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  • top-k selection/merge

    - by tcurdt
    I have n sorted lists. These lists are quite long (300000+ tuples). Selecting the top 10 of the individual lists is of course trivial - they are right at the head of the lists. Where it gets more interesting is when I want the top 10 of all the sorted lists. The question is whether there is an algorithm to calculate the combined top 10 having the correct order while cutting off the long tail of the lists. The goal is to reduce the required space. And if there is: How does one find the limit where is is safe to cut? Note: The actual counts are not important. Only the order is.

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  • What classes are useful for an aspiring software developer? [closed]

    - by Anonymouse
    I'm a freshman in college trying to graduate in 3 years with a Math/CS dual major, and I don't have a lot of time to be fooling around with useless classes. I've tested out of most of my gen eds and science-y courses, but I need to know: what math and cs courses are most important for someone interested in algorithm development? Math courses already taken: Calc I-III,Linear Algebra, Discrete Math. CS courses taken: Java. Math courses I'm planning to take: ODE, Linear Algebra II, Vector calc, Logic, (Analysis or Algebra), Stats, probability CS courses I'm planning to take: C(required), Data Structures, Numerical Methods, Intro to Analysis of Algorithms. Which is better, analysis or algebra? Did I take enough CS courses? Am I missing out on anything? Thanks.

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  • How to retrieve the ordered list of best articles having a minimum number of votes by using HSQL ?

    - by fabien7474
    I have a Vote domain class from my grails application containing properties like article_id and note I want to HQL query the Vote domain class in order to retrieve the 5 best rated articles having at least 10 votes. I tried : SELECT v.article_id, avg(v.note), count(*) FROM vote v where count(*) >= 10 group by v.article_id order by avg(v.note) desc limit 5; But unfortunately the insertion of where count(*) >= 10 throws an error. How can I do that in a simple way? Thank you for your help.

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  • Grab triangles within a lower triangle

    - by Tyler Rinker
    I have the need to grab all the thee element triangles that make up the lower triangle of a symmetric matrix. I can not think of how to grab all these pieces in the order of far left column working down and then next column to the right and so on. I know that the numbe rof mini triangles inside of the lower triangle is: n = x(x - 1)/2 where: x = nrow(mats[[i]]) Here I've created three matrices with letters (it's easier for me to conceptualize this way) and the elements in the order I'm looking for: FUN <- function(n) { matrix(LETTERS[1:(n*n)], n) } mats <- lapply(3:5, FUN) So this is the output I'd like to get (I put it in code rather than output format) for each of the matrices created above: list(c("B", "C", "F")) list(c("B", "C", "G"), c("C", "D", "H"), c("G", "H", "L")) list(c("B", "C", "H"), c("C", "D", "I"), c("D", "E", "J"), c("H", "I", "N"), c("I", "J", "O"), c("N", "O", "T")) How can I do this task in the fastest manner possible while staying in base R? Not sure if this visual of what I'm after is helpful but it may be:

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  • habtm multiple times with the same model

    - by Ermin
    I am trying to model a publications. A publication can have multiple authors and editors. Since it is possible that one person is an author of one publication and an editor of another, no separate models for Authors and Editors: class Publication < ActiveRecord::Base has_and_belongs_to_many :authors, :class_name=>'Person' has_and_belongs_to_many :editors, :class_name=>'Person' end The above code doesn't work, because it uses the same join table. Now I now that I can specify the name of the join table, but there is a warning in the API documentation is a warning about that which I don't understand: :join_table: Specify the name of the join table if the default based on lexical order isn’t what you want. WARNING: If you’re overwriting the table name of either class, the table_name method MUST be declared underneath any has_and_belongs_to_many declaration in order to work.

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  • Finding rank of the student -Sql Compact

    - by Jankhana
    I have a table like this : Name Mar1 Mar2 Mar3 Total xxx 80 80 80 240 yyy 60 70 50 180 aaa 85 65 75 225 I wanted to find the rank of the student based on total. I using SQL Compact 3.5 . As we have rank() function in sql server do we have something with which we can find the students rank??? When I used "select Total,rank() over (order by total desc) i1 from stmarks " it's giving error as " Major Error 0x80040E14, Minor Error 25501 select Total,rank() over (order by total desc) i1 from stmarks There was an error parsing the query. [ Token line number = 1,Token line offset = 21,Token in error = over ] " Do Sql Compact support rank() over or is there any another way???

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  • Potential problems porting to different architectures

    - by Brendan Long
    I'm writing a Linux program that currently compiles and works fine on x86 and x86_64, and now I'm wondering if there's anything special I'll need to do to make it work on other architectures. What I've heard is that for cross platform code I should: Don't assume anything about the size of a pointer, int or size_t Don't make assumptions about byte order (I don't do any bit shifting -- I assume gcc will optimize my power of two multiplication/division for me) Don't use assembly blocks (obvious) Make sure your libraries work (I'm using SQLite, libcurl and Boost, which all seem pretty cross-platform) Is there anything else I need to worry about? I'm not currently targeting any other architectures, but I expect to support ARM at some point, and I figure I might as well make it work on any architecture if I can. Also, regarding my second point about byte order, do I need to do anything special with text input? I read files with getline(), so it seems like that should be done automatically as well.

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  • Duplicates in a sorted java array

    - by Max Frazier
    I have to write a method that takes an array of ints that is already sorted in numerical order then remove all the duplicate numbers and return an array of just the numbers that have no duplicates. That array must then be printed out so I can't have any null pointer exceptions. The method has to be in O(n) time, can't use vectors or hashes. This is what I have so far but it only has the first couple numbers in order without duplicates and then just puts the duplicates in the back of the array. I can't create a temporary array because it gives me null pointer exceptions. public static int[] noDups(int[] myArray) { int j = 0; for (int i = 1; i < myArray.length; i++) { if (myArray[i] != myArray[j]) { j++; myArray[j] = myArray[i]; } } return myArray; }

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  • Diving into the RichTextBox (Silverlight TV #31)

    Mark Rideout, Program Manager on the Silverlight product team, joins John to dive deep into many of the RichTextBox control's features. Mark has worked on the text aspects of Silverlight since the first version. Here are just a few of the areas that Mark covers: Overview of RichTextBox vs. TextBlock and TextBox for rich content Wire-up logic for applying formatting Inline UI elements Using text position to point for simple and complex operations   Basic "position...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Problem with updating multiple rows which are in conflict with unique index

    - by GUZ
    I am using Microsoft SQL Server and I have a master-detail scenario where I need to store the order of details. So in the Detail table I have ID, MasterID, Position and some other columns. There is also a unique index on MasterID and Position. It works OK except one case: when I have some existing details and I change their order. For example when I change a detail on position 3 with a detail on position 2. When I save the detail on position 2 (which in the database has Position equal to 3) SQL Server protests, because the index uniqueness constraint. How to solve this problem in a reasonable way? Thank you in advance Lukasz Glaz

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  • Sharing some info with all DLLs pulled into a process

    - by JBRWilkinson
    Hi all, We've got an Enterprise system which has many processes (EXEs, services, DCOM servers, COM+ apps, ISAPI, MMC snapins) all of which make use of many COM components. We've recently seen failures in some of the customer deployments, but are finding it hard to troubleshoot the cause. In order to track down the problem, we've augmented the entire source with logging statements where errors occur. In order to identify which logs came from what processes, the C++ logging code (compiled into all components) uses the EXE name to name the log. This is good for some cases, but not all - COM+ apps, ISAPI and MMC snapins all have system EXE names and the logs end up interleaved. I saw this post about shared data sections which might help, but what I don't understand is who decides what goes in the shared section. Is there any way I can guarantee that a particular piece of code writes into the shared section before anyone else reads it? Or is there a better solution to this problem?

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  • how to give meaningful id to the things in database

    - by gcc
    There are a lot of manuals. I am trying to create an database to hold information of these documents. But, there is a small problem. How can I give meaningful id to the manuals? Are there any standard or logic behind the giving meaningful id to the documents? If there is no standard, can you tell me how I should do that? example: table : manual id | manual name EDIT: Not Meaningful ID 1 or M1 or foo 2 C2 bar 3 P123 name ... ... ... (i) (ii) (iii) (i) Not meaningful for me because if some item deleted, there can be gap. ex 1 33 100. (ii) random character can be confusing when one try to give a name to new manual (iii) Why giving name is not preferred is because finding a name to the manual as ID is hard after 500 manuals. Meaningful : New ID * Can be easily produced even if after 1000 manuals * Should not be so complicated

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  • Sort/Enumerate an NSArray from somewhere in the middle?

    - by Kenny Winker
    I have an NSArray, with objects ordered like so: a b c d e f I would like to enumerate through this array in this order: c d e f a b i.e. starting at some point that is not the beginning, but hitting all the items. I imagine this is a matter of sorting first and then enumerating the array, but I'm not sure if that's the best technique... or, frankly, how to sort the array like this. Edit Adding details: These will be relatively small arrays, varying from 3 to 10 objects. No concurrent access. I'd like to permanently alter the sort order of the array each time I do this operation.

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  • And at what point of modification to the original does source code with no license become owned by me?

    - by nathansizemore
    I've recently come across a publicly viewable project on Github that has no license associated with it. In this repo, there is a file with the logic and most of the code needed to work as a piece of a project I am working on. Not verbatim, but about 60% of it I'd like to use with various modifications. Once my code base is a little bit more stable, I plan to release what I've done under the WTFPL License. I've emailed the repo owner, and so far have not gotten a reply. I know I have the rights to fork the repo, but if I release a stripped down and modified version of the other project's file with mine, under the WTFPL, am I infringing on copyrights? Per Github's Terms of Service, by submitted a project on Github and making it viewable to the public, you are allowing other users to see and fork your project. Doesn't say anything about modifying, distributing, or using the fork. And at what point of modification to the original does it become owned by me?

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  • php search and replace

    - by Dave
    I am trying to create a database field merge into a document (rtf) using php i.e if I have a document that starts Dear Sir, Customer Name: [customer_name], Date of order: [order_date] After retrieving the appropriate database record I can use a simple search and replace to insert the database field into the right place. So far so good. I would however like to have a little more control over the data before it is replaced. For example I may wish to Title Case it, or convert a delimited string into a list with carriage returns. I would therefore like to be able to add extra formatting commands to the field to be replaced. e.g. Dear Sir, Customer Name: [customer_name, TC], Date of order: [order_date, Y/M/D] There may be more than one formatting command per field. Is there a way that I can now search for these strings? The format of the strings is not set in stone, so if I have to change the format then I can. Any suggestions appreciated.

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  • MySQL - get all unique values of a column, check if has a specific value

    - by gamers2000
    First off - apologies for the poor title, I have no idea how to describe it in a one-liner. I have a table - snippet is below. mysql> select * from playlistfiles; +-----------------------+--------------+-----------+ | FileName | PlaylistName | FileIndex | +-----------------------+--------------+-----------+ | File1 | Image1 | 0 | | File1 | Video1 | 2 | | File2 | Video1 | 0 | | File3 | Video1 | 1 | | File4 | Image1 | 1 | | File4 | Video1 | 3 | +-----------------------+--------------+-----------+ 6 rows in set (0.00 sec) What I need to do is to get all the FileNames and whether the file is in a playlist or not, as well as order them by FileIndex i.e. for the Image1 playlist, the output should be +-----------------------+------------+-----------+ | FileName | InPlaylist | FileIndex | +-----------------------+------------+-----------+ | File1 | 1 | 0 | | File2 | 0 | Null | | File3 | 0 | Null | | File4 | 1 | 1 | +-----------------------+------------+-----------+ and Video1 would be +-----------------------+------------+-----------+ | FileName | InPlaylist | FileIndex | +-----------------------+------------+-----------+ | File2 | 1 | 0 | | File3 | 1 | 1 | | File1 | 1 | 2 | | File4 | 1 | 3 | +-----------------------+------------+-----------+ In short, I need to be able to get all the unique FileNames from the table, and check if it is in a given table and if so, order it by FileIndex.

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  • Postgresql count+sort performance

    - by invictus
    I have built a small inventory system using postgresql and psycopg2. Everything works great, except, when I want to create aggregated summaries/reports of the content, I get really bad performance due to count()'ing and sorting. The DB schema is as follows: CREATE TABLE hosts ( id SERIAL PRIMARY KEY, name VARCHAR(255) ); CREATE TABLE items ( id SERIAL PRIMARY KEY, description TEXT ); CREATE TABLE host_item ( id SERIAL PRIMARY KEY, host INTEGER REFERENCES hosts(id) ON DELETE CASCADE ON UPDATE CASCADE, item INTEGER REFERENCES items(id) ON DELETE CASCADE ON UPDATE CASCADE ); There are some other fields as well, but those are not relevant. I want to extract 2 different reports: - List of all hosts with the number of items per, ordered from highest to lowest count - List of all items with the number of hosts per, ordered from highest to lowest count I have used 2 queries for the purpose: Items with host count: SELECT i.id, i.description, COUNT(hi.id) AS count FROM items AS i LEFT JOIN host_item AS hi ON (i.id=hi.item) GROUP BY i.id ORDER BY count DESC LIMIT 10; Hosts with item count: SELECT h.id, h.name, COUNT(hi.id) AS count FROM hosts AS h LEFT JOIN host_item AS hi ON (h.id=hi.host) GROUP BY h.id ORDER BY count DESC LIMIT 10; Problem is: the queries runs for 5-6 seconds before returning any data. As this is a web based application, 6 seconds are just not acceptable. The database is heavily populated with approximately 50k hosts, 1000 items and 400 000 host/items relations, and will likely increase significantly when (or perhaps if) the application will be used. After playing around, I found that by removing the "ORDER BY count DESC" part, both queries would execute instantly without any delay whatsoever (less than 20ms to finish the queries). Is there any way I can optimize these queries so that I can get the result sorted without the delay? I was trying different indexes, but seeing as the count is computed it is possible to utilize an index for this. I have read that count()'ing in postgresql is slow, but its the sorting that are causing me problems... My current workaround is to run the queries above as an hourly job, putting the result into a new table with an index on the count column for quick lookup. I use Postgresql 9.2.

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  • What are the differences between enterprise software/architecture patterns and open source software?

    - by Jeffrey
    I am mainly a business app developer and I hear terms like CQRS, ServiceBus, SOA, DDD, BDD, AOP a lot. My question is that do these patterns/practices exist only in the "enterprise" world? In contract to the enterprise world is the open source community. Highly trafficked sites like Digg, LiveJournal whenever there is an article mentioning about how they built/scaled their sites all I am hearing is what open source software (Memcached, NoSQL) they used in order to scale/simplify the way they tackle software problems and they rarely mention those above terms. Is it because they are not as sophisticated as those of enterprise level software (I doubt it)? Or are people just making up those terms/practices/patterns in order to keep them jobs? Or am I confusing myself with differences between software development and internet website scaling?

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  • mod_rewrite not working for a specific directory

    - by punkish
    This has got me completely foxed for a couple of days now, and I am convinced that I will look stupid once I solve it, but will be even stupider if I don't ask for help now. I have mod_rewrite working successfully on my localhost (no vhosts involved; this is my laptop, my development machine), and I use .htaccess in various directories to help rewrite crufty URLs to clean ones. EXCEPT... it doesn't work in one directory. Since it is impossible to reproduce my entire laptop in this question, I provide the following details. In my httpd.conf, I have mod_rewrite.so loaded. LoadModule rewrite_module modules/mod_rewrite.so In my httpd.conf, I have included another conf file like so Include /usr/local/apache2/conf/other/punkish.conf In my punkish.conf, I have directories defined like so DocumentRoot "/Users/punkish/Sites" <Directory "/Users/punkish/Sites"> Options ExecCGI AllowOverride None Order allow,deny Allow from all </Directory> <Directory "/Users/punkish/Sites/one"> Options FollowSymLinks AllowOverride All Order allow,deny Allow from all </Directory> <Directory "/Users/punkish/Sites/two"> Options FollowSymLinks AllowOverride All Order allow,deny Allow from all </Directory> In ~/Sites/one I have the following .htaccess file RewriteEngine On RewriteBase /one/ # If an actual file or directory is requested, serve directly RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d # Otherwise, pass everything through to the dispatcher RewriteRule ^(.*)$ index.cgi/$1 [L,QSA] and, everything works just fine. However, in my directory ~/Sites/two I have the following .htaccess file RewriteEngine On RewriteBase /two/ # If an actual file or directory is requested, serve directly RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d # Otherwise, pass everything through to the dispatcher RewriteRule ^(.*)$ index.cgi/$1 [L,QSA] and, nothing works. Nada. Zip. Zilch. I just get a 404. I have determined that mod_rewrite is not even looking at my ~/Sites/two/.htaccess by putting spurious commands in it and not getting any error other than 404. Another confounding issue -- I have turned on RewriteLog in my httpd.conf with RewriteLogLevel 3, but my rewrite_log is completely empty. I know this is hard to trouble shoot unless sitting physically at the computer in question, but I hope someone can give me some indication as to what is going on. **Update: ** There are no aliases involved anywhere. This is my laptop, and everything is under the above stated Document Root, so I just access each directory as http://localhost/. Yes, typos are a big possibility (I did say that I will look stupid once I solve it, however, for now, I have not discovered a single typo anywhere, and yes, I have restarted Apache about a dozen times now. I even thought that perhaps I had two different Apaches running, but no, I have only one, the one under /usr/local/apache2, and I installed it myself a while back.

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  • Process for beginning a Ruby on Rails project

    - by Daniel Beardsley
    I'm about to begin a Ruby on Rails project and I'd love to hear how others go through the process of starting an application design. I have quite a bit of experience with RoR, but don't have that many starting from scratch with only a vision experiences and would appreciate the wisdom of others who've been there. I'm looking for an order of events, reasons for the order, and maybe why each part is important. I can think of a few starting points, but I'm not sure where it's best to begin Model design and relationships (entities, how they relate, and their attributes) Think of user use-cases (or story-boards) and implement the minimum to get these done Create Model unit-tests then create the necessary migrations and AR models to get the tests to pass Hack out the most basic version of the simplest part of your application and go from there Start with a template for a rails app (like http://github.com/thoughtbot/suspenders) Do the boring gruntwork first (User auth, session management, ...) ...

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  • how to add column in SQL Query that incl. LEFT OUTER JOIN

    - by radbyx
    I have this Query: SELECT p.ProductName, dt.MaxTimeStamp, p.Responsible FROM Product p LEFT JOIN (SELECT ProductID, MAX(TimeStamp) AS MaxTimeStamp FROM StateLog WHERE State = 0 GROUP BY ProductID, Status) dt ON p.ProductID = dt.ProductID ORDER BY p.ProductName; It works like it should, but now I need to SELECT "State" out too. The tricky part is, that I only want the lastest "TimeStamp" where "State" was false. But now I also need the "State" for the lastest "TimeStamp". I tried this: SELECT p.ProductName, dt.State, dt.MaxTimeStamp, p.Responsible FROM Product p LEFT JOIN (SELECT ProductID, MAX(TimeStamp) AS MaxTimeStamp, State FROM StateLog WHERE State = 0 GROUP BY ProductID, Status) dt ON p.ProductID =dt.ProductID ORDER BY p.ProductName; But it didn't work, because it gave me the "State" for the lastest "TimeStamp". So I hope there is some clever heads out there that can help me. I'm guessing that this is either very simple or very hard to solve.

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  • How to compute a unicode string which bidirectional representation is specified?

    - by valdo
    Hello, fellows. I have a rather pervert question. Please forgive me :) There's an official algorithm that describes how bidirectional unicode text should be presented. http://www.unicode.org/reports/tr9/tr9-15.html I receive a string (from some 3rd-party source), which contains latin/hebrew characters, as well as digits, white-spaces, punctuation symbols and etc. The problem is that the string that I receive is already in the representation form. I.e. - the sequence of characters that I receive should just be presented from left to right. Now, my goal is to find the unicode string which representation is exactly the same. Means - I need to pass that string to another entity; it would then render this string according to the official algorithm, and the result should be the same. Assuming the following: The default text direction (of the rendering entity) is RTL. I don't want to inject "special unicode characters" that explicitly override the text direction (such as RLO, RLE, etc.) I suspect there may exist several solutions. If so - I'd like to preserve the RTL-looking of the string as much as possible. The string usually consists of hebrew words mostly. I'd like to preserve the correct order of those words, and characters inside those words. Whereas other character sequences may (and should) be transposed. One naive way to solve this is just to swap the whole string (this takes care of the hebrew words), and then swap inside it sequences of non-hebrew characters. This however doesn't always produce correct results, because actual rules of representation are rather complex. The only comprehensive algorithm that I see so far is brute-force check. The string can be divided into sequences of same-class characters. Those sequences may be joined in random order, plus any of them may be reversed. I can check all those combinations to obtain the correct result. Plus this technique may be optimized. For instance the order of hebrew words is known, so we only have to check different combinations of their "joining" sequences. Any better ideas? If you have an idea, not necessarily the whole solution - it's ok. I'll appreciate any idea. Thanks in advance.

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  • Optimally reducing maximum flow

    - by ArIck
    Given a parameter k, I'm trying to delete k edges from a directed graph such that the maximum flow is reduced by as much as possible. The graph has a source s and a sink t, and the capacity of each edge is one. The graph may or may not contain cycles. My proposed solution would be to first perform a topological sorting on the graph, using an algorithm that "forgives" cycles -- perhaps by ignoring edges that lead us back to the source. Then (assuming k = 1): i = 0 for each vertex u order by topological(u) for each edge (u, v) order by topological(v) descending if topological(v) > topological(u) then delete (u, v) if ++i = k then return else // edge doesn't contribute to max flow, ignore Would this work, or am I totally off-track here?

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