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  • Evenly select N elems from array

    - by ninuhadida
    Hi, I need to evenly select n elements from an array. I guess the best way to explain is by example. say I have: array [0,1,2,3,4] and I need to select 3 numbers.. 0,3,4. of course, if the array length <= n, I just need to return the whole array. I'm pretty sure there's a defined algorithm for this, been trying to search, and I took a look at Introduction to algorithms but couldn't find anything that met my needs (probably overlooked it) The problem I'm having is that I can't figure out a way to scale this up to any array [ p..q ], selecting N evenly elements. note: I can't just select the even elements from the example above.. A couple other examples; array[0,1,2,3,4,5,6], 3 elements ; I need to get 0,3,6 array[0,1,2,3,4,5], 3 elements ; I need to get 0, either 2 or 3, and 5

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  • How to manage and capture database changes across several developers?

    - by Matt Greer
    We have three developers and one tester all working against the same database. We change the schema of the database quite often, and every time we do it tends to have a ripple effect of headaches for everyone else. Are there good practices in place for .NET oriented development against MS SQL Server 2008 for managing this? I am thinking something similar to Rails Migrations and each dev and tester has their own local database. Or is that overkill? It'd at least be nice to have separate test and dev databases, but currently manually keeping two databases in sync is probably worse than our current predicament. LiquiBase seems promising, has anyone successfully used it in a similar environment? Or are there better approaches? We are using SQL Server 2008, VS 2008 and .NET 3.5 if that matters at all.

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  • What is your custom exception hierrarchy?

    - by bonefisher
    My question is: how would you create exception hierarchy in your application? Designing the architecture of an application, from my perspective, we could have three types of exceptions: the built-in (e.g.: InvalidOperationException) custom internal system faults (DB transaction failed on commit, DbTransactionFailedException) custom business exceptions (BusinessRuleViolationException) Class hierarchy: Exception MyAppInternalException DbTransactionFailedException MyServerTimeoutException ... MyAppBusinessRuleViolationException UsernameAlreadyExistsException ... where only MyAppInternalException & MyAppBusinessRuleViolationException would be catched.

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  • Bejeweled Blitz - How does it assert there is always a move?

    - by EvilTeach
    I have been playing Bejeweled Blitz for a while now. Yes, it is an addiction. In thinking about the game, I have observed that on some boards, the bottom runs dry (no moves) leaving only the top part of the board playable. Frequently that part of the board drys up, and one is left with moves in area cleared by the last move. The board never runs completely dry, so clearly the program is doing some sorts of calculation that allows it to choose what to drop to prevent it from running dry. I have noticed in this 'mode' that it is very common for the algorithm to drop jewels which causes more non-dry area to appear in the horizontal area. Perhaps less frequent is a drop which seems designed to open up the bottom part of the board again. So my question is "How would one go about designing an algorithm guarantee that there is always a move available.?"

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  • Options for keeping models and the UI in sync (in a desktop application context)

    - by Benju
    In my experience I have only had 2 patterns work for large-scale desktop application development when trying to keep the model and UI in sync. 1-An eventbus approach via a shared eventbus command objects are fired (ie:UserDemographicsUpdatedEvent) and have various parts of the UI update if they are bound to the same user object updated in this event. 2-Attempt to bind the UI directly to the model adding listeners to the model itself as needed. I find this approach rather clunky as it pollutes the domain model. Does anybody have other suggestions? In a web application with something like JSP binding to the model is easy as you ussually only care about the state of the model at the time your request comes in, not so in a desktop type application. Any ideas?

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  • Efficient algorithm for creating an ideal distribution of groups into containers?

    - by Inshim
    I have groups of students that need to be allocated into classrooms of a fixed capacity (say, 100 chairs in each). Each group must only be allocated to a single classroom, even if it is larger than the capacity (ie there can be an overflow, with students standing up) I need an algorithm to make the allocations with minimum overflows and under-capacity classrooms. A naive algorithm to do this allocation is horrendously slow when having ~200 groups, with a distribution of about half of them being under 20% of the classroom size. Any ideas where I can find at least some good starting point for making this algorithm lightning fast? Thanks!

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  • Historical / auditable database

    - by Mark
    Hi all, This question is related to the schema that can be found in one of my other questions here. Basically in my database I store users, locations, sensors amongst other things. All of these things are editable in the system by users, and deletable. However - when an item is edited or deleted I need to store the old data; I need to be able to see what the data was before the change. There are also non-editable items in the database, such as "readings". They are more of a log really. Readings are logged against sensors, because its the reading for a particular sensor. If I generate a report of readings, I need to be able to see what the attributes for a location or sensor was at the time of the reading. Basically I should be able to reconstruct the data for any point in time. Now, I've done this before and got it working well by adding the following columns to each editable table: valid_from valid_to edited_by If valid_to = 9999-12-31 23:59:59 then that's the current record. If valid_to equals valid_from, then the record is deleted. However, I was never happy with the triggers I needed to use to enforce foreign key consistency. I can possibly avoid triggers by using the extension to the "PostgreSQL" database. This provides a column type called "period" which allows you to store a period of time between two dates, and then allows you to do CHECK constraints to prevent overlapping periods. That might be an answer. I am wondering though if there is another way. I've seen people mention using special historical tables, but I don't really like the thought of maintainling 2 tables for almost every 1 table (though it still might be a possibility). Maybe I could cut down my initial implementation to not bother checking the consistency of records that aren't "current" - i.e. only bother to check constraints on records where the valid_to is 9999-12-31 23:59:59. Afterall, the people who use historical tables do not seem to have constraint checks on those tables (for the same reason, you'd need triggers). Does anyone have any thoughts about this? PS - the title also mentions auditable database. In the previous system I mentioned, there is always the edited_by field. This allowed all changes to be tracked so we could always see who changed a record. Not sure how much difference that might make. Thanks.

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  • Producer/consumer in Grails?

    - by Mulone
    Hi all, I'm trying to implement a Consumer/Producer app in Grails, after several unsuccessful attempts at implementing concurrent threads. Basically I want to store all the events coming from a clients (through separate AJAX calls) in a single queue and then process such a queue in a linear way as soon as new events are added. This looks like a Producer/Consumer problem: http://en.wikipedia.org/wiki/Producer-consumer_problem How can I implement this in Grails (maybe with a timer or even better by generating an event 'process queue')? Basically I'd like to a have a singleton service waiting for new events in the queue and processing them linearly (even if the queue is loaded by several concurrent processes). Any hints? Cheers!

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  • Struggling with a data modeling problem

    - by rpat
    I am struggling with a data model (I use MySQL for the database). I am uneasy about what I have come up with. If someone could suggest a better approach, or point me to some reference matter I would appreciate it. The data would have organizations of many types. I am trying to do a 3 level classification (Class, Category, Type). Say if I have 'Italian Restaurant', it will have the following classification Food Services Restaurants Italian However, an organization may belong to multiple groups. A restaurant may also serve Chinese and Italian. So it will fit into 2 classifications Food Services Restaurants Italian Food Services Restaurants Chinese The classification reference tables would be like the following: ORG_CLASS (RowId, ClassCode, ClassName) 1, FOOD, Food Services ORG_CATEGORY(RowId, ClassCode, CategoryCode, CategoryName) 1, FOOD, REST, Restaurants ORG_TYPE (RowId, ClassCode, CategoryCode, TypeCode, TypeName) 100, FOOD, REST, ITAL, Italian 101, FOOD, REST, CHIN, Chinese 102, FOOD, REST, SPAN, Spanish 103, FOOD, REST, MEXI, Mexican 104, FOOD, REST, FREN, French 105, FOOD, REST, MIDL, Middle Eastern The actual data tables would be like the following: I will allow an organization a max of 3 classifications. I will have 3 GroupIds each pointing to a row in ORG_TYPE. So I have my ORGANIZATION_TABLE ORGANIZATION_TABLE (OrgGroupId1, OrgGroupId2, OrgGroupId3, OrgName, OrgAddres) 100,103,NULL,MyRestaurant1, MyAddr1 100,102,NULL,MyRestaurant2, MyAddr2 100,104,105, MyRestaurant3, MyAddr3 During data add, a dialog could let the user choose the clssa, category, type and the corresponding GroupId could be populated with the rowid from the ORG_TYPE table. During Search, If all three classification are chosen, It will be more specific. For example, if Food Services Restaurants Italian is the criteria, the where clause would be 'where OrgGroupId1 = 100' If only 2 levels are chosen Food Services Restaurants I have to do 'where OrgGroupId1 in (100,101,102,103,104,105, .....)' - There could be a hundred in that list I will disallow class level search. That is I will force selection of a class and category The Ids would be integers. I am trying to see performance issues and other issues. Overall, would this work? or I need to throw this out and start from scratch.

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  • HMVC/PAC - how to handle shared abstractions/models?

    - by fig-gnuton
    In HMVC/PAC, what's the recommended way to code if two or more triads/agents share a common model/abstraction? Do you instantiate a new instance of that model wherever needed, and propogate a change in one to all the other instances via the controllers? Or do instantiate one model at some common upper level, and inject that instance wherever needed? (Or neither if I'm missing something fundamental about these patterns?)

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  • Need an ASP.NET MVC long running process with user feedback

    - by Jason
    I've been trying to create a controller in my project for delivering what could turn out to be quite complex reports. As a result they can take a relatively long time and a progress bar would certainly help users to know that things are progressing. The report will be kicked off via an AJAX request, with the idea being that periodic JSON requests will get the status and update the progress bar. I've been experimenting with the AsyncController as that seems to be a nice way of running long processes without tying up resources, but it doesn't appear to give me any way of checking on the progress (and seems to block further JSON requests and I haven't discovered why yet). After that I've tried resorting to storing progress in a static variable on the controller and reading the status from that - but to be honest that all seems a bit hacky! All suggestions gratefully accepted!

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  • Using OpenGL drawing operations in an object-oriented setting?

    - by Lion Kabob
    I've been plowing through basic shaders and whatnot for an application I'm writing, and I've been having trouble figuring out a high-level organization for the drawing calls. I'm thinking of having a singleton class which implements a number of basic drawing operations, taking data from "user" classes and passing that to the appropriate opengl calls. I'm wondering how people do this when writing their own applications, as the internet is chock full of basic "Your first shader" tutorials, but very little on suggested organization of drawing code. My particular environment is targeted at iPad/OpenGL ES 2.0, but I think the question stands for most environments.

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  • How to restrict access to a class's data based on state?

    - by Marcus Swope
    In an ETL application I am working on, we have three basic processes: Validate and parse an XML file of customer information from a third party Match values received in the file to values in our system Load customer data in our system The issue here is that we may need to display the customer information from any or all of the above states to an internal user and there is data in our customer class that will never be populated before the values have been matched in our system (step 2). For this reason, I would like to have the values not even be available to be accessed when the customer is in this state, and I would like to have to avoid some repeated logic everywhere like: if (customer.IsMatched) DisplayTextOnWeb(customer.SomeMatchedValue); My first thought for this was to add a couple interfaces on top of Customer that would only expose the properties and behaviors of the current state, and then only deal with those interfaces. The problem with this approach is that there seems to be no good way to move from an ICustomerWithNoMatchedValues to an ICustomerWithMatchedValues without doing direct casts, etc... (or at least I can't find one). I can't be the first to have come across this, how do you normally approach this? As a last caveat, I would like for this solution to play nice with FluentNHibernate :) Thanks in advance...

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  • Invoicing vs Quoting

    - by FreshCode
    If invoices can be voided, should they be used as quotations? I have an Invoices tables that is created from inventory associated with a Job. I could have a Quotes table as a halfway-house between inventory and invoices, but it feels like I would have duplicate data structures and logic just to handle an "Is this a quote?" bit. From a business perspective, quotes are different from invoices: a quote is sent prior to an undertaking and an invoice is sent once it is complete and payment is due, but how to represent this in my repository and model. What is an elegant way to store and manage quotes & invoices in a database?

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  • Is Multiple Iterators is possible in php?

    - by artvolk
    Good day! I know that C# allows multiple iterators using yield, like described here: http://stackoverflow.com/questions/1754041/is-multiple-iterators-is-possible-in-c In PHP there is and Iterator interface. Is it possible to implement more than one iteration scenario for a class?

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  • Unit of Work Pattern in .Net

    - by Jazza
    Does anyone have any concrete examples of a simple Unit of Work pattern in C# or Visual Basic that would handle the following scenario? I'm writing a WinForms application in which a customer can have multiple addresses associated with it. The user can add, edit and delete addresses belonging to the customer before the customer is saved back to the database. Therefore, at the time of saving, all the original addresses need to be deleted from the database and the new addresses added in a single transaction.

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  • CSS for top right corner of the page

    - by user102533
    How would I have a top right corner div as shown in the image. I want to do something similar though not exactly the same. I think the text is not an image. Also, I have seen some websites that has a page hover effect when a mouse is over the top right section. Any idea how to do that?

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  • How to create a "facade" table?

    - by tputkonen
    A legacy database contains a join table which links tables table1 and table2, and contains just two foreign keys: TABLE_ORIG: table1_id table2_id In order to utilize this table using JPA I would need to create a surrogate primary key to the link table. However, the existing table must not be modified at all. I would like to create another table which would contain also a primary key in addition to the foreign keys: TABLE_NEW: id table1_id table2_id All changes to TABLE_ORIG should be reflected in TABLE_NEW, and vice versa. Is this doable in mysql?

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  • Best XML Based Database

    - by monmonja
    I had been assigned to develop a system on where we would get a XML from multiple sources (millions of xml) and put them in some database like and judging from the xml i would receive, there wont be any concrete structure even if they are from the same source. With this reason i think i cannot suggest RDMS and currently looking at NoSQL databases. We need a system that could do CRUD and is fast on Read. I had been looking at MarkLogic and eXist, which are both XML based NoSQL databases, have anyone had experience with them? and any other suggestion? Thanks

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