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• How to export Oracle statistics

  - by A_M

  Hi, I am writing some new SQL queries and want to check the query plans that the Oracle query optimiser would come up with in production. My development database doesn't have anything like the data volumes of the production database. How can I export database statistics from a production database and re-import them into a development database? I don't have access to the production database, so I can't simply generate explain plans on production without going through a third party hosting organisation. This is painful. So I want a local database which is in some way representative of production on which I can try out different things. Also, this is for a legacy application. I'd like to "improve" the schema, by adding appropriate indexes. constraints, etc. I need to do this in my development database first, before rolling out to test and production. If I add an index and re-generate statistics in development, then the statistics will be generated around the development data volumes, which makes it difficult to assess the impact my changes on production. Does anyone have any tips on how to deal with this? Or is it just a case of fixing unexpected behaviour once we've discovered it on production? I do have a staging database with production volumes, but again I have to go through a third party to run queries against this, which is painful. So I'm looking for ways to cut out the middle man as much as possible. All this is using Oracle 9i. Thanks.

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• Assign click event to addon icon on navigation bar

  - by Charsee

  We have created a chrome extension for our app. Where we call a METHOD from a "js file" on CLICK event of the "extension icon" placed on the navigation bar. For this we use message passing between the app.js (file containing the METHOD to be called on icon click) and background.html (using a js file included in this html). The script used to pass message is:(from background.html) chrome.browserAction.onClicked.addListener(function (tab) { chrome.tabs.sendMessage(tab.id, "showPopup"); }); and to listen the message :(in app.js) chrome.extension.onMessage.addListener(function(request) { if (request === "showPopup") { showPopup(); } }); The click event works as expected. But now we want to do same thing in mozilla extension. and we can't pass message to app.js on the click of the icon,so that it can execute the containing methods. We have also added the app.js using pageMod, something like this exports.main = function(options, callbacks) { pageMod.PageMod({ include: ["*"], contentScriptWhen: 'start', contentScriptFile: [data.url('jquery-1.7.1.min.js'),data.url('app.js')] }); createAndAddNavBarButton(); }; function createAndAddNavBarButton() { var navBar = document.getElementById('nav-bar');//assume document has been defined if (!navBar){return;}; var nbBtn = document.createElement('navbaricon'); nbBtn.setAttribute('id', 'navButton'); nbBtn.setAttribute('image', data.url('icon_16.png')); nbBtn.onclick = function(){ showPopup(); return true; } navBar.appendChild(btn); } But the click event does nothing and showPopup() is undefined. When a new page loads event associated with it in the app.js executes without any error but the click event doesn't work. Is there a method from where we can assign click event directly to this icon, as we have done in the case of chrome extension.

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• Jquery Cycle in Drupal - onAfter effect not working.

  - by jdln

  Im using the views slideshow module for drupal which uses the jquery cycle plugin. Here is my first simple slideshow where everything works properly: smartpeopletalkfast.co.uk/slideshow3/one Here is my 2nd slideshow: smartpeopletalkfast.co.uk/slideshow3/two Im trying to use the onAfter function. I want the next and previous buttons to be hidden when at the end of their cycle. This is demonstrated here: jquery.malsup.com/cycle/after.html The first slideshow that's working has these controls: prev: #prev1, next: #next1 The 2nd slideshow has these: prev: #prev1, next: #next1, end: onAfterr, timeout: 0 And Ive added this to the beginning of my document head. <script type="text/javascript"> function onAfterr(curr, next, opts) { var index = opts.currSlide; $('#prev1')[index == 0 ? 'hide' : 'show'](); $('#next1')[index == opts.slideCount - 1 ? 'hide' : 'show'](); } </script> I changed onAfter to onAfterr in case of a conflict. Nothing ive tried works and ive no idea why! Thanks

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• What happens when value types are created?

  - by Bob

  I'm developing a game using XNA and C# and was attempting to avoid calling new struct() type code each frame as I thought it would freak the GC out. "But wait," I said to myself, "struct is a value type. The GC shouldn't get called then, right?" Well, that's why I'm asking here. I only have a very vague idea of what happens to value types. If I create a new struct within a function call, is the struct being created on the stack? Will it simply get pushed and popped and performance not take a hit? Further, would there be some memory limit or performance implications if, say, I need to create many instances in a single call? Take, for instance, this code: spriteBatch.Draw(tex, new Rectangle(x, y, width, height), Color.White); Rectangle in this case is a struct. What happens when that new Rectangle is created? What are the implications of having to repeat that line many times (say, thousands of times)? Is this Rectangle created, a copy sent to the Draw method, and then discarded (meaning no memory getting eaten up the more Draw is called in that manner in the same function)? P.S. I know this may be pre-mature optimization, but I'm mostly curious and wish to have a better understanding of what is happening.

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• Fetch the most viewed data in databases

  - by Erik Edgren

  I want to get the most viewed photo from the database but I don't know how I shall accomplish this. Here's my SQL at the moment: SELECT * FROM photos AS p, viewers AS v WHERE p.id = v.id_photo GROUP BY v.id_photo The databases: CREATE TABLE IF NOT EXISTS `photos` ( `id` int(10) NOT NULL AUTO_INCREMENT, `photo_filename` varchar(50) NOT NULL, `photo_camera` varchar(150) NOT NULL, `photo_taken` datetime NOT NULL, `photo_resolution` varchar(10) NOT NULL, `photo_exposure` varchar(10) NOT NULL, `photo_iso` varchar(3) NOT NULL, `photo_fnumber` varchar(10) NOT NULL, `photo_focallength` varchar(10) NOT NULL, `post_coordinates` text NOT NULL, `post_description` text NOT NULL, `post_uploaded` datetime NOT NULL, `post_edited` datetime NOT NULL, `checkbox_approxcoor` enum('0','1') NOT NULL DEFAULT '0', PRIMARY KEY (`id`), UNIQUE KEY `id` (`id`) ) CREATE TABLE IF NOT EXISTS `viewers` ( `id` int(10) NOT NULL AUTO_INCREMENT, `id_photo` int(10) DEFAULT '0', `ipaddress` text NOT NULL, `date_viewed` datetime NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `id` (`id`) ) The data in viewers looks like this: (1, 85, '3892a0ab97d6ff325f285b27b847070f', '2012-06-21 22:49:25'), (2, 84, '3892a0ab97d6ff325f285b27b847070f', '2012-06-21 22:49:25'), (3, 85, '3892a0ab97d6ff325f285b27b847070f', '2012-06-21 22:49:25'); One single row from the database for photos to understand how the rows looks like in this database: (85, 'P1170986.JPG', 'Panasonic DMC-LX3', '2012-06-19 18:00:40', '3968x2232', '10/8000', '80', '50/10', '51/10', '', '', '2012-06-19 18:45:17', '0000-00-00 00:00:00', '0') At the moment the SQL only prints the photo with ID 84. In this case it's wrong - it should print out the photo with ID 85. How can I fix this problem? Thanks in advance.

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• Go - Using a map for its set properties with user defined types

  - by Seth Hoenig

  I'm trying to use the built-in map type as a set for a type of my own (Point, in this case). The problem is, when I assign a Point to the map, and then later create a new, but equal point and use it as a key, the map behaves as though that key is not in the map. Is this not possible to do? // maptest.go package main import "fmt" func main() { set := make(map[*Point]bool) printSet(set) set[NewPoint(0, 0)] = true printSet(set) set[NewPoint(0, 2)] = true printSet(set) _, ok := set[NewPoint(3, 3)] // not in map if !ok { fmt.Print("correct error code for non existent element\n") } else { fmt.Print("incorrect error code for non existent element\n") } c, ok := set[NewPoint(0, 2)] // another one just like it already in map if ok { fmt.Print("correct error code for existent element\n") // should get this } else { fmt.Print("incorrect error code for existent element\n") // get this } fmt.Printf("c: %t\n", c) } func printSet(stuff map[*Point]bool) { fmt.Print("Set:\n") for k, v := range stuff { fmt.Printf("%s: %t\n", k, v) } } type Point struct { row int col int } func NewPoint(r, c int) *Point { return &Point{r, c} } func (p *Point) String() string { return fmt.Sprintf("{%d, %d}", p.row, p.col) } func (p *Point) Eq(o *Point) bool { return p.row == o.row && p.col == o.col }

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• WM_NOTIFY and superclass chaining issue in Win32

  - by DasMonkeyman

  For reference I'm using the window superclass method outlined in this article. The specific issue occurs if I want to handle WM_NOTIFY messages (i.e. for custom drawing) from the base control in the superclass I either need to reflect them back from the parent window or set my own window as the parent (passed inside CREATESTRUCT for WM_(NC)CREATE to the base class). This method works fine if I have a single superclass. If I superclass my superclass then I run into a problem. Now 3 WindowProcs are operating in the same HWND, and when I reflect WM_NOTIFY messages (or have them sent to myself from the parent trick above) they always go to the outermost (most derived) WindowProc. I have no way to tell if they're messages intended for the inner superclass (base messages are supposed to go to the first superclass) or messages intended for the outer superclass (messages from the inner superclass are intended for the outer superclass). These messages are indistinguishable because they all come from the same HWND with the same control ID. Is there any way to resolve this without creating a new window to encapsulate each level of inheritance? Sorry about the wall of text. It's a difficult concept to explain. Here's a diagram. single superclass: SuperA::WindowProc() - Base::WindowProc()---\ ^--------WM_NOTIFY(Base)--------/ superclass of a superclass: SuperB::WindowProc() - SuperA::WindowProc() - Base::WindowProc()---\ ^--------WM_NOTIFY(Base)--------+-----------------------/ ^--------WM_NOTIFY(A)-----------/ The WM_NOTIFY messages in the second case all come from the same HWND and control ID, so I cannot distinguish between the messages intended for SuperA (from Base) and messages intended for SuperB (from SuperA). Any ideas?

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• Getting rid of nested using(...) statements

  - by Ghostrider

  Sometimes I need to use several disposable objects within a function. Most common case is having StreamReader and StreamWriter but sometimes it's even more than this. Nested using statements quickly add up and look ugly. To remedy this I've created a small class that collects IDisposable objects and disposes of them when it itself is disposed. public class MultiDispose : HashSet<IDisposable>, IDisposable { public MultiDispose(params IDisposable[] objectsToDispose) { foreach (IDisposable d in objectsToDispose) { this.Add(d); } } public T Add<T>(T obj) where T : IDisposable { base.Add(obj); return obj; } public void DisposeObject(IDisposable obj) { obj.Dispose(); base.Remove(obj); } #region IDisposable Members public void Dispose() { foreach (IDisposable d in this) { d.Dispose(); } } #endregion } So my code now looks like this: using (MultiDispose md = new MultiDispose()) { StreamReader rdr = md.Add(new StreamReader(args[0])); StreamWriter wrt = md.Add(new StreamWriter(args[1])); WhateverElseNeedsDisposing w = md.Add(new WhateverElseNeedsDisposing()); // code } Is there anything wrong with this approach that can cause problems down the road? I left the Remove function inherited from the HashSet on purpose so that the class would be more flexible. Surely misusing this function can lead to objects not being disposed of properly, but then there many other ways to shoot yourself in the foot without this class.

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• Retrieve only the superclass from a class hierarchy

  - by user1792724

  I have an scenario as the following: @Entity @Table(name = "ANIMAL") @Inheritance(strategy = InheritanceType.JOINED) public class Animal implements Serializable { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "S_ANIMAL") @SequenceGenerator(name = "S_ANIMAL", sequenceName = "S_ANIMAL", allocationSize = 1) public int getNumero() { return numero; } public void setNumero(int numero) { this.numero = numero; } . . . } and as the subclass: @Entity @Table(name = "DOG") public class Dog extends Animal { private static final long serialVersionUID = -7341592543130659641L; . . . } I have a JPA Select statement like this: SELECT a FROM Animal a; I'm using Hibernate 3.3.1 As I can see the framework retrieves instances of Animal and also of Dog using a left outer join. Is there a way to Select only the "part" Animal? I mean, the previous Select will get all the Animals, those that are only Animals but not Dogs and those that are Dogs. I want them all, but in the case of Dogs I want to only retrieve the "Animal part" of them. I found the @org.hibernate.annotations.Entity(polymorphism = PolymorphismType.EXPLICIT) but as I could see this only works if Animal isn't an @Entity. Thanks a lot.

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• Divide and conquer of large objects for GC performance

  - by Aperion

  At my work we're discussing different approaches to cleaning up a large amount of managed ~50-100MB memory.There are two approaches on the table (read: two senior devs can't agree) and not having the experience the rest of the team is unsure of what approach is more desirable, performance or maintainability. The data being collected is many small items, ~30000 which in turn contains other items, all objects are managed. There is a lot of references between these objects including event handlers but not to outside objects. We'll call this large group of objects and references as a single entity called a blob. Approach #1: Make sure all references to objects in the blob are severed and let the GC handle the blob and all the connections. Approach #2: Implement IDisposable on these objects then call dispose on these objects and set references to Nothing and remove handlers. The theory behind the second approach is since the large longer lived objects take longer to cleanup in the GC. So, by cutting the large objects into smaller bite size morsels the garbage collector will processes them faster, thus a performance gain. So I think the basic question is this: Does breaking apart large groups of interconnected objects optimize data for garbage collection or is better to keep them together and rely on the garbage collection algorithms to processes the data for you? I feel this is a case of pre-optimization, but I do not know enough of the GC to know what does help or hinder it.

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• Question about Client IDs

  - by George

  I have a user control that is emmitting javascript using the ClientId function. For example: Out &= "ValidatorHookupControlID(" & Quote & ddlMonth.ClientID & Quote & "), document.all(" & Quote & CustomValidator1.ClientID & Quote & "));" & vbCrLf It appears to me that the ClientID function DOES not return the ultimate ID that is sent to the browser. Instead, the ClientID function only appears to be aware of its current parent control, which in this case is a the User Control and so the ID that is returned is the ID "dtmPassportExpirationDate_ddlMonth" When in fact the usercontrol is included in a master page and the ultimate ID that is used is: "ctl00_phPageContent_dtmPassportExpirationDate_ddlMonth" I may be nuts, but that's what it appears to be doing. I expect that the ClientID function would return the ultimate ID used in the HTML. Am I missing something?

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• Using Tcl DSL in Python

  - by Sridhar Ratnakumar

  I have a bunch of Python functions. Let's call them foo, bar and baz. They accept variable number of string arguments and does other sophisticated things (like accessing the network). I want the "user" (let's assume he is only familiar with Tcl) to write scripts in Tcl using those functions. Here's an example (taken from Macports) that user can come up with: post-configure { if {[variant_isset universal]} { set conflags "" foreach arch ${configure.universal_archs} { if {${arch} == "i386"} {append conflags "x86 "} else { if {${arch} == "ppc64"} {append conflags "ppc_64 "} else { append conflags ${arch} " " } } } set profiles [exec find ${worksrcpath} -name "*.pro"] foreach profile ${profiles} { reinplace -E "s|^(CONFIG\[ \\t].*)|\\1 ${conflags}|" ${profile} # Cures an isolated case system "cd ${worksrcpath}/designer && \ ${qt_dir}/bin/qmake -spec ${qt_dir}/mkspecs/macx-g++ -macx \ -o Makefile python.pro" } } } Here, variant_issset, reinplace are so on (other than Tcl builtins) are implemented as Python functions. if, foreach, set, etc.. are normal Tcl constructs. post-configure is a Python function that accepts, well, a Tcl code block that can later be executed (which in turns would obviously end up calling the above mentioned Python "functions"). Is this possible to do in Python? If so, how? from Tkinter import *; root= Tk(); root.tk.eval('puts [array get tcl_platform]') is the only integration I know of, which is obviously very limited (not to mention the fact that it starts up X11 server on mac).

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• tabs using jquery

  - by sea_1987

  I currently have a tabbed system in place, however it not doing exactly as I need it too, I was hoping that by navigating to the URL with #tab2 suffixed on then end it would navigate to my tabbed page and the tab that is present in the URL would be the one that is active, however the first tab in the sequence is always active, is there a way to check what is being passed in the URL first and if there is #tabid present then make that tab the current tab? My javascript currently looks like this, $(".tab_content").hide(); //Hide all content $("ul.tabNavigation li.shortlist").addClass("active").show(); //Activate first tab (in this case second because of floats) $(".tab_content#shortlist").show(); //Show first tab content //On Click Event $("ul.tabNavigation li").click(function() { $("ul.tabNavigation li").removeClass("active"); //Remove any "active" class $(this).addClass("active"); //Add "active" class to selected tab $(".tab_content").hide(); //Hide all tab content var activeTab = $(this).find("a").attr("href"); //Find the href attribute value to identify the active tab + content $(activeTab).fadeIn(); //Fade in the active ID content return false; });

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• Float addition promoted to double?

  - by Andreas Brinck

  I had a small WTF moment this morning. Ths WTF can be summarized with this: float x = 0.2f; float y = 0.1f; float z = x + y; assert(z == x + y); //This assert is triggered! (Atleast with visual studio 2008) The reason seems to be that the expression x + y is promoted to double and compared with the truncated version in z. (If i change z to double the assert isn't triggered). I can see that for precision reasons it would make sense to perform all floating point arithmetics in double precision before converting the result to single precision. I found the following paragraph in the standard (which I guess I sort of already knew, but not in this context): 4.6.1. "An rvalue of type float can be converted to an rvalue of type double. The value is unchanged" My question is, is x + y guaranteed to be promoted to double or is at the compiler's discretion? UPDATE: Since many people has claimed that one shouldn't use == for floating point, I just wanted to state that in the specific case I'm working with, an exact comparison is justified. Floating point comparision is tricky, here's an interesting link on the subject which I think hasn't been mentioned.

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• Copying a subset of data to an empty database with the same schema

  - by user193655

  I would like to export part of a database full of data to an empty database. Both databases has the same schema. I want to maintain referential integrity. To simplify my cases it is like this: MainTable has the following fields: 1) MainID integer PK 2) Description varchar(50) 3) ForeignKey integer FK to MainID of SecondaryTable SecondaryTable has the following fields: 4) MainID integer PK (referenced by (3)) 5) AnotherDescription varchar(50) The goal I'm trying to accomplish is "export all records from MainTable using a WHERE condition", for example all records where MainID < 100. To do it manually I shuold first export all data from SecondaryTable contained in this select: select * from SecondaryTable ST outer join PrimaryTable PT on ST.MainID=PT.MainID then export the needed records from MainTable: select * from MainTable where MainID < 100. This is manual, ok. Of course my case is much much much omre complex, I have 200+ tables, so donig it manually is painful/impossible, I have many cascading FKs. Is there a way to force the copy of main table only "enforcing referntial integrity". so that my query is something like: select * from MainTable where MainID < 100 WITH "COPYING ALL FK sources" In this cases also the field (5) will be copied. ====================================================== Is there a syntax or a tool to do this? Table per table I'd like to insert conditions (like MainID <100 is only for MainTable, but I have also other tables).

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• Access 2007 and Special/Unicode Characters in SQL

  - by blockcipher

  I have a small Access 2007 database that I need to be able to import data from an existing spreadsheet and put it into our new relational model. For the most part this seems to work pretty well. Part of the process is attempting to see if a record already exists in a target table using SQL. For example, if I extract book information out of the current row in the spreadsheet, it may contain a title and abstract. I use SQL to get the ID of a matching record, if it exists. This works fine except when I have data that's in a non-English language. In this case, it seems that there is some punctuation that is causing me problems. At least I think it's punctuation as I do have some fields that do not have punctuation and are non-English that do not give me any problems. Is there a built-in function that can escape these characters? Currently I have a small function that will escape the single quote character, but that isn't enough. Or, is there a list of Unicode characters that can interfere with how SQL wants data quoted? Thanks in advance.

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• IE 8 issue where window.close() is not occuring after winword.exe is fired to print a document

  - by Dave

  In my web application, a popup page is called using window.open javascript. There is a Print button on the page that has an onclick event that calls a printchecks() function. The code in the printchecks() function is function printchecks(){ window.print(); window.close(); } Issue is that the window.print brings up the printer dialog fine and then you select a printer. The page is actually then printed and is a reference to an rtf document that opens in winword.exe behind the scenes. For some reason in IE 8, the window.close() does not occur. This worked in IE 7. In both cases, WINWORD.EXE process appears to run in the background after the page is printed but in the case of IE 8, control is not give back to that popup page until the WINWORD.EXE process dies which takes a minute or so. I am thinking that becasue control is not being sent back to the page in IE 8, the page is not closed automatically. You can close the page after control is given back after the minute or so. This does happen in IE on both Windows XP and Windows 7. Any ideas if there is a setting in IE 8 or some other reason this may be occuring?

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• Unexpected $end in PHP file

  - by mattbd

  I'm working on a PHP contact form, but I can't get it to work. I get the following error in the Apache server log, running on an Ubuntu Server VM: PHP Parse error: syntax error, unexpected $end in /home/matthew/Sites/contactFormResponse.php on line 75, referer: http://192.168.1.4/contactForm.php From googling this error, it sounds like it's normally caused by either using the short PHP tag when the server's not set up to recognise them, or by having a block of code that isn't closed correctly. But as far as I can see that isn't the case here - as far as I can see it's all closed correctly. Here's the PHP code: <?php error_reporting(E_ALL); // Define variables to hold the name, email address and message, and import the information into the variables $name = $_POST['NameInput']; $email = $_POST['EmailAddress']; $telno = $_POST['ContactNumber']; $querytype = $_POST['QueryType']; $bookingstartdate = $_POST['BookingStartDay'] . $_POST['BookingStartMonth'] . $_POST['BookingStartYear']; $bookingenddate = $_POST['BookingEndDay'] . $_POST['BookingEndMonth'] . $_POST['BookingEndYear']; $message = $_POST['QueryText']; // Validate the inputs - send it if it's OK if(3 < strlen($name) && 3 < strlen($email)) { $email_message = <<< EMAIL Message from contact form at holidaychalet.co.uk Name: $name Email: $email Contact Number: $telno Query Type: $querytype Booking Start Date: $bookingstartdate Booking End Date: $bookingenddate The message: $message EMAIL; $headers = "cc:[email protected]\r\n"; if(mail('matthew@localhost','Contact form email', $email_message, $headers)) { echo "Thanks for completing the form! I'll be in touch shortly!"; } else { echo "Something went wrong - please use the back button and try again"; } } else { echo "You didn't complete the form fully enough! Please use go back using your web browser's back button"; } ?>

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• resizing images with imagemagick via shell script

  - by jml

  Hi there, I don't really know that much about bash scripts OR imagemagick, but I am attempting to create a script in which you can give some sort of regexp matching pattern for a list of images and then process those into new files that have a given filename prefix. for example given the following dir listing: allfiles01.jpg allfiles02.jpg allfiles03.jpg i would like to call the script like so: ./resisemany.sh allfiles*.jpg 30 newnames*.jpg the end result of this would be that you get a bunch of new files with newnames, the numbers match up, so far what i have is: IMAGELIST=$1 RESIEZFACTOR=$2 NUMIMGS=length($IMAGELIST) for(i=0; i<NUMIMGS; i++) convert $IMAGELIST[i] -filter bessel -resize . RESIZEFACTOR . % myfile.JPG Thanks for any help... The parts that I obviously need help with are 1. how to give a bash script matching criteria that it understands 2. how to use the $2 without having it match the 2nd item in the image list 3. how to get the length of the image list 4. how to create a proper for loop in such a case 5. how to do proper text replacement for a shell command whereby you are appending items as i allude to. jml

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• How should I organize my mvc templates?

  - by CatZ

  Hi, In the new version of MVC we have been given display and editor templates. I was wondering how to make the best possible use of these. I was at first thinking in the line of creating one for a collection and one for an item in the case I want to display either as a list or single but it does not really make sense to me. I'll show you what I mean and please comment if this is wrong. I have trouble figuring it out myself. <%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<IEnumerable<DisplayPhoneModel>>" %> <% foreach (var item in Model){%> <%= Html.DisplayFor(x => item) %> <%}%> So in my tiny reality that would for every item in the model search for a display template for DisplayPhoneModel. That display template could then simply look like. <%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<DisplayPhoneModel>" %> <%= Html.LabelFor(x => x.PhoneType) %>&nbsp;<%= Html.LabelFor(x => x.PhoneNumber) %> So, question is if there is a better way to handle this? Am I at all on the right path?

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• Generic property- specify the type at runtime

  - by Lirik

  I was reading a question on making a generic property, but I'm a little confused at by the last example from the first answer (I've included the relevant code below): You have to know the type at compile time. If you don't know the type at compile time then you must be storing it in an object, in which case you can add the following property to the Foo class: public object ConvertedValue { get { return Convert.ChangeType(Value, Type); } } That's seems strange: it's converting the value to the specified type, but it's returning it as an object when the value was stored as an object. Doesn't the returned object still require un-boxing? If it does, then why bother with the conversion of the type? I'm also trying to make a generic property whose type will be determined at run time: public class Foo { object Value {get;set;} Type ValType{get;set;} Foo(object value, Type type) { Value = value; ValType = type; } // I need a property that is actually // returned as the specified value type... public object ConvertedValue { get { return Convert.ChangeType(Value, ValType); } } } Is it possible to make a generic property? Does the return property still require unboxing after it's accessed?

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• Most efficient way to update attribute of one instance

  - by Begbie00

  Hi all - I'm creating an arbitrary number of instances (using for loops and ranges). At some event in the future, I need to change an attribute for only one of the instances. What's the best way to do this? Right now, I'm doing the following: 1) Manage the instances in a list. 2) Iterate through the list to find a key value. 3) Once I find the right object within the list (i.e. key value = value I'm looking for), change whatever attribute I need to change. for Instance within ListofInstances: if Instance.KeyValue == SearchValue: Instance.AttributeToChange = 10 This feels really inefficient: I'm basically iterating over the entire list of instances, even through I only need to change an attribute in one of them. Should I be storing the Instance references in a structure more suitable for random access (e.g. dictionary with KeyValue as the dictionary key?) Is a dictionary any more efficient in this case? Should I be using something else? Thanks, Mike

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• URL equals and checking Internet access

  - by James P.

  On http://java.sun.com/j2se/1.5.0/docs/api/java/net/URL.html it states that: Compares this URL for equality with another object. If the given object is not a URL then this method immediately returns false. Two URL objects are equal if they have the same protocol, reference equivalent hosts, have the same port number on the host, and the same file and fragment of the file. Two hosts are considered equivalent if both host names can be resolved into the same IP addresses; else if either host name can't be resolved, the host names must be equal without regard to case; or both host names equal to null. Since hosts comparison requires name resolution, this operation is a blocking operation. Note: The defined behavior for equals is known to be inconsistent with virtual hosting in HTTP. According to this, equals will only work if name resolution is possible. Since I can't be sure that a computer has internet access at a given time, should I just use Strings to store addresses instead? Also, how do I go about testing if access is available when requested?

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• Time complexity to fill hash table (homework)?

  - by Heathcliff

  This is a homework question, but I think there's something missing from it. It asks: Provide a sequence of m keys to fill a hash table implemented with linear probing, such that the time to fill it is minimum. And then Provide another sequence of m keys, but such that the time fill it is maximum. Repeat these two questions if the hash table implements quadratic probing I can only assume that the hash table has size m, both because it's the only number given and because we have been using that letter to address a hash table size before when describing the load factor. But I can't think of any sequence to do the first without knowing the hash function that hashes the sequence into the table. If it is a bad hash function, such that, for instance, it hashes every entry to the same index, then both the minimum and maximum time to fill it will take O(n) time, regardless of what the sequence looks like. And in the average case, where I assume the hash function is OK, how am I suppossed to know how long it will take for that hash function to fill the table? Aren't these questions linked to the hash function stronger than they are to the sequence that is hashed? As for the second question, I can assume that, regardless of the hash function, a sequence of size m with the same key repeated m-times will provide the maximum time, because it will cause linear probing from the second entry on. I think that will take O(n) time. Is that correct? Thanks

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• CEIL is one too high for exact integer divisions

  - by Synetech

  This morning I lost a bunch of files, but because the volume they were one was both internally and externally defragmented, all of the information necessary for a 100% recovery is available; I just need to fill in the FAT where required. I wrote a program to do this and tested it on a copy of the FAT that I dumped to a file and it works perfectly except that for a few of the files (17 out of 526), the FAT chain is one single cluster too long, and thus cross-linked with the next file. Fortunately I know exactly what the problem is. I used ceil in my EOF calculation because even a single byte over will require a whole extra cluster: //Cluster is the starting cluster of the file //Size is the size (in bytes) of the file //BPC is the number of bytes per cluster //NumClust is the number of clusters in the file //EOF is the last cluster of the file’s FAT chain DWORD NumClust = ceil( (float)(Size / BPC) ) DWORD EOF = Cluster + NumClust; This algorithm works fine for everything except files whose size happens to be exactly a multiple of the cluster size, in which case they end up being one cluster too much. I thought about it for a while but am at a loss as to a way to do this. It seems like it should be simple but somehow it is surprisingly tricky. What formula would work for files of any size?

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