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  • Transpose a file in bash

    - by Thrawn
    Hi all, I have a huge tab-separated file formatted like this X column1 column2 column3 row1 0 1 2 row2 3 4 5 row3 6 7 8 row4 9 10 11 I would like to transpose it in an efficient way using only using commands (I could write a ten or so lines Perl script to do that, but it should be slower to execute than the native bash functions). So the output should look like X row1 row2 row3 row4 column1 0 3 6 9 column2 1 4 7 10 column3 2 5 8 11 I thought of a solution like this cols=`head -n 1 input | wc -w` for (( i=1; i <= $cols; i++)) do cut -f $i input | tr $'\n' $'\t' | sed -e "s/\t$/\n/g" >> output done But it's slow and doesn't seem the most efficient solution. I've seen a solution for vi in this post, but it's still over-slow. Any thoughts/suggestions/brilliant ideas? :-)

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  • Efficiency Question for an Ajax App

    - by Kubi
    Hi, Currently I am dealing with a web application which uses a txt file as a database for testing for now. But we will connect it to a server later on. My question is, if there is a more efficient way to get my objects than the way I am using now. During the page_init I am getting all my objects into a Collection as List, then I am populating the ajax toolkit accordion objects in the page with that. I have some client side buttons which fires callbacks for getting some other objects to populate the accordions in an update panel. And I am using .net Collections too much like dictionary and list, I am wondering if using arrays is more efficient. Could you advise me about how to make this site better and faster ? Is it better or possible to initialize those TravelP objects in javascript at the beginning and use it like that ? Any comments would be greatly appreciated, Thanks

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  • Diff Algorithm

    - by Daniel Magliola
    I've been looking like crazy for an explanation of a diff algorithm that works and is efficient. The closest I got is this link to RFC 3284 (from several Eric Sink blog posts), which describes in perfectly understandable terms the data format in which the diff results are stored. However, it has no mention whatsoever as to how a program would reach these results while doing a diff. I'm trying to research this out of personal curiosity, because I'm sure there must be tradeoffs when implementing a diff algorithm, which are pretty clear sometimes when you look at diffs and wonder "why did the diff program chose this as a change instead of that?"... Does anyone know where I can find a description of an efficient algorithm that'd end up outputting VCDIFF? By the way, if you happen to find a description of the actual algorithm used by SourceGear's DiffMerge, that'd be even better. NOTE: longest common subsequence doesn't seem to be the algorithm used by VCDIFF, it looks like they're doing something smarter, given the data format they use. Thanks!

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  • string matching algorithms used by lucene

    - by iamrohitbanga
    i want to know the string matching algorithms used by Apache Lucene. i have been going through the index file format used by lucene given here. it seems that lucene stores all words occurring in the text as is with their frequency of occurrence in each document. but as far as i know that for efficient string matching it would need to preprocess the words occurring in the Documents. example: search for "iamrohitbanga is a user of stackoverflow" (use fuzzy matching) in some documents. it is possible that there is a document containing the string "rohit banga" to find that the substrings rohit and banga are present in the search string, it would use some efficient substring matching. i want to know which algorithm it is. also if it does some preprocessing which function call in the java api triggers it.

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  • What "already invented" algorithm did you invent?

    - by Guy
    In my question Insert Update stored proc on SQL Server I explained an efficient way of doing an insert/update - perhaps THE most efficient. It's nothing amazing but it's a small algorithm that I came up with in a mini-Eureka moment. Although I had "invented" it by myself and secretly hoped that I was the first to do so I knew that it had probably been around for years but after posting on a couple of lists and not getting confirmation I had never found anything definitive written up about it. So my questions: What software algorithm did you come up with that you thought that you'd invented? Or better yet, did you invent one?

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  • Sudoku solver evaluation function

    - by Rich
    Hi, So I'm trying to write a simple genetic algorithm for solving a sudoku (not the most efficient way, I know, but it's just to practice evolutionary algorithms). I'm having some problems coming up with an efficient evaluation function to test if the puzzle is solved or not and how many errors there are. My first instinct would be to check if each row and column of the matrix (doing it in octave, which is similar to matlab) have unique elements by ordering them, checking for duplicates and then putting them back the way they were, which seems long winded. Any thoughts? Sorry if this has been asked before...

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  • What is considered a long execution time?

    - by stjowa
    I am trying to figure out just how "efficient" my server-side code is. Using start and end microtime(true) values, I am able to calculate the time it took my script to run. I am getting times from .3 - .5 seconds. These scripts do a number of database queries to return different values to the user. What is considered an efficient execution time for PHP scripts that will be run online for a website? Note: I know it depends on exactly what is being done, but just consider this a standard script that reads from a database and returns values to the user. Also, I look at Google and see them search the internet in .15 seconds and I feel like my script is crap. Thanks.

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  • data structure problems

    - by Ashish
    hey guys, please help me in finding the solution to some of these Amazon questions: given a file containing approx 10 million words, design a data structure for finding the anagrams Write a program to display the ten most frequent words in a file such that your program be efficient in all complexity measures. you have a file with millions of lines of data. Only two lines are identical; the rest are all unique. Each line is so long that it may not even fit in the memory. What is the most efficient solution for finding the identical lines?

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  • How write an ads server

    - by Nisanio
    Hi everyone I want to write an ads server (like OpenX), just for fun and learning (they aren't the same). But my idea, more than writing an entire application with web interface and so on, is to write a very tiny core that provides the basic functionality in the most efficient way, like a library that other people can use to write a complete application more fitted to their needs. The objective is to make it small, very efficient and fast. Can someone help me with a list of the minimal functionality needed for this kind of application?. An Ads Server isn't only a banner delivery, there are differents methods (for example OpenX uses a very weird javascript code that i don't understand completely) Any help or guidance is more than welcome...Thanks

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  • Super wide, but not so tall, bitmap?

    - by Erik Karlsson
    Howdy folks. Is there any way to create a more space/resource efficient bitmap? Currently i try to render a file, approx 800 px high but around 720000px wide. It crashes my application, presumebly because of the share memory-size of the bitmap. Can i do it more efficient, like creating it as an gif directly and not later when i save it? I try to save a series of lines/rectangles from a real world reading, and i want it to be 1px per 1/100th of a second. Any input? And btw, i never manage to ogon using google open id : /

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  • Efficiency of data structures in C99 (possibly affected by endianness)

    - by Ninefingers
    Hi All, I have a couple of questions that are all inter-related. Basically, in the algorithm I am implementing a word w is defined as four bytes, so it can be contained whole in a uint32_t. However, during the operation of the algorithm I often need to access the various parts of the word. Now, I can do this in two ways: uint32_t w = 0x11223344; uint8_t a = (w & 0xff000000) >> 24; uint8_t b = (w & 0x00ff0000) >> 16; uint8_t b = (w & 0x0000ff00) >> 8; uint8_t d = (w & 0x000000ff); However, part of me thinks that isn't particularly efficient. I thought a better way would be to use union representation like so: typedef union { struct { uint8_t d; uint8_t c; uint8_t b; uint8_t a; }; uint32_t n; } word32; Using this method I can assign word32 w = 0x11223344; then I can access the various parts as I require (w.a=11 in little endian). However, at this stage I come up against endianness issues, namely, in big endian systems my struct is defined incorrectly so I need to re-order the word prior to it being passed in. This I can do without too much difficulty. My question is, then, is the first part (various bitwise ands and shifts) efficient compared to the implementation using a union? Is there any difference between the two generally? Which way should I go on a modern, x86_64 processor? Is endianness just a red herring here? I could inspect the assembly output of course, but my knowledge of compilers is not brilliant. I would have thought a union would be more efficient as it would essentially convert to memory offsets, like so: mov eax, [r9+8] Would a compiler realise that is what happening in the bit-shift case above? If it matters, I'm using C99, specifically my compiler is clang (llvm). Thanks in advance.

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  • Django equivalent for latest entry for each user

    - by paul-ogrady
    Hi, I'm surprised this question hasn't come up. Couldn't find much on the web. Using Entry.objects.latest('created_at') I can recover the latest entry for all Entry objects, but say if I want the latest entry for each user? This is something similar to an SQL latest record query. But how do I achieve this using the ORM? Here is my approach I'm wondering if it is the most efficient way to do what I want. First I perform a sub query: Objects are grouped by user and the Max (latest) created_by field is returned for each user (created_at__max) I then filter Entry objects based on the results in the subquery and get the required objects. Entry.objects.filter(created_at__in=Entry.objects.values('user').annotate(Max('created_at')).values_list('created_at__max')) or using a manager: class UsersLatest(models.Manager): def get_query_set(self): return Super(UsersLatest,self).get_query_set().filter(created_at__in=self.model.objects.values('user').annotate(Max('created_at')).values_list('created_at__max')) Is there a more efficient way? possibly without sub query? Thanks, Paul

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  • MySQL vs PHP when retrieving a random item

    - by andufo
    Hi, which is more efficient (when managing over 100K records): A. Mysql SELECT * FROM user ORDER BY RAND(); of course, after that i would already have all the fields from that record. B. PHP use memcached to have $cache_array hold all the data from "SELECT id_user FROM user ORDER BY id_user" for 1 hour or so... and then: $id = array_rand($cache_array); of course, after that i have to make a MYSQL call with: SELECT * FROM user WHERE id_user = $id; so... which is more efficient? A or B?

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  • Efficiently detect corrupted jpeg file?

    - by Jacco
    Is there an efficient way of detecting if a jpeg file is corrupted? Background info:   solutions needs to work from within a php script   the jpeg files are on disk   manual checking is no option (user uploaded data) I know that imagecreatefromjpeg(string $filename); can do it. But it is quite slow at doing so. Does anybody know a faster/more efficient solutions?

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  • Pros and cons of ways of storing an unsigned int without an unsigned int data type

    - by fields
    I have values that are 64-bit unsigned ints, and I need to store them in mongodb, which has no unsigned int type. I see three main possibilities for storing them in other field types, and converting on going in and out: Using a signed int is probably easiest and most space efficient, but has the disadvantage that they're not human readable and if someone forgets to do the conversion, some of them will work, which may obscure errors. Raw binary is probably most difficult for inexperienced programmers to deal with, and also suffers from non-human-readability. A string representation is the least space efficient (~40 bytes in unicode vs 8 bytes per field), but then at least all of the possible values will map properly, and for querying only a conversion to string is required instead of a more complicated conversion. I need these values to be available from different platforms, so a single driver-specific solution isn't an option. Any major pros and cons I've missed? Which one would you use?

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  • Join one row to multiple rows in another table

    - by Ghostrider
    I have a table to entities (lets call them people) and properties (one person can have an arbitrary number of properties). Ex: People Name Age -------- Jane 27 Joe 36 Jim 16 Properties Name Property ----------------- Jane Smart Jane Funny Jane Good-looking Joe Smart Joe Workaholic Jim Funny Jim Young I would like to write an efficient select that would select people based on age and return all or some of their properties. Ex: People older than 26 Name Properties Jane Smart, Funny, Good-looking Joe Smart, Workaholic It's also acceptable to return one of the properties and total property count. The query should be efficient: there are millions of rows in people table, hundreds of thousands of rows in properties table (so most people have no properties). There are hundreds of rows selected at a time. Is there any way to do it?

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  • Implementing Role based Helpers

    - by Cynics
    So my question is how would you implement your handwritten Helpers based on the role of current user. Would it be efficient to change the behaviour at request time? e.g. the Helper somehow figures out the role of user, and include the proper SubModule? module ApplicationHelper module LoggedInHelper # Some functions end module GuestHelper # The Same functions end # If User is Guest then include GuestHelper # If User is LoggedIn then include LoggedInHelper end Is it efficient this way? is it rails way? I've got a whole bunch of function that act like this, and I don't want to wrap every single one of them in an if statement def menu_actions if current_user.nil? # User is guest { "Log in" => link_to "Login", "/login" } else # User is Logged In { "Log out" => link_to "Logout", "/logout" } end end Thank you for your time and thoughts.

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  • Utilising cssText to set styles with JavaScript

    - by Rajat
    I was going through Nicholas Zakas presentation on JavaScript here : http://www.slideshare.net/nzakas/writing-efficient-javascript (slide number: 89/139) He recommends using cssText property whenever you are setting a bunch of styles through JavaScript. The best solution is obviously adding those styles to a class and then using JS to add the classname to an element.However, in many situations, We resort to just setting the properties directly within JS when the number of properties are low. It seems from his presentation that using cssText property would be more efficient in such scenarios.I tried to look up more on the property but couldn't find much information. Has anyone used the 'cssText' property ? It would be great to have some more technical info on how the property helps.

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  • Can 3D OpenGL game written in Python look good and run fast?

    - by praavDa
    I am planning to write an simple 3d(isometric view) game in Java using jMonkeyEngine - nothing to fancy, I just want to learn something about OpenGL and writing efficient algorithms (random map generating ones). When I was planning what to do, I started wondering about switching to Python. I know that Python didn't come into existence to be a tool to write 3d games, but is it possible to write good looking games with this language? I have in mind 3d graphics, nice effects and free CPU time to power to rest of game engine? I had seen good looking java games - and too be honest, I was rather shocked when I saw level of detail achieved in Runescape HD. On the other hand, pygame.org has only 2d games, with some starting 3d projects. Are there any efficient 3d game engines for python? Is pyopengl the only alternative? Good looking games in python aren't popular or possible to achieve? I would be grateful for any information / feedback.

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  • Nesting maximum amount of shapes on a surface

    - by Fuu
    In industry, there is often a problem where you need to calculate the most efficient use of material, be it fabric, wood, metal etc. So the starting point is X amount of shapes of given dimensions, made out of polygons and/or curved lines, and target is another polygon of given dimensions. I assume many of the current CAM suites implement this, but having no experience using them or of their internals, what kind of computational algorithm is used to find the most efficient use of space? Can someone point me to a book or other reference that discusses this topic?

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