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  • Internal loop only runs once, containing loop runs endlessly

    - by Mark
    noob question I'm afraid. I have a loop that runs and rotates the hand of a clock and an internal loop that checks the angle of the hand if it is 90, 180, 270 and 360. On these 4 angles the corresponding div is displayed and its siblings removed. The hand loops and loops eternally, which is what I want, but the angle check only runs the loop once through the whole 360. As the hand passes through the angles it is correctly displaying and removing divs but is doesn't continue after the first revolution of the clock. I've obviously messed up somewhere and there is bound to be a more efficient way of doing all this. I am using jQueryRotate.js for my rotations. Thanks for your time. jQuery(document).ready(function(){ var angle = 0; setInterval(function(){ jQuery("#hand").rotate(angle); function movehand(){ if (angle == 90) { jQuery("#intervention").fadeIn().css("display","block").siblings().css("display","none"); } else if (angle == 180) { jQuery("#management").fadeIn().css("display","block").siblings().css("display","none"); } else if (angle == 270) { jQuery("#prevention").fadeIn().css("display","block").siblings().css("display","none"); } else if (angle == 360) { jQuery("#reaction").fadeIn().css("display","block").siblings().css("display","none"); } else {movehand;} }; movehand(); angle+=1; },10); });

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  • Set a datetime for next or previous sunday at specific time

    - by Marc
    I have an app where there is always a current contest (defined by start_date and end_date datetime). I have the following code in the application_controller.rb as a before_filter. def load_contest @contest_last = Contest.last @contest_last.present? ? @contest_leftover = (@contest_last.end_date.utc - Time.now.utc).to_i : @contest_leftover = 0 if @contest_last.nil? Contest.create(:start_date => Time.now.utc, :end_date => Time.now.utc + 10.minutes) elsif @contest_leftover < 0 @winner = Organization.order('votes_count DESC').first @contest_last.update_attributes!(:organization_id => @winner.id, :winner_votes => @winner.votes_count) if @winner.present? Organization.update_all(:votes_count => 0) Contest.create(:start_date => @contest_last.end_date.utc, :end_date => Time.now.utc + 10.minutes) end end My questions: 1) I would like to change the :end_date to something that signifies next Sunday at a certain time (eg. next Sunday at 8pm). Similarly, I could then set the :start_date to to the previous Sunday at a certain time. I saw that there is a sunday() class (http://api.rubyonrails.org/classes/Time.html#method-i-sunday), but not sure how to specify a certain time on that day. 2) For this situation of always wanting the current contest, is there a better way of loading it in the app? Would caching it be better and then reloading if a new one is created? Not sure how this would be done, but seems to be more efficient. Thanks!

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  • Implementation of MVC with SQLite and NSURLConnection, use cases?

    - by user324723
    I'm interested in knowing how others have implemented/designed database & web services in their iphone app and how they simplified it for the entire application. My application is dependent on these services and I can't figure out a efficient way to use them together due to the (semi)complexity of my requirements. My past attempts on combining them haven't been completely successful or at least optimal in my mind. I'm building a database driven iphone app that uses a relational database in sqlite and consumes web services based on missing content or user interaction. Like this hasn't been done before...right? Since I am using a relational database - any web services consumed requires normalization, parsing the result and persisting it to the database before it can be displayed in a table view controller. The applications UI consists of nested(nav controller) table views where a user can select a cell and be taken to the next table view where it attempts to populate the table views data source from the database. If nothing exists in the database then it will send a request via web services to download its content, thus download - parse - persist - query - display. Since the user has the ability to request a refresh of this data it still requires the same process. Quickly describing what I've implemented and tried to run with - 1st attempt - Used a singleton web service class that handled sending web service requests, parsing the result and returning it to the table view controller via delegate protocols. Once the controller received that data it would then be responsible for persisting it to the database and re-returning the result. I didn't like the idea of only preventing the case where the app delegate selector doesn't exists(released) causing the app to crash. 2nd attempt - Used NSNotificationCenter for easy access to both database and web services but later realized it was more complex due to adding and removing observers per view(which isn't advised anyways).

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  • JavaScript - Efficiently find all elements containing one of a large set of strings

    - by noah
    I have a set of strings and I need to find all all of the occurrences in an HTML document. Where the string occurs is important because I need to handle each case differently: String is all or part of an attribute. e.g., the string is foo: <input value="foo"> - Add class ATTR to the element. String is the full text of an element. e.g., <button>foo</button> - Add class TEXT to the element. String is inline in the text of an element. e.g., <p>I love foo</p> - Wrap the text in a span tag with class TEXT. Also, I need to match the longest string first. e.g., if I have foo and foobar, then <p>I love foobar</p> should become <p>I love <span class="TEXT">foobar</span></p>, not <p>I love <span class="TEXT">foo</span>bar</p>. The inline text is easy enough: Sort the strings descending by length and find and replace each in document.body.innerHTML with <span class="TEXT">$1</span>, although I'm not sure if that is the most efficient way to go. For the attributes, I can do something like this: sortedStrings.each(function(it) { document.body.innerHTML.replace(new RegExp('(\S+?)="[^"]*'+escapeRegExChars(it)+'[^"]*"','g'),function(s,attr) { $('[+attr+'*='+it+']').addClass('ATTR'); }); }); Again, that seems inefficient. Lastly, for the full text elements, a depth first search of the document that compares the innerHTML to each string will work, but for a large number of strings, it seems very inefficient. Any answer that offers performance improvements gets an upvote :)

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  • Why is BorderLayout calling setSize() and setBounds()?

    - by ags
    I'm trying to get my head around proper use of the different LayoutManagers to make my GUI design skills more efficient and effective. For me, that usually requires a detailed understanding of what is going on under the hood. I've found some good discussion of the interaction and consequences of a Container using BorderLayout containing a Container using FlowLayout. I understand it for the most part, but wanted to confirm my mental model and to do so I am looking at the code for BorderLayout. In the code snippet below taken from BorderLayout.layoutContainer(), note the calls to the child Component's setSize() method followed by setBounds(). Looking at the source for these methods of Component, setSize() actually calls setBounds() with the current values for Component.x and Component.y. Why is this done (and not entirely redudant?) Doesn't the setBounds() call completely overwrite the results of the setSize() call? if ((c=getChild(NORTH,ltr)) != null) { c.setSize(right - left, c.height); Dimension d = c.getPreferredSize(); c.setBounds(left, top, right - left, d.height); top += d.height + vgap; } I'm also tring to understand where/when the child Component's size is initially set (before the LayoutManager.layoutContainer() method is called). Finally, this post itself raises a "meta-question": in a situation like this, where the source is available elsewhere, is the accepteed protocol to include the entire method? Or some other way to make it easier for folks to participate in the thread? Thanks.

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  • A good data model for finding a user's favorite stories

    - by wings
    Original Design Here's how I originally had my Models set up: class UserData(db.Model): user = db.UserProperty() favorites = db.ListProperty(db.Key) # list of story keys # ... class Story(db.Model): title = db.StringProperty() # ... On every page that displayed a story I would query UserData for the current user: user_data = UserData.all().filter('user =' users.get_current_user()).get() story_is_favorited = (story in user_data.favorites) New Design After watching this talk: Google I/O 2009 - Scalable, Complex Apps on App Engine, I wondered if I could set things up more efficiently. class FavoriteIndex(db.Model): favorited_by = db.StringListProperty() The Story Model is the same, but I got rid of the UserData Model. Each instance of the new FavoriteIndex Model has a Story instance as a parent. And each FavoriteIndex stores a list of user id's in it's favorited_by property. If I want to find all of the stories that have been favorited by a certain user: index_keys = FavoriteIndex.all(keys_only=True).filter('favorited_by =', users.get_current_user().user_id()) story_keys = [k.parent() for k in index_keys] stories = db.get(story_keys) This approach avoids the serialization/deserialization that's otherwise associated with the ListProperty. Efficiency vs Simplicity I'm not sure how efficient the new design is, especially after a user decides to favorite 300 stories, but here's why I like it: A favorited story is associated with a user, not with her user data On a page where I display a story, it's pretty easy to ask the story if it's been favorited (without calling up a separate entity filled with user data). fav_index = FavoriteIndex.all().ancestor(story).get() fav_of_current_user = users.get_current_user().user_id() in fav_index.favorited_by It's also easy to get a list of all the users who have favorited a story (using the method in #2) Is there an easier way? Please help. How is this kind of thing normally done?

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  • Help ! How do I get the total number rows from my mssql paging procedure ?

    - by The_AlienCoder
    Ok I have a table in my MSSQL database that stores comments. My desire is to be able to page though the records using [Back],[Next], page numbers & [Last] buttons in my datalist. I figured the most efficient way was to use a stored procedure that only returns a certain number of rows within a partcular range. Here is what I came up with @PageIndex INT, @PageSize INT, @postid int AS SET NOCOUNT ON begin WITH tmp AS ( SELECT comments.*, ROW_NUMBER() OVER (ORDER BY dateposted ASC) AS Row FROM comments WHERE (comments.postid = @postid)) SELECT tmp.* FROM tmp WHERE Row between (@PageIndex - 1) * @PageSize + 1 and @PageIndex*@PageSize end RETURN Now everything works fine and I have been able implement [Next] and [Back] buttons in my datalist pager.Now I need the total number of all comments(not in the cuurent page) so that I can implement my page numbers and the[Last] button on my pager. In other words I want to return the total number of rows in my first select statement i.e WITH tmp AS ( SELECT comments.*, ROW_NUMBER() OVER (ORDER BY dateposted ASC) AS Row FROM comments WHERE (comments.postid = @postid)) set @TotalRows = @@rowcount @@rowcount doesnt work and raises an error.I also cant get count.* to work either. Is there another way to get the total amount of rows or is my approach doomed.

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  • SQL Structure of DB table with different types of columns

    - by Dmitry Dvornikov
    I have a problem with the optimization of the structure of the database. I'll try to explain it exactly. I create a project, where we can add different values??, but this values must have different types of the columns in the database (eg, int, double , varchar). What is the best way to store the different types of values ??in the database. In the project I'm using Propel 1.6. The point is availability to add value with 'int', 'varchar' and other columns types, to search the table was efficient. In total, I have two ideas. The first is to create a table of "value", which will have columns: "id ", "value_int", "value_double", "value_varchar", etc - with the corresponding column types. Depending on the type of values??, records will be saved with the value in the appropriate column (the rest will be NULL). The second solution is to create separate tables such as "value_int", "value_varchar" etc. There would be columns: "id", "value", which correspond to the relevant types of "value" (ie, such as int, varchar, etc). I must admit that I do not believe any of the above solutions, originally I was thinking about one table "value", where the column would be a "text" type - but this solution would probably be even worse. I would like to know your opinion on this topic, maybe something else would be better. Thanks in advance. EDIT: For example : We have three tables: USER: [table of users] * id * name FIELD: [table of profile fields - where the column 'type' is the type of field, eg int or varchar) * id * type * name VALUE : * id * User_id - ( FK user.id ) * Field_id - ( FK field.id ) * value So we have in each row an user in USER table, and the profile is stored in the VALUE table. Bit each profile field may have a different type (column 'type' in the FIELD table), and based on that I would want this value to add to the appropriate column of the appropriate type.

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  • gl_FragColor and glReadPixels

    - by chun0216
    I am still trying to read pixels from fragment shader and I have some questions. I know that gl_FragColor returns with vec4 meaning RGBA, 4 channels. After that, I am using glReadPixels to read FBO and write it in data GLubyte *pixels = new GLubyte[640*480*4]; glReadPixels(0, 0, 640,480, GL_RGBA, GL_UNSIGNED_BYTE, pixels); This works fine but it really has speed issue. Instead of this, I want to just read RGB so ignore alpha channels. I tried: GLubyte *pixels = new GLubyte[640*480*3]; glReadPixels(0, 0, 640,480, GL_RGB, GL_UNSIGNED_BYTE, pixels); instead and this didn't work though. I guess it's because gl_FragColor returns 4 channels and maybe I should do something before this? Actually, since my returned image (gl_FragColor) is grayscale, I did something like float gray = 0.5 //or some other values gl_FragColor = vec4(gray,gray,gray,1.0); So is there any efficient way to use glReadPixels instead of using the first 4 channels method? Any suggestion? By the way, this is on opengl es 2.0 code.

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  • CUDA - multiple kernels to compute a single value

    - by Roger
    Hey, I'm trying to write a kernel to essentially do the following in C float sum = 0.0; for(int i = 0; i < N; i++){ sum += valueArray[i]*valueArray[i]; } sum += sum / N; At the moment I have this inside my kernel, but it is not giving correct values. int i0 = blockIdx.x * blockDim.x + threadIdx.x; for(int i=i0; i<N; i += blockDim.x*gridDim.x){ *d_sum += d_valueArray[i]*d_valueArray[i]; } *d_sum= __fdividef(*d_sum, N); The code used to call the kernel is kernelName<<<64,128>>>(N, d_valueArray, d_sum); cudaMemcpy(&sum, d_sum, sizeof(float) , cudaMemcpyDeviceToHost); I think that each kernel is calculating a partial sum, but the final divide statement is not taking into account the accumulated value from each of the threads. Every kernel is producing it's own final value for d_sum? Does anyone know how could I go about doing this in an efficient way? Maybe using shared memory between threads? I'm very new to GPU programming. Cheers

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  • [MySQL] Efficiently store last X records per item

    - by Saif Bechan
    I want to store the last X records in an MySQL database in an efficient way. So when the 4th record is stored the first should be deleted. The way I do this not is first run a query getting the items. Than check what I should do then insert/delete. There has to be a better way to do this. Any suggestions? Edit I think I should add that the records stored do not have a unique number. They have a mixed par. For example article_id and user_id. Then I want to make a table with the last X items for user_x. Just selecting the article from the table grouped by user and sorted by time is not an option for me. The table where I do the sort and group on has millions of records and gets hit a lot for no reason. So making a table in between with the last X records is way more effient. PS. I am not using this for articles and users.

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  • odp.net SQL query retrieve set of rows from two input arrays.

    - by Karl Trumstedt
    I have a table with a primary key consisting of two columns. I want to retrieve a set of rows based on two input arrays, each corresponding to one primary key column. select pkt1.id, pkt1.id2, ... from PrimaryKeyTable pkt1, table(:1) t1, table(:2) t2 where pkt1.id = t1.column_value and pkt1.id2 = t2.column_value I then bind the values with two int[] in odp.net. This returns all different combinations of my resulting rows. So if I am expecting 13 rows I receive 169 rows (13*13). The problem is that each value in t1 and t2 should be linked. Value t1[4] should be used with t2[4] and not all the different values in t2. Using distinct solves my problem, but I'm wondering if my approach is wrong. Anyone have any pointers on how to solve this the best way? One way might be to use a for-loop accessing each index in t1 and t2 sequentially, but I wonder what will be more efficient. Edit: actually distinct won't solve my problem, it just did it based on my input-values (all values in t2 = 0)

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  • Good way to identify similar images?

    - by Nick
    I've developed a simple and fast algorithm in PHP to compare images for similarity. Its fast (~40 per second for 800x600 images) to hash and a unoptimised search algorithm can go through 3,000 images in 22 mins comparing each one against the others (3/sec). The basic overview is you get a image, rescale it to 8x8 and then convert those pixels for HSV. The Hue, Saturation and Value are then truncated to 4 bits and it becomes one big hex string. Comparing images basically walks along two strings, and then adds the differences it finds. If the total number is below 64 then its the same image. Different images are usually around 600 - 800. Below 20 and extremely similar. Are there any improvements upon this model I can use? I havent looked at how relevant the different components (hue, saturation and value) are to the comparison. Hue is probably quite important but the others? To speed up searches I could probably split the 4 bits from each part in half, and put the most significant bits first so if they fail the check then the lsb doesnt need to be checked at all. I dont know a efficient way to store bits like that yet still allow them to be searched and compared easily. I've been using a dataset of 3,000 photos (mostly unique) and there havent been any false positives. Its completely immune to resizes and fairly resistant to brightness and contrast changes.

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  • VB.NET Syntax Coding

    - by Yiu Korochko
    I know many people ask how some of these are done, but I do not understand the context in which to use the answers, so... I'm building a code editor for a subversion of Python language, and I found a very decent way of highlighting keywords in the RichTextBox through this: bluwords.Add(KEYWORDS GO HERE) If scriptt.Text.Length > 0 Then Dim selectStart2 As Integer = scriptt.SelectionStart scriptt.Select(0, scriptt.Text.Length) scriptt.SelectionColor = Color.Black scriptt.DeselectAll() For Each oneWord As String In bluwords Dim pos As Integer = 0 Do While scriptt.Text.ToUpper.IndexOf(oneWord.ToUpper, pos) >= 0 pos = scriptt.Text.ToUpper.IndexOf(oneWord.ToUpper, pos) scriptt.Select(pos, oneWord.Length) scriptt.SelectionColor = Color.Blue pos += 1 Loop Next scriptt.SelectionStart = selectStart2 End If (scriptt is the richtextbox) But when any decent amount of code is typed (or loaded via OpenFileDialog) chunks of the code go missing, the syntax selection falls apart, and it just plain ruins it. I'm looking for a more efficient way of doing this, maybe something more like visual studio itself...because there is NO NEED to highlight all text, set it black, then redo all of the syntaxing, and the text begins to over-right if you go back to insert characters between text. Also, in this version of Python, hash (#) is used for comments on comment only lines and double hash (##) is used for comments on the same line. Now I saw that someone had asked about this exact thing, and the working answer to select to the end of the line was something like: ^\'[^\r\n]+$|''[^\r\n]+$ which I cannot seem to get into practice. I also wanted to select text between quotes and turn it turquoise, such as between the first quotation mark and the second, the text is turquoise, and the same between the 3rd and 4th etcetera... Any help is appreciated!

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  • Mimic Coldfusion's debug output in PHP?

    - by TekiusFanatikus
    I'm trying to mimic Coldfusion's debug output in PHP. Here's an example of what it looks like (ie. Execution Time section): I've turned to XDebug. Ideally, the exception stack error output would be what I'd be looking for. However, it only shows up when an exception occurs. I also tried something like (in our CMS-ish app) this (original question here): $content.= "<?php xdebug_start_trace('e:/xdebug/trace');?>"; $content.= "<?php require('".$page['file_'.LG]."'); ?>"; $content.= "<?php xdebug_stop_trace();?>"; ... $content.= "<?php echo readfile('e:/xdebug/trace.xt');?>"; However, I get an insane, browser crashing HTML table dropped at the bottom of page. Not very efficient. My php.ini config: xdebug.trace_format = 2 xdebug.collect_vars = 1 xdebug.collect_params = 4 xdebug.dump_globals = 1 xdebug.dump.SERVER = 'REQUEST_URI' xdebug.show_local_vars = 1 xdebug.show_mem_delta = 1 I'm just wondering if someone has already done something similar?

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  • Faster quadrature decoder loops with Python code

    - by Kelei
    I'm working with a BeagleBone Black and using Adafruit's IO Python library. Wrote a simple quadrature decoding function and it works perfectly fine when the motor runs at about 1800 RPM. But when the motor runs at higher speeds, the code starts missing some of the interrupts and the encoder counts start to accumulate errors. Do you guys have any suggestions as to how I can make the code more efficient or if there are functions which can cycle the interrupts at a higher frequency. Thanks, Kel Here's the code: # Define encoder count function def encodercount(term): global counts global Encoder_A global Encoder_A_old global Encoder_B global Encoder_B_old global error Encoder_A = GPIO.input('P8_7') # stores the value of the encoders at time of interrupt Encoder_B = GPIO.input('P8_8') if Encoder_A == Encoder_A_old and Encoder_B == Encoder_B_old: # this will be an error error += 1 print 'Error count is %s' %error elif (Encoder_A == 1 and Encoder_B_old == 0) or (Encoder_A == 0 and Encoder_B_old == 1): # this will be clockwise rotation counts += 1 print 'Encoder count is %s' %counts print 'AB is %s %s' % (Encoder_A, Encoder_B) elif (Encoder_A == 1 and Encoder_B_old == 1) or (Encoder_A == 0 and Encoder_B_old == 0): # this will be counter-clockwise rotation counts -= 1 print 'Encoder count is %s' %counts print 'AB is %s %s' % (Encoder_A, Encoder_B) else: #this will be an error as well error += 1 print 'Error count is %s' %error Encoder_A_old = Encoder_A # store the current encoder values as old values to be used as comparison in the next loop Encoder_B_old = Encoder_B # Initialize the interrupts - these trigger on the both the rising and falling GPIO.add_event_detect('P8_7', GPIO.BOTH, callback = encodercount) # Encoder A GPIO.add_event_detect('P8_8', GPIO.BOTH, callback = encodercount) # Encoder B # This is the part of the code which runs normally in the background while True: time.sleep(1)

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  • Saving multiple items per single database cell...

    - by eugeneK
    Hi, i have a countries list. Each user can check multiple countries. Once saved, this "user country list" will be used to get whether other users fit into countries certain user chose. Question is what would be the most efficient approach to this problem... I have one, one to save user selection as delimited list like Canada,USA,France ... in single varchar(max) field but problem with it would be that once user from Germany enters page i perform this check on. To search for Germany i would be needed to get all items and un-delimit each field to check against value or to use sql 'like' which again is pretty damn slow.. If you have better solution or some tips i would be glad to hear. Just to make sure, many users will have their own selections of countries from which and only they want to have users to land on their page. While millions of users will reach those pages. So the faster approach will be the better. technology, MSSQL and ASP.NET thanks

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  • mysql image disable print download

    - by Vish
    Hi, We use a Flex AIR client and a WAMP server. Tiff images are stored in MySQL. Currently, I can download the image from AIR client and it prompts for a download dialog. Things are fine till this point. We got a new requirement. Requirement is that only some users can print the image which gets downloaded. For other users, they should not be able to print the tiff image. Wondering how to accomplish this. One idea, not sure if its efficient, is to convert the image requested to pdf at the server side, disable print option there(hope there are API's available) and send back the pdf. Please let me know btter ideas. Also, is there a way to prevent file download dialog from popping up everytime the file is requested for download? Can we just get the file stream to the client and manipulate it to open with a particular viewer or write it to pdf... Please help.

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  • Why do I get "Bad File Descriptor" when I try to read a file with Perl?

    - by Magicked
    I'm trying to read a binary file 40 bytes at a time, then check to see if all those bytes are 0x00, and if so ignore them. If not, it will write them back out to another file (basically just cutting out large blocks of null bytes). This may not be the most efficient way to do this, but I'm not worried about that. However, right now I'm getting a "Bad File Descriptor" error and I cannot figure out why. my $comp = "\x00" * 40; my $byte_count = 0; my $infile = "/home/magicked/image1"; my $outfile = "/home/magicked/image1_short"; open IN, "<$infile"; open OUT, ">$outfile"; binmode IN; binmode OUT; my ($buf, $data, $n); while (read (IN, $buf, 40)) { ### Problem is here ### $boo = 1; for ($i = 0; $i < 40; $i++) { if ($comp[$i] != $buf[$i]) { $i = 40; print OUT $buf; $byte_count += 40; } } } die "Problems! $!\n" if $!; close OUT; close IN; I marked with a comment where it is breaking. Thanks for any help!

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  • Rand(); with exclusion to and already randomly generated number..?

    - by Stefan
    Hey, I have a function which calls a users associated users from a table. The function then uses the rand(); function to chose from the array 5 randomly selected userID's however!... In the case where a user doesnt have many associated users but above the min (if below the 5 it just returns the array as it is) then it gives bad results due to repeat rand numbers... How can overcome this or exclude a previously selected rand number from the next rand(); function call. Here is the section of code doing the work. Bare in mind this must be highly efficient as this script is used everywhere. $size = sizeof($users)-1; $nusers[0] = $users[rand(0,$size)]; $nusers[1] = $users[rand(0,$size)]; $nusers[2] = $users[rand(0,$size)]; $nusers[3] = $users[rand(0,$size)]; $nusers[4] = $users[rand(0,$size)]; return $nusers; Thanks in advance! Stefan

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  • Am I understanding premature optimization correctly?

    - by Ed Mazur
    I've been struggling with an application I'm writing and I think I'm beginning to see that my problem is premature optimization. The perfectionist side of me wants to make everything optimal and perfect the first time through, but I'm finding this is complicating the design quite a bit. Instead of writing small, testable functions that do one simple thing well, I'm leaning towards cramming in as much functionality as possible in order to be more efficient. For example, I'm avoiding multiple trips to the database for the same piece of information at the cost of my code becoming more complex. One part of me wants to just not worry about redundant database calls. It would make it easier to write correct code and the amount of data being fetched is small anyway. The other part of me feels very dirty and unclean doing this. :-) I'm leaning towards just going to the database multiple times, which I think is the right move here. It's more important that I finish the project and I feel like I'm getting hung up because of optimizations like this. My question is: is this the right strategy to be using when avoiding premature optimization?

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  • Splitting a set of object into several subsets of 'similar' objects

    - by doublep
    Suppose I have a set of objects, S. There is an algorithm f that, given a set S builds certain data structure D on it: f(S) = D. If S is large and/or contains vastly different objects, D becomes large, to the point of being unusable (i.e. not fitting in allotted memory). To overcome this, I split S into several non-intersecting subsets: S = S1 + S2 + ... + Sn and build Di for each subset. Using n structures is less efficient than using one, but at least this way I can fit into memory constraints. Since size of f(S) grows faster than S itself, combined size of Di is much less than size of D. However, it is still desirable to reduce n, i.e. the number of subsets; or reduce the combined size of Di. For this, I need to split S in such a way that each Si contains "similar" objects, because then f will produce a smaller output structure if input objects are "similar enough" to each other. The problems is that while "similarity" of objects in S and size of f(S) do correlate, there is no way to compute the latter other than just evaluating f(S), and f is not quite fast. Algorithm I have currently is to iteratively add each next object from S into one of Si, so that this results in the least possible (at this stage) increase in combined Di size: for x in S: i = such i that size(f(Si + {x})) - size(f(Si)) is min Si = Si + {x} This gives practically useful results, but certainly pretty far from optimum (i.e. the minimal possible combined size). Also, this is slow. To speed up somewhat, I compute size(f(Si + {x})) - size(f(Si)) only for those i where x is "similar enough" to objects already in Si. Is there any standard approach to such kinds of problems? I know of branch and bounds algorithm family, but it cannot be applied here because it would be prohibitively slow. My guess is that it is simply not possible to compute optimal distribution of S into Si in reasonable time. But is there some common iteratively improving algorithm?

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  • Reading a binary file in perl: Bad File Descriptor

    - by Magicked
    I'm trying to read a binary file 40 bytes at a time, then check to see if all those bytes are 0x00, and if so ignore them. If not, it will write them back out to another file (basically just cutting out large blocks of null bytes). This may not be the most efficient way to do this, but I'm not worried about that. However, right now I'm getting a "Bad File Descriptor" error and I cannot figure out why. my $comp = "\x00" * 40; my $byte_count = 0; my $infile = "/home/magicked/image1"; my $outfile = "/home/magicked/image1_short"; open IN, "<$infile"; open OUT, ">$outfile"; binmode IN; binmode OUT; my ($buf, $data, $n); while (read (IN, $buf, 40)) { ### Problem is here ### $boo = 1; for ($i = 0; $i < 40; $i++) { if ($comp[$i] != $buf[$i]) { $i = 40; print OUT $buf; $byte_count += 40; } } } die "Problems! $!\n" if $!; close OUT; close IN; I marked with a comment where it is breaking. Thanks for any help!

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  • Validating JSP's and HTML Forms, Server-side or Client-side, or both?

    - by CitadelCSAlum
    I am aware that I can Google "HTML Form Validation" and would get a billion tutorials. I am well aware that I can use simple JavaScript to validate form input, but I have been told that this is not necessarily an efficient method. I have also heard that it is a best practice to validate both client and server-side code. OK! Well, What exactly does this mean besides writing code on both? Does it mean I do some with JavaScript and other with Servlet's or does it mean that I write identical validation methods on both? My real question is can anybody give me insight and direction as how to go about validation my HTML forms. I am using JSP's and Servlet's and I have tons of form validation to do. I have already done minor form validation with regex in Java, but want to figure out if Im heading in the right track before I write any more code. Only productive answers please, If I wanted negative feedback on how inexperienced I was, I would have gone to Reddit. Thanks!

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  • Change a finder method w/ parameters to an association

    - by Sai Emrys
    How do I turn this into a has_one association? (Possibly has_one + a named scope for size.) class User < ActiveRecord::Base has_many :assets, :foreign_key => 'creator_id' def avatar_asset size = :thumb # The LIKE is because it might be a .jpg, .png, or .gif. # More efficient methods that can handle that are OK. ;) self.assets.find :first, :conditions => ["thumbnail = '#{size}' and filename LIKE ?", self.login + "_#{size}.%"] end end EDIT: Cuing from AnalogHole on Freenode #rubyonrails, we can do this: has_many :assets, :foreign_key => 'creator_id' do def avatar size = :thumb find :first, :conditions => ["thumbnail = ? and filename LIKE ?", size.to_s, proxy_owner.login + "_#{size}.%"] end end ... which is fairly cool, and makes syntax a bit better at least. However, this still doesn't behave as well as I would like. Particularly, it doesn't allow for further nice find chaining (such that it doesn't execute this find until it's gotten all its conditions). More importantly, it doesn't allow for use in an :include. Ideally I want to do something like this: PostsController def show post = Post.get_cache(params[:id]) { Post.find(params[:id], :include => {:comments => {:users => {:avatar_asset => :thumb}} } ... end ... so that I can cache the assets together with the post. Or cache them at all, really - e.g. get_cache(user_id){User.find(user_id, :include => :avatar_assets)} would be a good first pass. This doesn't actually work (self == User), but is correct in spirit: has_many :avatar_assets, :foreign_key => 'creator_id', :class_name => 'Asset', :conditions => ["filename LIKE ?", self.login + "_%"] (Also posted on Refactor My Code.)

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