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• O(log n) algorithm to find the element having rank i in union of pre-sorted lists

  - by Eternal Learner

  Given two sorted lists, each containing n real numbers, is there a O(log?n) time algorithm to compute the element of rank i (where i coresponds to index in increasing order) in the union of the two lists, assuming the elements of the two lists are distinct? I can think of using a Merge procedure to merge the 2 lists and then find the A[i] element in constant time. But the Merge would take O(n) time. How do we solve it in O(log n) time?

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• Extending Throwable in Java

  - by polygenelubricants

  Java lets you create an entirely new subtype of Throwable, e.g: public class FlyingPig extends Throwable { ... } Now, very rarely, I may do something like this: throw new FlyingPig("Oink!"); and of course elsewhere: try { ... } catch (FlyingPig porky) { ... } My questions are: Is this a bad idea? And if so, why? What could've been done to prevent this subtyping if it is a bad idea? Since it's not preventable (as far as I know), what catastrophies could result? If this isn't such a bad idea, why not? How can you make something useful out of the fact that you can extends Throwable?

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• What resources will help me understand the fundamentals of Relational Database Systems.

  - by Rachel

  This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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• Is a "factory" method the right pattern?

  - by jdt141

  Hey all - So I'm working to improve an existing implementation. I have a number of polymorphic classes that are all composed into a higher level container class. The problem I'm dealing with at the moment is that the higher level container class, well, sucks. It looks something like this, which I really don't have a problem with (as the polymorphic classes in the container should be public). My real issue is the constructor... /* * class1 and class 2 derive from the same superclass */ class Container { public: boost::shared_ptr<ComposedClass1> class1; boost::shared_ptr<ComposedClass2> class2; private: ... } /* * Constructor - builds the objects that we need in this container. */ Container::Container(some params) { class1.reset(new ComposedClass1(...)); class2.reset(new ComposedClass2(...)); } What I really need is to make this container class more re-usable. By hard-coding up the member objects and instantiating them, it basically isn't and can only be used once. A factory is one way to build what I need (potentially by supplying a list of objects and their specific types to be created?) Other ways to get around this problem? Seems like someone should have solved it before... Thanks!

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• How to build a web site which gives a sub-domain dynamically to every registered user?

  - by coderex

  Suppose i have a site and i wish to give a sub-domain for each registered users. like my site http://site.com/ and the test-user is a user registered on my site and site want to make sub-domain for that user. Like http://test-user.site.com Like http://test-user1.site.com for test-user1. Hop you understood the requirement. How can i create a sub-domain using my sites back-end. or dynamically while register

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• C# reference collection for storing reference types

  - by ivo s

  I like to implement a collection (something like List<T>) which would hold all my objects that I have created in the entire life span of my application as if its an array of pointers in C++. The idea is that when my process starts I can use a central factory to create all objects and then periodically validate/invalidate their state. Basically I want to make sure that my process only deals with valid instances and I don't re-fetch information I already fetched from the database. So all my objects will basically be in one place - my collection. A cool thing I can do with this is avoid database calls to get data from the database if I already got it (even if I updated it after retrieval its still up-to-date if of course some other process didn't update it but that a different concern). I don't want to be calling new Customer("James Thomas"); again if I initted James Thomas already sometime in the past. Currently I will end up with multiple copies of the same object across the appdomain - some out of sync other in sync and even though I deal with this using timestamp field on the MSSQL server I'd like to keep only one copy per customer in my appdomain (if possible process would be better). I can't use regular collections like List or ArrayList for example because I cannot pass parameters by their real local reference to the their existing Add() methods where I'm creating them using ref so that's not to good I think. So how can this be implemented/can it be implemented at all ? A 'linked list' type of class with all methods working with ref & out params is what I'm thinking now but it may get ugly pretty quickly. Is there another way to implement such collection like RefList<T>.Add(ref T obj)? So bottom line is: I don't want re-create an object if I've already created it before during the entire application life unless I decide to re-create it explicitly (maybe its out-of-date or something so I have to fetch it again from the db). Is there alternatives maybe ?

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• Best way to plan a task ?

  - by Indigo Praveen

  Hi All, As I am very new to programming, I am very curious about learning the best ways/practices of programming. Whenever I want to write any program , I strat directly with coding while some guys say that you should plan your program first before starting the code. But I don't understand the real value of creating the class diagrams and all that kind of stuff coz I think that ultimately I have to write the code. Can you guys please share your experiences about how you are doing your programming means what is your first step when you start an application.

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• Ways to clean up java applications.

  - by Begui

  How do java people handle clean up of their apps when the program receives a kill signal? For instance, there is an application i connect to which wants any third party app ( my app) to send a "finish" command. What is the best say to send that "finish" command if one does a kill -9 on me.

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• Temporary storage for keeping data between program iterations?

  - by mr.b

  I am working on an application that works like this: It fetches data from many sources, resulting in pool of about 500,000-1,500,000 records (depends on time/day) Data is parsed Part of data is processed in a way to compare it to pre-existing data (read from database), calculations are made, and stored in database. Resulting dataset that has to be stored in database is, however, much smaller in size (compared to original data set), and ranges from 5,000-50,000 records. This process almost always updates existing data, perhaps adds few more records. Then, data from step 2 should be kept somehow, somewhere, so that next time data is fetched, there is a data set which can be used to perform calculations, without touching pre-existing data in database. I should point out that this data can be lost, it's not irreplaceable (key information can be read from database if needed), but it would speed up the process next time. Application components can (and will be) run off different computers (in the same network), so storage has to be reachable from multiple hosts. I have considered using memcached, but I'm not quite sure should I do so, because one record is usually no smaller than 200 bytes, and if I have 1,500,000 records, I guess that it would amount to over 300 MB of memcached cache... But that doesn't seem scalable to me - what if data was 5x that amount? If it were to consume 1-2 GB of cache only to keep data in between iterations (which could easily happen)? So, the question is: which temporary storage mechanism would be most suitable for this kind of processing? I haven't considered using mysql temporary tables, as I'm not sure if they can persist between sessions, and be used by other hosts in network... Any other suggestion? Something I should consider?

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• Should I update an application when a used framework release a new version?

  - by Alex

  I have an application that use several libraries and frameworks, should I update my application to use the latest version of those frameworks when a new stable version is available? For example, migrate from python 2.x to python 3.x, or from spring 2.5 to spring 3.0, but the question es very general, not language specific. If I keep the application updated to use the latest stable frameworks versions then I will have new features available in case I need them. If I don't, then may be in a future I will need to do the update and it will be a lot of work to update the application. Is there any best practice about this?

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• Dynamically specify the type in C#

  - by Lirik

  I'm creating a custom DataSet and I'm under some constrains: I want the user to specify the type of the data which they want to store. I want to reduce type-casting because I think it will be VERY expensive. I will use the data VERY frequently in my application. I don't know what type of data will be stored in the DataSet, so my initial idea was to make it a List of objects, but I suspect that the frequent use of the data and the need to type-cast will be very expensive. The basic idea is this: class DataSet : IDataSet { private Dictionary<string, List<Object>> _data; /// <summary> /// Constructs the data set given the user-specified labels. /// </summary> /// <param name="labels"> /// The labels of each column in the data set. /// </param> public DataSet(List<string> labels) { _data = new Dictionary<string, List<object>>(); foreach (string label in labels) { _data.Add(label, new List<object>()); } } #region IDataSet Members public List<string> DataLabels { get { return _data.Keys.ToList(); } } public int Count { get { _data[_data.Keys[0]].Count; } } public List<object> GetValues(string label) { return _data[label]; } public object GetValue(string label, int index) { return _data[label][index]; } public void InsertValue(string label, object value) { _data[label].Insert(0, value); } public void AddValue(string label, object value) { _data[label].Add(value); } #endregion } A concrete example where the DataSet will be used is to store data obtained from a CSV file where the first column contains the labels. When the data is being loaded from the CSV file I'd like to specify the type rather than casting to object. The data could contain columns such as dates, numbers, strings, etc. Here is what it could look like: "Date","Song","Rating","AvgRating","User" "02/03/2010","Code Monkey",4.6,4.1,"joe" "05/27/2009","Code Monkey",1.2,4.5,"jill" The data will be used in a Machine Learning/Artificial Intelligence algorithm, so it is essential that I make the reading of data very fast. I want to eliminate type-casting as much as possible, since I can't afford to cast from 'object' to whatever data type is needed on every read. I've seen applications that allow the user to pick the specific data type for each item in the csv file, so I'm trying to make a similar solution where a different type can be specified for each column. I want to create a generic solution so I don't have to return a List<object> but a List<DateTime> (if it's a DateTime column) or List<double> (if it's a column of doubles). Is there any way that this can be achieved? Perhaps my approach is wrong, is there a better approach to this problem?

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• Python: Recursively access dict via attributes as well as index access?

  - by Luke Stanley

  I'd like to be able to do something like this: from dotDict import dotdictify life = {'bigBang': {'stars': {'planets': [] } } } dotdictify(life) #this would be the regular way: life['bigBang']['stars']['planets'] = {'earth': {'singleCellLife': {} }} #But how can we make this work? life.bigBang.stars.planets.earth = {'singleCellLife': {} } #Also creating new child objects if none exist, using the following syntax life.bigBang.stars.planets.earth.multiCellLife = {'reptiles':{},'mammals':{}} My motivations are to improve the succinctness of the code, and if possible use similar syntax to Javascript for accessing JSON objects for efficient cross platform development.(I also use Py2JS and similar.)

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• Include everything, Separate with "using"

  - by Dave

  I'm developing a C++ library. It got me thinking of the ways Java and C# handle including different components of the libraries. For example, Java uses "import" to allow use of classes from other packages, while C# simply uses "using" to import entire modules. My questions is, would it be a good idea to #include everything in the library in one massive include and then just use the using directive to import specific classes and modules? Or would this just be down right crazy? EDIT: Good responses so far, here are a few mitigating factors which I feel add to this idea: 1) Internal #includes are kept as normal (short and to the point) 2) The file which includes everything is optionally supplied with the library to those who wish to use it3) You could optionally make the big include file part of the pre-compiled header

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• Why did Matz choose to make Strings mutable in Ruby?

  - by Seth Tisue

  It's the reverse of this question: http://stackoverflow.com/questions/93091/why-cant-strings-be-mutable-in-java-and-net Was this choice made in Ruby only for efficiency, or was there some other reason?

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• What do you call functions which get and set?

  - by nickf

  The jQuery framework has a lot of functions which will either retrieve or mutate values depending on the parameters passed: $(this).html(); // get the html $(this).html('blah'); // set the html Is there a standard name for functions which behave like this?

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• Bi-directional view model syncing with "live" collections and properties (MVVM)

  - by Schneider

  I am getting my knickers in a twist recently about View Models (VM). Just like this guy I have come to the conclusion that the collections I need to expose on my VM typically contain a different type to the collections exposed on my business objects. Hence there must be a bi-directional mapping or transformation between these two types. (Just to complicate things, on my project this data is "Live" such that as soon as you change a property it gets transmitted to other computers) I can just about cope with that concept, using a framework like Truss, although I suspect there will be a nasty surprise somewhere within. Not only must objects be transformed but a synchronization between these two collections is required. (Just to complicate things I can think of cases where the VM collection might be a subset or union of business object collections, not simply a 1:1 synchronization). I can see how to do a one-way "live" sync, using a replicating ObservableCollection or something like CLINQ. The problem then becomes: What is the best way to create/delete items? Bi-directinal sync does not seem to be on the cards - I have found no such examples, and the only class that supports anything remotely like that is the ListCollectionView. Would bi-directional sync even be a sensible way to add back into the business object collection? All the samples I have seen never seem to tackle anything this "complex". So my question is: How do you solve this? Is there some technique to update the model collections from the VM? What is the best general approach to this?

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• Time/resource allocation on a Stylish vs. Functional user interface

  - by jasonk

  When developing applications how much focus/time do you place on an application’s style vs. functionality. Battleship gray apps drive me insane. On the other hand maximizing a business application’s "style" can tax time and financial resources. Applications need to be appealing to resell or meet basic customer expectations, but defining a healthy medium can be difficult. What would you say are reasonable "standards" for allocating develop time/resources should be dedicated to stylizing a business application?

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• Is there a recommended way to use the Observer pattern in MVP using GWT?

  - by Tomislav Nakic-Alfirevic

  I am thinking about implementing a user interface according to the MVP pattern using GWT, but have doubts about how to proceed. These are (some of) my goals: - the presenter knows nothing about the UI technology (i.e. uses nothing from com.google.*) - the view knows nothing about the model or the presenter - the model knows nothing of the view or the presenter (...obviously) I would place an interface between the view and the presenter and use the Observer pattern to decouple the two: the view generates events and the presenter gets notified. What confuses me is that java.util.Observer and java.util.Observable are not supported in GWT. This suggests that what I'm doing is not the recommended way to do it, as far as GWT is concerned, which leads me to my questions: what is the recommended way to implement MVP using GWT, specifically with the above goals in mind? How would you do it?

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• doubleton pattern in C++

  - by benjamin button

  I am aware of the singleton pattern in C++. but what is the logic to get two instances of the object? is there any such pattern where we could easily get 2 pattern. for the logic i could think of is that i can change the singleton pattern itself to have two objects created inside the class.this works. but if the requirement grows like if i need only 3 or only 4 what is the deswign pattern that i could think of to qualify such requirement?

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• do's and don'ts for writing mysql queries

  - by nik

  One thing I always wonder while writing query is that am I writing most optimized query or not? I know certain things like: 1) using SELECT field1, filed2 instead of SELECT * 2) Giving proper indexes to the tables but I am sure there are more things that should be kept in mind for writing queries, since most of the database can only grow more and optimal query will help gr8 in execution time, Can u share some tips and tricks on writing queries?

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• Change an access Primary key with relationships

  - by DiegoMaK

  I have a database in access 2007 accdb extension , there are more or less 30-40 tables with related primary key "local_number". it is a text primary key with 10 lenght. How can I change the length of this primary key to 30 WITHOUT delete previosly all the 30 relationship. 2,A similar question. I need add a compose primary key to my PK "local_number". I need Add a "Date" as composed PK. Then access just allow this if I first delete all relationships. How can Avoid this warning and change my PK ignoring this message.

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• Database model for saving random boolean expressions

  - by zarko.susnjar

  I have expressions like this: (cat OR cats OR kitten OR kitty) AND (dog OR dogs) NOT (pigeon OR firefly) Anyone having idea how to make tables to save those? Before I got request for usage of brackets, I limited usage of operators to avoid ambiguous situations. So only ANDs and NOTs or only ORs and saved those in this manner: operators id | name 1 | AND 2 | OR 3 | NOT keywords id | keyword 1 | cat 2 | dog 3 | firefly expressions id | operator | keywordId 1 | 0 | 1 1 | 1 | 2 1 | 3 | 3 which was: cat AND dog NOT firefly But now, I'm really puzzled...

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• javascript logo / mascot / insignia

  - by dreftymac

  Does JavaScript have a mascot, logo, insignia or otherwise stylistically engaging representation or alias? If not, who would be the best person/organization to get some momentum behind this kind of thing? Doug Crockford?

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• Which should be created first ER Diagram OR Class Diagram?

  - by isthatacode

  The very first step i created a DFD. Then i moved on to create a Class Diagram. And while doing that i felt that i should create the ER diagram first. As there were many details which could not be captured in a Class diagram. So, my question should i create ERD first OR Class Diagrams ? your valuable inputs are appreciated guys!!! thanks for reading

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• How build my own Application Setting

  - by adisembiring

  I want to build a ApplicationSetting for my application. The ApplicationSetting can be stored in a properties file or in a database table. The settings are stored in key-value pairs. E.g. ftp.host = blade ftp.username = dummy ftp.pass = pass content.row_pagination = 20 content.title = How to train your dragon. I have designed it as follows: Application settings reader: interface IApplicationSettingReader { read(); } DatabaseApplicationSettingReader { dao appSettingDao; AppSettings read() { List<AppSettingEntity> listEntity = appSettingsDao.findAll(); Map<String, String> map = new HaspMap<String, String>(); foreach (AppSettingEntity entity : listEntity) { map.put(entity.getConfigName(), entity.getConfigValue()); } return new AppSettings(map); } } DatabaseApplicationSettingReader { dao appSettingDao; AppSettings read() { //read from some properties file return new AppSettings(map); } } Application settings class: AppSettings { private static AppSettings instance; private Map map; Public AppSettings(Map map) { this.map = map; } public static AppSettings getInstance() { if (instance == null) { throw new RuntimeException("Object not configure yet"); } return instance; } public static configure(IApplicationSettingReader reader) { instance = reader.read(); } public String getFtpSetting(String param) { return map.get("ftp." + param); } public String getContentSetting(String param) { return map.get("content." + param); } } Test class: AppSettingsTest { IApplicationSettingReader reader; @Before public void setUp() throws Exception { reader = new DatabaseApplicationSettingReader(); } @Test public void getContentSetting_should_get_content_title() { AppSettings.configure(reader); Instance settings = AppSettings.getInstance(); String title = settings.getContentSetting("title"); assertNotNull(title); Sysout(title); } } My questions are: Can you give your opinion about my code, is there something wrong? I configure my application setting once, while the application start, I configure the application setting with appropriate reader (DbReader or PropertiesReader), I make it singleton. The problem is, when some user edit the database or file directly to database or file, I can't get the changed values. Now, I want to implement something like ApplicationSettingChangeListener. So if the data changes, I will refresh my application settings. Do you have any suggestions how this can be implemented?

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