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• Collection type generated by for with yield

  - by Jesper

  When I evaluate a for in Scala, I get an immutable IndexedSeq (a collection with array-like performance characteristics, such as efficient random access): scala> val s = for (i <- 0 to 9) yield math.random + i s: scala.collection.immutable.IndexedSeq[Double] = Vector(0.6127056766832756, 1.7137598183155291, ... Does a for with a yield always return an IndexedSeq, or can it also return some other type of collection class (a LinearSeq, for example)? If it can also return something else, then what determines the return type, and how can I influence it? I'm using Scala 2.8.0.RC3.

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• Is shortening properties names worth it?

  - by raam86

  in how to node Blog rolling with node.js and mongoDB the author mentions it's a good idea to shorten proprieties names: ....oft-reported issue with mongoDB is the size of the data on the disk... each and every record stores all the field-names .... This means that it can often be more space-efficient to have properties such as 't', or 'b' rather than 'title' or 'body', however for fear of confusion I would avoid this unless truly required! I am aware of solutions of how to do it I am more intrested in when is it truly required?

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• Javascript find if english alphabets only

  - by Alec Smart

  Hello, Am trying to find some text only if it contains english letters and numbers using Javascript/jQuery. Am wondering what is the most efficient way to do this? Since there could be thousands of words, it should be as fast as possible and I don't want to use regex. var names[0] = 'test'; var names[1] = '???'; var names[2] = '??????'; for (i=0;i<names.length;i++) { if (names[i] == ENGLISHMATCHCODEHERE) { // do something here } } Thank you for your time.

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• Using UIImageViews for 'pages' in an iPhone/iPad storybook app?

  - by outtoplayinc

  I'm new to iPhone programming, and well, what seems obvious to me may seem silly to a seasoned coder. I did a few 'switching views' tutorials on Youtube, and basically, they seems to work nicely for adding pages to a storybook type app. You add a UIViewController and associated view for each page. My question is would this become insanely slow, or a memory hog if I continued this method for say....35+ pages? Each page would also have a sound file associated with it that would play narration when a page load and stops when we leave. Basically, think of a powerpoint type app, with sound, possibly animated image elements, next & back buttons. I'm probably thinking of this very simplistically, but that's where my experience is at for the moment. Any insight or tips as to better and or more efficient ways to proceed would be greatly appreciated.

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• solutions for rapid front-end development?

  - by fayer

  im using mvc framework and i have learned some techniques that help me with different parts of RAD. models: doctrine/visual paradigm controllers/libraries: various design patterns now i only need to know what technique/solution i should use for the views so that i can create views more rapidly. cause i don't think it's efficient to code css/html manually, even though i understand it. its the same principle when using visual paradigm to create both my mysql database tables and doctrine model classes. i believe in using right tools will boost up development speed. so what could i use for the views to save time and energy and don't reinvent the wheel all the time? dreamweaver? any css generation tools? 960/blueprint for layout? suggestions? thanks

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• C#, Fastest (Best?) Method of Identifying Duplicate Files in an Array of Directories

  - by Nate Greenwood

  I want to recurse several directories and find duplicate files between the n number of directories. My knee-jerk idea at this is to have a global hashtable or some other data structure to hold each file I find; then check each subsequent file to determine if it's in the "master" list of files. Obviously, I don't think this would be very efficient and the "there's got to be a better way!" keeps ringing in my brain. Any advice on a better way to handle this situation would be appreciated.

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• JavaScript BubbleSort

  - by Alyn

  Hi, Have a bubblesort routine similar the this. I need to make it more efficient by stopping the loop when the array is sorted or if the array is already sorted. function sortNumbers(listbox) { var x, y, holder; // The Bubble Sort method. for(x = 0; x < ranarray.length; x++) { for(y = 0; y < (ranarray.length-1); y++) { if(ranarray[y] > ranarray[y+1]) { holder = ranarray[y+1]; ranarray[y+1] = ranarray[y]; ranarray[y] = holder; } } }

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• Some exam questions about C++ vectors and arrays...

  - by xbonez

  Hey guys, I have a CS exam tomorrow. Just want to get a few questions cleared up. Thanks a lot, and I really appreciate the help. Que 1. What are parallel vectors? Vectors of the same length that contain data that is meant to be processed together Vectors that are all of the same data type Vectors that are of the same length Any vector of data type parallel Que 2. Arrays are faster and more efficient than vectors. True False Que 3. Arrays can be a return type of a function call. True False Que 4. Vectors can be a return type of a function call. True False

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• what good orm api will work well with scala or erlang

  - by Emotu Balogun

  I'm considering taking up scala programming but i'm really concerned about what will become of my ORM based applications. I currently use hibernate as my ORM and i find it a really reliable tool. I'd like to know if there's any ORM tool as efficient but written in scala, or will hibernate work seamlessly with it. i don't want to have to start writing endless sql queries again (like the days of JDBC). I also have the same thought about erlang. is there a good orm out there for erlang?? and can i use erlang with other DBMS like oracle and mysql with ORM

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• Warn user when new data is inserted on database

  - by João Menighin

  I don't know how to search about this so I'm kinda lost (the two topics I saw here were closed). I have a news website and I want to warn the user when a new data is inserted on the database. I want to do that like here on StackOverflow where we are warned without reloading the page or like in facebook where you are warned about new messages/notifications without reloading. Which is the best way to do that? Is it some kind of listener with a timeout that is constantly checking the database? It doesn't sounds efficient... Thanks in advance.

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• Enumerating combinations in a distributed manner

  - by Reyzooti

  I have a problem where I must analyse 500C5 combinations (255244687600) of something. Distributing it over a 10 node cluster where each cluster processes roughly 10^6 combinations per second means the job will be complete in about 7hours. The problem I have is distributing the 255244687600 combinations over the 10 nodes. I'd like to present each node with 25524468760, however the algorithms I'm using can only produce the combinations sequentially, I'd like to be able to pass the set of elements and a range of combination indicies eg: [0-10^7) or [10^7,2.0 10^7) etc and have the nodes themselves figure out the combinations. The algorithms I'm using at the moment are from the following: http://home.roadrunner.com/~hinnant/combinations.html A logical question I've considered using a master node, that enumerates each of the combinations and sends work to each of the nodes, however the overhead incurred in iterating the combinations from a single node and communicating back and forth work is enormous, and will subsequently lead to the master node becoming the bottleneck. Are there any good combination iterating algorithms geared up for efficient/optimal distributed enumeration?

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• efficiently compare two BitArrays of the same length

  - by BobTurbo

  How would I do this? I am trying to count when both arrays have the same value of TRUE/1 at the same index. As you can see, my code has multiple bitarrays and is looping through each one and comparing them with a comparisonArray with another loop. It doesn't seem to be very efficient and I need it to be. foreach (bitArrayTuple in bitarryList) { for (int i = 0; i < arrayLength; i++) if (bArrayTuple.Item2[i] && comparisonArray[i]) bitArrayTuple.Item1++; } where Item1 is the count and Item2 is a bitarray.

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• Use count or have a field that tallies?

  - by Dan LaManna

  Fairly simple concept, making an extremely basic message board system and I want users to have a post count. Now I was debating on whether or not to have a tally in their row that is added each time a post by them is created, or subtracted by one each time a post of theirs is deleted. However I'm sure that performing a count query when the post count is requested would be more accurate due to unforseen circumstances (say a thread gets deleted and it doesn't lower their tally properly), however this seems like it would be less efficient to run a query EVERY time their post count is loaded, especially in the case of them having 10 posts on the same page and it lists their post count each post. Thoughts/Advice? Thanks

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• Finding group maxes in SQL join result

  - by Gene

  Two SQL tables. One contestant has many entries: Contestants Entries Id Name Id Contestant_Id Score -- ---- -- ------------- ----- 1 Fred 1 3 100 2 Mary 2 3 22 3 Irving 3 1 888 4 Grizelda 4 4 123 5 1 19 6 3 50 Low score wins. Need to retrieve current best scores of all contestants ordered by score: Best Entries Report Name Entry_Id Score ---- -------- ----- Fred 5 19 Irving 2 22 Grizelda 4 123 I can certainly get this done with many queries. My question is whether there's a way to get the result with one, efficient SQL query. I can almost see how to do it with GROUP BY, but not quite. In case it's relevant, the environment is Rails ActiveRecord and PostgreSQL.

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• Is select() Ok to implemnet single socket read/write timeout ?

  - by chmike

  I have an application processing network communication with blocking calls. Each thread manages a single connection. I've added a timeout on the read and write operation by using select prior to read or write on the socket. Select is known to be inefficient when dealing with large number of sockets. But is it ok, in term of performance to use it with a single socket or are there more efficient methods to add timeout support on single sockets calls ? The benefit of select is to be portable.

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• Effective way of String spliting C#

  - by openidsujoy

  I have a completed string like this N:Pay in Cash++RGI:40++R:200++T:Purchase++IP:N++IS:N++PD:PC++UCP:598.80++UPP:0.00++TCP:598.80++TPP:0.00++QE:1++QS:1++CPC:USD++PPC:Points++D:Y++E:Y++IFE:Y++AD:Y++IR:++MV:++CP:~ ~N:ERedemption++RGI:42++R:200++T:Purchase++IP:N++IS:N++PD:PC++UCP:598.80++UPP:0.00++TCP:598.80++TPP:0.00++QE:1++QS:1++CPC:USD++PPC:Points++D:Y++E:Y++IFE:Y++AD:Y++IR:++MV:++CP: this string is like this It's list of PO's(Payment Options) which are separated by ~~ this list may contains one or more PO contains only Key-Value Pairs which separated by : spaces are denoted by ++ I need to extract the values for Key "RGI" and "N". I can do it via for loop , I want a efficient way to do this. any help on this.

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• Is scala functional programming slower than traditional coding?

  - by Fred Haslam

  In one of my first attempts to create functional code, I ran into a performance issue. I started with a common task - multiply the elements of two arrays and sum up the results: var first:Array[Float] ... var second:Array[Float] ... var sum=0f; for(ix<-0 until first.length) sum += first(ix) * second(ix); Here is how I reformed the work: sum = first.zip(second).map{ case (a,b) => a*b }.reduceLeft(_+_) When I benchmarked the two approaches, the second method takes 40 times as long to complete! Why does the second method take so much longer? How can I reform the work to be both speed efficient and use functional programming style?

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• How do I ensure data consistency in this concurrent situation?

  - by MalcomTucker

  The problem is this: I have multiple competing threads (100+) that need to access one database table Each thread will pass a String name - where that name exists in the table, the database should return the id for the row, where the name doesn't already exist, the name should be inserted and the id returned. There can only ever be one instance of name in the database - ie. name must be unique How do I ensure that thread one doesn't insert name1 at the same time as thread two also tries to insert name1? In other words, how do I guarantee the uniqueness of name in a concurrent environment? This also needs to be as efficient as possible - this has the potential to be a serious bottleneck. I am using MySQL and Java. Thanks

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• 2D Engine scrolling on OpenGL via hardware?

  - by drudru

  hi, I'm using OpenGL as the bottom end for a 2D tiling engine. When everything is 2D, it is simple to optimize certain issues. For example, scrolling. If I know a certain section of the screen needs to scroll off the bottom, then I can just blit over that portion. I'm evening moving more than 1 pixel at a time. Without explicit hardware support (think old nintendo hw), this requires a lot of pixel writes. An on chip bitblt would be the next best thing. Essentially, I'm looking at how I can optimize my GL calls to use VRAM texture renders as efficient hardware blits. Is it possible to have GL scroll the framebuffer, or should I just resign myself to double-buffering and re-rendering an entire scene for each frame? Thx

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• Best strategy for HTML parcial rendering based on multiple dropdown values

  - by pv2008

  I have a View that renders something like this: "Item 1" and "Item 2" are <tr> elements from a table. After the user change "Value 1" or "Value 2" I would like to call a Controller and put the result (some HTML snippet) in the div marked as "Result of...". I have some vague notions of JQuery. I know how to bind to the onchage event of the Select element, and call the $.ajax() function, for example. But I wonder if this can be achieved in a more efficient way in ASP.NET MVC2.

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• Stringification of a macro value

  - by SF.

  I faced a problem - I need to use a macro value both as string and as integer. #define RECORDS_PER_PAGE 10 /*... */ #define REQUEST_RECORDS \ "SELECT Fields FROM Table WHERE Conditions" \ " OFFSET %d * " #RECORDS_PER_PAGE \ " LIMIT " #RECORDS_PER_PAGE ";" char result_buffer[RECORDS_PER_PAGE][MAX_RECORD_LEN]; /* ...and some more uses of RECORDS_PER_PAGE, elsewhere... */ This fails with a message about "stray #", and even if it worked, I guess I'd get the macro names stringified, not the values. Of course I can feed the values to the final method ( "LIMIT %d ", page*RECORDS_PER_PAGE ) but it's neither pretty nor efficient. It's times like this when I wish the preprocessor didn't treat strings in a special way and would process their content just like normal code. For now, I cludged it with #define RECORDS_PER_PAGE_TXT "10" but understandably, I'm not happy about it. How to get it right?

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• What is the fastest method to calculate substring

  - by Misha Moroshko

  I have a huge "binary" string, like: 1110 0010 1000 1111 0000 1100 1010 0111.... It's length is 0 modulo 4, and may reach 500,000. I have also a corresponding array: {14, 2, 8, 15, 0, 12, 10, 7, ...} (every number in the array corresponds to 4 bits in the string) Given this string, this array, and a number N, I need to calculate the following substring string.substr(4*N, 4), i.e.: for N=0 the result should be 1110 for N=1 the result should be 0010 I need to perform this task many many times, and my question is what would be the fastest method to calculate this substring ? One method is to calculate the substring straight forward: string.substr(4*N, 4). I'm afraid this one is not efficient for such huge strings. Another method is to use array[N].toString(2) and then wrap the result with zeros if needed. I'm not sure how fast is this. May be you have any other ideas ?

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• Mysql search design

  - by neil

  I'm designing a mysql database, and i'd like some input on an efficient way to store blog/article data for searching. Right now, I've made a separate column that stores the content to be searched - no duplicate words, no words shorter than four letters, and no words that are too common. So, essentially, it's a list of keywords from the original article. Also searched would be a list of tags, and the title field. I'm not quite sure how mysql indexes fulltext columns, so would storing the data like that be ineffective, or redundant somehow? A lot of the articles are on the same topic, so would the score be hurt by so many of the rows having similar keywords? Also, for this project, solutions like sphinx, lucene or google custom seach can't be used -- only php & mysql. Thanks!

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• How do I know if my PHP application is using too much memory?

  - by John

  I'm working on a PHP web application that let's users network with each other, book events, message etc... I launched it a few months ago and at the moment, there's only about 100 users. I set up the application on a VPS with ubuntu 9.10, apache 2, mysql 5 and php 5. I had 360 Mb of RAM, but upgraded to 720 MB a few minutes ago. Lately, my web application has been experiencing outages due to excessive memory usage. From what I can tell in error logs, it seems the server automatically kills apache processes that consume too much memory. As a result, I upgraded memory from 360 MB to 720 MB as a stop-gap measure. So my question is, how do I go about resolving these outage issues? How do I know if my website's need for more memory is due to poor code or if it's part of the website's natural growth? What's the most efficient way to determine which PHP scripts consume the most memory?

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• Is it a good idea to apply some basic macros to simplify code in a large project?

  - by DoctorT

  I've been working on a foundational c++ library for some time now, and there are a variety of ideas I've had that could really simplify the code writing and managing process. One of these is the concept of introducing some macros to help simplify statements that appear very often, but are a bit more complicated than should be necessary. For example, I've come up with this basic macro to simplify the most common type of for loop: #define loop(v,n) for(unsigned long v=0; v<n; ++v) This would enable you to replace those clunky for loops you see so much of: for (int i = 0, i < max_things; i++) With something much easier to write, and even slightly more efficient: loop (i, max_things) Is it a good idea to use conventions like this? Are there any problems you might run into with different types of compilers? Would it just be too confusing for someone unfamiliar with the macro(s)?

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