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• Practical size limitations for RDBMS

  - by grenade

  I am working on a project that must store very large datasets and associated reference data. I have never come across a project that required tables quite this large. I have proved that at least one development environment cannot cope at the database tier with the processing required by the complex queries against views that the application layer generates (views with multiple inner and outer joins, grouping, summing and averaging against tables with 90 million rows). The RDBMS that I have tested against is DB2 on AIX. The dev environment that failed was loaded with 1/20th of the volume that will be processed in production. I am assured that the production hardware is superior to the dev and staging hardware but I just don't believe that it will cope with the sheer volume of data and complexity of queries. Before the dev environment failed, it was taking in excess of 5 minutes to return a small dataset (several hundred rows) that was produced by a complex query (many joins, lots of grouping, summing and averaging) against the large tables. My gut feeling is that the db architecture must change so that the aggregations currently provided by the views are performed as part of an off-peak batch process. Now for my question. I am assured by people who claim to have experience of this sort of thing (which I do not) that my fears are unfounded. Are they? Can a modern RDBMS (SQL Server 2008, Oracle, DB2) cope with the volume and complexity I have described (given an appropriate amount of hardware) or are we in the realm of technologies like Google's BigTable? I'm hoping for answers from folks who have actually had to work with this sort of volume at a non-theoretical level.

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• Figuring out the Nyquist performance limitation of an ADC on an example PIC microcontroller

  - by AKE

  I'm spec-ing the suitability of a dsPIC microcontroller for an analog-to-digital application. This would be preferable to using dedicated A/D chips and a separate dedicated DSP chip. To do that, I've had to run through some computations, pulling the relevant parameters from the datasheets. I'm not sure I've got it right -- would appreciate a check! (EDITED NOTE: The PIC10F220 in the example below was selected ONLY to walk through a simple example to check that I'm interpreting Tacq, Fosc, TAD, and divisor correctly in working through this sort of Nyquist analysis. The actual chips I'm considering for the design are the dsPIC33FJ128MC804 (with 16b A/D) or dsPIC30F3014 (with 12b A/D).) A simple example: PIC10F220 is the simplest possible PIC with an ADC Runs at clock speed of 8MHz. Has an instruction cycle of 0.5us (4 clock steps per instruction) So: Taking Tacq = 6.06 us (acquisition time for ADC, assume chip temp. = 50*C) [datasheet p34] Taking Fosc = 8MHz (? clock speed) Taking divisor = 4 (4 clock steps per CPU instruction) This gives TAD = 0.5us (TAD = 1/(Fosc/divisor) ) Conversion time is 13*TAD [datasheet p31] This gives conversion time 6.5us ADC duration is then 12.56 us [? Tacq + 13*TAD] Assuming at least 2 instructions for load/store: This is another 1 us [0.5 us per instruction] Which would give max sampling rate of 73.7 ksps (1/13.56) Supposing 8 more instructions for real-time processing: This is another 4 us Thus, total ADC/handling time = 17.56us (12.56us + 1us + 4us) So expected upper sampling rate is 56.9 ksps. Nyquist frequency for this sampling rate is therefore 28 kHz. If this is right, it suggests the (theoretical) performance suitability of this chip's A/D is for signals that are bandlimited to 28 kHz. Is this a correct interpretation of the information given in the data sheet in obtaining the Nyquist performance limit? Any opinions on the noise susceptibility of ADCs in PIC / dsPIC chips would be much appreciated! AKE

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• Is There a Time at which to ignore IDisposable.Dispose?

  - by Mystagogue

  Certainly we should call Dipose() on IDisposable objects as soon as we don't need them (which is often merely the scope of a "using" statement). If we don't take that precaution then bad things, from subtle to show-stopping, might happen. But what about "the last moment" before process termination? If your IDisposables have not been explicitly disposed by that point in time, isn't it true that it no longer matters? I ask because unmanaged resources, beneath the CLR, are represented by kernel objects - and the win32 process termination will free all unmanaged resources / kernel objects anyway. Said differently, no resources will remain "leaked" after the process terminates (regardless if Dispose() was called on lingering IDisposables). Can anyone think of a case where process termination would still leave a leaked resource, simply because Dispose() was not explicitly called on one or more IDisposables? Please do not misunderstand this question: I am not trying to justify ignoring IDisposables. The question is just technical-theoretical. EDIT: And what about mono running on Linux? Is process termination there just as "reliable" at cleaning up unmanaged "leaks?"

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• SAP related testing

  - by mgj

  Dear all, One notion that has been prevalent mostly as rumours for many aspiring programmers is that the testing phase of the SDLC(Software Development Life Cycle) is not that challenging and interesting as one's job as a tester after a period of time becomes monotonous because a person does the same thing repeatedly over and over again. Thats why many have this complexion of looking for a developers job rather than that of testers. Don't testers have a space for themselves in software companies to grow..? Please feel free to express your views for or against this. How true is that, could you please give e.g.'s of instances( need not be practical, even theoretical would suffice) which actually contradict this statement wrt a tester's career specifically wrt the SAP domain. E.g.'s from other domains are also welcome. This question is not meant to hurt someone's feelings who is in the testing domain. Its just that for e.g. in my case I want to know what actually would be the challenge's a tester could also face in real life situations.Something that would make their job also interesting and fun-filled. I myself am pro-testing and also interested in pursuing testing as a profession in a sw co, just curious to know more about it so...:) Thanks..:)

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• Is my heuristic algorithm correct? (Sudoku solver)

  - by Aposperite

  First of -yes this IS a homework- but it's primarily a theoretical question rather than a practical one, I am simply asking a confirmation if I am thinking correctly or any hints if I am not. I have been asked to compile a simple Sudoku solver (on Prolog but that is not so important right now) with the only limitation being that it must utilize a heuristic function using Best-First Algorithm. The only heuristic function I have been able to come up with is explained below: 1. Select an empty cell. 1a. If there are no empty cells and there is a solution return solution. Else return No. 2. Find all possible values it can hold. %% It can't take values currently assigned to cells on the same line/column/box. 3. Set to all those values a heuristic number starting from 1. 4. Pick the value whose heuristic number is the lowest && you haven't checked yet. 4a. If there are no more values return no. 5. If a solution is not found: GoTo 1. Else Return Solution. // I am sorry for errors in this "pseudo code." If you want any clarification let me know. So am I doing this right or is there any other way around and mine is false? Thanks in advance.

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• Why not use tables for layout in HTML?

  - by Bno

  It seems to be the general opinion that tables should not be used for layout in HTML. Why? I have never (or rarely to be honest) seen good arguments for this. The usual answers are: It's good to separate content from layoutBut this is a fallacious argument; Cliche Thinking. I guess it's true that using the table element for layout has little to do with tabular data. So what? Does my boss care? Do my users care?Perhaps me or my fellow developers who have to maintain a web page care... Is a table less maintainable? I think using a table is easier than using divs and CSS.By the way... why is using a div or a span good separation of content from layout and a table not? Getting a good layout with only divs often requires a lot of nested divs. Readability of the codeI think it's the other way around. Most people understand html, few understand CSS. It's better for SEO not to use tablesWhy? Can anybody show some evidence that it is? Or a statement from Google that tables are discouraged from an SEO perspective? Tables are slower.An extra tbody element has to be inserted. This is peanuts for modern web browsers. Show me some benchmarks where the use of a table significantly slows down a page. A layout overhaul is easier without tables, see css Zen Garden.Most web sites that need an upgrade need new content (html) as well. Scenarios where a new version of a web site only needs a new CSS file are not very likely. Zen Garden is a nice web site, but a bit theoretical. Not to mention its misuse of CSS. I am really interested in good arguments to use divs + CSS instead of tables.

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• Embedding Lua functions as member variables in Java

  - by Zarion

  Although the program I'm working on is in Java, answering this from a C perspective is also fine, considering that most of this is either language-agnostic, or happens on the Lua side of things. In the outline I have for the architecture of a game I'm programming, individual types of game objects within a particular class (eg: creatures, items, spells, etc.) are loaded from a data file. Most of their properties are simple data types, but I'd like a few of these members to actually contain simple scripts that define, for example, what an item does when it's used. The scripts will be extremely simple, since all fundamental game actions will be exposed through an API from Java. The Lua is simply responsible for stringing a couple of these basic functions together, and setting arguments. The question is largely about the best way to store a reference to a specific Lua function as a member of a Java class. I understand that if I store the Lua code as a string and call lua_dostring, Lua will compile the code fresh every time it's called. So the function needs to be defined somehow, and a reference to this specific function wrapped in a Java function object. One possibility that I've considered is, during the data loading process, when the loader encounters a script definition in a data file, it extracts this string, decorates the function name using the associated object's unique ID, calls lua_dostring on the string containing a full function definition, and then wraps the generated function name in a Java function object. A function declared in script run with lua_dostring should still be added to the global function table, correct? I'm just wondering if there's a better way of going about this. I admit that my knowledge of Lua at this point is rather superficial and theoretical, so it's possible that I'm overlooking something obvious.

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• Use an Array to Cycle Through a MySQL Where Statement

  - by Ryan

  I'm trying to create a loop that will output multiple where statements for a MySQL query. Ultimately, my goal is to end up with these four separate Where statements: `fruit` = '1' AND `vegetables` = '1' `fruit` = '1' AND `vegetables` = '2' `fruit` = '2' AND `vegetables` = '1' `fruit` = '2' AND `vegetables` = '2' My theoretical code is pasted below: <?php $columnnames = array('fruit','vegetables'); $column1 = array('1','2'); $column2 = array('1','2'); $where = ''; $column1inc =0; $column2inc =0; while( $column1inc <= count($column1) ) { if( !empty( $where ) ) $where .= ' AND '; $where = "`".$columnnames[0]."` = "; $where .= "'".$column1[$column1inc]."'"; while( $column2inc <= count($column2) ) { if( !empty( $where ) ) $where .= ' AND '; $where .= "`".$columnnames[1]."` = "; $where .= "'".$column2[$column2inc]."'"; echo $where."\n"; $column2inc++; } $column1inc++; } ?> When I run this code, I get the following output: `fruit` = '1' AND `vegetables` = '1' `fruit` = '1' AND `vegetables` = '1' AND `vegetables` = '2' `fruit` = '1' AND `vegetables` = '1' AND `vegetables` = '2' AND `vegetables` = '' Does anyone see what I am doing incorrectly? Thanks.

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• Can you have a Dynamic Data Field which consists of a list of fields?

  - by Telos

  This is a purely theoretical question (at least until I start trying to implement it) but here goes. I wrote a web form a long time ago which has a configurable section for getting information. Basically for some customers there are no fields, for other customers there are up to 20 fields. I got it working by dynamically creating the fields at just the right time in the page lifecycle and going through a lot of headaches. 2 years later, I need to make some pretty big updates to this web form and there are some nifty new technologies. I've worked with ASP.NET Dynamic Data just a bit and, well, I half-crazed plan just occurred to me: The Ticket object has a one-to-many relationship to ExtendedField, we'll call that relationship Fields for brevity. Using that, the idea would be to create a FieldTemplate that dynamically generated the list of fields and displayed it. The big questions here would probably be: 1) Can a single field template resolve to multiple web controls without breaking things? 2) Can dynamic data handle updating/inserting multiple rows in such a fashion? 3) There was a third question I had a few minutes ago, but coworkers interrupted me and I forgot. So now the third question is: what is the third question? So basically, does this sound like it could work or am I missing a better/more obvious solution?

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• Combining cache methods - memcache/disk based

  - by Industrial

  Hi! Here's the deal. We would have taken the complete static html road to solve performance issues, but since the site will be partially dynamic, this won't work out for us. What we have thought of instead is using memcache + eAccelerator to speed up PHP and take care of caching for the most used data. Here's our two approaches that we have thought of right now: Using memcache on all<< major queries and leaving it alone to do what it does best. Usinc memcache for most commonly retrieved data, and combining with a standard harddrive-stored cache for further usage. The major advantage of only using memcache is of course the performance, but as users increases, the memory usage gets heavy. Combining the two sounds like a more natural approach to us, even though the theoretical compromize in performance. Memcached appears to have some replication features available as well, which may come handy when it's time to increase the nodes. What approach should we use? - Is it stupid to compromize and combine the two methods? Should we insted be focusing on utilizing memcache and instead focusing on upgrading the memory as the load increases with the number of users? Thanks a lot!

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• Using memory-based cache together with conventional cache

  - by Industrial

  Hi! Here's the deal. We would have taken the complete static html road to solve performance issues, but since the site will be partially dynamic, this won't work out for us. What we have thought of instead is using memcache + eAccelerator to speed up PHP and take care of caching for the most used data. Here's our two approaches that we have thought of right now: Using memcache on all<< major queries and leaving it alone to do what it does best. Usinc memcache for most commonly retrieved data, and combining with a standard harddrive-stored cache for further usage. The major advantage of only using memcache is of course the performance, but as users increases, the memory usage gets heavy. Combining the two sounds like a more natural approach to us, even though the theoretical compromize in performance. Memcached appears to have some replication features available as well, which may come handy when it's time to increase the nodes. What approach should we use? - Is it stupid to compromize and combine the two methods? Should we insted be focusing on utilizing memcache and instead focusing on upgrading the memory as the load increases with the number of users? Thanks a lot!

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• C89, Mixing Variable Declarations and Code

  - by rutski

  I'm very curious to know why exactly C89 compilers will dump on you when you try to mix variable declarations and code, like this for example: rutski@imac:~$ cat test.c #include <stdio.h> int main(void) { printf("Hello World!\n"); int x = 7; printf("%d!\n", x); return 0; } rutski@imac:~$ gcc -std=c89 -pedantic test.c test.c: In function ‘main’: test.c:7: warning: ISO C90 forbids mixed declarations and code rutski@imac:~$ Yes, you can avoid this sort of thing by staying away from -pedantic. But then your code is no longer standards compliant. And as anybody capable of answering this post probably already knows, this is not just a theoretical concern. Platforms like Microsoft's C compiler enforce this quick in the standard under any and all circumstances. Given how ancient C is, I would imagine that this feature is due to some historical issue dating back to the extraordinary hardware limitations of the 70's, but I don't know the details. Or am I totally wrong there?

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• Why are symbols not frozen strings?

  - by Alex Chaffee

  I understand the theoretical difference between Strings and Symbols. I understand that Symbols are meant to represent a concept or a name or an identifier or a label or a key, and Strings are a bag of characters. I understand that Strings are mutable and transient, where Symbols are immutable and permanent. I even like how Symbols look different from Strings in my text editor. What bothers me is that practically speaking, Symbols are so similar to Strings that the fact that they're not implemented as Strings causes a lot of headaches. They don't even support duck-typing or implicit coercion, unlike the other famous "the same but different" couple, Float and Fixnum. The mere existence of HashWithIndifferentAccess, and its rampant use in Rails and other frameworks, demonstrates that there's a problem here, an itch that needs to be scratched. Can anyone tell me a practical reason why Symbols should not be frozen Strings? Other than "because that's how it's always been done" (historical) or "because symbols are not strings" (begging the question). Consider the following astonishing behavior: :apple == "apple" #=> false, should be true :apple.hash == "apple".hash #=> false, should be true {apples: 10}["apples"] #=> nil, should be 10 {"apples" => 10}[:apples] #=> nil, should be 10 :apple.object_id == "apple".object_id #=> false, but that's actually fine All it would take to make the next generation of Rubyists less confused is this: class Symbol < String def initialize *args super self.freeze end (and a lot of other library-level hacking, but still, not too complicated) See also: http://onestepback.org/index.cgi/Tech/Ruby/SymbolsAreNotImmutableStrings.red http://www.randomhacks.net/articles/2007/01/20/13-ways-of-looking-at-a-ruby-symbol Why does my code break when using a hash symbol, instead of a hash string? Why use symbols as hash keys in Ruby? What are symbols and how do we use them? Ruby Symbols vs Strings in Hashes Can't get the hang of symbols in Ruby

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• Using memcache together with conventional cache

  - by Industrial

  Hi! Here's the deal. We would have taken the complete static html road to solve performance issues, but since the site will be partially dynamic, this won't work out for us. What we have thought of instead is using memcache + eAccelerator to speed up PHP and take care of caching for the most used data. Here's our two approaches that we have thought of right now: Using memcache on all<< major queries and leaving it alone to do what it does best. Usinc memcache for most commonly retrieved data, and combining with a standard harddrive-stored cache for further usage. The major advantage of only using memcache is of course the performance, but as users increases, the memory usage gets heavy. Combining the two sounds like a more natural approach to us, even though the theoretical compromize in performance. Memcached appears to have some replication features available as well, which may come handy when it's time to increase the nodes. What approach should we use? - Is it stupid to compromize and combine the two methods? Should we insted be focusing on utilizing memcache and instead focusing on upgrading the memory as the load increases with the number of users? Thanks a lot!

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• Detecting an online poker cheat

  - by Tom Gullen

  It recently emerged on a large poker site that some players were possibly able to see all opponents cards as they played through exploiting a security vulnerability that was discovered. A naïve cheater would win at an incredibly fast rate, and these cheats are caught very quickly usually, and if not caught quickly they are easy to detect through a quick scan through their hand histories. The more difficult problem occurs when the cheater exhibits intelligence, bluffing in spots they are bound to be called in, calling river bets with the worst hands, the basic premise is that they lose pots on purpose to disguise their ability to see other players cards, and they win at a reasonably realistic rate. Given: A data set of millions of verified and complete information hand histories Theoretical unlimited computer power Assume the game No Limit Hold'em, although suggestions on Omaha or limit poker may be beneficial How could we reasonably accurately classify these cheaters? The original 2+2 thread appeals for ideas, and I thought that the SO community might have some useful suggestions. It's an interesting problem also because it is current, and has real application in bettering the world if someone finds a creative solution, as there is a good chance genuine players will have funds refunded to them when identified cheaters are discovered.

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• Need Help finding an appropriate task asignment algoritm for a collage project involving coordinatin

  - by Trif Mircea

  Hello. I am a long time lurker here and have found over time many answers regarding jquery and web development topics so I decided to ask a question of my own. This time I have to create a c++ project for collage which should help manage the workflow of a company providing all kinds of services through in the field teams. The ideas I have so far are: client-server application; the server is a dispatcher where all the orders from clients get and the clients are mobile devices (PDAs) each team in the field having one a order from a client is a task. Each task is made up of a series of subtasks. You have a database with estimations on how long a task should take to complete you also know what tasks or subtasks each team on the field can perform based on what kind of specialists made up the team (not going to complicate the problem by adding needed materials, it is considered that if a member of a team can perform a subtask he has the stuff needed) Now knowing these factors, what would a good task assignment algorithm be? The criteria is: how many tasks can a team do, how many tasks they have in the queue, it could also be location, how far away are they from the place but I don't think I can implement that.. It needs to be efficient and also to adapt quickly is the human dispatcher manually assigns a task. Any help or leads would be really appreciated. Also I'm not 100% sure in the idea so if you have another way you would go about creating such an application please share, even if it just a quick outline. I have to write a theoretical part too so even if the ideas are far more complex that what i outlined that would be ok ; I'd write those and implement what I can.

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• Improve Log Exceptions

  - by Jaider

  I am planning to use log4net in a new web project. In my experience, I see how big the log table can get, also I notice that errors or exceptions are repeated. For instance, I just query a log table that have more than 132.000 records, and I using distinct and found that only 2.500 records are unique (~2%), the others (~98%) are just duplicates. so, I came up with this idea to improve logging. Having a couple of new columns: counter and updated_dt, that are updated every time try to insert same record. If want to track the user that cause the exception, need to create a user_log or log_user table, to map N-N relationship. Create this model may made the system slow and inefficient trying to compare all these long text... Here the trick, we should also has a hash column of binary of 16 or 32, that hash the message and the exception, and configure an index on it. We can use HASHBYTES to help us. I am not an expert in DB, but I think that will made the faster way to locate a similar record. And because hashing doesn't guarantee uniqueness, will help to locale those similar record much faster and later compare by message or exception directly to make sure that are unique. This is a theoretical/practical solution, but will it work or bring more complexity? what aspects I am leaving out or what other considerations need to have? the trigger will do the job of insert or update, but is the trigger the best way to do it?

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• Is the Java classpath final after JVM startup?

  - by Jens

  Hi, I have read a lot about the Java class loading process lately. Often I came across texts that claimed that it is not possible to add classes to the classpath during runtime and load them without class loader hackery (URLClassLoaders etc.) As far as I know classes are loaded dynamically. That means their bytecode representation is only loaded and transformed to a java.lang.Class object when needed. So shouldn't it be possible to add a JAR or *.class file to the classpath after the JVM started and load those classes, provided they haven't been loaded yet? (To be clear: In this case the classpath is simple folder on the filesystem. "Adding a JAR or *.class file" simply means dropping them in this folder.) And if not, does that mean that the classpath is searched on JVM startup and all fully qualified names of the found classes are cached in an internal "list"? It would be nice of you if you could point me to some sources in your answers. Preferably the offical SUN documentation: Sun JVM Spec. I have read the spec but could not find anything about the classpath and if it's finalized on JVM startup. P.s. This is a theoretical question. I just want to know if it is possible. There is nothing practical I want to achieve. There is just my thirst for knowledge :)

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• Is there a good way to copy a Gtk widget?

  - by Jake

  Is there a way, using the Gtk library in C, to clone a Gtk button (for instance), and pack it somewhere else in the app. I know you can't pack the same widget twice. And that this code obviously wouldn't work, but shows what happens when I attempt a shallow copy of the button: GtkButton *a = g_object_new(GTK_TYPE_BUTTON, "label", "o_0", NULL); GtkButton *b = g_memdup(b, sizeof *b); gtk_box_pack_start_defaults(GTK_BOX(vbox), GTK_WIDGET(b)); There is surrounding code which creates a vbox and packs it in a window and runs gtk_main(). This will result in these hard to understand error messages: (main:6044): Gtk-CRITICAL **: gtk_widget_hide: assertion `GTK_IS_WIDGET (widget)' failed (main:6044): Gtk-CRITICAL **: gtk_widget_realize: assertion `GTK_WIDGET_ANCHORED (widget) || GTK_IS_INVISIBLE (widget)' failed ** Gtk:ERROR:/build/buildd/gtk+2.0-2.18.3/gtk/gtkwidget.c:8431:gtk_widget_real_map: assertion failed: (GTK_WIDGET_REALIZED (widget)) Along the same lines, if I were to write my own GObject (not necessarily a Gtk widget), is there a good way to write a copy constructor. Im thinking it should be an interface with optional hooks and based mostly on the properties, handling the class's hierarchy in some way. I'd want to do this: GtkButton *b = copyable_copy(COPYABLE(a)); If GtkButton could use a theoretical copyable interface.

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• How can I perform this query between related tables without using UNION?

  - by jeremy

  Suppose I have two separate tables that I watch to query. Both of these tables has a relation with a third table. How can I query both tables with a single, non UNION based query? I want the result of the search to rank the results by comparing a field on each table. Here's a theoretical example. I have a User table. That User can have both CDs and books. I want to find all of that user's books and CDs with a single query matching a string ("awesome" in this example). A UNION based query might look like this: SELECT "book" AS model, name, ranking FROM book WHERE name LIKE 'Awesome%' UNION SELECT "cd" AS model, name, ranking FROM cd WHERE name LIKE 'Awesome%' ORDER BY ranking DESC How can I perform a query like this without the UNION? If I do a simple left join from User to Books and CDs, we end up with a total number of results equal to the number of matching cds timse the number of matching books. Is there a GROUP BY or some other way of writing the query to fix this?

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• List of Big-O for PHP functions?

  - by Kendall Hopkins

  After using PHP for a while now, I've noticed that not all PHP built in functions as fast as expected. Consider the below two possible implementations of a function that finds if a number is prime using a cached array of primes. //very slow for large $prime_array $prime_array = array( 2, 3, 5, 7, 11, 13, .... 104729, ... ); $result_array = array(); foreach( $array_of_number => $number ) { $result_array[$number] = in_array( $number, $large_prime_array ); } //still decent performance for large $prime_array $prime_array => array( 2 => NULL, 3 => NULL, 5 => NULL, 7 => NULL, 11 => NULL, 13 => NULL, .... 104729 => NULL, ... ); foreach( $array_of_number => $number ) { $result_array[$number] = array_key_exists( $number, $large_prime_array ); } This is because in_array is implemented with a linear search O(n) which will linearly slow down as $prime_array grows. Where the array_key_exists function is implemented with a hash lookup O(1) which will not slow down unless the hash table gets extremely populated (in which case it's only O(logn)). So far I've had to discover the big-O's via trial and error, and occasionally looking at the source code. Now for the question... I was wondering if there was a list of the theoretical (or practical) big O times for all* the PHP built in functions. *or at least the interesting ones For example find it very hard to predict what the big O of functions listed because the possible implementation depends on unknown core data structures of PHP: array_merge, array_merge_recursive, array_reverse, array_intersect, array_combine, str_replace (with array inputs), etc.

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• barebones sort algorithm

  - by user309322

  i have been asked to make a simple sort aglorithm to sort a random series of 6 numbers into numerical order. However i have been asked to do this using "Barebones" a theoretical language put forward in the Book Computer Science an overview. Some information on the language can be found here http://www.brouhaha.com/~eric/software/barebones/ Just to clarify i am a student teacher and have been doing anaysis on "mini-programing languages" and their uses in a teaching environment, i suggested to my tutor that i look at barebones and asked what sort of exmaple program i should write . He suggested a simple sort algorithm. Now since looking at the language i cant understand how i can do this without using arrays and if statements. The code to swap the value of variables would be while a not 0 do; incr Aux1; decr a; end; while b not 0 do; incr Aux2 decr b end; while Aux1 not 0 do; incr a; decr Aux1; end; while Aux2 not 0 do; incr b; decr Aux2; end; however the language does not provide < or operators

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• How to exclude rows where matching join is in an SQL tree

  - by Greg K

  Sorry for the poor title, I couldn't think how to concisely describe this problem. I have a set of items that should have a 1-to-1 relationship with an attribute. I have a query to return those rows where the data is wrong and this relationship has been broken (1-to-many). I'm gathering these rows to fix them and restore this 1-to-1 relationship. This is a theoretical simplification of my actual problem but I'll post example table schema here as it was requested. item table: +------------+------------+-----------+ | item_id | name | attr_id | +------------+------------+-----------+ | 1 | BMW 320d | 20 | | 1 | BMW 320d | 21 | | 2 | BMW 335i | 23 | | 2 | BMW 335i | 34 | +------------+------------+-----------+ attribute table: +---------+-----------------+------------+ | attr_id | value | parent_id | +---------+-----------------+------------+ | 20 | SE | 21 | | 21 | M Sport | 0 | | 23 | AC | 24 | | 24 | Climate control | 0 | .... | 34 | Leather seats | 0 | +---------+-----------------+------------+ A simple query to return items with more than one attribute. SELECT item_id, COUNT(DISTINCT(attr_id)) AS attributes FROM item GROUP BY item_id HAVING attributes > 1 This gets me a result set like so: +-----------+------------+ | item_id | attributes | +-----------+------------+ | 1 | 2 | | 2 | 2 | | 3 | 2 | -- etc. -- However, there's an exception. The attribute table can hold a tree structure, via parent links in the table. For certain rows, parent_id can hold the ID of another attribute. There's only one level to this tree. Example: +---------+-----------------+------------+ | attr_id | value | parent_id | +---------+-----------------+------------+ | 20 | SE | 21 | | 21 | M Sport | 0 | .... I do not want to retrieve items in my original query where, for a pair of associated attributes, they related like attributes 20 & 21. I do want to retrieve items where: the attributes have no parent for two or more attributes they are not related (e.g. attributes 23 & 34) Example result desired, just the item ID: +------------+ | item_id | +------------+ | 2 | +------------+ How can I join against attributes from items and exclude these rows? Do I use a temporary table or can I achieve this from a single query? Thanks.

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• iPhone Development - calling external JSON API (will Apple reject?)

  - by RPM1984

  Ok guys, so im new to iPhone development, so apologies if this is a silly question, but before i actually create my app i want to know if this is possible, and if Apple will reject this. (Note this is all theoretical) So i'd have a API (.NET) that runs on a cloud server somewhere and can return HTML/JSON/XML. I'll have a website that can access this API and allow customers to do some stuff (but this is not important for this question). I would then like my iPhone app to make a call to this API which would return JSON data. So my iPhone app might make a call to http://myapp/Foos which would return a JSON string of Foo objects. The iPhone app would then parse this JSON and do some funky stuff with it. So, that's the background, now the questions: Is this possible? (that is, call an external cloud API over HTTP, parse JSON response?) What are the chances of Apple rejecting this application (because it would be calling a non-Apple API) Are there any limitations (security, libraries, etc) on the iPhone/Objective-C/Cocoa that might hinder this solution? On this website, they seem to be doing exactly what im asking. Thoughts, suggestions, links would be greatly appreciated...

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• Finding What You Need in R: function arguments/parameters from outside the function's package

  - by doug

  Often in R, there are a dozen functions scattered across as many packages--all of which have the same purpose but of course differ in accuracy, performance, theoretical rigor, and so on. How do you gather all of these in one place before you start your task? So for instance: the generic plot function. Setting secondary ticks is much easier (IMHO) using a function outside of the base package, minor.tick(nx=n, ny=n, tick.ratio=n), found in Hmisc. Of course, that doesn't show up in plot's docstring. Likewise, the data-input arguments to 'plot' can be supplied by an object returned from the function 'hexbin', again, from a library outside of the base installation (where 'plot' resides). What would be great obviously is a programmatic way to gather these function arguments from the various libraries and put them in a single namespace. edit: (trying to re-state my example just above more clearly:) the arguments to plot supplied in the base package for, e.g., setting the axis tick frequency are xaxp/yaxp; however, one can also set a/t/f via a function outside of the base package, again, as in the minor.tick function from the Hmisc package--but you wouldn't know that just from looking at the plot method signature. Is there a meta function in R for this? So far, as i come across them, i've been manually gathering them in a TextMate 'snippet' (along with the attendant library imports). This isn't that difficult or time consuming, but i can only update my snippet as i find out about these additional arguments/parameters. Is there a canonical R way to do this, or at least an easier way? Just in case that wasn't clear, i am not talking about the case where multiple packages provide functions directed to the same statistic or view (e.g., 'boxplot' in the base package; 'boxplot.matrix' in gplots; and 'bplots' in Rlab). What i am talking is the case in which the function name is the same across two or more packages.

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