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  • Why is apache/passenger unable to open the sqlite3 rails database file?

    - by sendos
    I'm running apache2/passenger2.0.3 (ubuntu 9.10 packages). I can start up Webrick in the rails folder and run the app perfectly as I do on my development box with script/server Why then does apache/passenger fail to open the database, throwing a 500 and putting the following in the log? Status: 500 Internal Server Error could not open database: unable to open database file /usr/lib/ruby/1.8/sqlite3/errors.rb:62:in `check'...

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  • Reviews Cheyney Group Marketing: What accounting softwares are available in the market for small businesses?

    - by user224313
    Accounting is the language of business, and good accounting software can save you hundreds of hours at the business equivalent of Berlitz. There's no substitute for an accounting pro who knows the ins and outs of tax law, but today's desktop packages can help you with everything from routine bookkeeping to payroll, taxes, and planning. Each package also produces files that you can hand off to an accountant as needed. Small-business managers have more accounting software options than ever, including subscription Web-based options that don't require their users to install or update software. Many businesses, however--including those that need to track large inventories or client databases, and those that prefer not to entrust their data to the cloud--may be happier with a desktop tool. We looked at three general-purpose, small-business accounting packages: Acclivity AccountEdgePro 2012 (both the product and the company were previously called MYOB), Intuit QuickBooks Premier 2012, and Sage's Sage 50 Complete 2013 (the successor to Peachtree Complete). All three packages offer a solid array of tools for tracking income and expenses, invoicing, managing payroll, and creating reports. These full-featured and highly mature programs don't come cheap. Acclivity AccountEdge Pro, at $299, is the least expensive; and prices climb if you opt to use common time-saving add-ons such as payroll services, or if you add licenses for multiple user accounts. All three are solid on the basics, but they have distinct differences in style and focus. The more you know about your accounting requirements, the more closely you'll want to look at the software you're thinking of buying. Sage 50 Complete should appeal most to people who understand the fine points of accounting and can use the product's many customization features (especially for businesses that manage inventory). QuickBooks works hard to appeal to newbies who need only the basics and might be intimidated by the level of detail and technical language exposed in the other two packages. At the same time, it also has a slew of third-party add-ons that meet specific needs and greatly expand its capabilities. AccountEdge Pro balances accessibility with a strong feature set at an affordable price. It's especially suitable for businesses that need to provide simultaneous access to multiple users.

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  • Safari: how to re-open MULTIPLE previously closed tabs?

    - by courteous
    CMD + Z in Safari (6.0.1) will re-open the last closed tab. Is there any way to re-open multiple previously closed tabs (as in, say, Chrome)? A closely related question from 2011: Are there any extensions or tricks to reopen several closed tabs in Safari Update Safari is now at 6.0.2: having the ability to re-open multiple closed tabs would still very much improve usability (i.e. not having to go searching the History). Is the answer still "impossible"?

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  • How do I configure Gnome 3 so that it doesn't pop up a dialog for 'open with files' when I mount a drive?

    - by michael
    I am running Gnome 3 on Ubuntu 11.10. In the file manager, when I click a drive under 'Devices', Gnome 3 always pops up a dialog with the choices 'open with files' and 'eject' and then I need to click 'open with files' to get rid of that dialog. Is there a way to configure Gnome 3 not to do that? I am in file manager already, clicking a drive should show the content in the right pane. Why does it still ask me to 'open with files'?

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  • What are your favorite open source tools? (that are not very famous)

    - by sucuri
    I believe every system administrator is used to open source by now. From Apache to Firefox or Linux, everyone uses it at least a little bit. However, most open source developers are not good in marketing, so I know that there are hundreds of very good tools out there that very few people know. To fill this gap, share your favorite open source tool that you use in your day-to-day work that is not very famous. *I will post mine in the comments.

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  • How to open a document using an application launched via NSTask?

    - by zneak
    Hello world, I've grown tired of the built-in open Mac OS X command, mostly because it runs programs with your actual user ID instead of the effective user ID; this results in the fact sudo open Foo opens Foo with its associated application with your account instead of the root account, and it annoys me. So I decided to make some kind of replacement. So far I've been successful: I can open any program under the open -a or open -b fashion, and support optionally waiting. I'm using NSTask for that purpose. However, I'd like to be able to open documents too. As far as I can see, you need to use NSWorkspace for that, but using NSWorkspace to launch programs results in them being launched with your account's credentials instead of your command line program's credentials. Which is precisely what the default open tool does, and precisely what I don't want. So, how can I have a program request that another program opens a document without using NSWorkspace? From the NSTask object, I can have the process ID, but that's about it.

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  • Cannot start tor with vidalia, failed to bind listening port because of tor-socks running

    - by ganjan
    I get these errors trying to run tor with vidalia Apr 19 21:55:15.371 [Notice] Tor v0.2.1.30. This is experimental software. Do not rely on it for strong anonymity. (Running on Linux i686) Apr 19 21:55:15.372 [Notice] Initialized libevent version 1.4.13-stable using method epoll. Good. Apr 19 21:55:15.373 [Notice] Opening Socks listener on 127.0.0.1:9050 Apr 19 21:55:15.373 [Warning] Could not bind to 127.0.0.1:9050: Address already in use. Is Tor already running? Apr 19 21:55:15.373 [Warning] Failed to parse/validate config: Failed to bind one of the listener ports. Apr 19 21:55:15.373 [Error] Reading config failed--see warnings above. I don't think tor is running. Here is a nmap scan of my localhost Starting Nmap 5.21 ( http://nmap.org ) at 2011-04-19 21:59 CEST Nmap scan report for localhost (127.0.0.1) Host is up (0.0000050s latency). Hostname localhost resolves to 2 IPs. Only scanned 127.0.0.1 rDNS record for 127.0.0.1: localhost.localdomain Not shown: 989 closed ports PORT STATE SERVICE 22/tcp open ssh 53/tcp open domain 80/tcp open http 139/tcp open netbios-ssn 445/tcp open microsoft-ds 631/tcp open ipp 3128/tcp open squid-http 3306/tcp open mysql 9000/tcp open cslistener 9050/tcp open tor-socks 10000/tcp open snet-sensor-mgmt I see tor-socks is running here, probably be the cause of the problem. How do I stop this from starting up? I want to use vidalia so I can monitor whats going on.

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  • Refactoring a custom User model to user UserProfile: Should I create a custom UserManager or add use

    - by BryanWheelock
    I have been refactoring an app that had customized the standard User model from django.contrib.auth.models by creating a UserProfile and defining it with AUTH_PROFILE_MODULE. The problem is the attributes in UserProfile are used throughout the project to determine the User sees. I had been creating tests and putting in this type of statement repeatedly: user = User.objects.get(pk=1) user_profile = user.get_profile() if user_profile.karma > 10: do_some_stuff() This is tedious and I'm now wondering if I'm violating the DRY principle. Would it make more sense to create a custom UserManager that automatically loads the UserProfile data when the user is requested. I could even iterate over the UserProfile attributes and append them to the User model. This would save me having to update all the references to the custom model attributes that litter the code. Of course, I'd have to reverse to process for to allow the User and UserProfile models to be updated correctly. Which approach is more Django-esque?

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  • Trying to pass Model down to partial, how do I do this?

    - by mrblah
    My action creates a strongly typed viewdata, which is passed to my view. In the view, I pass the Model to the render partial method. public ActionResult Index() { ViewDataForIndex vd = new ViewDataForIndex(); vd.Users = Users.GetAll(); return View(vd); } public class ViewDataForIndex: ViewData { public IList<User> Users {get;set;} } now in the view: <%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<ViewDataForIndex>" %> <% Html.RenderPartial("~/controls/blah.ascx", ViewData.Model); %> and in blah.ascx: <%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl" %> how do I access my model now? if I wanted to create a strongly typed class for my ViewUserControl, how would I do that? inherit from?

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  • How do I prevent jagged edges alongside the surfaces of my 3d model?

    - by badcodenotreat
    Lets say I've implemented in openGL a crude model viewer with shading which renders a series of blocks, such that I have something that looks like this. http://i.imgur.com/TsF7K.jpg Whenever I rotate my model to the side, it causes an unwanted jagged effect along any surface with a steep viewing angle. http://i.imgur.com/Bgl9o.jpg I'm pretty sure this is due to the polygon offset I used to prevent z-fighting between the model and the wireframe, however I'm not able to find the factor/unit parameters in openGL which prevent this unwanted effect. what are the best values of factor and unit for glPolygonOffset to prevent this? would implementing anti-aliasing alleviate the problem? is the trade off in performance trivial/significant? is this perhaps a shading issue? should i try a solution along this line of thought?

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  • Providing localized error messages for non-attributed model validation in ASP.Net MVC 2?

    - by Lance McNearney
    I'm using the DataAnnotations attributes along with ASP.Net MVC 2 to provide model validation for my ViewModels: public class ExamplePersonViewModel { [Required(ErrorMessageResourceName = "Required", ErrorMessageResourceType = typeof(Resources.Validation))] [StringLength(128, ErrorMessageResourceName = "StringLength", ErrorMessageResourceType = typeof(Resources.Validation))] [DataType(DataType.Text)] public string Name { get; set; } [Required(ErrorMessageResourceName = "Required", ErrorMessageResourceType = typeof(Resources.Validation))] [DataType(DataType.Text)] public int Age { get; set; } } This seems to work as expected (although it's very verbose). The problem I have is that there are behind-the-scenes model validations being performed that are not tied to any specific attribute. An example of this in the above model is that the Age property needs to be an int. If you try to enter a non-integer value on the form, it will error with the following (non-localized) message: The field Age must be a number. How can these non-attribute validation messages be localized? Is there a full list of these messages available so I can make sure they are all localized?

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  • How can I call model methods or properties from Django Admin?

    - by kg
    Is there a natural way to display model methods or properties in the Django admin site? In my case I have base statistics for a character that are part of the model, but other things such as status effects which affect the total calculation for that statistic: class Character(models.Model): base_dexterity = models.IntegerField(default=0) @property def dexterity(stat_name): total = self.base_dexterity total += sum(s.dexterity for s in self.status.all()]) return total It would be nice if I could display the total calculated statistic alongside the field to change the base statistic in the Change Character admin page, but it is not clear to me how to incorporate that information into the page.

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  • Rails - How do i update a records value in a join model ?

    - by ChrisWesAllen
    I have a join model in a HABTM relationship with a through association (details below). I 'm trying to find a record....find the value of that records attribute...change the value and update the record but am having a hard time doing it. The model setup is this User.rb has_many :choices has_many :interests, :through => :choices Interest.rb has_many :choices has_many :users, :through => :choices Choice.rb belongs_to :user belongs_to :interest and Choice has the user_id, interest_id, score as fields. And I find the ?object? like so @choice = Choice.where(:user_id => @user.id, :interest_id => interest.id) So the model Choice has an attribute called :score. How do I find the value of the score column....and +1/-1 it and then resave? I tried @choice.score = @choice.score + 1 @choice.update_attributes(params[:choice]) flash[:notice] = "Successfully updated choices value." but I get "undefined method score"......What did i miss?

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  • Rails setting OR conditions in validate_presence_of in a model?

    - by Jty.tan
    In a rails model, is it possible to do something like class Example < ActiveRecord::Base #associations validates_presence_of :item_id, (:user_id OR :user_email) #functions end Where the model has 3 columns of :item_id, :user_id, and :user_email? I want the model to be valid as long as I have a :user_id or a :user_email. Idea being that if the item is recommended to a person who isn't currently signed up, it can be associated via email address for when the recommended person signs up. Or is there a different method that I can use instead?

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  • how to pass session variable to model in RoR?

    - by siulamvictor
    I used a global variable in my app for passing information before. But I got a problem and thanks everyone here suggested me to store those data in session with database. I tried, but I found that I can't access the session variable in Model. I googled and knew this is the Model normal behavior, RoR won't pass the session variable to Model. So how to pass the value of the session variable into Models? or is there any other method for my use case? I need a variable storing a value, which is required in all MVCs, and should be independent between different concurrent users. Thanks everyone. :)

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  • What are the requirements of a collection type when model binding?

    - by Richard Ev
    I have been reviewing model binding with collections, specifically going through this article http://weblogs.asp.net/nmarun/archive/2010/03/13/asp-net-mvc-2-model-binding-for-a-collection.aspx However, the model I would like to use in my code does not implement collections using generic lists. Instead it uses its own collection classes, which inherit from a custom generic collection base class, the declaration of which is public abstract class CollectionBase<T> : IEnumerable<T> The collections in my POSTed action method are all non-null, but contain no elements. Can anyone advise?

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  • Django admin panel doesn't work after modify default user model.

    - by damienix
    I was trying to extend user profile. I founded a few solutions, but the most recommended was to create new user class containing foreign key to original django.contrib.auth.models.User class. I did it with this so i have in models.py: class UserProfile(models.Model): user = models.ForeignKey(User, unique=True) website_url = models.URLField(verify_exists=False) and in my admin.py from django.contrib import admin from someapp.models import * from django.contrib.auth.admin import UserAdmin # Define an inline admin descriptor for UserProfile model class UserProfileInline(admin.TabularInline): model = UserProfile fk_name = 'user' max_num = 1 # Define a new UserAdmin class class MyUserAdmin(UserAdmin): inlines = [UserProfileInline, ] # Re-register UserAdmin admin.site.unregister(User) admin.site.register(User, MyUserAdmin) And now when I'm trying to create/edit user in admin panel i have an error: "Unknown column 'content_userprofile.id' in 'field list'" where content is my appname. I was trying to add line AUTH_PROFILE_MODULE = 'content.UserProfile' to my settings.py but with no effect. How to tell panel admin to know how to correctly display fields in user form?

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  • DropDownList and SelectListItem Array Item Updates in MVC

    - by Rick Strahl
    So I ran into an interesting behavior today as I deployed my first MVC 4 app tonight. I have a list form that has a filter drop down that allows selection of categories. This list is static and rarely changes so rather than loading these items from the database each time I load the items once and then cache the actual SelectListItem[] array in a static property. However, when we put the site online tonight we immediately noticed that the drop down list was coming up with pre-set values that randomly changed. Didn't take me long to trace this back to the cached list of SelectListItem[]. Clearly the list was getting updated - apparently through the model binding process in the selection postback. To clarify the scenario here's the drop down list definition in the Razor View:@Html.DropDownListFor(mod => mod.QueryParameters.Category, Model.CategoryList, "All Categories") where Model.CategoryList gets set with:[HttpPost] [CompressContent] public ActionResult List(MessageListViewModel model) { InitializeViewModel(model); busEntry entryBus = new busEntry(); var entries = entryBus.GetEntryList(model.QueryParameters); model.Entries = entries; model.DisplayMode = ApplicationDisplayModes.Standard; model.CategoryList = AppUtils.GetCachedCategoryList(); return View(model); } The AppUtils.GetCachedCategoryList() method gets the cached list or loads the list on the first access. The code to load up the list is housed in a Web utility class. The method looks like this:/// <summary> /// Returns a static category list that is cached /// </summary> /// <returns></returns> public static SelectListItem[] GetCachedCategoryList() { if (_CategoryList != null) return _CategoryList; lock (_SyncLock) { if (_CategoryList != null) return _CategoryList; var catBus = new busCategory(); var categories = catBus.GetCategories().ToList(); // Turn list into a SelectItem list var catList= categories .Select(cat => new SelectListItem() { Text = cat.Name, Value = cat.Id.ToString() }) .ToList(); catList.Insert(0, new SelectListItem() { Value = ((int)SpecialCategories.AllCategoriesButRealEstate).ToString(), Text = "All Categories except Real Estate" }); catList.Insert(1, new SelectListItem() { Value = "-1", Text = "--------------------------------" }); _CategoryList = catList.ToArray(); } return _CategoryList; } private static SelectListItem[] _CategoryList ; This seemed normal enough to me - I've been doing stuff like this forever caching smallish lists in memory to avoid an extra trip to the database. This list is used in various places throughout the application - for the list display and also when adding new items and setting up for notifications etc.. Watch that ModelBinder! However, it turns out that this code is clearly causing a problem. It appears that the model binder on the [HttpPost] method is actually updating the list that's bound to and changing the actual entry item in the list and setting its selected value. If you look at the code above I'm not setting the SelectListItem.Selected value anywhere - the only place this value can get set is through ModelBinding. Sure enough when stepping through the code I see that when an item is selected the actual model - model.CategoryList[x].Selected - reflects that. This is bad on several levels: First it's obviously affecting the application behavior - nobody wants to see their drop down list values jump all over the place randomly. But it's also a problem because the array is getting updated by multiple ASP.NET threads which likely would lead to odd crashes from time to time. Not good! In retrospect the modelbinding behavior makes perfect sense. The actual items and the Selected property is the ModelBinder's way of keeping track of one or more selected values. So while I assumed the list to be read-only, the ModelBinder is actually updating it on a post back producing the rather surprising results. Totally missed this during testing and is another one of those little - "Did you know?" moments. So, is there a way around this? Yes but it's maybe not quite obvious. I can't change the behavior of the ModelBinder, but I can certainly change the way that the list is generated. Rather than returning the cached list, I can return a brand new cloned list from the cached items like this:/// <summary> /// Returns a static category list that is cached /// </summary> /// <returns></returns> public static SelectListItem[] GetCachedCategoryList() { if (_CategoryList != null) { // Have to create new instances via projection // to avoid ModelBinding updates to affect this // globally return _CategoryList .Select(cat => new SelectListItem() { Value = cat.Value, Text = cat.Text }) .ToArray(); } …}  The key is that newly created instances of SelectListItems are returned not just filtered instances of the original list. The key here is 'new instances' so that the ModelBinding updates do not update the actual static instance. The code above uses LINQ and a projection into new SelectListItem instances to create this array of fresh instances. And this code works correctly - no more cross-talk between users. Unfortunately this code is also less efficient - it has to reselect the items and uses extra memory for the new array. Knowing what I know now I probably would have not cached the list and just take the hit to read from the database. If there is even a possibility of thread clashes I'm very wary of creating code like this. But since the method already exists and handles this load in one place this fix was easy enough to put in. Live and learn. It's little things like this that can cause some interesting head scratchers sometimes…© Rick Strahl, West Wind Technologies, 2005-2012Posted in MVC  ASP.NET  .NET   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • Why Keep These 10 A Penny " How Long Will It Take To Program in Blah Blah Blah Language Questions" Open Yet Close This Question..? [migrated]

    - by user866190
    Why keep this question open and others like it open which basically asks how long does it take to learn a programming language? Yet I ask a valid question which basically asks how esteemed is a mathematics degree from the UK open university and would software employers hire whilst you are the course.. and it gets closed I love the advice I get from this site and I appreciate the fact that Software Technicians of all types use this site, but it's a bit shallow if you can't ask a question with a little bit of the real world involved

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  • How to open write reserved excel file in python with win32com?

    - by user261935
    Hello, I'm trying to open a write-protected ms excel 2007 file using win32com in python -- I know the password. I can open it with user input of the password into the excel dialog box. I want to be able to open the file without any user interaction. I've tried the following, but it still pops up the dialog box. app.Workbooks.Open("filename.xls", WriteResPassword="secret") Any ideas what I'm doing wrong please? Thanks, Dave.

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  • How is it that i am getting two different open ids for the same site for the same user

    - by Salvin Francis
    I was under the impression that the open id for a user remains constant. I am allowing users to setup open id with my site with 2 different screens in my app... I was under the impression that the open id for a user is constant and will not change and I was planning to save it to my database for a given user, However, to my suprise, I found different ids for the same user using the same google account in the two different screens. How does open id actually work ?

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  • Usage of putty in command line from Hudson

    - by kij
    Hi, I'm trying to use putty in command line from an hudson job. The command is the following one: putty -ssh -2 -P 22 USERNAME@SERVER_ADDR -pw PASS -m command.txt Where 'command.txt' is a shell script to execute in the server through SSH. If i launch this command from the Window command prompt, it works, the shell script is executed on the server machine. If i launch a build of the hudson job configured with this batch command, it doesn't work. The build is running... and running... and running.. without doing anything, and i have to stop it manually. So my question is: Is it possible to launch an external programm (i.e. putty) from an hudson job ? ps: i tried SSH plugin but... not a really good plugin (pre/post build, fail status of the commands launched not caught by hudson, etc.) Thanks in advance for your help. Best regards. kij EDIT: These are the build logs: [workspace] $ cmd /c call C:\WINDOWS\TEMP\hudson7429256014041663539.bat C:\Hudson\jobs\Artifact deployer\workspace>putty -ssh -2 -P 22 USER@SERV_ADD -pw PASS -m com.txt Le build a été annulé Finished: ABORTED And the Hudson.err.log file at the same time (after a stop): 3 juin 2010 18:27:28 hudson.model.Run run INFO: Artifact deployer #6 aborted java.lang.InterruptedException at java.lang.ProcessImpl.waitFor(Native Method) at hudson.Proc$LocalProc.join(Proc.java:179) at hudson.Launcher$ProcStarter.join(Launcher.java:278) at hudson.tasks.CommandInterpreter.perform(CommandInterpreter.java:83) at hudson.tasks.CommandInterpreter.perform(CommandInterpreter.java:58) at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19) at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:601) at hudson.model.Build$RunnerImpl.build(Build.java:174) at hudson.model.Build$RunnerImpl.doRun(Build.java:138) at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:416) at hudson.model.Run.run(Run.java:1241) at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46) at hudson.model.ResourceController.execute(ResourceController.java:88) at hudson.model.Executor.run(Executor.java:124) My shell script only write "hello" in a "hello.txt" file on the server, and nothing is done.

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  • When I try to click and launch some of the links set to open in new window, it is being treated as a pop-up window [migrated]

    - by Test Developer
    For the past few days, we are facing issue with the chrome browser behavior. This is related to opening links set to open in new tab/window. The details are as follow: I have a collection of links and each link points to different resource to be opened in a new tab/window. The code is as follow: <a class="cssClass" rid="1114931" href="http://www.domain.com/resources/abc.html" title="Link1" tabindex="4">Link 1</a> And there are few checks/filters over accessing the resources which have been implemented as onClick handler over the links. In case any of the validations fails, the onClick handler returns false and the default behavior of the link does not happens i.e. links does not get open. One of such (last) checks includes AJAX call in sync mode. The code is as follow: var link_clickHandler = function(evt/* Event */) { var objTarget = jQuery(evt.target); if(check1) { return false; } else if(check2) { return false; } else if(check3) { var blnRetVal = false; jQuery.ajax( { "async" : false, "type" : "GET", "contentType" : "application/json; charset=utf-8", "url" : "index.php", "data" : 'resourceid=' + intResourceId, "dataType" : "json", "forceData" : true, "success" : function(data) { if(check1) { blnRetVal = true; } } "error" : function(error) { } } ); return blnRetVal; } }; jQuery("a.cssClass").live("click", link_clickHandler); ISSUE: The issue is that Chrome is behaving very weirdly manner. In case all of the checks are passed and onClick handler returns true, sometimes the resource get opened in a new tab/window and sometimes it get opened as a pop-up (which should never). Tried to capture any pattern but could not succeed. Any solution or even helping in understanding behavior would be really appreciated.

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  • To sample or not to sample...

    - by [email protected]
    Ideally, we would know the exact answer to every question. How many people support presidential candidate A vs. B? How many people suffer from H1N1 in a given state? Does this batch of manufactured widgets have any defective parts? Knowing exact answers is expensive in terms of time and money and, in most cases, is impractical if not impossible. Consider asking every person in a region for their candidate preference, testing every person with flu symptoms for H1N1 (assuming every person reported when they had flu symptoms), or destructively testing widgets to determine if they are "good" (leaving no product to sell). Knowing exact answers, fortunately, isn't necessary or even useful in many situations. Understanding the direction of a trend or statistically significant results may be sufficient to answer the underlying question: who is likely to win the election, have we likely reached a critical threshold for flu, or is this batch of widgets good enough to ship? Statistics help us to answer these questions with a certain degree of confidence. This focuses on how we collect data. In data mining, we focus on the use of data, that is data that has already been collected. In some cases, we may have all the data (all purchases made by all customers), in others the data may have been collected using sampling (voters, their demographics and candidate choice). Building data mining models on all of your data can be expensive in terms of time and hardware resources. Consider a company with 40 million customers. Do we need to mine all 40 million customers to get useful data mining models? The quality of models built on all data may be no better than models built on a relatively small sample. Determining how much is a reasonable amount of data involves experimentation. When starting the model building process on large datasets, it is often more efficient to begin with a small sample, perhaps 1000 - 10,000 cases (records) depending on the algorithm, source data, and hardware. This allows you to see quickly what issues might arise with choice of algorithm, algorithm settings, data quality, and need for further data preparation. Instead of waiting for a model on a large dataset to build only to find that the results don't meet expectations, once you are satisfied with the results on the initial sample, you can  take a larger sample to see if model quality improves, and to get a sense of how the algorithm scales to the particular dataset. If model accuracy or quality continues to improve, consider increasing the sample size. Sampling in data mining is also used to produce a held-aside or test dataset for assessing classification and regression model accuracy. Here, we reserve some of the build data (data that includes known target values) to be used for an honest estimate of model error using data the model has not seen before. This sampling transformation is often called a split because the build data is split into two randomly selected sets, often with 60% of the records being used for model building and 40% for testing. Sampling must be performed with care, as it can adversely affect model quality and usability. Even a truly random sample doesn't guarantee that all values are represented in a given attribute. This is particularly troublesome when the attribute with omitted values is the target. A predictive model that has not seen any examples for a particular target value can never predict that target value! For other attributes, values may consist of a single value (a constant attribute) or all unique values (an identifier attribute), each of which may be excluded during mining. Values from categorical predictor attributes that didn't appear in the training data are not used when testing or scoring datasets. In subsequent posts, we'll talk about three sampling techniques using Oracle Database: simple random sampling without replacement, stratified sampling, and simple random sampling with replacement.

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