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  • Segmenting a double array of labels

    - by Ami
    The Problem: I have a large double array populated with various labels. Each element (cell) in the double array contains a set of labels and some elements in the double array may be empty. I need an algorithm to cluster elements in the double array into discrete segments. A segment is defined as a set of pixels that are adjacent within the double array and one label that all those pixels in the segment have in common. (Diagonal adjacency doesn't count and I'm not clustering empty cells). |-------|-------|------| | Jane | Joe | | | Jack | Jane | | |-------|-------|------| | Jane | Jane | | | | Joe | | |-------|-------|------| | | Jack | Jane | | | Joe | | |-------|-------|------| In the above arrangement of labels distributed over nine elements, the largest cluster is the “Jane” cluster occupying the four upper left cells. What I've Considered: I've considered iterating through every label of every cell in the double array and testing to see if the cell-label combination under inspection can be associated with a preexisting segment. If the element under inspection cannot be associated with a preexisting segment it becomes the first member of a new segment. If the label/cell combination can be associated with a preexisting segment it associates. Of course, to make this method reasonable I'd have to implement an elaborate hashing system. I'd have to keep track of all the cell-label combinations that stand adjacent to preexisting segments and are in the path of the incrementing indices that are iterating through the double array. This hash method would avoid having to iterate through every pixel in every preexisting segment to find an adjacency. Why I Don't Like it: As is, the above algorithm doesn't take into consideration the case where an element in the double array can be associated with two unique segments, one in the horizontal direction and one in the vertical direction. To handle these cases properly, I would need to implement a test for this specific case and then implement a method that will both associate the element under inspection with a segment and then concatenate the two adjacent identical segments. On the whole, this method and the intricate hashing system that it would require feels very inelegant. Additionally, I really only care about finding the large segments in the double array and I'm much more concerned with the speed of this algorithm than with the accuracy of the segmentation, so I'm looking for a better way. I assume there is some stochastic method for doing this that I haven't thought of. Any suggestions?

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  • When is performance gain significant enough to implement that optimization?

    - by Zwei steinen
    Hi, following the text book, I do measure performance whenever I try optimizing my code. Sometimes, however, the performance gain is rather small and I can't decisively decide whether I should implement that optimization. For example, when a fix shortens an average response time of 100ms to 90ms under some conditions, should I implement that fix? What if it shortens 200ms to 190ms? How many condition should I try before I can conclude that it will be beneficial overall? I guess it's not possible to give a straight forward answer to this, as it depends on too many things, but is there a good rule of thumb that I should follow? Are there any guideline/best-practices?

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  • Why is it useful to count the number of bits?

    - by Scorchin
    I've seen the numerous questions about counting the number of set bits in a insert type of input, but why is it useful? For those looking for algorithms about bit counting, look here: http://stackoverflow.com/questions/1517848/counting-common-bits-in-a-sequence-of-unsigned-longs http://stackoverflow.com/questions/472325/fastest-way-to-count-number-of-bit-transitions-in-an-unsigned-int http://stackoverflow.com/questions/109023/best-algorithm-to-count-the-number-of-set-bits-in-a-32-bit-integer

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  • UK Postcode search

    - by Imran
    I want to build a website where you can search by entering the postcode (UK). I know that RoyalMail owns the Database to do this (it's only very expensive, $100K). What are my options?

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  • Unable to validate e-mail format

    - by Aishwarya Shiva Pareek
    I am using this code which was suggested by my friend to validate an email id format in C#. public bool IsValidEmail(string strIn) { string strPattern = "^([0-9a-zA-Z]([-.\\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\\w]*[0-9a-zA-Z]\\.)+[a-zA-Z]{2,9})$"; if (System.Text.RegularExpressions.Regex.IsMatch(strIn, strPattern)) { return true; } return false; } When I pass the value of the strIn as [email protected] This function returns false. Please tell me whats wrong with it?

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  • Best practice - When to evaluate conditionals of function execution

    - by Tesserex
    If I have a function called from a few places, and it requires some condition to be met for anything it does to execute, where should that condition be checked? In my case, it's for drawing - if the mouse button is held down, then execute the drawing logic (this is being done in the mouse movement handler for when you drag.) Option one says put it in the function so that it's guaranteed to be checked. Abstracted, if you will. public function Foo() { DoThing(); } private function DoThing() { if (!condition) return; // do stuff } The problem I have with this is that when reading the code of Foo, which may be far away from DoThing, it looks like a bug. The first thought is that the condition isn't being checked. Option two, then, is to check before calling. public function Foo() { if (condition) DoThing(); } This reads better, but now you have to worry about checking from everywhere you call it. Option three is to rename the function to be more descriptive. public function Foo() { DoThingOnlyIfCondition(); } private function DoThingOnlyIfCondition() { if (!condition) return; // do stuff } Is this the "correct" solution? Or is this going a bit too far? I feel like if everything were like this function names would start to duplicate their code. About this being subjective: of course it is, and there may not be a right answer, but I think it's still perfectly at home here. Getting advice from better programmers than I is the second best way to learn. Subjective questions are exactly the kind of thing Google can't answer.

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  • Is there a website to look up common, already written functions?

    - by pinnacler
    I'm sitting here writing a function that I'm positive has been written before, somewhere on earth. It's just too common to have not been attempted, and I'm wondering why I can't just go to a website and search for a function that I can then copy and paste into my project in 2 seconds, instead of wasting my day reinventing the wheel. Sure there are certain libraries you can use, but where do you find these libraries and when they are absent, is there a site like I'm describing? Possibly a wiki of some type that contains free code that anybody can edit and improve? Edit: I can code things fine, I just don't know HOW to do them. So for example, right now, I'm trying to localize a robot/car/point in space. I KNOW there is a way to do it, just based off of range and distance. Triangulation and Trilateration. How to code that is a different story. A site that could have psuedo code, step by step how to do that would be ridiculously helpful. It would also ensure the optimal solution since everybody can edit it. I'm also writing in Matlab, which I hate because it's quirky, adding to my desire for creating a website like I describe.

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  • Is Java assert broken?

    - by BlairHippo
    While poking around the questions, I recently discovered the assert keyword in Java. At first, I was excited. Something useful I didn't already know! A more efficient way for me to check the validity of input parameters! Yay learning! But then I took a closer look, and my enthusiasm was not so much "tempered" as "snuffed-out completely" by one simple fact: you can turn assertions off.* This sounds like a nightmare. If I'm asserting that I don't want the code to keep going if the input listOfStuff is null, why on earth would I want that assertion ignored? It sounds like if I'm debugging a piece of production code and suspect that listOfStuff may have been erroneously passed a null but don't see any logfile evidence of that assertion being triggered, I can't trust that listOfStuff actually got sent a valid value; I also have to account for the possibility that assertions may have been turned off entirely. And this assumes that I'm the one debugging the code. Somebody unfamiliar with assertions might see that and assume (quite reasonably) that if the assertion message doesn't appear in the log, listOfStuff couldn't be the problem. If your first encounter with assert was in the wild, would it even occur to you that it could be turned-off entirely? It's not like there's a command-line option that lets you disable try/catch blocks, after all. All of which brings me to my question (and this is a question, not an excuse for a rant! I promise!): What am I missing? Is there some nuance that renders Java's implementation of assert far more useful than I'm giving it credit for? Is the ability to enable/disable it from the command line actually incredibly valuable in some contexts? Am I misconceptualizing it somehow when I envision using it in production code in lieu of statements like if (listOfStuff == null) barf();? I just feel like there's something important here that I'm not getting. *Okay, technically speaking, they're actually off by default; you have to go out of your way to turn them on. But still, you can knock them out entirely.

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  • Find location using only distance and bearing?

    - by pinnacler
    Triangulation works by checking your angle to three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and it's to my right at 90 degrees." Repeat 2 more times for different targets and angles. Trilateration works by checking your distance from three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and I'm 100 meters away from that." Repeat 2 more times for different targets and ranges. But both of those methods rely on knowing WHAT you're looking at. Say you're in a forest and you can't differentiate between trees, but you know where key trees are. These trees have been hand picked as "landmarks." You have a robot moving through that forest slowly. Do you know of any ways to determine location based solely off of angle and range, exploiting geometry between landmarks? Note, you will see other trees as well, so you won't know which trees are key trees. Ignore the fact that a target may be occluded. Our pre-algorithm takes care of that. 1) If this exists, what's it called? I can't find anything. 2) What do you think the odds are of having two identical location 'hits?' I imagine it's fairly rare. 3) If there are two identical location 'hits,' how can I determine my exact location after I move the robot next. (I assume the chances of having 2 occurrences of EXACT angles in a row, after I reposition the robot, would be statistically impossible, barring a forest growing in rows like corn). Would I just calculate the position again and hope for the best? Or would I somehow incorporate my previous position estimate into my next guess? If this exists, I'd like to read about it, and if not, develop it as a side project. I just don't have time to reinvent the wheel right now, nor have the time to implement this from scratch. So if it doesn't exist, I'll have to figure out another way to localize the robot since that's not the aim of this research, if it does, lets hope it's semi-easy.

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  • What is the best euphemism for a non-developer?

    - by Edward Tanguay
    I'm writing a description for a piece of software that targets the user who is "not technically minded", i.e. a person who uses "browser/office/email" and has a low tolerance for anything technical, he just "wants it to work" without being involved in any of the technical details. What is the best non-disparaging term you have seen to describe this kind of user? non-technical user low-tech user office user normal user technically challenged user non-developer computer joe Surely there is some official, politically-correct retronym for this kind of user that the press and software marketing use.

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  • Algorithm possible amounts (over)paid for a specific price, based on denominations

    - by Wrikken
    In a current project, people can order goods delivered to their door and choose 'pay on delivery' as a payment option. To make sure the delivery guy has enough change customers are asked to input the amount they will pay (e.g. delivery is 48,13, they will pay with 60,- (3*20,-)). Now, if it were up to me I'd make it a free field, but apparantly higher-ups have decided is should be a selection based on available denominations, without giving amounts that would result in a set of denominations which could be smaller. Example: denominations = [1,2,5,10,20,50] price = 78.12 possibilities: 79 (multitude of options), 80 (e.g. 4*20) 90 (e.g. 50+2*20) 100 (2*50) It's international, so the denominations could change, and the algorithm should be based on that list. The closest I have come which seems to work is this: for all denominations in reversed order (large=>small) add ceil(price/denomination) * denomination to possibles baseprice = floor(price/denomination) * denomination; for all smaller denominations as subdenomination in reversed order add baseprice + (ceil((price - baseprice) / subdenomination) * subdenomination) to possibles end for end for remove doubles sort Is seems to work, but this has emerged after wildly trying all kinds of compact algorithms, and I cannot defend why it works, which could lead to some edge-case / new countries getting wrong options, and it does generate some serious amounts of doubles. As this is probably not a new problem, and Google et al. could not provide me with an answer save for loads of pages calculating how to make exact change, I thought I'd ask SO: have you solved this problem before? Which algorithm? Any proof it will always work?

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  • How/when to hire new programmers, and how to integrate them?

    - by Shaul
    Hiring new programmers, especially in a small company, can often present a Catch-22 situation. We have too much work to do, so we need to hire new programmers. But we can't hire new programmers now, because they will need mentoring and several months of learning curve in your industry/product/environment before they're useful, and none of the programmers has time to be a mentor to a new programmer, because they're all completely swamped with the current work load. That may be a slightly frivolous way of describing the situation, but nevertheless, it's difficult for a small company on a tight budget to justify hiring someone who is not only going to be unproductive for a long time, but will also take away from the performance of the current programmers. How have you dealt with this kind of situation? When is the best time to hire someone? What are the best tasks to assign to a new team member so that they can learn their way around your code base and start getting their hands dirty as quickly as possible? How do you get the new guy useful without bogging your existing programmers down in too much mentoring? Any comments & suggestions you have are much appreciated!

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  • Where does "foo" come from in coding examples? [closed]

    - by ThePower
    Possible Duplicates: Using “Foo” and “Bar” in examples To foo bar, or not to foo bar: that is the question. Possible Duplicates: Using "Foo" and "Bar" in examples To foo bar, or not to foo bar: that is the question. Bit of a general question here, but it's something I would like to know! Whenever I am looking for resolutions to my C# problems online, I always come across "foo" being used as an example. Does this represent anything or is it just one of those unexplained catchy object names, used by many people in examples?

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  • Zoom image to pixel level

    - by zaf
    For an art project, one of the things I'll be doing is zooming in on an image to a particular pixel. I've been rubbing my chin and would love some advice on how to proceed. Here are the input parameters: Screen: sw - screen width sh - screen height Image: iw - image width ih - image height Pixel: px - x position of pixel in image py - y position of pixel in image Zoom: zf - zoom factor (0.0 to 1.0) Background colour: bc - background colour to use when screen and image aspect ratios are different Outputs: The zoomed image (no anti-aliasing) The screen position/dimensions of the pixel we are zooming to. When zf is 0 the image must fit the screen with correct aspect ratio. When zf is 1 the selected pixel fits the screen with correct aspect ratio. One idea I had was to use something like povray and move the camera towards a big image texture or some library (e.g. pygame) to do the zooming. Anyone think of something more clever with simple pseudo code? To keep it more simple you can make the image and screen have the same aspect ratio. I can live with that. I'll update with more info as its required.

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  • Does code in the constructor add to code in subclass constructors?

    - by Jeremy Rudd
    Does code in the constructor add to code in subclass constructors? Or does the subclass's constructor override the superclass? Given this example superclass constructor: class Car{ function Car(){ trace("CAR") } } ...and this subclass constructor: class FordCar extends Car{ function FordCar(){ trace("FORD") } } When an instance of FordCar is created, will this trace "Car" and "Ford" ??

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  • Extract all text from a HTML page without losing context

    - by grmbl
    For a translation program I am trying to get a 95% accurate text from a HTML file in order to translate the sentences and links. For example: <div><a href="stack">Overflow</a> <span>Texts <b>go</b> here</span></div> Should give me 2 results to translate: Overflow Texts <b>go</b> here Any suggestions or commercial packages available for this problem?

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  • Random access gzip stream

    - by jkff
    I'd like to be able to do random access into a gzipped file. I can afford to do some preprocessing on it (say, build some kind of index), provided that the result of the preprocessing is much smaller than the file itself. Any advice? My thoughts were: Hack on an existing gzip implementation and serialize its decompressor state every, say, 1 megabyte of compressed data. Then to do random access, deserialize the decompressor state and read from the megabyte boundary. This seems hard, especially since I'm working with Java and I couldn't find a pure-java gzip implementation :( Re-compress the file in chunks of 1Mb and do same as above. This has the disadvantage of doubling the required disk space. Write a simple parser of the gzip format that doesn't do any decompressing and only detects and indexes block boundaries (if there even are any blocks: I haven't yet read the gzip format description)

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  • How do you get your self focused with so many distractions around? (which you can't or don't want to

    - by Teja Kantamneni
    This question is definitely for a programmer and is centric towards a programmer. But if somebody feels it should not belong here I would not mind deleting it. I don't think this need to go as a WIKI, but if feel like it is a WIKI, I can do that too. The Question is: As a programmer you have to keep yourself up to date with the latest technologies and for that every programmer will generally follow some technology blogs and some social networking sites like (twitter, FB, SO, DZONE etc), how to keep your self focused on the things and still want to follow the technology trends? No Subjective or argumentative answers, Just want to know what practices other fellow programmers do for this...

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  • Have you been in cases where TDD increased development time?

    - by BillyONeal
    Hello everyone :) I was reading http://stackoverflow.com/questions/2512504/tdd-how-to-start-really-thinking-tdd and I noticed many of the answers indicate that tests + application should take less time than just writing the application. In my experience, this is not true. My problem though is that some 90% of the code I write has a TON of operating system calls. The time spent to actually mock these up takes much longer than just writing the code in the first place. Sometimes 4 or 5 times as long to write the test as to write the actual code. I'm curious if there are other developers in this kind of a scenario.

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