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  • Data storage advice needed: Best way to store location + time data?

    - by sobedai
    I have a project in mind that will require the majority of queries to be keyed off of lat/long as well as date + time. Initially, I was thinking of a standard RDBMS where lat, long, and the datetime field are properly indexed. Then, I began thinking of a document based system where the document was essentially a timestamp and each document has lat/long with in it. Each document could have n objects associated with it. I'm looking for advice on what would be the best type of storage engine for this sort of thing is - which of the above idea would be better or if there is something else completely that is the ideal solution. Thanks

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  • Experiences teaching or learning map/reduce/etc before recursion?

    - by Jay
    As far as I can see, the usual (and best in my opinion) order for teaching iterting constructs in functional programming with Scheme is to first teach recursion and maybe later get into things like map, reduce and all SRFI-1 procedures. This is probably, I guess, because with recursion the student has everything that's necessary for iterating (and even re-write all of SRFI-1 if he/she wants to do so). Now I was wondering if the opposite approach has ever been tried: use several procedures from SRFI-1 and only when they are not enough (for example, to approximate a function) use recursion. My guess is that the result would not be good, but I'd like to know about any past experiences with this approach.

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  • C# loop - break vs. continue

    - by Terrapin
    In a C# (feel free to answer for other languages) loop, what's the difference between break and continue as a means to leave the structure of the loop, and go to the next iteration? Example: foreach (DataRow row in myTable.Rows){ if (someConditionEvalsToTrue) { break; //what's the difference between this and continue ? //continue; }}

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  • How to have the controller change its behavior depending on the view?

    - by Ian Boyd
    If from one view a user enters some invalid data, e.g.:     E-mail: [email protected]     then i want the controller to: not place the data into the model color the text box reddish not allow the user to save But it's possible that if the user enters the same invalid data in a different view i want the controller to: place the data into the model color the text box reddish allow the user to save But it's possible that if the user enters the same invalid data in a different view i want the controller to: place the data into the model color the text box bluish allow the user to save And it's possible that another view will: place the data into the model leave the text box uncolored allow the user to save And it's possible that another view will: auto-correct the data, placing it into the model color the text-box reddish allow the user to have And it's possible for another view to: auto-correct the data, placing it into the model update the view with the new data color the text-box bluish allow the user to save [ad infinitum] Without using n-controllers for n-views, how do i do this?

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  • Count the number of objects in an Image

    - by kunjaan
    I am investigating the possibility of image processing to identify certain objects and also count them in an image. I will be given a picture and I need to identify the number of boxes present in that image. Does anybody have any experience with any Machine Vision/ Image Processing libraries like ImageJ, Fiji, JAI, jMagick ,Java Vision Toolkit? Which do you think is best suited for the job? What do you guys suggest? If the APIs can be used from Java, it would be better. Thank you. Edit: I am dealing with warehouse brown boxes. Yes I am talking about regular photos. The source is usually a mobile phone picture.

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  • Sequence Point and Evaluation Order( Preincrement)

    - by Josh
    There was a debate today among some of my colleagues and I wanted to clarify it. It is about the evaluation order and the sequence point in an expression. It is clearly stated in the standard that C/C++ does not have a left-to-right evaluation in an expression unlike languages like Java which is guaranteed to have a sequencial left-to-right order. So, in the below expression, the evaluation of the leftmost operand(B) in the binary operation is sequenced before the evaluation of the rightmost operand(C): A = B B_OP C The following expression according, to CPPReference under the subsection Sequenced-before rules(Undefined Behaviour) and Bjarne's TCPPL 3rd ed, is an UB x = x++ + 1; It could be interpreted as the compilers like BUT the expression below is said to be clearly a well defined behaviour in C++11 x = ++x + 1; So, if the above expression is well defined, what is the "fate" of this? array[x] = ++x; It seems the evaluation of a post-increment and post-decrement is not defined but the pre-increment and the pre-decrement is defined. NOTE: This is not used in a real-life code. Clang 3.4 and GCC 4.8 clearly warns about both the pre- and post-increment sequence point.

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  • How do software events work internally?

    - by Duddle
    Hello! I am a student of Computer Science and have learned many of the basic concepts of what is going on "under the hood" while a computer program is running. But recently I realized that I do not understand how software events work efficiently. In hardware, this is easy: instead of the processor "busy waiting" to see if something happened, the component sends an interrupt request. But how does this work in, for example, a mouse-over event? My guess is as follows: if the mouse sends a signal ("moved"), the operating system calculates its new position p, then checks what program is being drawn on the screen, tells that program position p, then the program itself checks what object is at p, checks if any event handlers are associated with said object and finally fires them. That sounds terribly inefficient to me, since a tiny mouse movement equates to a lot of cpu context switches (which I learned are relatively expensive). And then there are dozens of background applications that may want to do stuff of their own as well. Where is my intuition failing me? I realize that even "slow" 500MHz processors do 500 million operations per second, but still it seems too much work for such a simple event. Thanks in advance!

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  • What are the core mathematical concepts a good developer should know?

    - by Jose B.
    Since Graduating from a very small school in 2006 with a badly shaped & outdated program (I'm a foreigner & didn't know any better school at the time) I've come to realize that I missed a lot of basic concepts from a mathematical & software perspective that are mostly the foundations of other higher concepts. I.e. I tried to listen/watch the open courseware from MIT on Introduction to Algorithms but quickly realized I was missing several mathematical concepts to better understand the course. So what are the core mathematical concepts a good software engineer should know? And what are the possible books/sites you will recommend me?

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  • Add custom method to string object [closed]

    - by cru3l
    Possible Duplicate: Can I add custom methods/attributes to built-in Python types? In Ruby you can override any built-in object class with custom method, like this: class String def sayHello return self+" is saying hello!" end end puts 'JOHN'.downcase.sayHello # >>> 'john is saying hello!' How can i do that in python? Is there a normally way or just hacks?

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  • How do I load a second view correctly in Swift?

    - by slooker
    I have a view that I'm trying to load in Swift like this, but it crashes with this error: 'NSInternalInconsistencyException', reason: '-[UIViewController _loadViewFromNibNamed:bundle:] loaded the "DetailView" nib but the view outlet was not set.' Here is the code I'm trying to use to load it. Second View Controller import UIKit class DetailViewController: UIViewController { @IBOutlet var nameField: UITextField override func viewDidLoad() { super.viewDidLoad() } } Code to load the view controller: var newViewController = DetailViewController() @IBAction func buttonTapped(AnyObject) { println("button tapped!") self.presentViewController(newViewController, animated: true, nil) } What am I doing wrong?

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  • Highly efficient filesystem APIs for certain kinds of operations

    - by romkyns
    I occasionally find myself needing certain filesystem APIs which could be implemented very efficiently if supported by the filesystem, but I've never heard of them. For example: Truncate file from the beginning, on an allocation unit boundary Split file into two on an allocation unit boundary Insert or remove a chunk from the middle of the file, again, on an allocation unit boundary The only way that I know of to do things like these is to rewrite the data into a new file. This has the benefit that the allocation unit is no longer relevant, but is extremely slow in comparison to some low-level filesystem magic. I understand that the alignment requirements mean that the methods aren't always applicable, but I think they can still be useful. For example, a file archiver may be able to trim down the archive very efficiently after the user deletes a file from the archive, even if that leaves a small amount of garbage either side for alignment reasons. Is it really the case that such APIs don't exist, or am I simply not aware of them? I am mostly interested in NTFS, but hearing about other filesystems will be interesting too.

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  • Generate unique ID from multiple values with fault tolerance

    - by ojreadmore
    Given some values, I'd like to make a (pretty darn) unique result. $unique1 = generate(array('ab034', '981kja7261', '381jkfa0', 'vzcvqdx2993883i3ifja8', '0plnmjfys')); //now $unique1 == "sqef3452y"; I also need something that's pretty close to return the same result. In this case, 20% of the values is missing. $unique2 = generate(array('ab034', '981kja7261', '381jkfa0', 'vzcvqdx2993883i3ifja8')); //also $unique2 == "sqef3452y"; I'm not sure where to begin with such an algorithm but I have some assumptions. I assume that the more values given, the more accurate the resulting ID – in other words, using 20 values is better than 5. I also assume that a confidence factor can be calculated and adjusted. What would be nice to have is a weight factor where one can say 'value 1 is more important than value 3'. This would require a multidimensional array for input instead of one dimension. I just mashed on the keyboard for these values, but in practice they may be short or long alpha numeric values.

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  • Why "constructor-way" of declaring variable in "for-loop" allowed but in "if-statement" not allowed?

    - by PiotrNycz
    Consider this simple example: /*1*/ int main() { /*2*/ for (int i(7); i;){break;} /*3*/ if (int i(7)) {} /*4*/ } Why line-2 compiles just fine, whilst line-3 gives the error? This is little strange to me why if-statement is in this aspect treated worse than for-loop? If this is compiler specific - I tested with gcc-4.5.1: prog.cpp: In function 'int main()': prog.cpp:3:7: error: expected primary-expression before 'int' prog.cpp:3:7: error: expected ')' before 'int' I was inspired by this question [UPDATE] I know this compiles just fine: /*1*/ int main() { /*2*/ for (int i = 7; i;){break;} /*3*/ if (int i = 7) {} /*4*/ }

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  • In which situation is the c++/c# namespace approach better than the Java approach?

    - by mike g
    The reason I ask this is that c# could easily have copied the java convention, or a variation of it, but opted for the more flexible approach of explicitly declaring namespaces inside files. As a Java programmer often there are things that I wish I could do differently, but namespaces is not one of them. The flexbility has a certain overhead (extra braces, extra decisions for developers, making it harder to view a projects contributions to the namespace, at least without a specialist IDE). So what practical examples are there when this flexiblity is advantageous?

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  • What do you call the concept of dynamic data definition?

    - by DJTripleThreat
    Maybe this is simpler and more straightforward then what I'm thinking but I can't seem to find this concept on google anywhere. The concept is this: You have a table in a database and the table has a specified number of columns. However, it has been asked of me by previous clients that there also be a set of dynamic user defined columns that can be added on the fly. What is this concept called and is it considered a design pattern?

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  • How would you calculate all possible permutations of 0 through N iteratively?

    - by Bob Aman
    I need to calculate permutations iteratively. The method signature looks like: int[][] permute(int n) For n = 3 for example, the return value would be: [[0,1,2], [0,2,1], [1,0,2], [1,2,0], [2,0,1], [2,1,0]] How would you go about doing this iteratively in the most efficient way possible? I can do this recursively, but I'm interested in seeing lots of alternate ways to doing it iteratively.

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  • Does Anyone Still Prefer N-Tier Architecture After Having *Shipped* an MVC Application?

    - by Jim G.
    Other SO threads have asked people if they prefer N-Tier or MVC architecture. I'm not looking to continue that debate on this thread. I'm looking for something more specific. My Question: Does Anyone Still Prefer N-Tier Architecture After Having Shipped an MVC Application? Reason for My Question: Before I shipped an MVC web application, I wasn't convinced that it was superior to N-Tier Architecture. Specifically, if better unit testing was the only obvious benefit of MVC, then I saw no reason to switch gears and adopt a new architecture. But after having shipped an MVC application, I can see many benefits (which have been enumerated on other threads).

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  • What is the smallest amount of bits you can write twin-prime calculation?

    - by HH
    A succinct example in Python, its source. Explanation about the syntactic sugar here. s=p=1;exec"if s%p*s%~-~p:print`p`+','+`p+2`\ns*=p*p;p+=2\n"*999 The smallest amount of bits is defined by the smallest amount of 4pcs of things you can see with hexdump, it is not that precise measure but well-enough until an ambiguity. $ echo 's=p=1;exec"if s%p*s%~-~p:print`p`+','+`p+2`\ns*=p*p;p+=2\n"*999' > .test $ hexdump .test | wc 5 36 200 $ hexdump .test 0000000 3d73 3d70 3b31 7865 6365 6922 2066 2573 0000010 2a70 2573 2d7e 707e 703a 6972 746e 7060 0000020 2b60 2b2c 7060 322b 5c60 736e 3d2a 2a70 0000030 3b70 2b70 323d 6e5c 2a22 3939 0a39 000003e so in this case it is 31 because the initial parts are removed.

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  • Javascript: best solution to wait for all ajax callbacks to be executed

    - by glaz666
    Hi! Imagine we have to sources to be requested by ajax. I want to perform some actions when all callbacks are triggered. How this can be done besides this approach: (function($){ var sources = ['http://source1.com', 'http://source2.com'], guard = 0, someHandler = function() { if (guard != sources.length) { return; } //do some actions }; for (var idx in sources) { $.getJSON(sources[idx], function(){ guard++; someHandler(); }) } })(jQuery) What I don't like here is that in this case I can't handle response failing (eg. I can't set timeout for response to come) and overall approach (I suppose there should be a way to use more power of functional programming here) Any ideas? Regards!

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