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• CMS and Databases vs. DIY

  - by hozza

  I have been programming for many years now, primarily in PHP and the like and would consider myself an intermediate programmer. Some of my online projects have now gone global and very widely used, i am now in deep thought about scalability etc. All of my systems so far are written in PHP, no known database structure such as MySQL etc. Instead our databases use an 'operating system style' method of storing information, files and folders if you will. We also do not use any outside/third-party software or CMS, so far this has work out extremely well. Most people, when they hear about the way we do things, criticize and say that is an idiotic idea but normally after seeing our systems in more dept are converted to our way of doing things. Is it really that bad to not use a standard databasing systems and only using the one (slightly heavier than others) language of PHP? How well on the face of it will this kind of setup scale? N.B. Our systems include things such as account and user management, documentation development and task/project managing.

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• Optimal Data Structure for our own API

  - by vermiculus

  I'm in the early stages of writing an Emacs major mode for the Stack Exchange network; if you use Emacs regularly, this will benefit you in the end. In order to minimize the number of calls made to Stack Exchange's API (capped at 10000 per IP per day) and to just be a generally responsible citizen, I want to cache the information I receive from the network and store it in memory, waiting to be accessed again. I'm really stuck as to what data structure to store this information in. Obviously, it is going to be a list. However, as with any data structure, the choice must be determined by what data is being stored and what how it will be accessed. What, I would like to be able to store all of this information in a single symbol such as stack-api/cache. So, without further ado, stack-api/cache is a list of conses keyed by last update: `(<csite> <csite> <csite>) where <csite> would be (1362501715 . <site>) At this point, all we've done is define a simple association list. Of course, we must go deeper. Each <site> is a list of the API parameter (unique) followed by a list questions: `("codereview" <cquestion> <cquestion> <cquestion>) Each <cquestion> is, you guessed it, a cons of questions with their last update time: `(1362501715 <question>) (1362501720 . <question>) <question> is a cons of a question structure and a list of answers (again, consed with their last update time): `(<question-structure> <canswer> <canswer> <canswer> and ` `(1362501715 . <answer-structure>) This data structure is likely most accurately described as a tree, but I don't know if there's a better way to do this considering the language, Emacs Lisp (which isn't all that different from the Lisp you know and love at all). The explicit conses are likely unnecessary, but it helps my brain wrap around it better. I'm pretty sure a <csite>, for example, would just turn into (<epoch-time> <api-param> <cquestion> <cquestion> ...) Concerns: Does storing data in a potentially huge structure like this have any performance trade-offs for the system? I would like to avoid storing extraneous data, but I've done what I could and I don't think the dataset is that large in the first place (for normal use) since it's all just human-readable text in reasonable proportion. (I'm planning on culling old data using the times at the head of the list; each inherits its last-update time from its children and so-on down the tree. To what extent this cull should take place: I'm not sure.) Does storing data like this have any performance trade-offs for that which must use it? That is, will set and retrieve operations suffer from the size of the list? Do you have any other suggestions as to what a better structure might look like?

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• Is it dangerous for me to give some of my Model classes Control-like methods?

  - by Pureferret

  In my personal project I have tried to stick to MVC, but I've also been made aware that sticking to MVC too tightly can be a bad thing as it makes writing awkward and forces the flow of the program in odd ways (i.e. some simple functions can be performed by something that normally wouldn't, and avoid MVC related overheads). So I'm beginning to feel justified in this compromise: I have some 'manager programs' that 'own' data and have some way to manipulate it, as such I think they'd count as both part of the model, and part of the control, and to me this feels more natural than keepingthem separate. For instance: One of my Managers is the PlayerCharacterManager that has these methods: void buySkill(PlayerCharacter playerCharacter, Skill skill); void changeName(); void changeRole(); void restatCharacter(); void addCharacterToGame(); void createNewCharacter(); PlayerCharacter getPlayerCharacter(); List<PlayerCharacter> getPlayersCharacter(Player player); List<PlayerCharacter> getAllCharacters(); I hope the mothod names are transparent enough that they don't all need explaining. I've called it a manager because it will help manage all of the PlayerCharacter 'model' objects the code creates, and create and keep a map of these. I may also get it to store other information in the future. I plan to have another two similar classes for this sort of control, but I will orchestrate when and how this happens, and what to do with the returned data via a pure controller class. This splitting up control between informed managers and the controller, as opposed to operating just through a controller seems like it will simplify my code and make it flow more. My question is, is this a dangerous choice, in terms of making the code harder to follow/test/fix? Is this somethign established as good or bad or neutral? I oculdn't find anything similar except the idea of Actors but that's not quite why I'm trying to do. Edit: Perhaps an example is needed; I'm using the Controller to update the view and access the data, so when I click the 'Add new character to a player button' it'll call methods in the controller that then go and tell the PlayerCharacterManager class to create a new character instance, it'll call the PlayerManager class to add that new character to the player-character map, and then it'll add this information to the database, and tell the view to update any GUIs effected. That is the sort of 'control sequence' I'm hoping to create with these manager classes.

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• Unit testing a text index

  - by jplot

  Consider a text index such as a suffix tree or a suffix array supporting Count queries (number of occurrences of a pattern) and Locate queries (the positions of all the occurrences of a pattern) over a given text. How would you go about unit testing such a class ? What I have in mind is to generate a big random string then extract a random substring from this big string and compare the results of both queries with naive implementations (such as string::find). Another idea I have is to find the most frequent substring of length l appearing in the original string (using perhaps a naive method) and use these substrings for testing the index. This isn't the best way, so what would be a good design of the unit tests for a text index ? In case it matters, this is in C++ using google test.

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• Most efficient Implementation a Tree in C++

  - by Topo

  I need to write a tree where each element may have any number of child elements, and because of this each branch of the tree may have any length. The tree is only going to receive elements at first and then it is going to use exclusively for iterating though it's branches in no specific order. The tree will have several million elements and must be fast but also memory efficient. My plan makes a node class to store the elements and the pointers to its children. When the tree is fully constructed, it would be transformed it to an array or something faster and if possible, loaded to the processor's cache. Construction and the search on the tree are two different problems. Can I focus on how to solve each problem on the best way individually? The construction of has to be as fast as possible but it can use memory as it pleases. Then the transformation into a format that give us speed when iterating the tree's branches. This should preferably be an array to avoid going back and forth from RAM to cache in each element of the tree. So the real question is which is the structure to implement a tree to maximize insert speed, how can I transform it to a structure that gives me the best speed and memory?

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• What's beyond c,c++ and data structure?

  - by sagacious

  I have learnt c and c++ programming languages.i have learnt data structure too. Now i'm confused what to do next?my aim is to be a good programmer. i want to go deeper into the field of programming and making the practical applications of what i have learnt. So,the question takes the form-what to do next?Or is there any site where i can see advantage of every language with it's features? sorry,if there's any language error and thanks in advance.

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• Are "skip deltas" unique to svn?

  - by echinodermata

  The good folks who created the SVN version control system use a structure they refer to as "skip deltas" to store the revision history of files internally. A revision is stored as a delta against an earlier revision. However, revision N is not necessarily stored as a delta against revision N-1, like this: 0 <- 1 <- 2 <- 3 <- 4 <- 5 <- 6 <- 7 <- 8 <- 9 Instead, revision N is stored as a delta against N-f(N), where f(N) is the greatest power of two that divides N: 0 <- 1 2 <- 3 4 <- 5 6 <- 7 0 <------ 2 4 <------ 6 0 <---------------- 4 0 <------------------------------------ 8 <- 9 (Superficially it looks like a skip list but really it's not that similar - for instance, skip deltas are not interested in supporting insertion in the middle of the list.) You can read more about it here. My question is: Do other systems use skip deltas? Were skip deltas known/used/published before SVN, or did the creators of SVN invent it themselves?

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• Most efficient way to store this collection of moduli and remainders?

  - by Bryan

  I have a huge collection of different moduli and associated with each modulus a fairly large list of remainders. I want to store these values so that I can efficiently determine whether an integer is equivalent to any one of the remainders with respect to any of the moduli (it doesn't matter which, I just want a true/false return). I thought about storing these values as a linked-list of balanced binary trees, but I was wondering if there is a better way? EDIT Perhaps a little more detail would be helpful. As for the size of this structure, it will be holding about 10s of thousands of (prime-1) moduli and associated to each modulus will be a variable amount of remainders. Most moduli will only have one or two remainders associated to it, but a very rare few will have a couple hundred associated to it. This is part of a larger program which handles numbers with a couple thousand (decimal) digits. This program will benefit more from this table being as large as possible and being able to be searched quickly. Here's a small part of the dataset where the moduli are in parentheses and the remainders are comma separated: (46) k = 20 (58) k = 15, 44 (70) k = 57 (102) k = 36, 87 (106) k = 66 (156) k = 20, 59, 98, 137 (190) k = 11, 30, 68, 87, 125, 144, 182 (430) k = 234 (520) k = 152, 282 (576) k = 2, 11, 20, 29, 38, 47, 56, 65, 74, ...(add 9 each time), 569 I had said that the moduli were prime, but I was wrong they are each one below a prime.

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• I have data that sends in "bursts" of 100 records with a significant delay. How do I structure my classes for multithreading?

  - by makerofthings7

  My datasource sends information in 100 batches of 100 records with a delay of 1 to 3 seconds between batches. I would like to start processing data as soon as it's received, but I'm not sure how to best approach this. Some ideas I've been playing with include: yield Concurrent Dictionary ConcurrentDictionary with INotifyProperyChanged Events etc. As you can see I'm all over the place, and would appreciate some tested guidance on how to approach this

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• I need some help creating a non-binary tree (or some other data structure that will better solve my problem)

  - by EDO

  I have about ten lists of numbers and some strings. Each list has about <= 30K lines. Each line on a list has a distinct number. I need to build an efficient way of finding all the lines in each list that has the same 'control' number (or key for dB guys) and comparing what is in their string parts. I am writing this in Java. I have thought about using trees but my brain cells are about burnt now. I need some help.

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• Data structure supporting the following operations

  - by 500865

  I'm looking for a data structure for working with a set of data which is most efficient to do the following : Check whether an item has been categorized or not. (The categorized and uncategorized set are disjoint sets). Get the category of an item. Get all the items in a particular category. Get all the uncategorized items. Remove a particular item from the data set. I was thinking of having a Dictionary<String, Set<String>> to hold all the items in a given category, but that doesn't solve 2.

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• Is this bad practice?

  - by gekod

  I just wanted to ask for your opinion on a situation that occurs sometimes and which I don't know what would be the most elegant way to solve it. Here it goes: We have module A which reads an entry from a database and sends a request to module B containing ONLY the information from the entry module B would need to accomplish it's job (to keep modularity I just give it the information it needs - module B has nothing to do with the rest of the information from the read DB entry). Now after finishing it's job, module B has to reply to a module C if it succeeded or failed. To do this module B replies with the information it has gotten from module A and some variable meaning success or fail. Now here comes the problem: module C needs to find that entry again BUT the information it has gotten from module B is not enough to uniquely find the exact same entry again. I don't think that module A giving more information to module B which it doesn't need to do it's job but which it could then give back to module C would be a good practice because this would mean giving some module information it doesn't really need. What do you think?

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• Is there a data structure for this type of list/map?

  - by Nick

  Perhaps there's a name for what I want, but I'm not aware of it. I need something similar to a LinkedHashMap in Java, but where it returns the 'previous' value if there's no value at the specified key. That is, I have a list of objects stored by an integer key (which is in units of time in my case): ; key->value 10->A 15->B 20->C So, if I were to query for a value for key 0-9, it would return null. The special part is if I queried for something 10 <= i <= 14 it would return A. Or, for i = 20, it would return C. Is there a data structure for this?

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• Data structure for file search

  - by poly

  I've asked this question before and I got a few answers/idea, but I'm not sure how to implement them. I'm building a telecom messaging solution. Currently, I'm using a database to save my transaction/messages for the network stack I've built, and as you know it's slower than using a data structure (hash, linkedlist, etc...). My problem is that the data can be really huge, and it won't fit in the memory. I was thinking of saving the records in a file and the a key and line number in a hash, then if I want to access some record then I can get the line number from the hash, and get it from the file. I don't know how efficient is this; I think the database is doing a way better job than this on my behalf. Please share whatever you have in mind.

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• What is the best way to store a table in C++

  - by Topo

  I'm programming a decision tree in C++ using a slightly modified version of the C4.5 algorithm. Each node represents an attribute or a column of your data set and it has a children per possible value of the attribute. My problem is how to store the training data set having in mind that I have to use a subset for each node so I need a quick way to only select a subset of rows and columns. The main goal is to do it in the most memory and time efficient possible (in that order of priority). The best way I have thought of is to have an array of arrays (or std::vector), or something like that, and for each node have a list (array, vector, etc) or something with the column,line(probably a tuple) pairs that are valid for that node. I now there should be a better way to do this, any suggestions? UPDATE: What I need is something like this: In the beginning I have this data: Paris 4 5.0 True New York 7 1.3 True Tokio 2 9.1 False Paris 9 6.8 True Tokio 0 8.4 False But for the second node I just need this data: Paris 4 5.0 New York 7 1.3 Paris 9 6.8 And for the third node: Tokio 2 9.1 Tokio 0 8.4 But with a table of millions of records with up to hundreds of columns. What I have in mind is keep all the data in a matrix, and then for each node keep the info of the current columns and rows. Something like this: Paris 4 5.0 True New York 7 1.3 True Tokio 2 9.1 False Paris 9 6.8 True Tokio 0 8.4 False Node 2: columns = [0,1,2] rows = [0,1,3] Node 3: columns = [0,1,2] rows = [2,4] This way on the worst case scenario I just have to waste size_of(int) * (number_of_columns + number_of_rows) * node That is a lot less than having an independent data matrix for each node.

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• I need to create an employee schedule/appointments program, but I don't know how to set it up

  - by robz228

  I work for a gym. I am the programmer, its just me, nobody else! Gets really frustrating when there's nobody to bounce conceptual ideas off of. I'm getting rid of our archaic paper binder systems for tracking appointments and what not. I've made a lot of things successfully already, now I'm trying to tackle the personal training department. What I want: Trainer information and work schedule Appointment booking that can be done by time slot with all available trainers for that time, or by trainer with all available hours for that trainer What I've tried so far: I started with an 'appointments' database, a 'trainers' database, and a 'schedules' database. This became so complicated trying to fit the schedule in that I scrapped it. Does anyone know know the best way to structure the tables for this and how to sort of make them communicate correctly? I don't need specific code, I just need help understand how to make this thing!

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• Handling timeout in network application

  - by user2175831

  How can I handle timeouts in a network application. I'm implementing a provisioning system on a Linux server, the code is huge so I'm going to put the algorithm, it works as like this Read provisioning commands from file Send it to another server using TCP Save the request in hash. Receive the response then if successful response received then remove request from hash if failed response received then retry the message The problem I'm in now is when the program didn't receive the response for a timeout reason then the request will be waiting for a response forever and won't be retried. And please note that I'll be sending hundreds of commands and I have to monitor the timeout commands for all of them. I tried to use timer but that didn't help because I'll end up with so many waiting timers and I'm not sure if this is a good way of doing this. The question is how can I save the message in some data structure and check to remove or retry it later when there is no response from the other end? Please note that I'm willing to change the algorithm to anything you suggest that could deal with the timeouts.

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• Data structure for grid with negative indeces

  - by The Secret Imbecile

  Sorry if this is an insultingly obvious concept, but it's something I haven't done before and I've been unable to find any material discussing the best way to approach it. I'm wondering what's the best data structure for holding a 2D grid of unknown size. The grid has integer coordinates (x,y), and will have negative indices in both directions. So, what is the best way to hold this grid? I'm programming in c# currently, so I can't have negative array indices. My initial thought was to have class with 4 separate arrays for (+x,+y),(+x,-y),(-x,+y), and (-x,-y). This seems to be a valid way to implement the grid, but it does seem like I'm over-engineering the solution, and array resizing will be a headache. Another idea was to keep track of the center-point of the array and set that as the topological (0,0), however I would have the issue of having to do a shift to every element of the grid when repeatedly adding to the top-left of the grid, which would be similar to grid resizing though in all likelihood more frequent. Thoughts?

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• design for interruptable operations

  - by tpaksu

  I couldn't find a better topic but here it is; 1) When user clicks a button, code starts t work, 2) When another button is clicked, it would stop doing whatever it does and start to run the second button's code, 3) Or with not user interaction, an electrical power down detected from a connected device, so our software would cancel the current event and start doing the power down procedure. How is this design mostly applied to code? I mean "stop what you are doing" part? If you would say events, event handlers etc. how do you bind a condition to the event? and how do you tell the program without using laddered if's to end it's process? method1(); if (powerdown) return; method2(); if (powerdown) return; etc.

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• MATLAB: What is an appropriate Data Structure for a Matrix with Random Variable Entries?

  - by user12707

  I'm working in an area that is related to simulation and trying to design a data structure that can include random variables within matrices. I am currently coding in MATLAB. To motivate this let me say I have the following matrix: [a b; c d] I want to find a data structure that will allow for a, b, c, d to be either real numbers or random variables. As an example, let's say that a = 1, b = -1, c = 2 but let d be a normally distributed random variable with mean 20 and SD 40. The data structure that I have in mind will give no value to d. However, I also want to be able to design a function that can take in the structure, simulate an uniform(0,1), obtain a value for d using an inverse CDF and then spit out an actual matrix. I have several ideas to do this (all related to the MATLAB icdf function) but would like to know how more experienced programmers would do it. In this application, it's important that the structure is as "lean" as possible since I will be working with very very large matrices and memory will be an issue.

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• Data Structures using C or C++?

  - by user362439

  What are the advantages of using C++ based Classes/Objects over using legacy C Structures for managing standard Data Structures like Linked List, Stack, Tree, Queue ..etc? Let me know if the question is not clear.

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• Trie VS Suffix Tree VS Suffix Array

  - by ukrania

  Hello everyone, Which one is the structure that provides best performance results? Trie, Suffix Tree or Suffix Array? There are other equivalent structures? What are good Java implementations of these structures? Thanks for your answers. Best Regards, ukrania

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• Persistent (purely functional) Red-Black trees on disk performance

  - by Waneck

  I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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• What Software Engineering Areas should be stressed upon while Interviewing Candidate for Fulltime So

  - by Rachel

  Hi, This question is somewhat related to other posts which I found on Stackoverflow but not exactly and so am prompted to ask about it. I know we must ask for Data-Structures and Algorithms but what specific data-structures or Algorithms or other CS Concepts should be asked while interviewing Sr. Software Engineering Fulltime Position as compared with Software Engineering Position. Thanks.

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• Best way to save complex Python data structures across program sessions (pickle, json, xml, database

  - by Malcolm

  Looking for advice on the best technique for saving complex Python data structures across program sessions. Here's a list of techniques I've come up with so far: pickle/cpickle json jsonpickle xml database (like SQLite) Pickle is the easiest and fastest technique, but my understanding is that there is no guarantee that pickle output will work across various versions of Python 2.x/3.x or across 32 and 64 bit implementations of Python. Json only works for simple data structures. Jsonpickle seems to correct this AND seems to be written to work across different versions of Python. Serializing to XML or to a database is possible, but represents extra effort since we would have to do the serialization ourselves manually. Thank you, Malcolm

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