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• Python, Ruby, and C#: Use cases?

  - by thaorius

  Hi everyone. For as long as I can remember, I've always had a "favorite" language, which I use for most projects, until, for some particular reason, there is no way/point on using it for project XYZ. At that point, I find myself rusty (and sometimes outdated) on other languages+libraries+toolchains. So I decided, I would just use some languages/libs/tools for some things, and some for other, effectively keeping them fresh (there would obviously be exceptions, I'm not looking for an arbitrary rule set, but some guidelines). I wanted an opinion on what would be your standard use cases (new projects) for Python, Ruby, and C# (Mono). At the moment, I have time like this:Languages: C#: Mid-Large Sized Projects (mainly server-side daemons) High Performance (I hardly ever need C's performance, but Python just doesn't cut it) Relatively Low Footprint (vs the JVM, for example) Ruby: Web Applications Python: General Use Scripts (automation, system config, etc) Small-Mid Sized Projects Prototyping Web Applications About Ruby, I have no idea what to use it for that I can't use Python for (specially considering Python is more easily found installed by default). And I like both languages (though I'm really new to Ruby), which makes things even worse. As for C#, I have not used a Windows powered computer in a few years, I don't make things for Windows computers, and I don't mind waiting for Mono to implement some new features. That being said, I haven't found many people on the internet using it for server-sided *nix programming (not web related). I would appreciate some insight on this too. Thanks for your time.

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• How to retrieve view of MultiIndex DataFrame

  - by Henry S. Harrison

  This question was inspired by this question. I had the same problem, updating a MultiIndex DataFrame by selection. The drop_level=False solution in Pandas 0.13 will allow me to achieve the same result, but I am still wondering why I cannot get a view from the MultiIndex DataFrame. In other words, why does this not work?: >>> sat = d.xs('sat', level='day', copy=False) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python27\lib\site-packages\pandas\core\frame.py", line 2248, in xs raise ValueError('Cannot retrieve view (copy=False)') ValueError: Cannot retrieve view (copy=False) Of course it could be only because it is not implemented, but is there a reason? Is it somehow ambiguous or impossible to implement? Returning a view is more intuitive to me than returning a copy then later updating the original. I looked through the source and it seems this situation is checked explicitly to raise an error. Alternatively, is it possible to get the same sort of view from any of the other indexing methods? I've experimented but have not been successful. [edit] Some potential implementations are discussed here. I guess with the last question above I'm wondering what the current best solution is to index into arbitrary multiindex slices and cross-sections.

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• PHP arrays - How to 1-dimensional array into nested multidimensional array?

  - by sombe

  When retrieving a hierarchical structure from MySQL (table with one ID column and one PARENT column signifying the hierarchical relationships), I map the result into an enumerated array as follows (for this example the numbers are arbitrary): Array ( [3] => Array ( [7] => Array () ), [7] => Array ( [8] => Array () ) ) Notice 3 is the parent of 7, and 7 is the parent of 8 (this could go on and on; and any parent could have multiple children). I wanted to shrink this array into a nested multidimensional array as follows: Array ( [3] => Array ( [7] => Array ( [8] => Array () ) ) ) That is, each NEW id is automatically assigned an empty array. Regardless, any ID's children will be pushed into their parent's array. Take a look at the following illustration for further clarification: This will probably result in a complicated recursive operation, since I always have to check whether a parent with any certain ID already exists (and if so, push the value into its array). Is there a built-in php function that can assist me with this? Do you have any idea as to how to go about constructing this? For what it's worth I'm using this to built a navigation bar in wordpress (which can contain categories, subcategories, posts... essentially anything).

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• What makes people think that NNs have more computational power than existing models?

  - by Bubba88

  I've read in Wikipedia that neural-network functions defined on a field of arbitrary real/rational numbers (along with algorithmic schemas, and the speculative `transrecursive' models) have more computational power than the computers we use today. Of course it was a page of russian wikipedia (ru.wikipedia.org) and that may be not properly proven, but that's not the only source of such.. rumors Now, the thing that I really do not understand is: How can a string-rewriting machine (NNs are exactly string-rewriting machines just as Turing machines are; only programming language is different) be more powerful than a universally capable U-machine? Yes, the descriptive instrument is really different, but the fact is that any function of such class can be (easily or not) turned to be a legal Turing-machine. Am I wrong? Do I miss something important? What is the cause of people saying that? I do know that the fenomenum of undecidability is widely accepted today (though not consistently proven according to what I've read), but I do not really see a smallest chance of NNs being able to solve that particular problem. Add-in: Not consistently proven according to what I've read - I meant that you might want to take a look at A. Zenkin's (russian mathematician) papers after mid-90-s where he persuasively postulates the wrongness of G. Cantor's concepts, including transfinite sets, uncountable sets, diagonalization method (method used in the proof of undecidability by Turing) and maybe others. Even Goedel's incompletness theorems were proven in right way in only 21-st century.. That's all just to plug Zenkin's work to the post cause I don't know how widespread that knowledge is in CS community so forgive me if that did look stupid. Thank you!

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• What algorithms compute directions from point A to point B on a map?

  - by A. Rex

  How do map providers (such as Google or Yahoo! Maps) suggest directions? I mean, they probably have real-world data in some form, certainly including distances but also perhaps things like driving speeds, presence of sidewalks, train schedules, etc. But suppose the data were in a simpler format, say a very large directed graph with edge weights reflecting distances. I want to be able to quickly compute directions from one arbitrary point to another. Sometimes these points will be close together (within one city) while sometimes they will be far apart (cross-country). Graph algorithms like Dijkstra's algorithm will not work because the graph is enormous. Luckily, heuristic algorithms like A* will probably work. However, our data is very structured, and perhaps some kind of tiered approach might work? (For example, store precomputed directions between certain "key" points far apart, as well as some local directions. Then directions for two far-away points will involve local directions to a key points, global directions to another key point, and then local directions again.) What algorithms are actually used in practice? PS. This question was motivated by finding quirks in online mapping directions. Contrary to the triangle inequality, sometimes Google Maps thinks that X-Z takes longer and is farther than using an intermediate point as in X-Y-Z. But maybe their walking directions optimize for another parameter, too? PPS. Here's another violation of the triangle inequality that suggests (to me) that they use some kind of tiered approach: X-Z versus X-Y-Z. The former seems to use prominent Boulevard de Sebastopol even though it's slightly out of the way. (Edit: this example doesn't work anymore, but did at the time of the original post. The one above still works as of early November 2009.)

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• Hashing the state of a complex object in .NET

  - by Jan

  Some background information: I am working on a C#/WPF application, which basically is about creating, editing, saving and loading some data model. The data model contains of a hierarchy of various objects. There is a "root" object of class A, which has a list of objects of class B, which each has a list of objects of class C, etc. Around 30 classes involved in total. Now my problem is that I want to prompt the user with the usual "you have unsaved changes, save?" dialog, if he tries to exit the program. But how do I know if the data in current loaded model is actually changed? There is of course ways to solve this, like e.g. reloading the model from file and compare against the one in memory value by value or make every UI control set a flag indicating the model has been changed. Now instead, I want to create a hash value based on the model state on load and generate a new value when the user tries to exit, and compare those two. Now the question: So inspired of that, I was wondering if there exist some way to generate a hash value from the (value)state of some arbitrary complex object? Preferably in a generic way, e.g. no need to apply attributes to each involved class/field. One idea could be to use some of .NET's serialization functionality (assuming it will work out-of-the-box in this case) and apply a hash function to the content of the resulting file. However, I guess there exist some more suitable approach. Thanks in advance.

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• Performance difference in for loop condition?

  - by CSharperWithJava

  Hello all, I have a simple question that I am posing mostly for my curiousity. What are the differences between these two lines of code? (in C++) for(int i = 0; i < N, N > 0; i++) for(int i = 0; i < N && N > 0; i++) The selection of the conditions is completely arbitrary, I'm just interested in the differences between , and &&. I'm not a beginner to coding by any means, but I've never bothered with the comma operator. Are there performance/behavior differences or is it purely aesthetic? One last note, I know there are bigger performance fish to fry than a conditional operator, but I'm just curious. Indulge me. Edit Thanks for your answers. It turns out the code that prompted this question had misused the comma operator in the way I've described. I wondered what the difference was and why it wasn't a && operator, but it was just written incorrectly. I didn't think anything was wrong with it because it worked just fine. Thanks for straightening me out.

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• Why can't decimal numbers be represented exactly in binary?

  - by Barry Brown

  There have been several questions posted to SO about floating-point representation. For example, the decimal number 0.1 doesn't have an exact binary representation, so it's dangerous to use the == operator to compare it to another floating-point number. I understand the principles behind floating-point representation. What I don't understand is why, from a mathematical perspective, are the numbers to the right of the decimal point any more "special" that the ones to the left? For example, the number 61.0 has an exact binary representation because the integral portion of any number is always exact. But the number 6.10 is not exact. All I did was move the decimal one place and suddenly I've gone from Exactopia to Inexactville. Mathematically, there should be no intrinsic difference between the two numbers -- they're just numbers. By contrast, if I move the decimal one place in the other direction to produce the number 610, I'm still in Exactopia. I can keep going in that direction (6100, 610000000, 610000000000000) and they're still exact, exact, exact. But as soon as the decimal crosses some threshold, the numbers are no longer exact. What's going on? Edit: to clarify, I want to stay away from discussion about industry-standard representations, such as IEEE, and stick with what I believe is the mathematically "pure" way. In base 10, the positional values are: ... 1000 100 10 1 1/10 1/100 ... In binary, they would be: ... 8 4 2 1 1/2 1/4 1/8 ... There are also no arbitrary limits placed on these numbers. The positions increase indefinitely to the left and to the right.

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• Number of simple mutations to change one string to another?

  - by mstksg

  Hi; I'm sure you've all heard of the "Word game", where you try to change one word to another by changing one letter at a time, and only going through valid English words. I'm trying to implement an A* Algorithm to solve it (just to flesh out my understanding of A*) and one of the things that is needed is a minimum-distance heuristic. That is, the minimum number of one of these three mutations that can turn an arbitrary string a into another string b: 1) Change one letter for another 2) Add one letter at a spot before or after any letter 3) Remove any letter Examples aabca => abaca: aabca abca abaca = 2 abcdebf => bgabf: abcdebf bcdebf bcdbf bgdbf bgabf = 4 I've tried many algorithms out; I can't seem to find one that gives the actual answer every time. In fact, sometimes I'm not sure if even my human reasoning is finding the best answer. Does anyone know any algorithm for such purpose? Or maybe can help me find one? Thanks.

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• Flexible forms and supporting database structure

  - by sunwukung

  I have been tasked with creating an application that allows administrators to alter the content of the user input form (i.e. add arbitrary fields) - the contents of which get stored in a database. Think Modx/Wordpress/Expression Engine template variables. The approach I've been looking at is implementing concrete tables where the specification is consistent (i.e. user profiles, user content etc) and some generic field data tables (i.e. text, boolean) to store non-specific values. Forms (and model fields) would be generated by first querying the tables and retrieving the relevant columns - although I've yet to think about how I would setup validation. I've taken a look at this problem, and it seems to be indicating an EAV type approach - which, from my brief research - looks like it could be a greater burden than the blessings it's flexibility would bring. I've read a couple of posts here, however, which suggest this is a dangerous route: How to design a generic database whose layout may change over time? Dynamic Database Schema I'd appreciate some advice on this matter if anyone has some to give regards SWK

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• Efficient algorithm for Next button on a MySQL result set

  - by David Grayson

  I have a website that lets people view rows in a table (each row is a picture). There are more than 100,000 rows. You can view different subsets of the rows, and you can view them with different sort orders. While you are viewing one of the rows, you can click the "Next" or "Previous" buttons to go the next/previous row in the list. How would you implement the "Next" and "Previous" features of the website? More specifically, if you have an arbitrary query that returns a list of up to 100,000+ rows, and you know some information about the current row someone is viewing, how do you determine the NEXT row efficiently? Here is the pseudo-code of the solution I came up with when the website was young, and it worked well when there were only 1000 rows, but now that there are 100,000 rows I think it is eating up too much memory. int nextRowId(string query, int currentRowId) { array allRowIds = mysql_query(query); // Takes up a lot of memory! int currentIndex = (index of currentRowId in allRowIds); // Takes time! return allRowIds[currentIndex+1]; } While you are thinking about this problem, remember that the website can store more information about the current row than just its ID (for example, the position of the current row in the result set), and this information can be used as a hint to help determine the ID of the next row. Edit: Sorry for not mentioning this earlier, but this isn't just a static website: rows can often be added to the list, and rows can be re-ordered in the list. (Much rarer, rows can be removed from the list.) I think that I should worry about that kind of thing, but maybe you can convince me otherwise.

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• Distinct or group by on some columns but not others

  - by Nazadus

  I have a view that I'm trying to filter with something similar to DISTINCT on some columns but not others. I have a view like this: Name LastName Zip Street1 HouseholdID (may not be unique because it may have multiple addresses -- think of it in the logical sense as grouping persons but not physical locations; If you lookup HouseholdID 4130, you may get two rows.. or more, because the person may have mutiple mailing locations) City State I need to pull all those columns but filter on LastName,Zip, and Street1. Here's the fun part: The filter is arbitrary -- meaning I don't care which one of the duplicates goes away. This is for a mail out type thing and the other information is not used for any other reason than than to look up a specific person if needed (I have no idea why). So.. given one of the records, you can easily figure out the removed ones. As it stands now, my Sql-Fu fails me and I'm filtering in C# which is incredibly slow and is pretty much a foreach that starts with an empty list and adds the row in if the combined last name, zip, and street aren't are not in the list. I feel like I'm missing a simple / basic part of SQL that I should be understanding.

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• PyGTK: Trouble with size of ScrolledWindow

  - by canavanin

  Hi everyone! I am using PyGTK and the gtk.Assistant. On one page I have placed a treeview (one column, just strings) in a gtk.ScrolledWindow (I wanted the vertical scrollbar, since the list contains about 35 items). Everything is working fine; the only thing that bugs me is that I have not been able to figure out from the documentation how to set the size of the scrolled window. Currently only three items are displayed at a time; I would like to set this number to 10 or so. Below is the code. As you can see I have tried using a gtk.Adjustment to influence the scrolled window's size, but as - once more - I have been incompetent at retrieving the required info from the documentation, I don't actually know what values should be put into there. self.page7 = gtk.VBox() # The gtk.Adjustment: page_size = gtk.Adjustment(lower=10, page_size=100) # just used some arbitrary numbers here >_< scrolled_win = gtk.ScrolledWindow(page_size) scrolled_win.set_policy(gtk.POLICY_AUTOMATIC, gtk.POLICY_AUTOMATIC) # only display scroll bars when required self.character_traits_treeview = gtk.TreeView() self.character_traits_treestore = gtk.TreeStore(str) self.character_traits_treeview.set_model(self.character_traits_treestore) tc = gtk.TreeViewColumn("Character traits") self.character_traits_treeview.append_column(tc) cr = gtk.CellRendererText() tc.pack_start(cr, True) tc.add_attribute(cr, "text", 0) self.character_trait_selection = self.character_traits_treeview.get_selection() self.character_trait_selection.connect('changed', self.check_number_of_character_trait_selections) self.character_trait_selection.set_mode(gtk.SELECTION_MULTIPLE) self.make_character_traits_treestore() # adding the treeview to the scrolled window: scrolled_win.add(self.character_traits_treeview) self.page7.pack_start(scrolled_win, False, False, 0) self.assistant.append_page(self.page7) self.assistant.set_page_title(self.page7, "Step 7: Select 2-3 character traits") self.assistant.set_page_type(self.page7, gtk.ASSISTANT_PAGE_CONTENT) self.assistant.set_page_complete(self.page7, False) def check_number_of_character_trait_selections(self, blah): # ... def make_character_traits_treestore(self): # ... I know I should RTFM, but as I can't make head or tail of it, and as further searching, too, has been to no avail, I'm just hoping that someone on here can give me a hint. Thanks a lot in advance! PS: Here are the links to: the gtk.ScrolledWindow documentation the gtk.Adjustment documentation

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• CMS for managing plain-text content, with tagging

  - by user575606

  Hi, We have some quite-specific requirements for our app that a CMS may help us with, and were hoping that someone may know of a CMS that matches these requirements (it's quite a laborous task to download each CMS and verify this manually). We want a CMS to allow users to create and manage articles, but storing the articles in plain-text only. All of the CMSs that we have looked at so far are geared towards creating HTML pages. We want the CMS to manage workflow (approval process), and tracking of history. The requirements for plain text only is that the intent is to allow business people to generate content which we are going to display in our Silverlight application - we don't want to go down the route of hosting and displaying arbitrary HTML in the app as we want the styling to be seamless with our app, amongst other reasons. We would also want to allow the user to be able to link between articles, but not to external sites (i.e. HTML with no formatting, or some other way of specifying article links), and the third requirement is the ability to tag articles and search on articles. Does anyone know of any non-HTML targetted CMS systems that may match these requirements? Thanks, Gary

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• What about race condition in multithreaded reading?

  - by themoob

  Hi, According to an article on IBM.com, "a race condition is a situation in which two or more threads or processes are reading or writing some shared data, and the final result depends on the timing of how the threads are scheduled. Race conditions can lead to unpredictable results and subtle program bugs." . Although the article concerns Java, I have in general been taught the same definition. As far as I know, simple operation of reading from RAM is composed of setting the states of specific input lines (address, read etc.) and reading the states of output lines. This is an operation that obviously cannot be executed simultaneously by two devices and has to be serialized. Now let's suppose we have a situation when a couple of threads access an object in memory. In theory, this access should be serialized in order to prevent race conditions. But e.g. the readers/writers algorithm assumes that an arbitrary number of readers can use the shared memory at the same time. So, the question is: does one have to implement an exclusive lock for read when using multithreading (in WinAPI e.g.)? If not, why? Where is this control implemented - OS, hardware? Best regards, Kuba

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• Getting the first of a GROUP BY clause in SQL

  - by Michael Bleigh

  I'm trying to implement single-column regionalization for a Rails application and I'm running into some major headaches with a complex SQL need. For this system, a region can be represented by a country code (e.g. us) a continent code that is uppercase (e.g. NA) or it can be NULL indicating the "default" information. I need to group these items by some relevant information such as a foreign key (we'll call it external_id). Given a country and its continent, I need to be able to select only the most specific region available. So if records exist with the country code, I select them. If, not I want a records with the continent code. If not that, I want records with a NULL code so I can receive the default values. So far I've figured that I may be able to use a generated CASE statement to get an arbitrary sort order. Something like this: SELECT *, CASE region WHEN 'us' THEN 1 WHEN 'NA' THEN 2 ELSE 3 END AS region_sort FROM my_table WHERE region IN ('us','NA') OR region IS NULL GROUP BY external_id ORDER BY region_sort The problem is that without an aggregate function the actual data returned by the GROUP BY for a given row seems to be untameable. How can I massage this query to make it return only the first record of the region_sort ordered groups?

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• 2D platformer gravity physics with slow-motion

  - by DD

  Hi all, I fine tuned my 2d platformer physics and when I added slow-motion I realized that it is messed up. The problem I have is that for some reason the physics still depends on framerate. So when I scale down time elapsed, every force is scaled down as well. So the jump force is scaled down, meaning in slow-motion, character jumps vertically smaller height and gravity force is scaled down as well so the character goes further in the air without falling. I'm sending update function in hopes that someone can help me out here (I separated vertical (jump, gravity) and walking (arbitrary walking direction on a platform - platforms can be of any angle) vectors): characterUpdate:(float)dt { //Compute walking velocity walkingAcceleration = direction of platform * walking acceleration constant * dt; initialWalkingVelocity = walkingVelocity; if( isWalking ) { if( !isJumping ) walkingVelocity = walkingVelocity + walkingAcceleration; else walkingVelocity = walkingVelocity + Vector( walking acceleration constant * dt, 0 ); } // Compute jump/fall velocity if( !isOnPlatform ) { initialVerticalVelocity = verticalVelocity; verticalVelocity = verticalVelocity + verticalAcceleration * dt; } // Add walking velocity position = position + ( walkingVelocity + initialWalkingVelocity ) * 0.5 * dt; //Add jump/fall velocity if not on a platform if( !isOnPlatform ) position = position + ( verticalVelocity + initialVerticalVelocity ) * 0.5 * dt; verticalAcceleration.y = Gravity * dt; }

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• Is it possible to get the parsed text of a SqlCommand with SqlParameters?

  - by Burg

  What I am trying to do is create some arbitrary sql command with parameters, set the values and types of the parameters, and then return the parsed sql command - with parameters included. I will not be directly running this command against a sql database, so no connection should be necessary. So if I ran the example program below, I would hope to see the following text (or something similar): WITH SomeTable (SomeColumn) AS ( SELECT N':)' UNION ALL SELECT N'>:o' UNION ALL SELECT N'^_^' ) SELECT SomeColumn FROM SomeTable And the sample program is: using System; using System.Data; using System.Data.SqlClient; namespace DryEraseConsole { class Program { static void Main(string[] args) { const string COMMAND_TEXT = @" WITH SomeTable (SomeColumn) AS ( SELECT N':)' UNION ALL SELECT N'>:o' UNION ALL SELECT @Value ) SELECT SomeColumn FROM SomeTable "; SqlCommand cmd = new SqlCommand(COMMAND_TEXT); cmd.CommandText = COMMAND_TEXT; cmd.Parameters.Add(new SqlParameter { ParameterName = "@Value", Size = 128, SqlDbType = SqlDbType.NVarChar, Value = "^_^" }); Console.WriteLine(cmd.CommandText); Console.ReadKey(); } } } Is this something that is achievable using the .net standard libraries? Initial searching says no, but I hope I'm wrong.

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• How to add an extra plist property using CMake?

  - by Jesse Beder

  I'm trying to add the item <key>UIStatusBarHidden</key><true/> to my plist that's auto-generated by CMake. For certain keys, it appears there are pre-defined ways to add an item; for example: set(MACOSX_BUNDLE_ICON_FILE ${ICON}) But I can't find a way to add an arbitrary property. I tried using the MACOSX_BUNDLE_INFO_PLIST target property as follows: I'd like the resulting plist to be identical to the old one, except with the new property I want, so I just copied the auto-generated plist and set that as my template. But the plist uses some Xcode variables, which also look like ${foo}, and CMake grumbles about this: Syntax error in cmake code when parsing string <string>com.bedaire.${PRODUCT_NAME:identifier}</string> syntax error, unexpected cal_SYMBOL, expecting } (47) Policy CMP0010 is not set: Bad variable reference syntax is an error. Run "cmake --help-policy CMP0010" for policy details. Use the cmake_policy command to set the policy and suppress this warning. This warning is for project developers. Use -Wno-dev to suppress it. In any case, I'm not even sure that this is the right thing to do. I can't find a good example or any good documentation about this. Ideally, I'd just let CMake generate everything as before, and just add a single extra line. What can I do?

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• Run a command as cron would but from the command line.

  - by BCS

  I have a script that I'm trying to run from cron. When I run it from bash, it work just fine. However when I let cron do it's thing, I get a: myscript.sh: line 122: syntax error: unexpected end of file What I want is a way to run a command as if it was a cron job, but do it in my shell. As a side note: does anyone know what would be differnt under cron? (the script already has a #!/bin/sh line) To answer my own question: I added this to my crontab: * * * * * bcs for ((i=1; i <= 55; i++)) ; do find ~/.crontemp/ -name '*.run' -exec "{}" ";" ; sleep 1; done` and created this script: #!/bin/sh tmp=$(mktemp ~/.crontemp/cron.XXXXX) mknod $tmp.pipe p mv $tmp $tmp.pre echo $* '>' $tmp.pipe '1>&2' >> $tmp.pre echo rm $tmp.run >> $tmp.pre chmod 700 $tmp.pre mv $tmp.pre $tmp.run cat $tmp.pipe rm $tmp.pipe With that, I can run an arbitrary command with a delay of not more than one second. (And yes, I know there are all kinds of security issue involved in that)

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• Can C++ do something like an ML case expression?

  - by Nathan Andrew Mullenax

  So, I've run into this sort of thing a few times in C++ where I'd really like to write something like case (a,b,c,d) of (true, true, _, _ ) => expr | (false, true, _, false) => expr | ... But in C++, I invariably end up with something like this: bool c11 = color1.count(e.first)>0; bool c21 = color2.count(e.first)>0; bool c12 = color1.count(e.second)>0; bool c22 = color2.count(e.second)>0; // no vertex in this edge is colored // requeue if( !(c11||c21||c12||c22) ) { edges.push(e); } // endpoints already same color // failure condition else if( (c11&&c12)||(c21&&c22) ) { results.push_back("NOT BICOLORABLE."); return true; } // nothing to do: nodes are already // colored and different from one another else if( (c11&&c22)||(c21&&c12) ) { } // first is c1, second is not set else if( c11 && !(c12||c22) ) { color2.insert( e.second ); } // first is c2, second is not set else if( c21 && !(c12||c22) ) { color1.insert( e.second ); } // first is not set, second is c1 else if( !(c11||c21) && c12 ) { color2.insert( e.first ); } // first is not set, second is c2 else if( !(c11||c21) && c22 ) { color1.insert( e.first ); } else { std::cout << "Something went wrong.\n"; } I'm wondering if there's any way to clean all of those if's and else's up, as it seems especially error prone. It would be even better if it were possible to get the compiler complain like SML does when a case expression (or statement in C++) isn't exhaustive. I realize this question is a bit vague. Maybe, in sum, how would one represent an exhaustive truth table with an arbitrary number of variables in C++ succinctly? Thanks in advance.

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• Flash: Closest point to MovieClip

  - by LiraNuna

  I need to constrain a point inside a DisplayObject given to me by the artist. I got it working but only for the occations where the cursor is still inside bounds. The limited object is called limited. function onSqMouseMove(event:MouseEvent) { if(bounds.hitTestPoint(event.stageX, event.stageY, true)) { limited.x = event.stageX; limited.y = event.stageY; } else { /* Find closest point in the Sprite */ } } limited.addEventListener(MouseEvent.MOUSE_DOWN, function(event:MouseEvent) { stage.addEventListener(MouseEvent.MOUSE_MOVE, onSqMouseMove); }); limited.addEventListener(MouseEvent.MOUSE_UP, function(event:MouseEvent) { stage.removeEventListener(MouseEvent.MOUSE_MOVE, onSqMouseMove); }); How do I go about implementing the other half of the function? I am aware Sprite's startDrag accepts arguments, where the second one is the constraint rectangle, but in my case, bounds are an arbitrary shape. When the object is dragged outside the bounds, I want to calculate the closest point from the cursor to bounds' polygon. Just to note that bounds can have 'holes'.

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• How to map combinations of things to a relational database?

  - by Space_C0wb0y

  I have a table whose records represent certain objects. For the sake of simplicity I am going to assume that the table only has one row, and that is the unique ObjectId. Now I need a way to store combinations of objects from that table. The combinations have to be unique, but can be of arbitrary length. For example, if I have the ObjectIds 1,2,3,4 I want to store the following combinations: {1,2}, {1,3,4}, {2,4}, {1,2,3,4} The ordering is not necessary. My current implementation is to have a table Combinations that maps ObjectIds to CombinationIds. So every combination receives a unique Id: ObjectId | CombinationId ------------------------ 1 | 1 2 | 1 1 | 2 3 | 2 4 | 2 This is the mapping for the first two combinations of the example above. The problem is, that the query for finding the CombinationId of a specific Combination seems to be very complex. The two main usage scenarios for this table will be to iterate over all combinations, and the retrieve a specific combination. The table will be created once and never be updated. I am using SQLite through JDBC. Is there any simpler way or a best practice to implement such a mapping?

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• What happens to class members when malloc is used instead of new?

  - by Felix

  I'm studying for a final exam and I stumbled upon a curious question that was part of the exam our teacher gave last year to some poor souls. The question goes something like this: Is the following program correct, or not? If it is, write down what the program outputs. If it's not, write down why. The program: #include<iostream.h> class cls { int x; public: cls() { x=23; } int get_x(){ return x; } }; int main() { cls *p1, *p2; p1=new cls; p2=(cls*)malloc(sizeof(cls)); int x=p1->get_x()+p2->get_x(); cout<<x; return 0; } My first instinct was to answer with "the program is not correct, as new should be used instead of malloc". However, after compiling the program and seeing it output 23 I realize that that answer might not be correct. The problem is that I was expecting p2->get_x() to return some arbitrary number (whatever happened to be in that spot of the memory when malloc was called). However, it returned 0. I'm not sure whether this is a coincidence or if class members are initialized with 0 when it is malloc-ed. Is this behavior (p2->x being 0 after malloc) the default? Should I have expected this? What would your answer to my teacher's question be? (besides forgetting to #include <stdlib.h> for malloc :P)

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• How to disable MSBuild's <RegisterOutput> target on a per-user basis?

  - by Roger Lipscombe

  I like to do my development as a normal (non-Admin) user. Our VS2010 project build fails with "Failed to register output. Please try enabling Per-user Redirection or register the component from a command prompt with elevated permissions." Since I'm not at liberty to change the project file, is there any way that I can add user-specific MSBuild targets or properties that disable this step on a specific machine, or for a specific user? I'd prefer not to hack on the core MSBuild files. I don't want to change the project file because I might then accidentally check it back in. Nor do I want to hack on the MSBuild core files, because they might get overwritten by a service pack. Given that the Visual C++ project files (and associated .targets and .props files) have about a million places to alter the build order and to import arbitrary files, I was hoping for something along those lines. MSBuild imports/evaluates the project file as follows (I've only looked down the branches that interest me): Foo.vcxproj Microsoft.Cpp.Default.props Microsoft.Cpp.props $(UserRootDir)\Microsoft.Cpp.$(Platform).user.props Microsoft.Cpp.targets Microsoft.Cpp.$(Platform).targets ImportBefore\* Microsoft.CppCommon.targets The "RegisterOutput" target is defined in Microsoft.CppCommon.targets. I was hoping to replace this by putting a do-nothing "RegisterOutput" target in $(UserRootDir)\Microsoft.Cpp.$(Platform).user.props, which is %LOCALAPPDATA%\MSBuild\v4.0\Microsoft.Cpp.Win32.user.props (UserRootDir is set in Microsoft.Cpp.Default.props if it's not already set). Unfortunately, MSBuild uses the last-defined target, which means that mine gets overridden by the built-in one. Alternatively, I could attempt to set the %(Link.RegisterOutput) metadata, but I'd have to do that on all Link items. Any idea how to do that, or even if it'll work?

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