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• Is this feasbile with GIS?

  - by Gnu Engineer

  I'm just getting myself to familiarize with GIS but i like to know before hand if the following is feasible with current GIS apps/tools... I get the point for an address by geocoding. Easy part. Now if the point falls within a boundary (may be a city/county/state) then i need to get the data (any id/flag) associated with the boundary. Based on the id/flag i then apply some business logic. My question is... How do i define the boundary? What tools should i use for it? How can i store the boundary definition in database in order to check if the point falls within it? This has to be done in the back end and not in visual maps as we don't intend to show/use maps. How do i associate my custom data (id/flag) with the above boundary definition? Hope i'm having right assumption on capabilities of GIS. Most of examples what i see is around people trying to show maps with data which is exactly not what i'm looking for. Also please suggest me some tools/books on this.

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• iPhone dev: UIBarButtonItem or title not showing up in NavigationBar

  - by IceMan85

  Hello everyone, here my problem. I have a NavigationBar at the top, a TabBar at the bottom and a TableView at the center of the screen. Very normal situation. I set it all up in IB and I have set this in the app delegate : ExpensesListNavController *expensesListNavController; This in order to be able to add new views to the stack. I need to have 3 levels: - list of items in a TableView - OK - firstLevel: once pressed one cell a view is added to the stack - OK - second level: one pressed the "modify" button on the navBar on the firstLevel I want to show a new view that can be customized by the user. My Problem is coming when trying to add the "Modify" button in the "firstLevelView". Here-below my code -(IBAction) modify:(id)sender { if (editableDetailViewController == nil) { editableDetailViewController = [[editableDetailViewController alloc] init]; } editableDetailViewController.expense = expense; [appDelegate.expensesListNavController pushViewController:editableDetailViewController animated:YES]; editableDetailViewController = nil; } // Implement viewDidLoad to do additional setup after loading the view, typically from a nib. - (void)viewDidLoad { [super viewDidLoad]; appDelegate = [[UIApplication sharedApplication] delegate]; UIBarButtonItem *modifyButton = [[UIBarButtonItem alloc] initWithTitle:@"Modify" style:UIBarButtonItemStylePlain target:self action:@selector(modify:)]; appDelegate.expensesListNavController.navigationItem.rightBarButtonItem = modifyButton; appDelegate.expensesListNavController.navigationItem.title = @"Titoloooo"; NSLog(@"NavBar button has just been set !!"); [modifyButton release]; Nothing is being showed, neither title nor the button. Do you have any idea of what is happening ?? I really cannot figure out !!! Thanks a lot in advance, AM

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• Maintenance tool for Application Database

  - by Thierry

  Hello ! Does anybody know about a good tool which help maintaining the database of an application ? I'm working on an application which uses a database (Microsoft Sql Server). When a development requires to change something in the database (e.g., structure, data migration...), we create a script (Transact-SQL script) and add it into our revision control tool (subversion - that tool also contains our code). Each script must add a line in a log table to keep a trace of all the scripts that have been ran into a database. In order to build a database for our application, one needs to run all scripts ordered by their creation date. I'm not really happy with this technique notably because it make application migration a bit hard. If we want to install a new version of the application somewhere, e.g., migrate from version 1.3 to 2.1, we must get all the scripts between these two versions. Then run them and ensure that everything is done in a transaction... For sure we could built home-made tools to help but I wonder if some tools already exists to do that kind of job.

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• Why does the output look like this?

  - by cjk

  I have a c program below, I would like to send out a 32 bit message in a particular order Eg.0x00000001. #include <unistd.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <stdint.h> struct test { uint16_t a; uint16_t b; }; int main(int argc, char const *argv[]) { char buf[4]; struct test* ptr=(struct test*)buf; ptr->a=0x0000; ptr->b=0x0001; printf("%x %x\n",buf[0],buf[1]); //output is 0 0 printf("%x %x\n",buf[2],buf[3]); //output is 1 0 return 0; } Then I test it by print out the values in char array. I got output in the above comments. Shouldn't the output be 0 0 and 0 1? since but[3] is the last byte? Is there anything I missed? Thanks!

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• Eclipse cannot find existing project in build path

  - by PNS

  Here is probably one of the idiosyncrasies of Eclipse and its handling of build paths, which cannot be fixed despite all sorts of workarounds tested so far. The issue relates to a workspace of several projects, each of which compiles into its own JAR. Dependencies among the projects are resolved by adding the relevant ones to the build path (no Maven or other external tool or plugin is used), via Project -> Properties -> Java Build Path -> Projects Among all these projects, a couple (say, com.example.p1 and com.example.p2) refuse to recognize a third (and simple) one (say, com.example.p3), while all other projects do. So, although P3 is added to the build path, all related classes from P3 are imported properly and the source code of each such class is accessible by hitting F3, Eclipse keeps complaining that The import com.example.p3 cannot be resolved and SomeClass cannot be resolved to a type where com.example.p3.SomeClass is one of the P3 classes. If instead of the P3 project I put its compiled JAR in the build path, the issue disappears. However, code in P3 changes frequently and it is a time waste to keep compiling and refreshing the workspace so that the change is picked up, not to mention that this should not happen in an IDE anyway (and it does not for the other projects using P3). Among the workarounds tried are things like: Removing and adding again P1, P2, P3 Cleaning up and recompiling everything Checking whether any other project loads the P3 JAR Putting P3 at the top of the Eclipse build path "Order and Export" list Using the "Fix project setup" suggestion of Eclipse (available when hovering the mouse over the red-underlined-error compilation line). Actually, this option offers adding to the build path either P3 or its JAR, but if P3 is added, the issue reappears. Any ideas?

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• Implicit conversion between Scala collection types

  - by ebruchez

  I would like to implicitly convert between the Scala XML Elem object and another representation of an XML element, in my case dom4j Element. I wrote the following implicit conversions: implicit def elemToElement(e: Elem): Element = ... do conversion here ... implicit def elementToElem(e: Element): Elem = ... do conversion here ... So far so good, this works. Now I also need collections of said elements to convert both ways. First, do I absolutely need to write additional conversion methods? Things didn't seem to work if I didn't. I tried to write the following: implicit def elemTToElementT(t: Traversable[Elem]) = t map (elemToElement(_)) implicit def elementTToElemT(t: Traversable[Element]) = t map (elementToElem(_)) This doesn't look too ideal because if the conversion method takes a Traversable, then it also returns a Traversable. If I pass a List, I also get a Traversable out. So I assume the conversion should be parametrized somehow. So what's the standard way of writing these conversions in order to be as generic as possible?

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• Android newbie installing Eclipse, having issues....

  - by Jeff

  I am a web developer, new to app development and Java/Android. I am about to follow some tutorials to get started learning but I'm running into a wall. The Android dev site says the recommended way to build Android apps is in Java using the Eclipse plug in. So I downloaded Eclipse Classic and unzipped it on to get this error: "A Java Runtime Environment (JRE) or Java Development Kit (JDK) must be available in order to run Eclipse. No Java virtual machine was found after searching the following locations: /Users//Desktop/eclipse/Eclipse.app/Contents/MacOS/jre/bin/java java in your current PATH" Any idea what the issue is and how I can fix it? Again, newbie to java, jre, android, so I apologize if this question has already been asked. In my research I've discovered that most of the posts or solutions I've found are tough for me to follow. There's always a few unclear items that are probably prohibiting me from getting the answer I need. So I'm hoping someone can walk me through installing or configuring whatever I need to regarding Java so I can continue installing Eclipse and begin learning. I should probably note that I'm on Mac OSX 10.6.6 Snow Leopard. Please let me know if you need any other info. Thanks so much in advance for any and all help!!!

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• looking for advise on importing excel into mysql with php

  - by Ole Media

  Alright, see if I can pick your brains from you all. I'm currently working on a project where all the information comes from different clients, the only thing in common is that the received data is done with excel. The excel spread sheet that they present is just a bunch of references and codes, and the problem than I'm facing is that I need the references and codes to be entered in certain format in order for the website to work. The perfect situation will be to go to each client and teach how I would need the data, but I can't do that because of the large number of clients, and more importantly I will be interrupting their work flow. Each client has its own codes and reference model and they are not willing to change their process The good news is that there is a standard pattern for the codes, but I'm talking close to 200 thousand codes with a bunch of combination. They way that we are currently solving the problem is that we have a person who checks each excel sheet received, runs a few macros, and manually fixes those codes in which the macro was not able to fix. The person that is doing this, is already burn out and frustrated and I would like to automatize this process with php. Suggestions?

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• Implementing Unowned relationship Google App Engine

  - by nwallman

  My question is more of a best practices question on how to implement unowned relationships with Google App Engine. I am using JDO to do my persistence and like recommended in the google docs I'm persisting my list of unowned relationships like so: @PersistenceCapable(identityType = IdentityType.APPLICATION) public class User implements Serializable, UserDetails { ... @Persistent private List<Key> groups; ... } Now I came across my predicament when I went to query that list of objects using they Key object. So when I get my list of group keys in order to actually return a list of Group objects I have to do a look up on that key to get the object. My question is what is the recommended way of doing a unowned look up on a model object? Should I have an instance of the PersistanceManagerFactory on my Model object so I can do a lookup? Should I have an instance of my GroupDAO object on my Model object so I can do a look up? Should I have a Utility to do this type of lookup? I'm new to this so I just want to know which is the best way to do this. Thanks.

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• Android Unit Testing - Resolution & Verification Problems

  - by Bill

  I just switched the way my Android project is being built and non of my unit tests work any more...I get errors like WARN/dalvikvm(575): VFY: unable to resolve static field X in ..... WARN/dalvikvm(575): VFY: unable to find class referenced in signature These errors only come from my Unit Tests, where classes defined in it can't even see other classes defined in the unit test. Before each project had its own directory with copies of the 3rd party jar files. I've read around that Dex does weird things with references but haven't been able to figure out how to fix this problem. Is there a better way to do this? I would love to see an example of a large Android workspace where there are multiple projects, jar references, etc... Is it possible to fix this with an Order/Export tweak ? The project is structured like this: Eclipse Workspace (PROJECT_HOME classpath variable) lib 3rd-party jars android.jar Java Project A Looks in PROJECT_HOME Java Project B Looks in PROJECT_HOME Depends on project A Android Project Depends on A & B Looks in PROJECT_HOME Android Test Project Depends on A , B, Android Project Looks in PROJECT_HOME

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• Could someone explain gtk2hs drag and drop to me, the listDND.hs demo just isn't doing it for me?

  - by Tom Carstens

  As the title says, I just don't get DND (or rather I understand the concept and I understand the order of callbacks, I just don't understand how to setup DND for actual usage.) I'd like to say that I've done DND stuff before in C, but considering I never really got that working... So I'm trying (and mostly succeeding, save DND) to write a text editor (using gtksourceview, because it has built in code highlighting.) Reasons are below if you want them. Anyways, there's not really a good DND demo or tutorial available for gtk2hs (listDND.hs just doesn't translate well in my head.) So what I'm asking is for code that demonstrates simple DND on a window widget (for example.) Ideally, it should accept drops from other windows (such as Thunar) and print out the information in string form. I think I can take it from there... Reasons: I'm running a fairly light weight setup, dwm and a few gtk+2 programs. I really don't want to have to pull in gtk+3 to get the current gedit from the repos (Arch Linux.) Currently, I'm using geany for all of my text editing needs, however, geany is a bit heavy for editing config files. Further, geany doesn't care for my terminal of choice (st;) so I don't even get the benefit of using it as an IDE. Meaning I'd like a lightweight text editor with syntax highlighting. I could configure emacs or vim or something, but that seems to me to be more of a hack then a proper solution. Thus my project was born. It's mostly working (aside from DND, all that's left is proper multi-tab support.) Admittedly, I could probably work this out if I wrote it in C, but there isn't that much state in a text editor so Haskell's been working fine with almost no need for mutable variables.

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• [C#] How to receive uncrackable data or so ? ;P

  - by Prix

  Hi, I am working on an C# application to communicate with my website and retrieve some information from it, using SSL which is working just fine. Now what i want/need is a way to receive encrypted or codified or obfuscated data that if some one cracks my application they will not be able to decrypt the data because it needs something from the server (api, website) but yet the application needs to decrypt it in order to use it... initally i was thinking of an inside RSA pair or keys, to send and receive the encrypt data but let's consider that someone has cracked the application, they could just replace those keys for keys they have made, so i was looking into some methods but havent found or been able to think of any way to harder this... I was learning about RSA, encryption and such and started developing this as a self learning and got involved with it and now i am trying to figure out a way to receive data like that... I have considered obfuscating and compiling my code with packers and etc but this is not about packing it etc... i am more interested in knowing a better way to secure what i described i know it may or is impossible but yet i am looking forward to some approch. I would appreciate advices, suggestions and C# code samples, if you need more information or anything please let me know.

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• Test the sequentiality of a column with a single SQL query

  - by LauriE

  Hey, I have a table that contains sets of sequential datasets, like that: ID set_ID some_column n 1 'set-1' 'aaaaaaaaaa' 1 2 'set-1' 'bbbbbbbbbb' 2 3 'set-1' 'cccccccccc' 3 4 'set-2' 'dddddddddd' 1 5 'set-2' 'eeeeeeeeee' 2 6 'set-3' 'ffffffffff' 2 7 'set-3' 'gggggggggg' 1 At the end of a transaction that makes several types of modifications to those rows, I would like to ensure that within a single set, all the values of "n" are still sequential (rollback otherwise). They do not need to be in the same order according to the PK, just sequential, like 1-2-3 or 3-1-2, but not like 1-3-4. Due to the fact that there might be thousands of rows within a single set I would prefer to do it in the db to avoid the overhead of fetching the data just for verification after making some small changes. Also there is the issue of concurrency. The way locking in InnoDB (repeatable read) works (as I understand) is that if I have an index on "n" then InnoDB also locks the "gaps" between values. If I combine set_ID and n to a single index, would that eliminate the problem of phantom rows appearing? Looks to me like a common problem. Any brilliant ideas? Thanks! Note: using MySQL + InnoDB

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• How can I perform this query between related tables without using UNION?

  - by jeremy

  Suppose I have two separate tables that I watch to query. Both of these tables has a relation with a third table. How can I query both tables with a single, non UNION based query? I want the result of the search to rank the results by comparing a field on each table. Here's a theoretical example. I have a User table. That User can have both CDs and books. I want to find all of that user's books and CDs with a single query matching a string ("awesome" in this example). A UNION based query might look like this: SELECT "book" AS model, name, ranking FROM book WHERE name LIKE 'Awesome%' UNION SELECT "cd" AS model, name, ranking FROM cd WHERE name LIKE 'Awesome%' ORDER BY ranking DESC How can I perform a query like this without the UNION? If I do a simple left join from User to Books and CDs, we end up with a total number of results equal to the number of matching cds timse the number of matching books. Is there a GROUP BY or some other way of writing the query to fix this?

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• Optimization of SQL query regarding pair comparisons

  - by InfiniteSquirrel

  Hi, I'm working on a pair comparison site where a user loads a list of films and grades from another site. My site then picks two random movies and matches them against each other, the user selects the better of the two and a new pair is loaded. This gives a complete list of movies ordered by whichever is best. The database contains three tables; fm_film_data - this contains all imported movies fm_film_data(id int(11), imdb_id varchar(10), tmdb_id varchar(10), title varchar(255), original_title varchar(255), year year(4), director text, description text, poster_url varchar(255)) fm_films - this contains all information related to a user, what movies the user has seen, what grades the user has given, as well as information about each film's wins/losses for that user. fm_films(id int(11), user_id int(11), film_id int(11), grade int(11), wins int(11), losses int(11)) fm_log - this contains records of every duel that has occurred. fm_log(id int(11), user_id int(11), winner int(11), loser int(11)) To pick a pair to show the user, I've created a mySQL query that checks the log and picks a pair at random. SELECT pair.id1, pair.id2 FROM (SELECT part1.id AS id1, part2.id AS id2 FROM fm_films AS part1, fm_films AS part2 WHERE part1.id <> part2.id AND part1.user_id = [!!USERID!!] AND part2.user_id = [!!USERID!!]) AS pair LEFT JOIN (SELECT winner AS id1, loser AS id2 FROM fm_log WHERE fm_log.user_id = [!!USERID!!] UNION SELECT loser AS id1, winner AS id2 FROM fm_log WHERE fm_log.user_id = [!!USERID!!]) AS log ON pair.id1 = log.id1 AND pair.id2 = log.id2 WHERE log.id1 IS NULL ORDER BY RAND() LIMIT 1 This query takes some time to load, about 6 seconds in our tests with two users with about 800 grades each. I'm looking for a way to optimize this but still limit all duels to appear only once. The server runs MySQL version 5.0.90-community.

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• Loading Javascript through an AJAX load through jQuery??

  - by Jason Axelrod

  I have an javascript that I place into a page using the code below. What the code does is place an object/embed code into a webpage. Simple javascript loader to a NicoVideo movie <script type="text/javascript" src="http://ext.nicovideo.jp/thumb_watch/sm13154955?w=640&h=395"></script> This works great in a webpage. But what if I want to load this javascript into a page using AJAX? This no longer works for the obvious reasons, you would need to eval the script in order to get it to run. However, I have no idea how to do this. I am using jQuery on my page; so keep that in mind. I have tried the following code, but it doesn't seem to work through AJAX, or even in a normal page load environment. <script>$.getScript("http://ext.nicovideo.jp/thumb_watch/sm13154955?w=640&h=395");</script> Any ideas on how I would get this to work?

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• Angularjs throws TypeError: Cannot read property 'indexOf' of undefined

  - by Ali

  I'm trying to debug the above code which I feel like this is very useful .< I can't even find what is wrong in my code and don't really know where to start since Angularjs still very new to me. I'm trying to localize Angularjs app. I know this is missing a lot of context in order to get a help, but I'm trying to see what information that I should give that would help on this debugging. I've gone through any indexOf in angularjs file and I can see few things is undefined but don't know if that would be helpful. So I've traced the problem here and this is what I have figured is the problem, but still counldn't figure out why... config(['$routeProvider', '$locationProvider', function ($routeProvider, $locationProvider) { $routeProvider.when('/:locale?/:username/badges', { templateUrl: '_partials/badges.html', controller: 'badges' }) .when('/:username/badges', { templateUrl: '_partials/badges.html', controller: 'badges' }) .when('/:username/teaching-resources', { templateUrl: '_partials/teaching-resources.html', controller: 'teachingResources' }) .when('/:username/makes', { templateUrl: '_partials/makes.html', controller: 'makes' }) .when('/:username/likes', { templateUrl: '_partials/likes.html', controller: 'likes' }) .when('/:username/events', { templateUrl: '_partials/events.html', controller: 'events' }) .when('/:username', { templateUrl: '_partials/badges.html', controller: 'badges' }); $routeProvider.otherwise({ redirectTo: '/error/404' }); The URL that I'm visiting for default page is: This will fail and throw the error. http://localhost:1969/en-US/user/someUserName This will work fine http://localhost:1969/user/someUserName UPDATE I figured out! This is the problem: $locationProvider.html5Mode(true); But why!?

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• How to protect and hidden form HTML/PHP with JS callback to AS3

  - by Jk_

  Hi guys, I'm developing a Flash website (as3) where I need to be able to upload directly to YouTube by using the DATA API. However in order to do so, I had to use a proper HTML form on top of my flash object. Why? Because of the Browser Based Upload restictions. I first hide the form using JQuery and with a little CSS the form is display just where I want it. Within flash I use ExternalInterface.call() to show/hide the form when I need it! ExternalInterface.call("YTUploader.showIt"); The upload process is working great my only problem is that the form can be displayed easily... You just need a tool like firebug and you can use the form wherever you want on my flash app. So I was wandering which will be the best way to 'protect' this form or the best way to limit its access. Any advices will be appreciated. Thanks for your time. Jk.

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• How to define 2-bit numbers in C, if possible?

  - by Eddy

  For my university process I'm simulating a process called random sequential adsorption. One of the things I have to do involves randomly depositing squares (which cannot overlap) onto a lattice until there is no more room left, repeating the process several times in order to find the average 'jamming' coverage %. Basically I'm performing operations on a large array of integers, of which 3 possible values exist: 0, 1 and 2. The sites marked with '0' are empty, the sites marked with '1' are full. Initially the array is defined like this: int i, j; int n = 1000000000; int array[n][n]; for(j = 0; j < n; j++) { for(i = 0; i < n; i++) { array[i][j] = 0; } } Say I want to deposit 5*5 squares randomly on the array (that cannot overlap), so that the squares are represented by '1's. This would be done by choosing the x and y coordinates randomly and then creating a 5*5 square of '1's with the topleft point of the square starting at that point. I would then mark sites near the square as '2's. These represent the sites that are unavailable since depositing a square at those sites would cause it to overlap an existing square. This process would continue until there is no more room left to deposit squares on the array (basically, no more '0's left on the array) Anyway, to the point. I would like to make this process as efficient as possible, by using bitwise operations. This would be easy if I didn't have to mark sites near the squares. I was wondering whether creating a 2-bit number would be possible, so that I can account for the sites marked with '2'. Sorry if this sounds really complicated, I just wanted to explain why I want to do this.

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• Need help extrapolating Java code

  - by Berlioz

  If anyone familiar with Rebecca Wirfs-Brock, she has a piece of Java code found in her book titled, Object Design: Roles, Responsibilities, and Collaborations. Here is the quote Applying Double Dispatch to a Specific Problem To implement the game Rock, Paper, Scissors we need to write code that determines whether one object “beats” another. The game has nine possible outcomes based on the three kinds of objects. The number of interactions is the cross product of the kinds of objects. Case or switch statements are often governed by the type of data that is being operated on. The object-oriented language equivalent is to base its actions on the class of some other object. In Java, it looks like this Here is the piece of Java code on page 16 ' import java.util.*; import java.lang.*; public class Rock { public static void main(String args[]) { } public static boolean beats(GameObject object) { if (object.getClass.getName().equals("Rock")) { result = false; } else if (object.getClass.getName().equals("Paper")) { result = false; } else if(object.getClass.getName().equals("Scissors")) { result = true; } return result; } }' ===This is not a very good solution. First, the receiver needs to know too much about the argument. Second, there is one of these nested conditional statements in each of the three classes. If new kinds of objects could be added to the game, each of the three classes would have to be modified. Can anyone share with me how to get this "less than optimal" piece of code to work in order to see it 'working'. She proceeds to demonstrate a better way, but I will spare you. Thanks

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• Html image link, not working

  - by Anders Metnik

  Hey I'm doing some testing while learning js + html5 and other web/mobile frameworks. I have a problem with one of my picture links, which I also need to change the picture dynamically and the target(hopefully). But it won't work. HTML: <div data-role="content" id="firstPageContent"> <p>I'm first in the source order so I'm shown as the page.</p> <p>View internal page called <a href="#second">second</a></p> <a href = "#second" id="mapLink" name="mapLink"><img id="mapLinkImage" alt="a map which links to the mapPage" src="images/main_header.png"/></a> <Button id="loadButton" onClick="load()"/> </div><!-- /content --> js: importScripts(dataManager.js); var mapLink=second; function load(){ alert('called'); document.getElementById('mapLinkImage').src="images/store.map.png"; document.getElementById('mapLink').href = "http://google.com"; } problem: It ain't showing the image as a link, just as a plain image. i think this will work now.

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• How do I write recursive anonymous functions?

  - by James T Kirk

  In my continued effort to learn scala, I'm working through 'Scala by example' by Odersky and on the chapter on first class functions, the section on anonymous function avoids a situation of recursive anonymous function. I have a solution that seems to work. I'm curious if there is a better answer out there. From the pdf: Code to showcase higher order functions def sum(f: Int => Int, a: Int, b: Int): Int = if (a > b) 0 else f(a) + sum(f, a + 1, b) def id(x: Int): Int = x def square(x: Int): Int = x * x def powerOfTwo(x: Int): Int = if (x == 0) 1 else 2 * powerOfTwo(x-1) def sumInts(a: Int, b: Int): Int = sum(id, a, b) def sumSquares(a: Int, b: Int): Int = sum(square, a, b) def sumPowersOfTwo(a: Int, b: Int): Int = sum(powerOfTwo, a, b) scala> sumPowersOfTwo(2,3) res0: Int = 12 from the pdf: Code to showcase anonymous functions def sum(f: Int => Int, a: Int, b: Int): Int = if (a > b) 0 else f(a) + sum(f, a + 1, b) def sumInts(a: Int, b: Int): Int = sum((x: Int) => x, a, b) def sumSquares(a: Int, b: Int): Int = sum((x: Int) => x * x, a, b) // no sumPowersOfTwo My code: def sumPowersOfTwo(a: Int, b: Int): Int = sum((x: Int) => { def f(y:Int):Int = if (y==0) 1 else 2 * f(y-1); f(x) }, a, b) scala> sumPowersOfTwo(2,3) res0: Int = 12

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• Understanding the singleton class when aliasing a instance method

  - by Backo

  I am using Ruby 1.9.2 and the Ruby on Rails v3.2.2 gem. I am trying to learn Metaprogramming "the right way" and at this time I am aliasing an instance method in the included do ... end block provided by the RoR ActiveSupport::Concern module: module MyModule extend ActiveSupport::Concern included do # Builds the instance method name. my_method_name = build_method_name.to_sym # => :my_method # Defines the :my_method instance method in the including class of MyModule. define_singleton_method(my_method_name) do |*args| # ... end # Aliases the :my_method instance method in the including class of MyModule. singleton_class = class << self; self end singleton_class.send(:alias_method, :my_new_method, my_method_name) end end "Newbiely" speaking, with a search on the Web I came up with the singleton_class = class << self; self end statement and I used that (instead of the class << self ... end block) in order to scope the my_method_name variable, making the aliasing generated dynamically. I would like to understand exactly why and how the singleton_class works in the above code and if there is a better way (maybe, a more maintainable and performant one) to implement the same (aliasing, defining the singleton method and so on), but "the right way" since I think it isn't so.

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• Obtaining command line arguments in a QT application

  - by morpheous

  The following snippet is from a little app I wrote using the QT framework. The idea is that the app can be run in batch mode (i.e. called by a script) or can be run interactively. It is important therefore, that I am able to parse command line arguments in order to know which mode in which to run etc. [Edit] I am debugging using QTCreator 1.3.1 on Ubuntu Karmic. The arguments are passed in the normal way (i.e. by adding them via the 'Project' settings in the QTCreator IDE). When I run the app, it appears that the arguments are not being passed to the application. The code below, is a snippet of my main() function. int main(int argc, char *argv[]) { //Q_INIT_RESOURCE(application); try { QApplication the_app(argc, argv); //trying to get the arguments into a list QStringList cmdline_args = QCoreApplication::arguments(); // Code continues ... } catch (const MyCustomException &e) { return 1; } return 0; } [Update] I have identified the problem - for some reason, although argc is correct, the elements of argv are empty strings. I put this little code snippet to print out the argv items - and was horrified to see that they were all empty. for (int i=0; i< argc; i++){ std::string s(argv[i]); //required so I can see the damn variable in the debugger std::cout << s << std::endl; } Does anyone know what on earth is going on (or a hammer)?

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• Algorithm to determine indices i..j of array A containing all the elements of another array B

  - by Skylark

  I came across this question on an interview questions thread. Here is the question: Given two integer arrays A [1..n] and B[1..m], find the smallest window in A that contains all elements of B. In other words, find a pair < i , j such that A[i..j] contains B[1..m]. If A doesn't contain all the elements of B, then i,j can be returned as -1. The integers in A need not be in the same order as they are in B. If there are more than one smallest window (different, but have the same size), then its enough to return one of them. Example: A[1,2,5,11,2,6,8,24,101,17,8] and B[5,2,11,8,17]. The algorithm should return i = 2 (index of 5 in A) and j = 9 (index of 17 in A). Now I can think of two variations. Let's suppose that B has duplicates. This variation doesn't consider the number of times each element occurs in B. It just checks for all the unique elements that occur in B and finds the smallest corresponding window in A that satisfies the above problem. For example, if A[1,2,4,5,7] and B[2,2,5], this variation doesn't bother about there being two 2's in B and just checks A for the unique integers in B namely 2 and 5 and hence returns i=1, j=3. This variation accounts for duplicates in B. If there are two 2's in B, then it expects to see at least two 2's in A as well. If not, it returns -1,-1. When you answer, please do let me know which variation you are answering. Pseudocode should do. Please mention space and time complexity if it is tricky to calculate it. Mention if your solution assumes array indices to start at 1 or 0 too. Thanks in advance.

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