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  • Are there any decent free JAVA data plotting libraries out there?

    - by Kurt W. Leucht
    On a recent JAVA project, we needed a free JAVA based real-time data plotting utility. After much searching, we found this tool called the Scientific Graphics Toolkit or SGT from NOAA. It seemed pretty robust, but we found out that it wasn't terribly configurable. Or at least not configurable enough to meet our needs. We ended up digging very deeply into the JAVA code and reverse engineering the code and changing it all around to make the plot tool look and act the way we wanted it to look and act. Of course, this killed any chance for future upgrades from NOAA. So what free or cheap JAVA based data plotting tools or libraries do you use? Followup: Thanks for the JFreeChart suggestions. I checked out their website and it looks like a very nice data charting and plotting utility. I should have made it clear in my original question that I was looking specifically to plot real-time data. I corrected my question above to make that point clear. It appears that JFreeChart support for live data is marginal at best, though. Any other suggestions out there?

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  • LRU cache design

    - by user297850
    Least Recently Used (LRU) Cache is to discard the least recently used items first How do you design and implement such a cache class? The design requirements are as follows: 1) find the item as fast as we can 2) Once a cache misses and a cache is full, we need to replace the least recently used item as fast as possible. How to analyze and implement this question in terms of design pattern and algorithm design?

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  • The subscription model behind CSS selectors?

    - by Martin Kristiansen
    With CSS selectors a query string body > h1.span subscribes to a specific type of nodes in the tree. Does anyone know how this is done? Selectors for transformations, how does the browser select the result set? And is there a trick to making it efficient? I imagine there being some sort of hierarchical type-tree for the entire structure to which the nodes subscribe and which is what is used when doing the selector queries — but this is only a guess. Does anyone know the real answer? Or even more interesting, what would be the best way to do dynamic lookups on a tree based on jQuery/CSS search queries?

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  • What is validating a binary search tree?

    - by dotnetdev
    I read on here of an exercise in interviews known as validating a binary search tree. How exactly does this work? What would one be looking for in validating a binary search tree? I have written a basic search tree, but never heard of this concept. Thanks

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  • ByteBuffer recycling class

    - by Chris Dennett
    Hi everyone, I'm wonder how I'd code up a ByteBuffer recycling class that can get me a ByteBuffer which is at least as big as the specified length, and which can lock up ByteBuffer objects in use to prevent their use while they are being used by my code. This would prevent re-construction of DirectByteBuffers and such over and over, instead using existing ones. Is there an existing Java library which can do this very effectively? I know Javolution can work with object recycling, but does that extend to the ByteBuffer class in this context with the requirements set out? Cheers, Chris

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  • Google Federated Login vs Hybrid Protocol vs Google Data Authentication. Whats's the Difference?

    - by johnfelix
    Hi, I am trying to implement Google Authentication in my website, in which I would also be pulling some Google Data using the Google Data API and I am using Google App Engine with Jinja2. My question is, so many ways are mentioned to do it. I am confused between Google Federated Login,Google Data Protocol, Hybrid Protocol. Are these things the same or different ways to do the same thing. From what I read and understood, which might be incorrect, Google Federated Login uses the hybrid protocol to authenticate and fetch the google data. Is there a proper guide to implement any one of these in python. Examples which I found at the google link are kind of different. From what I understood,correct me if i am wrong, I have to implement only the OpenID Consumer part. In order to implement Google Federated Login in Python, I saw that we need to download a separate library from the openid-enabled.com but I found a different library for the google data implementation at http://code.google.com/p/gdata-python-client/ As you can see, I am confused a lot :D. Please help me :) Thanks

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  • Effects of changing a node in a binary tree

    - by eSKay
    Suppose I want to change the orange node in the following tree. So, the only other change I'll need to make is in the left pointer of the green node. The blue node will remain the same. Am I wrong somewhere? Because according to this article (that explains zippers), even the blue node needs to be changed. Similarly, in this picture (recolored) from the same article, why do we change the orange nodes at all (when we change x)?

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  • hash of array in objective-c, how?

    - by Horace Ho
    How is a hash of integer array can be represented in objective-c? Here is the ruby hash as an example: hi_scores = { "John" => [1, 1000], "Mary" => [2, 8000], "Bob" => [5, 2000] } such that can be accessed by: puts hi_scores["Mary"][1] => 8000 hopefully easy to serialize too. Thanks!

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  • Can someone describe through code a practical example of backtracking with iteration instead of recursion?

    - by chrisapotek
    Recursion makes backtracking easy as it guarantees that you won't go through the same path again. So all ramifications of your path are visited just once. I am trying to convert a backtracking tail-recursive (with accumulators) algorithm to iteration. I heard it is supposed to be easy to convert a perfectly tail-recursive algorithm to iteration. But I am stuck in the backtracking part. Can anyone provide a example through code so myself and others can visualize how backtracking is done? I would think that a STACK is not needed here because I have a perfectly tail-recursive algorithm using accumulators, but I can be wrong here.

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  • Variadic templates in Scala

    - by Thomas Jung
    Suppose you want to have something like variadic templates (the ability to define n type parameters for a generic class) in Scala. For example you do not want to define Tuple2[+T1, +T2] and Tuple3[+T1, +T2, +T3] but Tuple[T*]. Are there other options than HLists?

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  • What is better, a STL list or a STL Map for 20 entries, considering order of insertion is as importa

    - by Abhijeet
    I have the following scenario.The implementation is required for a real time application. 1)I need to store at max 20 entries in a container(STL Map, STL List etc). 2)If a new entry comes and 20 entries are already present i have to overwrite the oldest entry with the new entry. Considering point 2, i feel if the container is full (Max 20 entries) 'list' is the best bet as i can always remove the first entry in the list and add the new one at last (push_back). However, search won't be as efficient. For only 20 entries, does it really make a big difference in terms of searching efficiency if i use a list in place of a map? Also considering the cost of insertion in map i feel i should go for a list? Could you please tell what is a better bet for me ?

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  • Generating permutation in Python with specific rule

    - by twfx
    Let say a=[A, B, C, D], each element has a weight w, and is set to 1 if selected, 0 if otherwise. I'd like to generate permutation in the below order 1,1,1,1 1,1,1,0 1,1,0,1 1,1,0,0 1,0,1,1 1,0,1,0 1,0,0,1 1,0,0,0 Let's w=[1,2,3,4] for item A,B,C,D ... and max_weight = 4. For each permutation, if the accum weight has exceeded max_weight, stop calculation for that permutation, move to next permutation. For eg. 1,1,1 --> 6 > 4, exceeded, stop, move to next 1,1,1 --> 6 > 4, exceeded, stop, move to next 1,1,0,1 --> 7 > 4 finished, move to next 1,1,0,0 --> 3 finished, move to next 1,0,1,1 --> 8 > 4, finished, stop, move to next 1,0,1,0 --> 4 finished, move to next 1,0,0,1 --> 5 > 4 finished, move to next 1,0,0,0 --> 1 finished, move to next [1,0,1,0] is the best combination which does not exceeded max_weight 4 My questions are What's the algorithm which generate the required permutation? Or any suggestion I could generate the permutation? As the number of element can be up to 10000, and the calculation stop if the accum weight for the branch exceeds max_weight, it is not necessary to generate all permutation first before the calculation. How can the algo in (1) generate permutation on the fly?

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  • How to efficiently save changes made in UI/main thread with Core Data?

    - by Jaanus
    So, there have been several posts here about importing and saving data from an external data source into Core Data. Apple documents a reasonable pattern for this: "import and save on background thread, merge saved objects to main thread." All fine and good. I have a related but different problem: the user is modifying data in the UI and main thread, and thus modifies state of some objects in the managed object context (MOC). I would like to save these changes from time to time. What is a good way to do that? Now, you could say that I could do the same: create a background thread with its own MOC and pass the changed objectID-s there. The catch-22 for me with this is that an object's ID changes when it is saved, and I cannot guarantee the order of things happening. I may end up passing a different objectID into the background thread for the same object, based on whether the object has been previously saved or not, and I don't know if Core Data can resolve this and see that different objectID-s are pointing to the same object and not create duplicates for me. (I could test this, but I'm lazywebbing with this question first.) One thought I had: I could always do MOC saves on a background thread, and queue them up with operationqueue, so that there is always only one save in progress. I would not create a new MOC, I would just use the same MOC as in main thread. Now, this is not thread safe and when someone modifies the MOC in main thread while it is being saved in background thread, the results will probably be catastrophic. But, minus the thread safety, you can see what kind of solution I'd wish for. To be clear, the problem I need to fix is that if I just do the save in main thread, it blocks the UI for an unacceptably long period of time, I want to move the save to background thread. So, questions: what about the reasoning of an object ID changing during saving, and Core Data being able to resolve them to the same object? Would this be the right way of addressing this problem? any other good ways of doing this?

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  • Magento resource model for table with compound primary key

    - by sdek
    I am creating a custom module for a Magento ecommerce site, and the module will center around a new (ie, custom) table that has a compound/composite primary key, or rather the table has two columns that make up the primary key. Does anybody know how to create your models/resource models based on a table with a compound key? To give a few more details, I have looked up several tutorials and also used the excellent moduleCreator script. But it seems like all the tutorials revolve around the table having a PK with just one column in it. Something like this: class <Namespace>_<Module>_Model_Mysql4_<Module> extends Mage_Core_Model_Mysql4_Abstract { public function _construct(){ $this->_init('<module_alias>/<table_alias>', '<table_primary_key_id>'); } } Also, I just noticed that looking at the database model almost all tables have a single primary key. I understand this has much to do with the EAV-style db structure, but still is it possible to use a table with a compound PK? I want to stick with the Magento framework/conventions if possible. Is it discouraged? Should I just change the structure of my custom table to have some dummy id column? I do have the ability to do that, but geez! (Another side note that I thought I would mention is that it looks like the Zend Framework provides a way to base a class on a table with compound primary key (see Example #20 on this page - about half-way down), so it seems that the Magento framework should also provide for it... I just don't see how.)

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