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• How can I test whether a csv file is currently open and being written to - the file, not a file hand

  - by Henry

  I've seen a few questions/answers here that deal with this, but none really give me an answer/solution. I've got a Clipper system writing csv files to a Windows directory. I have a perl script running on a Linux server that is reading a mount of that Windows directory and importing the files to a database. Right now we're using flag files to indicate when a csv is no longer being written to; the flag files gets written after the csv is done. I'd really rather just get what I need from the csv itself, but I can't seem to find a way to tell when the file is open and being written to. lsof doesn't seem to answer my need. I've tried using flock and open the file with an exclusive lock, thinking it might throw an error if the file is being modified, but it doesn't. Any thoughts?

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• Can you make a PHP function recursive without repeating it's name?

  - by alex

  It's always bugged me a recursive function needs to name itself, when a instantiated class can use $this and a static method can use self etc. Is there a similar way to do this in a recursive function without naming it again (just to cut down on maintenance)? Obviously I could use call_user_func or the __FUNCTION__ constant but I would prefer something less ugly. Update Thanks for your answers. I might stick to including the function name for simple functions, and make take the other approaches for anything more complicated.

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• How can I remove a duplicate object from a MongoDB array?

  - by andrewrk

  My data looks like this: foo_list: [ { id: '98aa4987-d812-4aba-ac20-92d1079f87b2', name: 'Foo 1', slug: 'foo-1' }, { id: '98aa4987-d812-4aba-ac20-92d1079f87b2', name: 'Foo 1', slug: 'foo-1' } { id: '157569ec-abab-4bfb-b732-55e9c8f4a57d', name: 'Foo 3', slug: 'foo-3' } ] Where foo_list is a field in a model called Bar. Notice that the first and second objects in the array are complete duplicates. Aside from the obvious solution of switching to PostgresSQL, what MongoDB query can I run to remove duplicate entries from foo_list? Similar answers that do not quite cut it: http://stackoverflow.com/a/16907596/432 http://stackoverflow.com/a/18804460/432 These questions answer the question if the array had bare strings in it. However in my situation the array is filled with objects. I hope it is clear that I am not interested in a query; I want the duplicates to be gone from the database forever.

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• What grid distributed computing frameworks are currently favoured for trading systems

  - by Rich

  There seems to a quite a few grid computing frameworks out there, but which ones are actually being used to any great extent by the investment banks for purposes of low latency distributing calculation? I'd be interested to hear answers covering both windows,Linux and cross platform. Also, what RPC mechanisms seem to be favoured most? I've heard that for reason of low latency and speed, the calculations themselves are quite often written in C++/C as calculations running on VMs are several orders of magnitude slower than native code. Does this seem to be a common scenario in practice? e.g distributed .NET grid framework running calculations written in native c++/c?

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• How do I escape a string for a shell command in nodejs (V8 Javascript engine)?

  - by Maciek

  In nodejs, the only way to execute external commands is via sys.exec(cmd). I'd like to call an external command and give it data via stdin. In nodejs there does yet not appear to be a way to open a command and then push data to it (only to exec and receive its standard+error outputs), so it appears the only way I've got to do this right now is via a single string command such as: var dangerStr = "bad stuff here"; sys.exec("echo '" + dangerStr + "' | somecommand"); Most answers to questions like this have focused on either regex which doesn't work for me in nodejs (which uses Google's V8 Javascript engine) or native features from other languages like Python. I'd like to escape dangerStr so that it's safe to compose an exec string like the one above. If it helps, dangerStr will contain JSON data.

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• pyschool is wrong ?

  - by geekkid

  I'm currently learning python and trying to do exercises at pyschools (if anyone knows what it is). Anyway, i have an exercise that asks me to do the following : Write a function percent(value, total) that takes in two numbers as arguments, and returns the percentage value as an integer. Here's my code: def percent(value, total): percent = value / total * 100 return int(percent) It works great in my Python Idle and it gives all the correct answers. however, when i run it in the pyschools website, it says that , for example , when the function is called with parameters 46 and 90 , the function returns 0. However, in my python idle , it correctly returns 51. What might be the problem ? Thank you very much for your help!

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• How do I secure a folder used to let users upload files?

  - by Eduardo Molteni

  I have a folder in my web server used for the users to upload photos using an ASP page. Is it safe enough to give IUSR write permissions to the folder? Must I secure something else? I am afraid of hackers bypassing the ASP page and uploading content directly to the folder. I'm using ASP classic and IIS6 on Windows 2003 Server. The upload is through HTTP, not FTP. Edit: Changing the question for clarity and changing my answers as comments.

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• How to stop C# compile on first error in VS 2010 (VS 2008 macros don't work)!

  - by Ben Robbins

  At work we have a C# solution with over 80 projects. Is it possible in VS 2010 to automatically stop compilation as soon as an error is encountered rather than the default behaviour which is to continue as far as possible and display a list of errors in the error window? I'm happy for it to stop either as soon as an error is encountered (file-level) or as soon as a project fails to build (project-level). I'd also note that in VS 2008 we used macros similar to some of the answers below but they don't work in VS 2010 (at least I couldn't get them to as the environment events don't seem to fire in VS 2010).

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• API For Flex Apps To Interact

  - by dimo414

  I have a large flex application (the app) running on one server, and many small flex applications (widgets) running on another server, which are to be included in the app so that visually the user see's one continuous application. Due to proprietary third party software, this structure cannot be changed. I am looking for some way to allow the app and the widgets to communicate, allowing the app to make changes to the widgets and the the widgets to notify the app when events are triggered, so that user interaction is fluid and continuous. There are a few related questions which indicate it's possible to do this by setting up event triggers and listeners. I am wondering if there is any standardized way to do this (the answers aren't very clear) or if anyone has developed a library or API to make this easier.

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• Doubt about constructor in JAVA

  - by Harry Joy

  I have few doubts regarding constructor in java Can a constructor be private? If yes then in which condition? Constructor is a method or not? If constructor does not return anything then why we are getting a new Object every time we call it. Whats the default access modifier of a constructor if we did not specify. Thanks & Regards Edit---------- Answer for 1 & 3 are very clear. But still doubt about 2&4 as i'm getting different answers for them.

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• Which libraries use the "We Know Where You Live" optimization for std::make_shared?

  - by KnowItAllWannabe

  Over two years ago, Stephan T. Lavavej described a space-saving optimization he implemented in Microsoft's implementation of std::make_shared, and I know from speaking with him that Microsoft has nothing against other library implementations adopting this optimization. If you know for sure whether other libraries (e.g., for Gnu C++, Clang, Intel C++, plus Boost (for boost::make_shared)) have adopted this implementation, please contribute an answer. I don't have ready access to that many make_shared implementations, nor am I wild about digging into the bowels of the ones I have to see if they've implemented the WKWYL optimization, but I'm hoping that SO readers know the answers for some libraries off-hand. I know from looking at the code that as of Boost 1.52, the WKWYL optimization had not been implemented, but Boost is now up to version 1.55. Note that this optimization is different from std::make_shared's ability to avoid a dedicated heap allocation for the reference count used by std::shared_ptr. For a discussion of the difference between WKWYL and that optimication, consult this question.

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• Result of Long Positive Integers & Search and element in array..

  - by AGeek

  Hi, I have two Questions for which I cannot find answers by googling, but I find these questions very important for preparation.. Kindly explain only the logic, I will be able to code. In Search of Efficient Logic..... in terms of Memory and Time. WAP to add two long positive integers. What Data structure / data type we can use to store the numbers and result. What is the best way to search an element from an array in shortest time. Size of the array could be large enough, and any elements could be stored in the array(i.e. no range). Thanks.

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• Performance of: if (OBJECT_INSTANCE is TYPE)

  - by Axonn

  I am working both in C# and ActionScript 3. Both language are type-aware, so you can do verifications such as: if (some_object_instance is SomeClassName_ThatIs_SomeType) I'm doing these kind of verifications in a few places. Might be a dumb question, but I will ask it anyway, and I want answers from both camps, C# and ActionScript: What goes on behind the scenes? Is it Reflection? If is, isn't this a long verification which might degrade performance if done in thousands of loops? And by "degrade performance" I mean, is it more intensive than say if (Math.sqrt(8) > Math.sin(10))

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• Django refresh page if change data by other user

  - by Fran Sobrino

  I have a test django app. In one page the test show the same question to all users. I'd like that when a user answers correctly, send a signal to other active user's browser to refresh to the next question. I have been learning about signals in django I learning work with them but I don't now how send the "refresh signal" to client browser. I think that it can do with a javascript code that check if a certain value (actual question) change and if change reload the page but I don't know this language and the information that I find was confused. Can anybody help me? Many Thanks.

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• How to obtain multiple lines in a single density plot, with a corrected scale?

  - by user1677055

  I have recently started working with microarray datasets and am trying to get my hands on R. I wish to make some plots out of my result data, but however I am stuck at the following. I have the following data (myData), cpg samp1 samp2 samp3 cpg1 0.43 0.32 0.21 cpg2 0.43 0.22 1.00 cpg3 0.11 0.99 0.78 cpg4 0.65 0.32 0.12 cpg5 0.11 0.43 0.89 And I wish to obtain a density plot for this, I did the following, plot (density(MyData$samp1), col="red") lines (density(MyData$samp2), col="green") lines (density(MyData$samp3), col="blue") But doing this does not give me correct plots, because not all sample curves fit within the plot limits. I did try looking for answers, but honestly i am still not able to work this out. Can you help me know how do i set my scale for the above? Or what additional should I do to the above code, so that all the curves are in range?? I have got many samples, so i need a something that could also automatically assign a different colour curve for each of my sample, after scaling it right. Thanks in advance..

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• MySql "comments" parameter as descriptor?

  - by Nick

  So, I'm trying to learn a lot at once, and this place is really helpful! I'm making a little running log website for myself and maybe a few other people, and I have it so that the user can add workouts for each day. With each workout, I have a variety of information the user can fill out for the workout, such as running distance, time, quality of run, course, etc... I store this in a MySql database as a table with fields titled "distance", "time", "runquality", etc... Now, these field titles don't match up with what I want displayed on the running log, so I was thinking of using the "Comments" attribute for a field to store its human-readable title--thus the field "runquality" would have "Quality of run" as its comment, and then I would pull the comment with a SQL query and display it instead of the field name. Is this a good theoretical/practical way of going about it? And what sort of SQL would I use to pull the comment for the field anyway? Secondly, suppose I want to add the ability for the user to create their own workout descriptors. So say a user wants to add a "temperature" descriptor for their workout. Should I create a script that adds fields to my workout table, or should I create a separate table listing only workout descriptors and somehow link the descriptor table with the "contents" table? I haven't learned any theory about database design or anything so any help is appreciated!

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• Copy a function in memory and execute it

  - by Elinghton

  Hi everybody, I would like to know how in C in can copy the content of a function into memroy and the execute it? I'm trying to do something like this: typedef void(*FUN)(int *); char * myNewFunc; char *allocExecutablePages (int pages) { template = (char *) valloc (getpagesize () * pages); if (mprotect (template, getpagesize (), PROT_READ|PROT_EXEC|PROT_WRITE) == -1) { perror ("mprotect"); } } void f1 (int *v) { *v = 10; } // allocate enough spcae but how much ?? myNewFunc = allocExecutablePages(...) /* Copy f1 somewere else * (how? assume that i know the size of f1 having done a (nm -S foo.o)) */ ((FUN)template)(&val); printf("%i",val); Thanks for your answers

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• Data Warehouse: One Database or many?

  - by drrollins

  At my new company, they keep all data associated with the data warehouse, including import, staging, audit, dimension and fact tables, together in the same physical database. I've been a database developer for a number of years now and this consolidation of function and form seems counter to everything I know. It seems to make security, backup/restore and performance management issues more manually intensive. Is this something that is done in the industry? Are there substantial reasons for doing or not doing it? The platform is Netezza. The size is in terabytes, hundreds of millions of rows. What I'm looking to get from answers to this question is a solid understanding of how right or wrong this path is. From your experience, what are the issues I should be focused on arguing if this is a path that will cause trouble for us down the road. If it is no big deal, then I'd like to know that as well.

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• iphone web app: open directions in external maps application

  - by munchybunch

  I've seen the answers for opening the Maps app in a native iPhone app, but is there any way to do this in a web app? I've tried changing window.location to http://maps.google.com/maps?q=cupertino for example, to no avail. I've tried using a simple anchor tag linked to http://maps.google.com/maps?q=cupertino, also to no avail. Has anyone gotten this to work before? I'm working on a map-heavy application, and I'd like to provide users with directions at the end. I figured it would be easiest to simply open it up in the Map application. Note: I'm currently testing with just the simulator, could that lead to problems? My iPhone is down for the count at the moment.

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• django: Selecting questions that was not asked

  - by Oleg Tarasenko

  Hi, I am creating small django application which holds some few questions (and answers for them) What I want to do is to show user random question, but only from those which was not solved by him yet. I wonder how to do this. For now, I defined user profile model this way: class UserProfile(models.Model): rank = models.IntegerField(default = 1) solvedQ = models.ManyToManyField(Question) user = models.ForeignKey(User, unique=True) So solved problems are added this way: if user.is_authenticated(): profile = user.get_profile() profile.rank += 1 profile.solvedQ.add(Question.objects.get(id=id)) Now if the view must show random question, but not from already solved list... Is there a good way to intersect Questions and solvedQuestions.... so question is chosen from the unsolved list?

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• Abstract Classes and ReadOnly Properties

  - by serhio

  Let's have three classes; Line PoliLine SuperPoliLine for all that three classes a Distance is defined. But only for the Line a Distance can be Set. Is there a possibility to build a common abstract (MustInherit) class Segment, having a Distance as (abstract +? ReadOnly) member? Question for VB.NET, but C# answers welcomed too. Business Background Imagine a Bus. It has a lot of Stations, MainStations, and 2 TerminalStations. So Line is between 2 Stations, PoliLine is between 2 MainStations, and SuperPoliLine is between 2 TerminalStations. All "lines" are "Segments", but only the distance A-B between 2 stations - Line can be defined.

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• System.Net.WebClient Class in .Net CompactFramework 3.5 ?

  - by Leen15

  Hi at all! I need to comunicate with a Server that give me async answers (streamer connection). I find this: http://msdn.microsoft.com/en-en/library/ms144211%28v=VS.80%29.aspx that generate this event: http://msdn.microsoft.com/en-en/library/system.net.webclient.openreadcompleted%28v=VS.80%29.aspx I think this is what i need, but i don't have the WebClient class in my System.Net of CompactFramework 3.5. How can i do? Thanks. EDIT: I've done a more clear question: httpRequest, httpResponse, send GET through Stream and Receive the Result in C#

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• Is there a way to set up a Linux pipe to non-buffering or line-buffering?

  - by ern0

  My program is controlling an external application on Linux, passing in input commands via a pipe to the external applications stdin, and reading output result via a pipe from the external applications stdout. The problem is that writes to pipes are buffered by block, and not by line, and therefore delays occur before my app receives data output by the external application. The external application cannot be altered to add explicit fflush() calls. When I set the external application to /bin/cat -n (it echoes back the input, with line numbers added), it works correctly, it seems, cat flushes after each line. The only way to force the external application to flush, is sending exit command to it; as it receives the command, it flushes, and all the answers appears on the stdout, just before exiting. I'm pretty sure, that Unix pipes are appropiate solution for that kind of interprocess communication (pseudo server-client), but maybe I'm wrong. (I've just copied some text from a similar question: Force another program's standard output to be unbuffered using Python)

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• How can I find out how many rows of a matrix satisfy a rather complicated criterion (in R)?

  - by Brani

  As an example, here is a way to get a matrix of all possible outcomes of rolling 4 (fair) dice. z <- as.matrix(expand.grid(c(1:6),c(1:6),c(1:6),c(1:6))) As you may already have understood, I'm trying to work out a question that was closed, though, in my opinion, it's a challenging one. I used counting techniques to solve it (I mean by hand) and I finaly arrived to a number of outcomes, with a sum of subset being 5, equal to 1083 out of 1296. That result is consistent with the answers provided to that question, before it was closed. I was wondering how could that subset of outcomes (say z1, where dim(z1) = [1083,4] ) be generated using R. Do you have any ideas? Thank you.

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• How Proxy server works with tcp/http connections?

  - by Vivek

  Since I am a beginner in the world of internet/networking, I always mess up with these kinds of doubts in my head while programming ;) .. My doubts are, While working behind a proxy, how my requests and responses work? Means my request headers and data will first reach to Proxy server- then proxy server sends it(same headers and data) to corresponding server. And server responses to it with a response header and body to the proxy server-then proxy server sends it to my computer. Wright? While using websockets we are upgrading our http connection to tcp. At this time what is happening @ Proxy server? Does the proxyserver also upgrades its connection to plain TCP? After opening such TCP connections, does the proxy server able to track/log those socket messsages? And most importantly, Is the proxy server transparent or acting like an original server infront of a client? Thanks for any answers or helpful links in advance.

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