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• Navigating through code with keyboard shortcuts

  - by MarceloRamires

  I'm starting to feel the need to run fastly through code with keyboard shortcuts, to arrive faster where I want to make any changes (avoiding use of mouse or long times holding [up], [left], [right] and [down]). I'm already using some: [home] - first position in current line [end] - last position in current line [ctrl] + [home] - first line of the entire code [ctrl] + [end] - last line of the entire code [pageup] - same vertical position, one screen above [pagedown] - same vertical position, one screen below [ctrl] + [pageup] - first line in current screen [ctrl] + [end] - last line in current screen [ctrl] + [left/right] - skipping word per word What have you got ? I use Visual Studio. (but I'm open to any answer, as I maybe can use others soon) obs: I've searched through stackoverflow and didn't find a nice question with this content, nor a list of keyboard code searching. If it's repeated, I'm sorry for not finding it, I'm here in my best intentions. This question is NOT about any shortcuts, and not only about visual studio, it's about running through code with shortcuts. Answers that suit the question so far: [Ctrl] + [-] - jumps to last cursor position [Ctrl] + [F3] - Jumps to next occurance of the word the curson is in [Shift] + [F3] - Same as the above, backwards. [F12] - Goes to definition of method/variable the cursor is in [Ctrl] + [ ] ] - Jumps to matching brace and select I'll ad more as there are answers.

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• Django: How can I identify the calling view from a template?

  - by bryan

  Short version: Is there a simple, built-in way to identify the calling view in a Django template, without passing extra context variables? Long (original) version: One of my Django apps has several different views, each with its own named URL pattern, that all render the same template. There's a very small amount of template code that needs to change depending on the called view, too small to be worth the overhead of setting up separate templates for each view, so ideally I need to find a way to identify the calling view in the template. I've tried setting up the views to pass in extra context variables (e.g. "view_name") to identify the calling view, and I've also tried using {% ifequal request.path "/some/path/" %} comparisons, but neither of these solutions seems particularly elegant. Is there a better way to identify the calling view from the template? Is there a way to access to the view's name, or the name of the URL pattern? Update 1: Regarding the comment that this is simply a case of me misunderstanding MVC, I understand MVC, but Django's not really an MVC framework. I believe the way my app is set up is consistent with Django's take on MVC: the views describe which data is presented, and the templates describe how the data is presented. It just happens that I have a number of views that prepare different data, but that all use the same template because the data is presented the same way for all the views. I'm just looking for a simple way to identify the calling view from the template, if this exists. Update 2: Thanks for all the answers. I think the question is being overthought -- as mentioned in my original question, I've already considered and tried all of the suggested solutions -- so I've distilled it down to a "short version" now at the top of the question. And right now it seems that if someone were to simply post "No", it'd be the most correct answer :) Update 3: Carl Meyer posted "No" :) Thanks again, everyone.

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• Reversible numerical calculations in Prolog

  - by user8472

  While reading SICP I came across logic programming chapter 4.4. Then I started looking into the Prolog programming language and tried to understand some simple assignments in Prolog. I found that Prolog seems to have troubles with numerical calculations. Here is the computation of a factorial in standard Prolog: f(0, 1). f(A, B) :- A > 0, C is A-1, f(C, D), B is A*D. The issues I find is that I need to introduce two auxiliary variables (C and D), a new syntax (is) and that the problem is non-reversible (i.e., f(5,X) works as expected, but f(X,120) does not). Naively, I expect that at the very least C is A-1, f(C, D) above may be replaced by f(A-1,D), but even that does not work. My question is: Why do I need to do this extra "stuff" in numerical calculations but not in other queries? I do understand (and SICP is quite clear about it) that in general information on "what to do" is insufficient to answer the question of "how to do it". So the declarative knowledge in (at least some) math problems is insufficient to actually solve these problems. But that begs the next question: How does this extra "stuff" in Prolog help me to restrict the formulation to just those problems where "what to do" is sufficient to answer "how to do it"?

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• need help with Java solution /newbie

  - by Racket

  Hi, I'm new to programming in general so i'm trying to be as specific as possible in this question. There's this book that i'm doing some exercises on. I managed to do more than half of what they say, but it's just one input that I have been struggling to find out. I'll write the question and thereafter my code, "Write an application that creates and prints a random phone number of the form XXX-XXX-XXXX. Include the dashes in the output. Do not let the first three digits contain an 8 or 9 (but don't be more restrictive than that), and make sure that the second set of three digits is not greater than 742. Hint: Think through the easiest way to construct the phone number. Each diigit does not have to be determined separately." OK, the highlighted sentence is what i'm looking at. Here's my code: import java.util.Random; public class PP33 { public static void main (String[] args) { Random rand = new Random(); int num1, num2, num3; num1 = rand.nextInt(900) + 100; num2 = rand.nextInt(643) + 100; num3 = rand.nextInt(9000) + 1000; System.out.println(num1+"-"+num2+"-"+num3); } } How am I suppose to do this? I'm on chapter 3 so we have not yet discussed if statements etcetera, but Aliases, String class, Packages, Import declaration, Random Class, Math Class, Formatting output (decimal- & numberFormat), Printf, Enumeration & Wrapper classes + autoboxing. So consider answer the question based only on these assumptions, please. The code doesn't have any errors. Thank you!

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• Numerical calculations in Prolog

  - by user8472

  While reading SICP I came across logic programming chapter 4.4. Then I started looking into the Prolog programming language and tried to understand some simple assignments in Prolog. I found that Prolog seems to have troubles with numerical calculations. Here is the computation of a factorial in standard Prolog: f(0, 1). f(A, B) :- A > 0, C is A-1, f(C, D), B is A*D. The issues I find is that I need to introduce two auxiliary variables (C and D), a new syntax (is) and that the problem is non-reversible (i.e., f(5,X) works as expected, but f(X,120) does not). Naively, I expect that at the very least C is A-1, f(C, D) above may be replaced by f(A-1,D), but even that does not work. My question is: Why do I need to do this extra "stuff" in numerical calculations but not in other queries? I do understand (and SICP is quite clear about it) that in general information on "what to do" is insufficient to answer the question of "how to do it". So the declarative knowledge in (at least some) math problems is insufficient to actually solve these problems. But that begs the next question: How does this extra "stuff" in Prolog help me to restrict the formulation to just those problems where "what to do" is sufficient to answer "how to do it"?

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• Spring bean initialization in a web app

  - by EugeneP

  We work with a web application and autowire beans using WebApplicationContextUtils in the init method. Could you clarify some details about bean initialization? The question rises from the static factory method. Suppose there's a bean that is created in a static factory method. As we can see, when the web app is deployed, the ContextLoaderListener initializes all the beans present in Spring xml config file. Now happens such a thing. In the static factory method we run a timer that starts ticking. But in reality we wouldn't want it to start ticking unless the bean is injected into a property of the object ! That is question number one - all the beans are automatically initialized on deploy - correct? And after that when we need an injection, it simply feels the link with the address of the object created during initialization, though OBJECT WAS CREATED ON WEB APP DEPLOY, immediately ! (I assume the default singleton-creation Spring behavior) Second question: are all copies of a web app use the same beans, so all beans are WEB-APP wide, every Spring bean is shared between all the copies of this web app running?

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• Is C++ (one of) the best language to learn at first

  - by AlexV

  C++ is one of the most used programming language in the world since like 25+ years. My first job as programmer was in C++ and I coded in C++ everyday for nearly 4 years. Now I do mostly PHP, but I will forever cherish this C++ background. C++ has helped me understand many "under the hood" features/behaviors/restrictions of many other (and different) programming languages like PHP and Delphi. I'm a full time programmer for 6+ years now and since I have a quite varied programming background I often get questions by "newbies" as where to start to become a "good" programmer. I think C++ is one of the best language to start with because it gives you a real usefull experience that will last and will teach you how things work under the hood. It's not the easier one to learn for a newbie, but in my opinion it's one that will reward in the long term. I would like to know your opinion on this matter to add to my arguments when I guide "newbies". After this introduction, here's my question : Is C++ (one of) the best language to learn at first for you. Since it's subjective, I've marked this question as community wiki. EDIT: This question is not about why Java (or C# or any other language) is better than C++ to start with, it's about what's make C++ a good choice or not a good choice to learn as one of your firsts languages. For example, for me C++ made me understand how the memory works. Now today in many languages everything is managed by the garbadge collector and some people don't even know that. I'm glad I know how it works underneath and I think it can help you to write better code.

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• Summarising grouped records in a dataframe in R (...again)

  - by monch1962

  Hello all, (I tried to ask this question earlier today, but later realised I over-simplified the question; the answers I received were correct, but I couldn't use them because of my over-simplification of the problem in the original question. Here's my 2nd attempt...) I have a data frame in R that looks like: "Timestamp", "Source", "Target", "Length", "Content" 0.1 , P1 , P2 , 5 , "ABCDE" 0.2 , P1 , P2 , 3 , "HIJ" 0.4 , P1 , P2 , 4 , "PQRS" 0.5 , P2 , P1 , 2 , "ZY" 0.9 , P2 , P1 , 4 , "SRQP" 1.1 , P1 , P2 , 1 , "B" 1.6 , P1 , P2 , 3 , "DEF" 2.0 , P2 , P1 , 3 , "IJK" ... and I want to convert this to: "StartTime", "EndTime", "Duration", "Source", "Target", "Length", "Content" 0.1 , 0.4 , 0.3 , P1 , P2 , 12 , "ABCDEHIJPQRS" 0.5 , 0.9 , 0.4 , P2 , P1 , 6 , "ZYSRQP" 1.1 , 1.6 , 0.5 , P1 , P2 , 4 , "BDEF" ... Trying to put this into English, I want to group consecutive records with the same 'Source' and 'Target' together, then print out a single record per group showing the StartTime, EndTime & Duration (=EndTime-StartTime) for that group, along with the sum of the Lengths for that group, and a concatenation of the Content (which will all be strings) in that group. The TimeOffset values will always increase throughout the data frame. I had a look at melt/recast and have a feeling that it could be used to solve the problem, but couldn't get my head around the documentation. I suspect it's possible to do this within R, but I really don't know where to start. In a pinch I could export the data frame out and do it in e.g. Python, but I'd prefer to stay within R if possible. Thanks in advance for any assistance you can provide

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• How to retrieve view of MultiIndex DataFrame

  - by Henry S. Harrison

  This question was inspired by this question. I had the same problem, updating a MultiIndex DataFrame by selection. The drop_level=False solution in Pandas 0.13 will allow me to achieve the same result, but I am still wondering why I cannot get a view from the MultiIndex DataFrame. In other words, why does this not work?: >>> sat = d.xs('sat', level='day', copy=False) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python27\lib\site-packages\pandas\core\frame.py", line 2248, in xs raise ValueError('Cannot retrieve view (copy=False)') ValueError: Cannot retrieve view (copy=False) Of course it could be only because it is not implemented, but is there a reason? Is it somehow ambiguous or impossible to implement? Returning a view is more intuitive to me than returning a copy then later updating the original. I looked through the source and it seems this situation is checked explicitly to raise an error. Alternatively, is it possible to get the same sort of view from any of the other indexing methods? I've experimented but have not been successful. [edit] Some potential implementations are discussed here. I guess with the last question above I'm wondering what the current best solution is to index into arbitrary multiindex slices and cross-sections.

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• Radio buttons being reset in FF on cache-refresh

  - by Andrew Song

  (This is technically an addendum to an earlier StackOverflow question I had posted, but my original post asked a different question which doesn't really cover this topic -- I don't want to edit my older question as I feel this is different enough to merit its own page) While browsing my website in Firefox 3.5 (and only FF3.5), I come across a page with two radio buttons that have the following HTML code: <input id="check1" type="radio" value="True" name="check" checked="checked"/> <input id="check2" type="radio" value="False" name="check"/> This page renders as expected, with 'check1' checked and 'check2' unchecked. When I then go to refresh the page by pressing Control + R, the two radio buttons render, but they are both unchecked even though the raw HTML code is the same (as above). If I do a cache-miss refresh (via Control + F5 or Control + Shift + R), the page returns back to the way you'd expect it. This is not a problem in any other browser I've tried except FF3.5. What is causing these radio buttons to be reset on a normal refresh? How can I avoid this?

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• LINQ - Querying a list filtered via a Many-to-Many reltionship

  - by user118190

  Please excuse the context of my question for I did not know how to exactly word it. To not complicate things further, here's my business requirement: "bring me back all the Employees where they belong in Department "X". So when I view this, it will display all of the Employees that belong to this Department. Here's my environment: Silverlight 3 with Entity Framework 1.0 and WCF Data Services 1.0. I am able to load and bind all kinds of lists (simple), no problem. I don't feel that my environment matters and that's why I feel it is a LINQ question more than the technologies. My question is for scenarios where I have 3 tables linked, i.e. entities (collections). For example, I have this in my EDM: Employee--EmployeeProject--Project. Here's the table design from the Database: Employee (table1) ------------- EmployeeID (PK) FirstName other Attributes ... EmployeeProject (table2) ------------- EmployeeProjectID (PK) EmployeeID (FK) ProjectID (FK) AssignedDate other Attributes ... Project (table3) ------------- ProjectID (PK) Name other Attributes ... Here's the EDM design from Entity Framework: ------------------------ Employee (entity1) ------------------------ (Scalar Properties) ------------------- EmployeeID (PK) FirstName other Attributes ... ------------------- (Navigation Properties) ------------------- EmployeeProjects ------------------------ EmployeeProject (entity2) ------------------------ (Scalar Properties) ------------------- EmployeeProjectID (PK) AssignedDate other Attributes ... ------------------- (Navigation Properties) ------------------- Employee Project ------------------------ Project (entity3) ------------------------ (Scalar Properties) ------------------- ProjectID (PK) Name other Attributes ... ------------------- (Navigation Properties) ------------------- EmployeeProjects So far, I have only been able to do: var filteredList = Context.Employees .Where(e => e.EmployeeProjects.Where(ep => ep.Project.Name == "ProjectX")) NOTE: I have updated the syntax of the query after John's post. As you can see, I can only query, the related entity (EmployeeProjects). All I want is being able to filter to Project from the Employee entity. Thanks for any advice.

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• Using a function found in a different file in a loop

  - by Anders

  This question is related to BuddyPress, and a follow-up question from this question I have a .csv-file with 790 rows and 3 columns where the first column is the group name, second is the group description and last (third) the slug. As far as I've been told I can use this code: <?php $groups = array(); if (($handle = fopen("groupData.csv", "r")) !== FALSE) { while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) { $group = array('group_id' = 'SOME ID', 'name' = $data[0], 'description' = $data[1], 'slug' = groups_check_slug(sanitize_title(esc_attr($data[2]))), 'date_created' = gmdate( "Y-m-d H:i:s" ), 'status' = 'public' ); $groups[] = $group; } fclose($handle); } foreach ($groups as $group) { groups_create_group($group); } With http://www.nomorepasting.com/getpaste.php?pasteid=35217 which is called bp-groups.php. The thing is that I can't make it work. I've created a new file with the code written above called groupgenerator.php uploaded the .csv file to the same folder and opened groupgenerator.php in my browser. But, i get this error: Fatal error: Call to undefined function groups_check_slug() in What am I doing wrong?

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• How to partition bits in a bit array with less than linear time

  - by SiLent SoNG

  This is an interview question I faced recently. Given an array of 1 and 0, find a way to partition the bits in place so that 0's are grouped together, and 1's are grouped together. It does not matter whether 1's are ahead of 0's or 0's are ahead of 1's. An example input is 101010101, and output is either 111110000 or 000011111. Solve the problem in less than linear time. Make the problem simpler. The input is an integer array, with each element either 1 or 0. Output is the same integer array with integers partitioned well. To me, this is an easy question if it can be solved in O(N). My approach is to use two pointers, starting from both ends of the array. Increases and decreases each pointer; if it does not point to the correct integer, swap the two. int * start = array; int * end = array + length - 1; while (start < end) { // Assume 0 always at the end if (*end == 0) { --end; continue; } // Assume 1 always at the beginning if (*start == 1) { ++start; continue; } swap(*start, *end); } However, the interview insists there is a sub-linear solution. This makes me thinking hard but still not get an answer. Can anyone help on this interview question?

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• Resources and techniques/methods for SCJP preparation ?

  - by BenoitParis

  I am passing the SCJP 6 exam in a month. I have the "SCJP Sun Certified Programmer for Java 6 Exam 310-065" book. It seems great for the exam. But I want your advice on this. Getting the closest possible to 100% would be great. I have found a site that answered some of the questions you ask yourself when you go trough the book. Here is it : http://www.janeg.ca/java2.html As you can see it was written for Java 2 :/ I have written another specific question here on StackOverflow about the usefulness of JVM specification and Java compiler code for the SCJP. Will Update the results here. Here it is. Please share the resources you used in preparing the exam. Please also specify any resources that you think might help. Any type of resource is welcome: books, code, specs, sites, wikies, papers, online tests, grandmas... Please also share on any method/technique that helped you prepare the exam. Please also comment on the return you got from the resource and the method (for the learning process and for points in the exam) I'll begin: Book : "SCJP Sun Certified Programmer for Java 6 Exam 310-065". Seems like the official book for the preparation. Technique : Writing code in a text editor and compiling it with javac to test a question. NO IDEs! It helps you get a a straight answer to a question you have. It helps you pay attention to every word in the code (and this is very important in the SCJP) EDIT: Added dimension: Are there good, up-to-date online tests?

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• What is the procedure for debugging a production-only error?

  - by Lord Torgamus

  Let me say upfront that I'm so ignorant on this topic that I don't even know whether this question has objective answers or not. If it ends up being "not," I'll delete or vote to close the post. Here's the scenario: I just wrote a little web service. It works on my machine. It works on my team lead's machine. It works, as far as I can tell, on every machine except for the production server. The exception that the production server spits out upon failure originates from a third-party JAR file, and is skimpy on information. I search the web for hours, but don't come up with anything useful. So what's the procedure for tracking down an issue that occurs only on production machines? Is there a standard methodology, or perhaps category/family of tools, for this? The error that inspired this question has already been fixed, but that was due more to good fortune than a solid approach to debugging. I'm asking this question for future reference. Some related questions: Test accounts and products in a production system Running test on Production Code/Server

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• Modelling in Agile Development

  - by bertzzie

  I'm writing a bachelor dissertation report where I'm developing a system with Agile methodology. Given that the development is an one man show, of course the "Agile" I did was not really agile at all (from my understanding at least). So I want some perspective from SO crowds, who is of course a professional, real world, developer with tons of experience. I think real world experience is better than the theory and experiments that I did. My question is: Do we model during development time when using Agile? UML? DFD? Or a Functional Specification is enough1? If modelling is not really necessary, what do we use to communicate to the user, as the user almost always won't understand UML or DFD? For my system, I use UI & UX Design with heavy prototyping, but then I don't have time to draw UML any more. Which one is better? 1 http://www.joelonsoftware.com/articles/fog0000000036.html I hope the question's not "subjective and argumentative" as I know this question exist because of my lack of understanding in the agile development. If it is, could someone just give me a pointer or reference about that? Possible duplicate: Do you use UML in Agile development practices?

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• Double hashing passwords - client & server

  - by J. Stoever

  Hey, first, let me say, I'm not asking about things like md5(md5(..., there are already topics about it. My question is this: We allow our clients to store their passwords locally. Naturally, we don't want them stored in plan text, so we hmac them locally, before storing and/or sending. Now, this is fine, but if this is all we did, then the server would have the stored hmac, and since the client only needs to send the hmac, not the plain text password, an attacker could use the stored hashes from the server to access anyone's account (in the catastrophic scenario where someone would get such an access to the database, of course). So, our idea was to encode the password on the client once via hmac, send it to the server, and there encode it a second time via hmac and match it against the stored, two times hmac'ed password. This would ensure that: The client can store the password locally without having to store it as plain text The client can send the password without having to worry (too much) about other network parties The server can store the password without having to worry about someone stealing it from the server and using it to log in. Naturally, all the other things (strong passwords, double salt, etc) apply as well, but aren't really relevant to the question. The actual question is: does this sound like a solid security design ? Did we overlook any flaws with doing things this way ? Is there maybe a security pattern for something like this ?

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• Where to give feedback on a new Feature is SO ?

  - by justjoe

  After using SO, for sometimes, i realize i got some problems. zen masters fighting each other on one of my question. Every side have their own arguments and Everybody seem right. Frankly, this make me confuse : How can i choose somebody's answer where personally i don't know the right answer. So, i would like to propose a feature 'i choose this because' for a user who asked. So at least he/she explain why he choose the particular answer. Maybe it's silly, but as somebody who getting helps from other's answer, i would like to know everybody get what they deserve. Usually in this kind of situation, i just upvote every good answer and check the one i think the right one. Second feature : every hot question always got plenty answer and comment. And if among person who answer it, start to debate then it will become a little bit hectic. Right now a page only have ability to sort answer based on oldest, newest votest. So, is it possible to make a new sort based on timeline what make comment and answer collide. I believe it will be more easy to read. this feature can only see by the person who create the question, or also for public.

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• What Getters and Setters should and shouldn't do.

  - by cyclotis04

  I've run into a lot of differing opinions on Getters and Setters lately, so I figured I should make it into it's own question. A previous question of mine received an immediate comment (later deleted) that stated setters shouldn't have any side effects, and a SetProperty method would be a better choice. Indeed, this seems to be Microsoft's opinion as well. However, their properties often raise events, such as Resized when a form's Width or Height property is set. OwenP also states "you shouldn't let a property throw exceptions, properties shouldn't have side effects, order shouldn't matter, and properties should return relatively quickly." Yet Michael Stum states that exceptions should be thrown while validating data within a setter. If your setter doesn't throw an exception, how could you effectively validate data, as so many of the answers to this question suggest? What about when you need to raise an event, like nearly all of Microsoft's Control's do? Aren't you then at the mercy of whomever subscribed to your event? If their handler performs a massive amount of information, or throws an error itself, what happens to your setter? Finally, what about lazy loading within the getter? This too could violate the previous guidelines. What is acceptable to place in a getter or setter, and what should be kept in only accessor methods?

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• Linq2Sql: query - subquery optimisation

  - by Budda

  I have the following query: IList<InfrStadium> stadiums = (from sector in DbContext.sectors where sector.Type=typeValue select new InfrStadium(sector.TeamId) ).ToList(); and InfrStadium class constructor: private InfrStadium(int teamId) { IList<Sector> teamSectors = (from sector in DbContext.sectors where sector.TeamId==teamId select sector) .ToList<>(); ... work with data } Current implementation perform 1+n queries, where n - number of records fetched the 1st time. I want to optimize that. And another one I would love to do using 'group' operator in way like this: IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IEnumerable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } But attempt to launch query causes the following error: Expression of type 'System.Int32' cannot be used for constructor parameter of type 'System.Collections.Generic.IEnumerable`1[InfrStadiumSector]' Question 1: Could you please explain, what is wrong here, I don't understand why 'team_sectors' is applied as 'System.Int32'? I've tried to change query a little (replace IEnumerable with IQueryeable): IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors.AsQueryable()) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IQueryeable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } In this case I've received another but similar error: Expression of type 'System.Int32' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable1[InfrStadiumSector]' of method 'System.Linq.IQueryable1[InfrStadiumSector] AsQueryableInfrStadiumSector' Question 2: Actually, the same question: can't understand at all what is going on here... P.S. I have another to optimize query idea (describe here: Linq2Sql: query optimisation) but I would love to find a solution with 1 request to DB).

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• What happens to class members when malloc is used instead of new?

  - by Felix

  I'm studying for a final exam and I stumbled upon a curious question that was part of the exam our teacher gave last year to some poor souls. The question goes something like this: Is the following program correct, or not? If it is, write down what the program outputs. If it's not, write down why. The program: #include<iostream.h> class cls { int x; public: cls() { x=23; } int get_x(){ return x; } }; int main() { cls *p1, *p2; p1=new cls; p2=(cls*)malloc(sizeof(cls)); int x=p1->get_x()+p2->get_x(); cout<<x; return 0; } My first instinct was to answer with "the program is not correct, as new should be used instead of malloc". However, after compiling the program and seeing it output 23 I realize that that answer might not be correct. The problem is that I was expecting p2->get_x() to return some arbitrary number (whatever happened to be in that spot of the memory when malloc was called). However, it returned 0. I'm not sure whether this is a coincidence or if class members are initialized with 0 when it is malloc-ed. Is this behavior (p2->x being 0 after malloc) the default? Should I have expected this? What would your answer to my teacher's question be? (besides forgetting to #include <stdlib.h> for malloc :P)

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• Should I pass a SqlDataReader by reference or not when passing it out to multiple threads.

  - by deroby

  Hi all, being new to c# I've run into this 'conundrum' when passing around a SqlDataReader between different threads. Without going into too much detail, the idea is to have a main thread fetching data from the database (a large recordset) and then have a helper-task run through this record by record and doing some stuff based upon the contents of this. There is no feedback to the recordset, it simply wades through until no records are left. This works fine, but given the nature of the job at hand it should be possible to have this job spread over different threads (CPUs) to maximize throughput (the order of execution is of no significance). The question then becomes, when I pass this recordset in a SqlDataReader, do I have to use ref or not ? It kind of boils down to the question : if I pass the object around without specifying ref, won't it create new copies in memory and have records processed n times ? Or, don't I risk having the record-position being moved forward while not all fields have been fully read yet ? The latter seems more like a 'data racing' issue and probably is covered by the lock()ing mechanism (or not?). My initial take on the problem was that it doesn't really hurt passing the variable using ref, yet as a colleague put it : "you only need ref when you're doing something wrong" =) Additionally using ref restricts me from applying a Using() construction too which isn't very nice either. I thus create a "basic" project that tackles the same approach but without the ref notation. Tests so far show that it works flawlessly on a Core2Duo (2cpu) using any number of threads, yet I'm still a bit wary... What do you experts think about this ? Use ref or not ? You can find the test-project here as it seems I can't upload it to this question directly ?!? ps: it's just a test-project and I'm new to c#, so please be gentle on me when breaking down the code =P

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• Partitioning data set in r based on multiple classes of observations

  - by Danny

  I'm trying to partition a data set that I have in R, 2/3 for training and 1/3 for testing. I have one classification variable, and seven numerical variables. Each observation is classified as either A, B, C, or D. For simplicity's sake, let's say that the classification variable, cl, is A for the first 100 observations, B for observations 101 to 200, C till 300, and D till 400. I'm trying to get a partition that has 2/3 of the observations for each of A, B, C, and D (as opposed to simply getting 2/3 of the observations for the entire data set since it will likely not have equal amounts of each classification). When I try to sample from a subset of the data, such as sample(subset(data, cl=='A')), the columns are reordered instead of the rows. To summarize, my goal is to have 67 random observations from each of A, B, C, and D as my training data, and store the remaining 33 observations for each of A, B, C, and D as testing data. I have found a very similar question to mine, but it did not factor in multiple variables. I feel silly asking this question because it seems so simple, but I'm stumped. Also, this is my first question on this site, so I apologize in advance for any faux pas on my part.

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• Arrays not matching correctly

  - by Nick Gibson

  userAnswer[] holds the string of the answer the user types in and is comparing it to answers[] to see if they match up and then spits out correct or wrong. j is equal to the question number. So if j was question 6, answers[j] should refer to answers[6] right? Then userAnswer[6] should compare to answers[6] and match if its correct. But its giving me wrong answers and displaying the answer I typed as correct. int abc, loopCount = 100; int j = quesNum, overValue, forLoop = 100; for (int loop = 1; loop < loopCount; loop++) { aa = r.nextInt(10+1); abc = (int) aa; String[] userAnswer = new String[x]; JOptionPane.showMessageDialog(null,abc); if(abc < x) { userAnswer[j] = JOptionPane.showInputDialog(null,"Question "+quesNum+"\n"+questions[abc]+"\n\nA: "+a[abc]+"\nB: "+b[abc]+"\nC: "+c[abc]+"\nD: "+d[abc]); if(userAnswer[j].equals(answers[j])) { JOptionPane.showMessageDialog(null,"Correct. \nThe Correct Answer is "+answers[abc]); } else { JOptionPane.showMessageDialog(null,"Wrong. \n The Correct Answer is "+answers[abc]); }//else }//if }//for

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• JavaScript: how to create a JS event that requires 2 seperate JS files to be loaded first while down

  - by Teddyk

  I want to perform asynchronous JavaScript downloads of two files that have dependencies attached to them. // asynch download of jquery and gmaps function addScript(url) { var script = document.createElement('script'); script.src = url; document.getElementsByTagName('head')[0].appendChild(script); } addScript('http://google.com/gmaps.js'); addScript('http://jquery.com/jquery.js'); // define some function dependecies function requiresJQuery() { ... } function requiresGmaps() { ... } function requiresBothJQueryGmaps() { ... } // do some work that has no dependencies on either JQuery or Google maps ... // QUESTION - Pseudo code below // now call a function that requires Gmaps to be loaded if (GmapsIsLoaded) { requiresGmaps(); } // QUESTION - Pseudo code below // then do something that requires both JQuery & Gmaps (or wait until they are loaded) if (JQueryAndGmapsIsLoaded) { requiresBothJQueryGmaps(); } Question: How can I create an event to indicate when: JQuery is loaded? Google Maps is loaded JQuery & Google Maps are both loaded?

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