points HP = Hit Points Units AP * Quantity * Random Factors * other factors (such as attrition) I take that and divide by the defending unit's HP to find the number of casualties of defending units. So, for example (simplified to take out some factors), if I have: 500 attackers with 50 AP vs 1000 defenders with 100 HP = 250 deaths. I wonder if that last step could be handled better to reduce the deaths piling up. Some ideas: I just change all the units with more HP? I make sure to set the Attacking unit's AP to be a max of the defender's HP to make sure they only kill 1 unit. (is that fair if I have less huge units vs many small units?) I spread the damage around more by including the defending unit's quantity more? i.e. in that scenario some are dead and some are 50% damage. (How would I track this every round?) Other better mathematical approaches?

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• How well do graduates from top universities perform and how does it feel compare to the rest of the world?

  - by Amumu

  I always have impressions to those who got admitted into top Universities like MIT, Standford... for studying Engineering. I don't actually know what they are doing in the University or what they will do, but I always feel they can perform higher level tasks with more complexities. I always think that they are good at create and applying mathematical model in real life and I tend to agree: If you can't apply math, it's your problems, not math. I am a junior software engineer on embedded devices. I am learning more on Linux kernel and low level stuffs. Even so, my will is not strong enough to pursue technical path forever, with a final purpose is to create something significant on my own. May I have a chance to get on their level if I keep learning through experience and self-study? In my opinion, Math is the must have requirement, since it seems that programs on those Universities are very Math oriented. Without very strong math skill, how can one perform good in science and researching beyond making regular business products?

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• Finite Numbers and ExplorerCanvas

  - by PhubarBaz

  I was working on my online mathematical graphing application, CloudGraph, and trying to make it work in IE. The app uses the HTML5 canvas element to draw graphs. Since IE doesn't support canvas yet I use ExplorerCanvas to provide that support for IE. However, it seems that when using excanvas, if you try to moveTo or drawTo a point that is not finite it loses it's mind and stops drawing anything else after that. I had no such problems in Firefox or Chrome so it took me awhile to figure out what was going on. Next I discovered that I needed a way to check if a variable was NaN or Inifinity or any other non-finite value so I could avoid calling moveTo() in that case. I started writing a long if statement, then I thought there has to be a better way. Sure enough there was. There just happens to be an isFinite() function built into Javascript just for this purpose. Who knew! It works great. Another difference I discovered with excanvas is that you must specify a starting point using a moveTo() when beginning a drawing path. Again, Chrome and Firefox are a lot more forgiving in this area so it took me a while to figure out why my lines weren't drawing. But, all is happy now and I'm a little wiser to the ways of the canvas.

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• Cube rotation DX10

  - by German

  Well I'm reading the Frank's Luna DirectX10 book and, while I'm trying to understand the first demo, I found something that's not very clear at least for me. In the updateScene method, when I press A, S, W or D, the angles mTheta and mPhi change, but after that, there are three lines of code that I don't understand exactly what they do: // Convert Spherical to Cartesian coordinates: mPhi measured from +y // and mTheta measured counterclockwise from -z. float x = 5.0f*sinf(mPhi)*sinf(mTheta); float z = -5.0f*sinf(mPhi)*cosf(mTheta); float y = 5.0f*cosf(mPhi); I mean, this explains that they do, it says that it converts the spherical coordinates to cartesian coordinates, but, mathematically, why? why the x value is calculated by the product of the sins of both angles? And the z by the product of the sine and cosine? and why the y just uses the cosine? After that, those values (x, y and z) are used to build the view matrix. The book doesn't explain (mathematically) why those values are calculated like that (and I didn't find anything to help me to understand it at the first Part of the book: "Mathematical prerequisites"), so it would be good if someone could explain me what exactly happen in those code lines or just give me a link that helps me to understand the math part. Thanks in advance!

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• How to pass an enum to Html.RadioButtonFor to get a list of radio buttons in MVC 2 RC 2, C#

  - by Matt W

  Hi, I'm trying to render a radio button list in MVC 2 RC 2 (C#) using the following line: <%= Html.RadioButtonFor(model => Enum.GetNames(typeof(DataCarry.ProtocolEnum)), null) %> but it's just giving me the following exception at runtime: Templates can be used only with field access, property access, single-dimension array index, or single-parameter custom indexer expressions. Is this possible and if so, how, please? Thanks, Matt.

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• WebBrowser control and XPath

  - by Neir0

  Hi, Can i use XPAth expressions to navigate through DOM elements in WebBrowser control? May be attaching javascript code and use document.evaluate function is right way?

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• Reg Ex parsing error - too many )'s

  - by Chris Herring

  Using regular expressions in .NET with the pattern ^%[^%]+%\Z and the string "few)few%" I get the error - System.ArgumentException: parsing "few)few%" - Too many )'s. Dim match As System.Text.RegularExpressions.Match = System.Text.RegularExpressions.Regex.Match("^%[^%]+%\Z", "few)few%") What would the issue be? Do I need to escape brackets in any input expression to reg ex? (I'm trying the determine if string has the wildcard % at the beginning and end of the string but not elsewhere in the string)

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• OWASP Regex Repository: Is this regex correct?

  - by Jacco

  I was looking at the regular expression for validating various data types from the (OWASP Regex Repository). One of the regular expressions in there is called safetext and looks like: ^[a-zA-Z0-9\s.\-]+$ My first question is: Is this regular expression correct? complementary question If this Regex Repository any good at all?

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• Shouldn’t Bind() pass child control’s values to GridView before Page.PreRender?

  - by SourceC

  hello, For controls such as the GridView, DetailsView, and FormView controls, data-binding expressions are resolved automatically during the control's PreRender event But doesn’t data source control perform updates prior to Page.PreRender event? Meaning, shouldn’t Bind() pass child control’s values to GridView ( so they can be passed to data source control as parameters ) before data source control updates the data source, thus before Page.PreRender event? thanx

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• JSLint -Tolerate inefficient subscripting?

  - by James Wiseman

  I'm reading the JSlint Options Documentation to understand each of the available options, and have come across one that I don't quite understand, and can't find any useful information regarding it elsewhere. sub - Tolerate inefficient subscripting true if subscript notation may be used for expressions better expressed in dot notation. Can anyone shed more light as to what this means? Thanks

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• Eval Smarty Code inside a Smarty Template

  - by clops

  Hi, is there a way to evaluate Smarty Code inside an existing Smarty template? For example, I may have the following construct: smartyTemplate.tpl <body> <div id="dynamicPart"> {$valueFromDatabase} </div> </body> Whereas the Smarty variable $valueFromDatabase contains another Smarty Template which I would like to be inserted in place of the variable and then evaluated as a template (with all the logic expressions in replacements neccessary).

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• Very simple regex not working

  - by Thomas Wanner

  I have read that to match a word inside of a string using Regular expressions (in .NET), I can use the word boundary specifier (\b) within the regex. However, none of these calls result in any matches Regex.Match("INSERT INTO TEST(Col1,Col2) VALUES(@p1,@p2)", "\b@p1\b"); Regex.Match("INSERT INTO TEST(Col1,Col2) VALUES(@p1,@p2)", "\bINSERT\b"); Is there anything I am doing wrong ?

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• Regex split into overlapping strings

  - by polygenelubricants

  I'm exploring the power of regular expressions, so I'm just wondering if something like this is possible: public class StringSplit { public static void main(String args[]) { System.out.println( java.util.Arrays.deepToString( "12345".split(INSERT_REGEX_HERE) ) ); // prints "[12, 23, 34, 45]" } } If possible, then simply provide the regex (and preemptively some explanation on how it works). If it's only possible in some regex flavors other than Java, then feel free to provide those as well. If it's not possible, then please explain why.

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• Irc server for ubuntu

  - by Ralphz

  The Ubuntu WIKI https://help.ubuntu.com/community/IrcServer it lists few IRC servers you can use in Ubuntu. My question is which one is you favorite one and more secure. I will also need one that will allow me to monitor rooms for regular expressions and run some scripts if regexp matches. Thanks

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• Find and replace in a block of text.

  - by David Tildon

  I have a database full of text fields that look like this: (paragraph of normal text) image:blog/clownboy.jpg (another paragraph) I'm trying to write a view helper for Rails that will take one of these big blocks of text, find bits like "image:blog/clownboy.jpg" and replace them with the corresponding <img src="blog/clownboy.jpg"> (without disturbing the surrounding whitespace) before outputting it to the user. I've been trying for an hour or so now, but I'm new to Ruby and the regular expressions are still a bit beyond me.

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