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• MAD method compression function

  - by Jacques

  I ran across the question below in an old exam. My answers just feels a bit short and inadequate. Any extra ideas I can look into or reasons I have overlooked would be great. Thanx Consider the MAD method compression function, mapping an object with hash code i to element [(3i + 7)mod9027]mod6000 of the 6000-element bucket array. Explain why this is a poor choice of compression function, and how it could be improved. I basically just say that the function could be improved by changing the value for p (or 9027) to an prime number and choosing an other constant for a (or 3) could also help.

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• Enforcing a query in MySql to use a specific index

  - by Hossein

  Hi, I have large table. consisting of only 3 columns (id(INT),bookmarkID(INT),tagID(INT)).I have two BTREE indexes one for each bookmarkID and tagID columns.This table has about 21 Million records. I am trying to run this query: SELECT bookmarkID,COUNT(bookmarkID) AS count FROM bookmark_tag_map GROUP BY tagID,bookmarkID HAVING tagID IN (-----"tagIDList"-----) AND count >= N which takes ages to return the results.I read somewhere that if make an index in which it has tagID,bookmarkID together, i will get a much faster result. I created the index after some time. Tried the query again, but it seems that this query is not using the new index that I have made.I ran EXPLAIN and saw that it is actually true. My question now is that how I can enforce a query to use a specific index? also comments on other ways to make the query faster are welcome. Thanks

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• big O notation algorithm

  - by niggersak

  Use big-O notation to classify the traditional grade school algorithms for addition and multiplication. That is, if asked to add two numbers each having N digits, how many individual additions must be performed? If asked to multiply two N-digit numbers, how many individual multiplications are required? . Suppose f is a function that returns the result of reversing the string of symbols given as its input, and g is a function that returns the concatenation of the two strings given as its input. If x is the string hrwa, what is returned by g(f(x),x)? Explain your answer - don't just provide the result!

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• Alternatives to javascript function-based iteration (e.g. jQuery.each())

  - by Colin

  I've been watching Google Tech Talks' Speed Up Your Javascript and in talking about loops, the speaker mentions to stay away from function-based iterations such as jQuery.each() (among others, at about 24:05 in the video). He briefly explains why to avoid them which makes sense, but admittedly I don't quite understand what an alternative would be. Say, in the case I want to iterate through a column of table cells and use the value to manipulate the adjacent cell's value (just a quick example). Can anyone explain and give an example of an alternative to function-based iteration?

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• Screen Capture with Open GL using glReadPixels

  - by Raja

  Hi, I created a CGRegisterScreenRefreshCallback(refreshCallback, NULL) and in the refreshCallback method get the list of rectangles which have changed. I am getting the rectangle data from frameBuffer using OpenGL glReadPixels. Is there a better way of screen capture either with/without opengl and also using OpenGL can I skip reading pixel by pixel ? I have looked at glGetTexImage and glCopyTexSubImage2D. Any simple code block which can explain how to use these functions to get the changed rectangle data would be very helpful ? Thanks, Raja.

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• problem with dmg file

  - by madalina

  Hello, I have created a dmg file named try.dmg which contains an executable application myapplication.app together with a compiled library mylibrary.lib; I used Disk Utility in order to create the try.dmg file. I mounted the try.dmg file on my computer and I opened the application myapplication.app with no problems. Still, I tried to do the same thing on another Macintosh, with the same operating system Mac OS X, but I got some problems: I mounted the try.dmg file and then when I tried to open the application myapplication.app I got an error message, that the application has quit unexpectedly. Can someone explain me what is it happening? How come this try.dmg file can be mounted and the application can be opened with no problems on my computer with Mac OS X, but on another computer with Mac OS X, after I mount the try.dmg file I get errors when I try opening the application? Thank you very much for your help. Best wishes, Madalina

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• User account design and security...

  - by espinet

  Before I begin, I am using Ruby on Rails and the Devise gem for user authentication. Hi, I was doing some research about account security and I found a blog post about the topic awhile ago but I can no longer find it again. I read something about when making a login system you should have 1 model for User, this contains a user's username, encrypted password, and email. You should also have a model for a user's Account. This contains everything else. A User has an Account. I don't know if I'm explaining this correctly since I haven't seen the blog post for several months and I lost my bookmark. Could someone explain how and why I should or shouldn't do this. My application deals with money so I need to cover my bases with security. Thanks.

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• iPhone Internationalization. What is the simplest workflow for me?

  - by dugla

  Hello, I am wising up and getting my internationalization act together. Right off the bat I am a bit swamped by all the docs Apple provides so I was wondering of someone could sketch a workflow for my situation. Before I begin, I browsed some Apple example code and noticed this NIB file - MainWindow.xib - in the Resources folder: This clearly has something to do with internationalization/localization. Could someone please explain how this is created and where in the workflow it happens? My app is fundamentally an imaging app with a few labels that I currently programmatically internationalize using NSLocalizedString(...). If I set all my labels programmatically and wrap all my strings with NSLocalizedString(...) can I completely ignore the NIB issues? Thanks in advance, Doug

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• Python: split a list based on a condition?

  - by Parand

  What's the best way, both aesthetically and from a performance perspective, to split a list of items into multiple lists based on a conditional? The equivalent of: good = [x for x in mylist if x in goodvals] bad = [x for x in mylist if x not in goodvals] is there a more elegant way to do this? Update: here's the actual use case, to better explain what I'm trying to do: # files looks like: [ ('file1.jpg', 33L, '.jpg'), ('file2.avi', 999L, '.avi'), ... ] IMAGE_TYPES = ('.jpg','.jpeg','.gif','.bmp','.png') images = [f for f in files if f[2].lower() in IMAGE_TYPES] anims = [f for f in files if f[2].lower() not in IMAGE_TYPES]

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• How to Render Partial View into a String

  - by DaveDev

  Hi all, I have the following code: public ActionResult SomeAction() { return new JsonpResult { Data = new { Widget = "some partial html for the widget" } }; } I'd like to modify it so that I could have public ActionResult SomeAction() { // will render HTML that I can pass to the JSONP result to return. var partial = RenderPartial(viewModel); return new JsonpResult { Data = new { Widget = partial } }; } is this possible? Could somebody explain how? note, I edited the question before posting the solution.

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• How do chains work in Rainbow tables?

  - by James Moore

  Hello, I was wondering if should one could explain in detail how chains work in rainbow tables as though you would a complete novice but with relevance to programming. I understand that a chain is 16 bytes long. 8 bytes mark the starting point and 8 mark the end. I also understand that in the filename we have the chain length i.e. 2400. Which means that between our starting point and end point in just 16 bytes we have 2400 possible clear texts? What? How does that work? in those 16 bytes how do i get my 2400 hashes and clear texts or am i miss understanding this? Your help is greatly appreciated. Thanks P.s. I have read the related papers and googled this topic a fair bit. I think im just missing something important to make these gears turn.

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• JQuery iterating through textboxes and changing its color

  - by bill-nielsen

  I'm trying to iterate through all the empty textboxes in a table and change its background colour. I'm using the following JQuery code: $("#btn2").click(function() { var emptyTextBoxes = $('input:text').filter(function() { return this.value == ""; }); emptyTextBoxes.each(function() { this.css('background-color', '#ffff00'); // $('#Col3Txtbx').css('background-color', '#ffff00'); }); }); This does not seem to refer to the textbox which seems strange to me. When I uncomment out the particular textbox, it does reset the background colour. Can someone explain to me what 'This' is referring to?

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• Returning an anonymous class that uses a final primitive. How does it work?

  - by Tim P

  Hi, I was wondering if someone could explain how the following code works: public interface Result { public int getCount(); public List<Thing> getThings(); } class SomeClass { ... public Result getThingResult() { final List<Thing> things = .. populated from something. final int count = 5; return new Result { @Override public int getCount() { return count; } @Override public List<Thing> getThings(); return things; } } } ... } Where do the primitive int , List reference and List instance get stored in memory? It can't be on the stack.. so where? Is there a difference between how references and primitives are handled in this situation? Thanks a bunch, Tim P.

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• mysql query performance help

  - by Stefano

  Hi I have a quite large table storing words contained in email messages mysql> explain t_message_words; +----------------+---------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------------+---------+------+-----+---------+----------------+ | mwr_key | int(11) | NO | PRI | NULL | auto_increment | | mwr_message_id | int(11) | NO | MUL | NULL | | | mwr_word_id | int(11) | NO | MUL | NULL | | | mwr_count | int(11) | NO | | 0 | | +----------------+---------+------+-----+---------+----------------+ table contains about 100M rows mwr_message_id is a FK to messages table mwr_word_id is a FK to words table mwr_count is the number of occurrencies of word mwr_word_id in message mwr_message_id To calculate most used words, I use the following query SELECT SUM(mwr_count) AS word_count, mwr_word_id FROM t_message_words GROUP BY mwr_word_id ORDER BY word_count DESC LIMIT 100; that runs almost forever (more than half an hour on the test server) mysql> show processlist; +----+------+----------------+--------+---------+------+----------------------+----------------------------------------------------- | Id | User | Host | db | Command | Time | State | Info +----+------+----------------+--------+---------+------+----------------------+----------------------------------------------------- processlist | 41 | root | localhost:3148 | tst_db | Query | 1955 | Copying to tmp table | SELECT SUM(mwr_count) AS word_count, mwr_word_id FROM t_message_words GROUP BY mwr_word_id | +----+------+----------------+--------+---------+------+----------------------+----------------------------------------------------- 3 rows in set (0.00 sec) Is there anything I can do to "speed up" the query (apart from adding more ram, more cpu, faster disks)? thank you in advance stefano

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• Maven copy project output into other project resources

  - by Thomas

  There are two projects: 1) applet project that outputs jar file 2) web app project that should host the jar file. After (1) finished building, the applet jar file should be copied into the webapp folder of (2). The purpose is that (2) will host the applet (1) on the Internet. A lot of examples explain how to use another project as a library dependency. Other examples, show how to use ant plugin to copy files. I am unsure on how to properly set this up, so that 'mvn install' on the parent project will do the copying at the right time.

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• android: having two listviews in two listactivities didn't work

  - by Yang

  I guess my previous question wasn't clear enough (http://stackoverflow.com/questions/2549585/android-failed-to-setcontentview-when-switching-to-listactivity), so I explain as follows. In my app I have two listactivities which uses two different listviews: public class Activity1 extends ListActivity { @Override public void onCreate(Bundle savedInstanceState) { try{ super.onCreate(savedInstanceState); setContentView(R.layout.listview1); } public class Activity2 extends ListActivity { @Override public void onCreate(Bundle savedInstanceState) { try{ super.onCreate(savedInstanceState); setContentView(R.layout.listview2); } } As required by android, listview must have an ID which is exactly "@android:id/list". If I set the listview in both listview1 and listview2 with the same ID, then they will end up using the same format of listview, which is not what I want. But if I set one of the IDs to be sth like "@+id/listview2", android gave me the error: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list' How do I handle this dilema?

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• Error while installing dependencies for PyGTK on Mac OS 10.6.3

  - by Winston C. Yang

  I tried to install the following dependencies for PyGTK 2.16.0 (the Python GIMP Tool Kit) on Mac OS 10.6.3: glib 2.25.5 gettext-0.18 libiconv-1.13.1 When I tried to install glib, I got the following error message: gconvert.c:55:2: error: #error GNU libiconv not in use but included iconv.h is from libiconv The libiconv web page talks about a circular dependency between gettext and libiconv---build one, then build the other, then build the first again. I tried to do this, though possibly incorrectly. (Will the following work: make distclean; ./configure; make; sudo make install?) The author of a posting had the same problem, and he solved it by installing libiconv-1.13.1. Could anyone explain the error in more detail, and how to correct it?

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• What are logical and path queries

  - by NomeN

  I'm reading a paper which mentions that a language for refactoring has three specific requirements. functional features (like ML) logical queries (like Datalog) path queries (like Datalog) I know what they mean by functional features, but I'm not totally clear on the latter two and can't find a clear explanation either. Although I have a good idea after what I could find on the subjects, I need to be sure so here goes: Could the SO-community please clearly explain to me what logical queries and path queries are? Or at the very least what the people from the paper meant?

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• css absolute position won't work with margin-left:auto margin-right: auto

  - by user1118019

  Say you have the following css applied to a div tag .divtagABS { position: absolute; margin-left: auto; margin-right:auto; } the margin-left and margin-right does not take effect but if you have relative, it works fine i.e. ,divtagREL { position: relative; margin-left: auto; margin-right:auto; } why is that? i just want to center an element can someone explain why setting margins to auto in absolute position does not work?

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• EndpointNotFoundException when working through tutorials in Learning WCF

  - by Nicholas

  I am working through the book Learning WCF and on the first tutorial lab HelloIndigo I am receiving the following error. Could not connect to http://localhost:8000/HelloIndigo/HelloIndigoService. TCP error code 10061: No connection could be made because the target machine actively refused it 127.0.0.1:8000. It appears in the Client project on the line string s = proxy.HelloIndigo(); EndpointAddress ep = new EndpointAddress("http://localhost:8000/HelloIndigo/HelloIndigoService"); IHelloIndigoService proxy = ChannelFactory<IHelloIndigoService>. CreateChannel(new BasicHttpBinding(), ep); string s = proxy.HelloIndigo(); Console.WriteLine(s); Console.WriteLine("Press <ENTER> to terminate Client"); Console.ReadLine(); I have intensively googled on this but I am none the wiser. Can anyone explain the issue and how to remedy?

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• How do I use a shared library (in this case JsonCpp) in my C++ program on Linux?

  - by Not Joe Bloggs

  I'm a new-ish C++ programmer, and I'm doing my first program on my own using C++. I decided I would like to use JSON to store some of the data I'm going to be using, and I've found a library to handle JSON, JsonCpp. I've installed the library using my Linux system's package manager, and in my C++ code, I've used in my source code file #include <json> and compiled it using g++ and it's -ljson and -L/usr/lib options (libjson.so is located in /usr/lib). However, the first usage of Json::Value, an object provided by the library, gives a compilation error of "Json has not declared". I'm sure my mistake is something simple, so could someone explain what I'm doing wrong? None of the books I had mention how to use shared libraries, so I've had to google to find this much.

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• Using Dijkstra's algorithm with negative edges?

  - by Riddler

  Most books explain the reason the algorithm doesn't work with negative edges as nodes are deleted from the priority queue after the node is arrived at since the algorithm assumes the shortest distance has been found. However since negative edges can reduce the distance, a future shorter distance might be found; but since the node is deleted it cannot be updated. Wouldn't an obvious solution to this be to not delete the node? Why not keep the node in the queue, so if a future shorter distance is found, it can be updated? If I am misunderstanding the problem, what is preventing the algorithm from being used with negative edges?

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• Check if hydrated doctrine result is NULL

  - by iggnition

  Hi, I'm trying to check if a result in my DQL is NULL. I got the following DQL query: $q = self::createQuery("l") ->select('i.*, s.aantal, m.naam, c.cat_naam, a.app_id') ->from('InstalledBase i, i.Spare s, i.Apparaat a, a.Categorie c, a.Merk m') ->execute(); return $q; Now i want to check if the s.aantal is NULL so i do: if(is_null($installedbase->Spare->spare_id)) when the variable is NOT null everything works, but when it is actually NULL i get a E notice message: Notice: Trying to get property of non-object in \installedbase\templates\_index.php on line 29 It does see that it is null though because the if condition is executed. Weird thing is i'm doing the exact same thing on another page where it works no problem. But i must be doing something wrong or stupid since those messages generally don't show for nothing. So can anybody explain this to me? :)

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• Mac OS X bluetooth programming sample ?

  - by tuttu47

  Hi, I am trying to develop an application using bluetooth in my MAC mini. However, after searching all over net, all that I could find was the "Bluetooth Device Access Guide" from apple, and not a single sample program ! Is any sample code for this available ? I will also explain what I am trying to do in my program, so that if any of you can help me.... I want pair my iPhone with my MAC programmatically over the PAN profile, and then send data (streams) both-ways. I paired them manually, and I was successfully able to transfer data. I just want to do that programmatically ! Any help would be appreciated ...

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• How to use a DHT for a social trading environment

  - by Lirik

  I'm trying to understand if a DHT can be used to solve a problem I'm working on: I have a trading environment where professional option traders can get an increase in their risk limit by requesting that fellow traders lend them some of their risk limit. The lending trader will can either search for traders with certain risk parameters which are part of every trader's profile, i.e. Greeks, or the lending trader can subscribe to requests from certain traders. I want this environment to be scalable and decentralized, but I don't know how traders can search for specific profile parameters when the data is contained in a DHT. Could anybody explain how this can be done?

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