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• When/Why ( if ever ) should i think about doing Generic Programming/Meta Programming

  - by hotadvice

  Hi there IMHO to me OOPS, design patterns make sense and i have been able to apply them practically. But when it comes to "generic programming /meta programming" of the Modern C++ kind, i am left confused. -- Is it a new programming/design paradigm ? -- Is it just limited to "library development"? If not, What design/coding situations call for using meta programming/generic programming. -- Does using templates mean i am doing generic programming? I have googled a lot on this topic but do not grasp the BIG PICTURE fully. Also see this post. After reading dicussions here under, up till now, I am sure ( might still not be correct): a) Generic programming and meta programming are two different concepts.

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• Pass a captured named regular expression to URL dictionary in generic view

  - by Trent Jurewicz

  I am working with a generic view in Django. I want to capture a named group parameter in the URL and pass the value to the URL pattern dictionary. For example, in the URLConf below, I want to capture the parent_slug value in the URL and pass it to the queryset dictionary value like so: urlpatterns = patterns('django.views.generic.list_detail', (r'^(?P<parent_slugs>[-\w])$', 'object_list', {'queryset':Promotion.objects.filter(category=parent_slug)}, 'promo_promotion_list'), ) Is this possible to do in one URLConf entry, or would it be wiser if I create a custom view to capture the value and pass the queryset directly to the generic view from my overridden view?

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• Python: how to run several scripts (or functions) at the same time under windows 7 multicore processor 64bit

  - by Gianni

  sorry for this question because there are several examples in Stackoverflow. I am writing in order to clarify some of my doubts because I am quite new in Python language. i wrote a function: def clipmyfile(inFile,poly,outFile): ... # doing something with inFile and poly and return outFile Normally I do this: clipmyfile(inFile="File1.txt",poly="poly1.shp",outFile="res1.txt") clipmyfile(inFile="File2.txt",poly="poly2.shp",outFile="res2.txt") clipmyfile(inFile="File3.txt",poly="poly3.shp",outFile="res3.txt") ...... clipmyfile(inFile="File21.txt",poly="poly21.shp",outFile="res21.txt") I had read in this example Run several python programs at the same time and i can use (but probably i wrong) from multiprocessing import Pool p = Pool(21) # like in your example, running 21 separate processes to run the function in the same time and speed my analysis I am really honest to say that I didn't understand the next step. Thanks in advance for help and suggestion Gianni

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• Reducing time in C# Forms Control.set_Text(string) function

  - by awshepard

  Hoping for a quick answer (which SO seems to be pretty good for)... I just ran a performance analysis with VS2010 on my app, and it turns out that I'm spending about 20% of my time in the Control.set_Text(string) function, as I'm updating labels in quite a few places in my app. The window has a timer object (Forms timer, not Threading timer) that has a timer1_Tick callback, which updates one label every tick (to give a stop-watch sort of effect), and updates about 15 labels once each second. Does anyone have quick suggestions for how to reduce the amount of time spent updating text on a form, other than increasing the update interval? Are there other structures or functions I should be using?

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• Keeping iPhone application in sync with GWT application.

  - by Reflog

  Hi, I'm working on an iPhone application that should work in offline and online modes. In it's online mode it's supposed to feed all the information the user enters to a webservice backed by GWT/GAE. In it's offline mode it's supposed to store the information locally, and when connection is available sync it up to the web service. Currently my plan is as follows: Provide a connection between an app and a webservice using Protobuffers for efficient over-the-wire communication Work with local DB using Core Data Poll the network status, and when available sync the database and keep some sort of local-db-to-remote-db key synchronization. The question is - am I in the right direction? Are the standard patterns for implementing this? Maybe someone can point me to an open-source application that works in a similar fashion? I am really new to iPhone coding, and would be very glad to hear any suggestions. Thanks

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• Extracting rightmost N bits of an integer

  - by srandpersonia

  In the yester Code Jam Qualification round http://code.google.com/codejam/contest/dashboard?c=433101#s=a&a=0 , there was a problem called Snapper Chain. From the contest analysis I came to know the problem requires bit twiddling stuff like extracting the rightmost N bits of an integer and checking if they all are 1. I saw a contestant's(Eireksten) code which performed the said operation like below: (((K&(1<<N)-1))==(1<<N)-1) I couldn't understand how this works. What is the use of -1 there in the comparison?. If somebody can explain this, it would be very much useful for us rookies. Also, Any tips on identifying this sort of problems would be much appreciated. I used a naive algorithm to solve this problem and ended up solving only the smaller data set.(It took heck of a time to compile the larger data set which is required to be submitted within 8 minutes.). Thanks in advance.

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• Data access strategy for a site like SO - sorted SQL queries and simultaneous updates that affect th

  - by Kaleb Brasee

  I'm working on a Grails web app that would be similar in access patterns to StackOverflow or MyLifeIsAverage - users can vote on entries, and their votes are used to sort a list of entries based on the number of votes. Votes can be placed while the sorted select queries are being performed. Since the selects would lock a large portion of the table, it seems that normal transaction locking would cause updates to take forever (given enough traffic). Has anyone worked on an app with a data access pattern such as this, and if so, did you find a way to allow these updates and selects to happen more or less concurrently? Does anyone know how sites like SO approach this? My thought was to make the sorted selects dirty reads, since it is acceptable if they're not completely up to date all of the time. This is my only idea for possibly improving performance of these selects and updates, but I thought someone might know a better way.

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• creative way for implementing Data object with it's corespanding buisness logic class in java

  - by ekeren

  I have a class that need to be serialized (for both persistentcy and client-server communication) for simplicity reasons lets call the classes Business a BusinessData and I prefix for their Interfaces. All the getter and setter are delegated from Business class to BusinessData class. I thought about implementing IBusinessData interface that will contain all the getter and setters and IBusiness interface that will extend it. I can either make Business extend BuisnessData so I will not need to implement all getter and setter delegates, or make some abstract class ForwardingBusinessData that will only delegate getter and setters. Any of the above option I loose my hierarchy freedom, does any of you have any creative solution for this problem... I also reviewed DAO pattern: http://java.sun.com/blueprints/patterns/DAO.html

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• How to build Object Oriented Skills?

  - by cedar715

  Being a core developer for couple of years, coding applications seeing the class diagrams, sequence diagrams, I decided to improve my self, taking the next step of designing. As I'm an OO developer, I'm interested in improving my design skills. For Example, I had a hard time designing a currency converter. My questions to the SO: Is it by experience the design skills can be acquired? Will learning books/blog/material over internet etc help? Is it that one needs the domain knowledge of the application being developed? Knowing Design patterns, principles? Studying 'Code Complete' book ? Need to have Problem-solving skills? In short, given a problem, I just want to solve it in Object-oriented way??

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• How does one modify the thread scheduling behavior when using Threading Building Blocks (TBB)?

  - by J Teller

  Does anyone know how to modify the thread scheduling (specifically affinity) when using TBB? Doing a high level analysis on a simple parallel-for application, it seems like TBB is specifying the underlying threads' affinity in a way that reduces performance. Specifically, the cores I'm running on have hyper-threading enabled, and it looks like TBB is affinitizing threads to the same core even if there is a different core left completely unloaded. FWIW, I realize it's likely that TBB is doing the "right thing" and that changing the threads' affinity will only reduce performance. I'd just like to experiment with it to see if that's really the case.

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• Speeding up jQuery empty() or replaceWith() Functions When Dealing with Large DOM Elements

  - by Levi Hackwith

  Let me start off by apologizing for not giving a code snippet. The project I'm working on is proprietary and I'm afraid I can't show exactly what I'm working on. However, I'll do my best to be descriptive. Here's a breakdown of what goes on in my application: User clicks a button Server retrieves a list of images in the form of a data-table Each row in the table contains 8 data-cells that in turn each contain one hyperlink Each request by the user can contain up to 50 rows (I can change this number if need be) That means the table contains upwards of 800 individual DOM elements My analysis shows that jQuery("#dataTable").empty() and jQuery("#dataTable).replaceWith(tableCloneObject) take up 97% of my overall processing time and take on average 4 - 6 seconds to complete. I'm looking for a way to speed up either of the above mentioned jQuery functions when dealing with massive DOM elements that need to be removed / replaced. I hope my explanation helps.

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• Reference-counted object is used after it is released

  - by EndyVelvet

  Doing code analysis of the project and get the message "Reference-counted object is used after it is released" on the line [defaults setObject: deviceUuid forKey: @ "deviceUuid"]; I watched this topic Obj-C, Reference-counted object is used after it is released? But the solution is not found. ARC disabled. // Get the users Device Model, Display Name, Unique ID, Token & Version Number UIDevice *dev = [UIDevice currentDevice]; NSString *deviceUuid; if ([dev respondsToSelector:@selector(uniqueIdentifier)]) deviceUuid = dev.uniqueIdentifier; else { NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; id uuid = [defaults objectForKey:@"deviceUuid"]; if (uuid) deviceUuid = (NSString *)uuid; else { CFStringRef cfUuid = CFUUIDCreateString(NULL, CFUUIDCreate(NULL)); deviceUuid = (NSString *)cfUuid; CFRelease(cfUuid); [defaults setObject:deviceUuid forKey:@"deviceUuid"]; } } Please help find the cause.

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• Screening (multi)collinearity in a regression model

  - by aL3xa

  I hope that this one is not going to be "ask-and-answer" question... here goes: (multi)collinearity refers to extremely high correlations between predictors in the regression model. How to cure them... well, sometimes you don't need to "cure" collinearity, since it doesn't affect regression model itself, but interpretation of an effect of individual predictors. One way to spot collinearity is to put each predictor as a dependent variable, and other predictors as independent variables, determine R2, and if it's larger than .9 (or .95), we can consider predictor redundant. This is one "method"... what about other approaches? Some of them are time consuming, like excluding predictors from model and watching for b-coefficient changes - they should be noticeably different. Of course, we must always bare in mind specific context/goal of analysis... Sometimes, only remedy is to repeat a research, but right now, I'm interested in various ways of screening redundant predictors when (multi)collinearity occurs in a regression model.

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• Creating an Excel Template for different data size

  - by dassouki

  I created an excel template for a file i've done for a routine work calculation. The file takes data from the data logger and does some analysis on it and outputs one number regardless of the input size. The problem I'm having is i have to modify the sheet to suit the number of rows, as everyday the data logger outputs a different number of rows. there are about 15 sheets in the workbook and it's annoying to have to change everyone of them everyday. What i'd like to do input the data logger csv, and boom the result gets outputted. Is there a way through vba or not to ahieve

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• Mercurial merge strategy per file type

  - by dls

  All: I want to use kdiff to merge all files with a certain suffix (say *.c, *.h) and I want to do two things (turn off premerge and use internal:other) for all files with another suffix (say *.mdl). The purpose of this is to allow me to employ a type of 'clobber merge' for a specific file type (ie: un-mergable files like configurations, auto-generated C, models, etc..) In my .hgrc I've tried: [merge-tools] kdiff3= clobbermerge=internal:other clobbermerge.premerge = False [merge-patterns] **.c = kdiff3 **.h = kdiff3 **.mdl = clobbermerge but it still triggers kdiff3 for all files. Thoughts? An extension of this would be to perform a 'clobber merge' on a directory - but once the syntax is clear for a file suffix, the dir should be easy.

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• JJIL Android Java Problem

  - by Danny_E

  Hey Guys, Long time reader never posted until now. Im having some trouble with Android, im implementing a library called JJIL its an open source imaging library. My problem is this i need to run some analysis on an image and to do so i need to have it in jjil.core.image format and once those processes are complete i need to convert the changed image from jjil.core.image to java.awt.image. I cant seem to find a method of doing this does anyone have any ideas or have any experience with this? I would be grateful of any help. Danny

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• Modern Web Development + General question

  - by ritu

  I have been given a nasty wake up a while ago when I discovered that my 10 years of experience was really equivalent of about 4 (got trapped in a big company doing the same thing over and over without realizing it) and is now paying a huge price. Question 1: I did servlets/JSP programming back in the day (2001-2003). Since then there have been libraries like GWT, YUI, etc. Is JSP still the preferred way of building web apps using Java? Question 2: Because I enjoyed what I was doing and needed to pay the bills, I didn't realize that the ground below me has shifted. How do avoid this in the future? My years of C system programming doesn't seem to matter a lot now to the young guys who talk about design patterns.

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• Leak caused by fread

  - by Jack

  I'm profiling code of a game I wrote and I'm wondering how it is possible that the following snippet causes an heap increase of 4kb (I'm profiling with Heapshot Analysis of Xcode) every time it is executed: u8 WorldManager::versionOfMap(FILE *file) { char magic[4]; u8 version; fread(magic, 4, 1, file); <-- this is the line fread(&version,1,1,file); fseek(file, 0, SEEK_SET); return version; } According to the profiler the highlighted line allocates 4.00Kb of memory with a malloc every time the function is called, memory which is never released. This thing seems to happen with other calls to fread around the code, but this was the most eclatant one. Is there anything trivial I'm missing? Is it something internal I shouldn't care about? Just as a note: I'm profiling it on an iPhone and it's compiled as release (-O2).

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• calculate next line numbers

  - by osomanden

  Weird question I guess.. But I am not very math wiz - soo here goes.. I am trying to create a patterne (or variable patterns based on selection) based on x and y numbers (2 rows and 4 columns) and the direction of the counting of x numbers like: 1-2-3-4 5-6-7-8 That one is easy, when number of x-columns is reached, next line and continue x count. But with eg. this one (still 2 rows and 4 columns): 1-2-3-4 8-7-6-5 upsie.. what if it is eg. 3++ rows and still 4 columns? 1-2-3-4 8-7-6-5 9-10-11-12 what would be the formula for this - or other possible variations (teaser for variations): 9-10-11-12 8-7-6-5 1-2-3-4 or reversed

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• fortran error I/O

  - by jpcgandre

  I get this error when compiling: forrtl: severe (256): unformatted I/O to unit open for formatted transfers, unit 27, file C:\Abaqus_JOBS\w.txt The error occurs in the beginning of the analysis. At the start, the file w.txt is created but is empty. The error may be related to the fact that I want to read from an empty file. My code is: OPEN(27, FILE = "C:/Abaqus_JOBS/w.txt", status = "UNKNOWN") READ(27, *, iostat=stat) w IF (stat .NE. 0) CALL del_file(27, stat) SUBROUTINE del_file(uFile, stat) IMPLICIT NONE INTEGER uFile, stat C If the unit is not open, stat will be non-zero CLOSE(unit=uFile, status='delete', iostat=stat) END SUBROUTINE Ref: Close multiple files If you agree with my opion about the cause of the error, is there a way to solve it? Thanks

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• Random List of millions of elements in Python Efficiently

  - by eWizardII

  Hello, I have read this answer potentially as the best way to randomize a list of strings in Python. I'm just wondering then if that's the most efficient way to do it because I have a list of about 30 million elements via the following code: import json from sets import Set from random import shuffle a = [] for i in range(0,193): json_data = open("C:/Twitter/user/user_" + str(i) + ".json") data = json.load(json_data) for j in range(0,len(data)): a.append(data[j]['su']) new = list(Set(a)) print "Cleaned length is: " + str(len(new)) ## Take Cleaned List and Randomize it for Analysis shuffle(new) If there is a more efficient way to do it, I'd greatly appreciate any advice on how to do it. Thanks,

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• Manual stack backtrace on Windows mobile (SEH)

  - by caahab

  Following situation: I'm developing an windows mobile application using the sdk 6. Target machine is a nautiz x7. To improve the error reporting I want to catch the structured exceptions (SEH) and do a stack backtrace to store some information for analysis. So far I have the information where the exception was thrown (windows core.dll) and I can backtrace the return adresses thru the stack. But what I want to know is, which instruction in my code caused the exception? Does anyone know how to use the available exception and context information to get the appropriate function/instruction address? Unfortunately windows mobile 6 sdk for pocketpc does not support all the helper functions to do stackwalks or mini dumps.

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• How can I use splne() with ggplot?

  - by David

  I would like to fit my data using spline(y~x) but all of the examples that I can find use a spline with smoothing, e.g. lm(y~ns(x), df=_). I want to use spline() specifically because I am using this to do the analysis represented by the plot that I am making. Is there a simple way to use spline() in ggplot? I have considered the hackish approach of fitting a line using geom_smooth(aes(x=(spline(y~x)$x, y=spline(y~x)$y)) but I would prefer not to have to resort to this. Thanks!

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• How should I handle searching through byte arrays in Java?

  - by Zombies

  Preliminary: I am writting my own httpclient in Java. I am trying to parse out the contents of chunked encoding. Here is my dilema: Since I am trying to parse out chunked http transfer encoding with a gzip payload there is a mix of ascii and binary. I can't just take the http resp content and convert it to a string and make use of StringUtils since the binary data can easily contain nil characters. So what I need to do is some basic things for parsing out each chunk and its chunk length (as per chunked transfer/HTTP/1.1 spec). Are there any helpful ways of searching through byte arrays of binary/part ascii data for certain patterns (like a CR LF) (instead of just a single byte) ? Or must I write the for loops for this?

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• Java source code generation frameworks

  - by Superfilin

  I have a set of Java 5 source files with old-style Doclet tags, comments and annotations. And based on that I would like to write a generator for another set of Java classes. What is the best way to do that? And are there any good standalone libraries for code analysis/generation in Java? Any shared exprience in this field is appreciated. So, far I have found these: JaxME's Java Source Reflection - seems good, but it does not seem to support annotations. Also it had no release since 2006. Annogen - uses JDK's Doclet generator, which has some bugs under 1.5 JDK. Also it had no releases for a long time. Javaparser - seems good as well and pretty recent, but only supports Visitor pattern for a single class i.e. no query mechanism like in the 2 above packages.

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