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• Help with possible Haskell type inference quiz questions

  - by Linda Cohen

  foldr:: (a -> b -> b) -> b -> [a] -> b map :: (a -> b) -> [a] -> [b] mys :: a -> a (.) :: (a -> b) -> (c -> a) -> c -> b what is inferred type of: a.map mys :: b.mys map :: c.foldr map :: d.foldr map.mys :: I've tried to create mys myself using mys n = n + 2 but the type of that is mys :: Num a => a -> a What's the difference between Num a = a - a and just a - a? Or what does 'Num a =' mean? Is it that mys would only take Num type? So anyways, a) I got [a] - [a] I think because it would just take a list and return it +2'd according to my definition of mys b) (a - b) - [a] - [b] I think because map still needs take both arguments like (*3) and a list then returns [a] which goes to mys and returns [b] c) I'm not sure how to do this 1. d) I'm not sure how to do this 1 either but map.mys means do mys first then map right? Are my answers and thoughts correct? If not, why not? THANKS!

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• UML Modelling in C++Builder 2010 Professional

  - by Gordon Brandly

  I'd like to do some basic class diagram UML models in the Pro version of C++Builder 2010. Embarcadero has a C++Builder Features Matrix document, one line of which says "UML Code Visualization – at any time, get a UML model view of your source code" and has a check in the "Professional" column of that table -- I assume this means it should be available to me. Yet, when I open an existing project and do a View | Model View, there's nothing in the Model View window. The only diagram I can find is on the Graph tab of the C++ Class Explorer. I wouldn't call that a UML diagram myself -- is that what Embarcadero is referring to? Embarcadero's table shows that many UML diagrams are not available in Pro, but it looks to me like Class Diagrams should be available. Other lines in that same table indicate that both "Full two-way class diagrams with synchronization between code and diagrams" and "Diagram hyper-linking and annotations" are also supposed to be available in Pro. The Class Explorer graph is one-way only as far as I can tell, so I hope they're referring to something else I haven't been able to find so far. Thanks for any insight into this.

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• Model binding & derived model classes

  - by Richard Ev

  Does ASP.NET MVC offer any simple way to get model binding to work when you have model classes that inherit from others? In my scenario I have a View that is strongly typed to List<Person>. I have a couple of classes that inherit from Person, namely PersonTypeOne and PersonTypeTwo. I have three strongly typed partial views with names that match these class names (and render form elements for the properties of their respective models). This means that in my main View I can have the following code: <% for(int i = 0; i < Model.Count; i++) { Html.RenderPartial(Model[i].GetType().Name, Model[i]); } %> This works well, apart from when the user submits the form the relevant controller action method just gets a List<Person>, rather than a list of Person, PersonTypeOne and PersonTypeTwo. This is pretty much as expected as the form submission doesn't contain enough information to tell the default model binder to create any instances of PersonTypeOne and PersonTypeTwo classes. So, is there any way to get such functionality from the default model binder?

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• ID not recognized in .ascx page

  - by Alexander

  I have the following code: <%@ Control Language="C#" AutoEventWireup="true" CodeBehind="DurationPicker.ascx.cs" Inherits="Permias.DurationPicker" %> <%@ Register TagPrefix="Club" Namespace="ClubSite" %> <div class="controlblock"> <table> <tr> <td> Start Date: </td> <td> <Club:DatePicker ID="dp1" runat="server" /> </td> <td> <Club:TimePicker ID="tp1" runat="server" /> </td> </tr> <tr> <td> End Date: </td> <td> <Club:DatePicker ID="dp2" runat="server" /> </td> <td> <Club:TimePicker ID="tp2" runat="server" /> </td> </tr> </table> </div> In my code behind I have public System.DateTime startDateTime { get { return dp1.SelectedDate.Add(tp1.SelectedTime.TimeOfDay); } set { dp1.SelectedDate = value; tp1.SelectedTime = value; } } However dp1 is underlined in red, which means it can't find dp1.. why is this?

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• Project euler problem 45

  - by Peter

  Hi, I'm not yet a skilled programmer but I thought this was an interesting problem and I thought I'd give it a go. Triangle, pentagonal, and hexagonal numbers are generated by the following formulae: Triangle T_(n)=n(n+1)/2 1, 3, 6, 10, 15, ... Pentagonal P_(n)=n(3n-1)/2 1, 5, 12, 22, 35, ... Hexagonal H_(n)=n(2n-1) 1, 6, 15, 28, 45, ... It can be verified that T_(285) = P_(165) = H_(143) = 40755. Find the next triangle number that is also pentagonal and hexagonal. Is the task description. I know that Hexagonal numbers are a subset of triangle numbers which means that you only have to find a number where Hn=Pn. But I can't seem to get my code to work. I only know java language which is why I'm having trouble finding a solution on the net womewhere. Anyway hope someone can help. Here's my code public class NextNumber { public NextNumber() { next(); } public void next() { int n = 144; int i = 165; int p = i * (3 * i - 1) / 2; int h = n * (2 * n - 1); while(p!=h) { n++; h = n * (2 * n - 1); if (h == p) { System.out.println("the next triangular number is" + h); } else { while (h > p) { i++; p = i * (3 * i - 1) / 2; } if (h == p) { System.out.println("the next triangular number is" + h); break; } else if (p > h) { System.out.println("bummer"); } } } } } I realize it's probably a very slow and ineffecient code but that doesn't concern me much at this point I only care about finding the next number even if it would take my computer years :) . Peter

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• Highlight image borders with Ajax request.

  - by Tek

  First, some visualization of the code. I have the following images that are dynamically generated from jquery. They're made upon user request: <img id="i13133" src="someimage.jpg" /> <img id="i13232" src="someimage1.jpg" /> <img id="i14432" src="someimage2.jpg" /> <img id="i16432" src="someimage3.jpg" /> <img id="i18422" src="someimage4.jpg" /> I have an AJAX loop that repeats every 15 seconds using jQuery and it contains the following code: Note: The if statement is inside the Ajax loop. Where imgId is the requested ID from the Ajax call. //Passes the IDs retrieved from Ajax, if the IDs exist on the page the animation is triggered. if ( $('#i' + imgId ).length ) { var pickimage = '#i' + imgId; var stop = false; function highlight(pickimage) { $(pickimage).animate({color: "yellow"}, 1000, function () { $(pickimage ).animate({color: "black"}, 1000, function () { if (!stop) highlight(pickimage); }); }); } // Start the loop highlight(pickimage); } It works great, even with multiple images. But I had originally used this with one image. The problem is I need an interrupt. Something like: $(img).click(function () { stop = true; }); There's two problems: 1.)This obviously stops all animations. I can't wrap my head around how I could write something that only stops the animation of the image that's clicked. 2.)The Ajax retrieves IDs, sometimes those IDs appear more than once every few minutes, which means it would repeat the animations on top of each other if the image exists. I could use some help figuring out how to detect if an animation is already running on an image, and do nothing if the animation is already triggered on an image.

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• tail call generated by clang 1.1 and 1.0 (llvm 2.7 and 2.6)

  - by ony

  After compilation next snippet of code with clang -O2 (or with online demo): #include <stdio.h> #include <stdlib.h> int flop(int x); int flip(int x) { if (x == 0) return 1; return (x+1)*flop(x-1); } int flop(int x) { if (x == 0) return 1; return (x+0)*flip(x-1); } int main(int argc, char **argv) { printf("%d\n", flip(atoi(argv[1]))); } I'm getting next snippet of llvm assembly in flip: bb1.i: ; preds = %bb1 %4 = add nsw i32 %x, -2 ; <i32> [#uses=1] %5 = tail call i32 @flip(i32 %4) nounwind ; <i32> [#uses=1] %6 = mul nsw i32 %5, %2 ; <i32> [#uses=1] br label %flop.exit I thought that tail call means dropping current stack (i.e. return will be to the upper frame, so next instruction should be ret %5), but according to this code it will do mul for it. And in native assembly there is simple call without tail optimisation (even with appropriate flag for llc) Can sombody explain why clang generates such code? As well I can't understand why llvm have tail call if it can simply check that next ret will use result of prev call and later do appropriate optimisation or generate native equivalent of tail-call instruction?

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• how do simple SQLAlchemy relationships work?

  - by Carson Myers

  I'm no database expert -- I just know the basics, really. I've picked up SQLAlchemy for a small project, and I'm using the declarative base configuration rather than the "normal" way. This way seems a lot simpler. However, while setting up my database schema, I realized I don't understand some database relationship concepts. If I had a many-to-one relationship before, for example, articles by authors (where each article could be written by only a single author), I would put an author_id field in my articles column. But SQLAlchemy has this ForeignKey object, and a relationship function with a backref kwarg, and I have no idea what any of it MEANS. I'm scared to find out what a many-to-many relationship with an intermediate table looks like (when I need additional data about each relationship). Can someone demystify this for me? Right now I'm setting up to allow openID auth for my application. So I've got this: from __init__ import Base from sqlalchemy.schema import Column from sqlalchemy.types import Integer, String class Users(Base): __tablename__ = 'users' id = Column(Integer, primary_key=True) username = Column(String, unique=True) email = Column(String) password = Column(String) salt = Column(String) class OpenID(Base): __tablename__ = 'openid' url = Column(String, primary_key=True) user_id = #? I think the ? should be replaced by Column(Integer, ForeignKey('users.id')), but I'm not sure -- and do I need to put openids = relationship("OpenID", backref="users") in the Users class? Why? What does it do? What is a backref?

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• DataGrid: dynamic DataTemplate for dynamic DataGridTemplateColumn

  - by Lukas Cenovsky

  I want to show data in a datagrid where the data is a collection of public class Thing { public string Foo { get; set; } public string Bar { get; set; } public List<Candidate> Candidates { get; set; } } public class Candidate { public string FirstName { get; set; } public string LastName { get; set; } ... } where the number of candidates in Candidates list varies at runtime. Desired grid layout looks like this Foo | Bar | Candidate 1 | Candidate 2 | ... | Candidate N I'd like to have a DataTemplate for each Candidate as I plan changing it during runtime - user can choose what info about candidate is displayed in different columns (candidate is just an example, I have different object). That means I also want to change the column templates in runtime although this can be achieved by one big template and collapsing its parts. I know about two ways how to achieve my goals (both quite similar): Use AutoGeneratingColumn event and create Candidates columns Add Columns manually In both cases I need to load the DataTemplate from string with XamlReader. Before that I have to edit the string to change the binding to wanted Candidate. Is there a better way how to create a DataGrid with unknown number of DataGridTemplateColumn? Note: This question is based on dynamic datatemplate with valueconverter

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• ANSI or OEM Codepage when using MME and DirectMusic?

  - by Carl Seleborg

  Hello, I noticed that when reading MIDI port names from MME, the names are multi-byte strings encoded using the ANSI Codepage, which my app uses by default. When receiving those names from the DirectMusic driver, the names are wide-character strings encoded with the OEM Codepage. See this article by Raymond Chen for a quick refresher on Codepages. On my German system, this means that when using the current codepage, which turns out to be the ANSI one, I get "Audiogerät" from MME, and "Audiogeröt" from DirectMusic, the latter being wrong. This gets fixed when I treat that last name as OEM-encoded instead. So how do I know with which codepage to decode those names? Why does the name coming from DirectMusic get encoded differently? Does it come from the USB driver? The COM framework? DirectMusic? How can I know for sure which codepage to use when reading the names of my MIDI ports? For info: I use the MultiByteToWideChar() and WideCharToMultiByte() functions to perform the conversions, with CP_ACP and CP_OEMCP as argument for the codepage to use. I use midiInGetDeviceCaps() to get MIDI port information from the MME subsystem... ... and convert MIDIINCAPS.szPname using the CP_ACP (ANSI) codepage. I use IID_IDirectMusic8::EnumPort() to get port information from DirectMusic... ... and convert DMUS_PORTCAPS.wszDescription using the CP_OEMCP codepage.

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• Calculate differences between rows while grouping with SQL

  - by Guido

  I have a postgresql table containing movements of different items (models) between warehouses. For example, the following record means that 5 units of model 1 have been sent form warehouse 1 to 2: source target model units ------ ------ ----- ----- 1 2 1 5 I am trying to build a SQL query to obtain the difference between units sent and received, grouped by models. Again with an example: source target model units ------ ------ ----- ----- 1 2 1 5 -- 5 sent from 1 to 2 1 2 2 1 2 1 1 2 -- 2 sent from 2 to 1 2 1 1 1 -- 1 more sent from 2 to 1 The result should be: source target model diff ------ ------ ----- ---- 1 2 1 2 -- 5 sent minus 3 received 1 2 2 1 I wonder if this is possible with a single SQL query. Here is the table creation script and some data, just in case anyone wants to try it: CREATE TEMP TABLE movements ( source INTEGER, target INTEGER, model INTEGER, units INTEGER ); insert into movements values (1,2,1,5); insert into movements values (1,2,2,1); insert into movements values (2,1,1,2); insert into movements values (2,1,1,1);

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• I need some pointers on how to implement inertia

  - by gargantaun

  Ok, so I've created a little plugin that takes a bunch of elements and creates a sort of never ending list. I'll try to explain... I have a div, and it's got about 20 elements tags in it. When the user scrolls up, the top element moves out of view and is moved to the bottom of the list. And vice-versa so that when the user scrolls down, the bottom element is moved to the top of the list. This is specifically for Mobile Safari (iPad, iPhone) web content and you can see the work in progress here... http://appliedworks.co.uk/files/times/SVGTests/drumView/drum.html You'll need an iPad or iPhone top see the scrolling in action. You can see the plugin code here... http://appliedworks.co.uk/files/times/SVGTests/drumView/drumView-0.1b.js What I would like to do is implement inertia so the scrolling slows to a halt in response to how fast or slow the user is scrolling when their finger leaves the screen. Just like the inertia commonly found in the iPhone / iPad UI. The problem is, every time an element moves to the top or the bottom of the list, the scollTop value for the parent div is adjusted to make it look like all the elements are staying in the same place. Which means the scrollTop value is never more than the top elements total height. So there's no value I can think of that I can keep on manipulating to give the illusion of inertia. I'm stumped. Does anyone have any suggestions?

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• Elegant way of parsing Data files for Simulation

  - by sc_ray

  I am working on this project where I need to read in a lot of data from .dat files and use the data to perform simulations. The data in my .dat file looks as follows: DeviceID InteractingDeviceID InteractionStartTime InteractionEndTime 1 2 1101 1105 1,2 1101 and 1105 are tab delimited and it means Device 1 interacted with Device 2 at 1101 ms and ended the interaction at 1105ms. I have a trace data sets that compile thousands of such interactions and my job is to analyze these interactions. The first step is to parse the file. The language of choice is C++. The approach I was thinking of taking was to read the file, for every line that's read create a Device Object. This Device object will contain the property DeviceId and an array/vector of structs, that will contain a list of all the devices the given DeviceId interacted with over the course of the simulation.The struct will contain the Interacting Device Id, Interaction Start Time and Interaction End Time. I have a two fold question here: Is my approach correct? If I am on the right track, how do I rapidly parse these tab delimited data files and create Device objects without excessive memory overhead using C++? A push in the right direction will be much appreciated. Thanks

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• Jrails and jquery-rails together?

  - by ecoologic

  I hope you forgive me if I'm a little confused about this. Jrails rewrites all the helper methods for rjs otherwise in prototype. Jquery-rails overrides rails.js (so I taught the rjs helpers as well, but I see it's not) and the rest of the libraries in jquery instead of prototype. Does it means that with just Jquery-rails I can't use rjs at all? Then do these gems work well together and let me completely forget prototype? Is there any disadvantage in using them together? I read some complaining about the fact that jrails uses jq 1.5 and now there is 1.8, but jquery-rails gives me the last version (is there retro compatibility?), but how will this affect my development (using both the gems together)? I mean have you got some examples of jquery-ui plugins I can't use or I could have problems with? Any help is appreciated. Don't get me wrong, I'm not against prototype, just I keep on having conflicts over conflicts using both of them, and I have to chose I pick Jquery.

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• Httaccess Rewriting URL issue: how to distinguish Listing and detail page

  - by Asad kamran

  I am developing an commerce site, Where users can post items in any categories( categories can be 2 to 4 levels) I want to generate URL for listing and details pages: Listing page will show list of items in inner category Detail Page will show all information for item in inner category (Inner category means Last Category in hierarchic i.e. in classified/autos4x4s/mitsubishi/lancer/ inner mean "lancer" Here are the Links i want to generate 1) www.example.com/classified/autos4x4s/mitsubishi/lancer/ (for Listing) 2) www.example.com/classified/autos4x4s/mitsubishi/lancer/2011/3/12/lanc er-2002-in-good-condition-14/ (for detail) I want to redirect to ads.php if just 4 categories exist in url and to detail.php if 6 items are passed(4 category name + 2 date and title) I write these rules: listing ads RewriteRule ^(.)/(.)/(.)/(.)/?$ ads.php?c1=$1&c2=$2&c3=$3&c4=$4 [NC,L] Detail pages RewriteRule ^(.)/(.)/(.)/(.)/(.)/(.)/?$ detail.php?c1=$1&c2=$2&c3=$3&c4=$4&dt=$5&at=$6 [NC,L] But all the sites page redirect to ads.php (Listing page) even home page. I changes the rules as follow: (Even though i donot want to Use Listing and Detail in start of url Why as i see on some site as i want:: dubai.dubizzle.com/classified/autos4x4s/mitsubishi/lancer/2011/3/12/l ancer-2002-in-good-condition-14/) Listing pages RewriteRule ^Listing/(.)/(.)/(.)/(.)/?$ ads.php?c1=$1&c2=$2&c3=$3&c4=$4 [NC,L] Detail pages RewriteRule ^Detail/(.)/(.)/(.)/(.)/(.)/(.)/?$ detail.php?c1=$1&c2=$2&c3=$3&c4=$4&dt=$5&at=$6 [NC,L] Now all other pages are fine, but when i pass www.example.com/classified/autos4x4s/mitsubishi/lancer/2011/3/12/lanc er-2002-in-good-condition-14/ it always goes to Listing page (ads.php) not to detail page. Any help would be appreciated.

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• Change classes instantiated with loadNibNamed

  - by Nick H247

  I am trying to change the class of objects created with a nib with the iPhone SDK. The reason for this is; i dont know until runtime what the class is that i want the nib object to be (though they will have the same UIView based super class), and i dont want to create a different nib for every eventuality - as the .nib will be the same for each, apart from the class of one object. I have been successful, with a couple of methods, but either have some knock on effects or am unsure of how safe the methods I have used are: Method 1: Override alloc, on the super class and set a c variable to the class I require: + (id) alloc { if (theClassIWant) { id object = [theClassIWant allocWithZone:NSDefaultMallocZone()]; theClassIWant = nil; return object; } return [BaseClass allocWithZone:NSDefaultMallocZone()]; } this works well, and i assume is 'reasonably' safe, though if I alloc a subclass myself (without setting 'theClassIWant') - an object of the base class is created. I also dont really like the idea of overriding alloc... Method 2: use object_setClass(self,theClassIWant) in initWithCoder (before calling initWithCoder on the super class): - (id) initWithCoder:(NSCoder *)aDecoder { if (theClassIWant) { // the framework doesn't like this: //[self release]; //self = [theClassIWant alloc]; // whoa now! object_setClass(self,theClassIWant); theClassIWant = nil; return [self initWithCoder:aDecoder]; } if (self = [super initWithCoder:aDecoder]) { ... this also works well, but not all the subclasses are necessarily going to be the same size as the super class, so this could be very unsafe! To combat this i tried releasing and re-allocing to the correct type within initWithCoder, but i got the following error from the framework: "This coder requires that replaced objects be returned from initWithCoder:" dont quite get what this means! i am replacing an object in initWithCoder... Any comments on the validity of these methods, or suggestions of improvements or alternatives welcome!

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• Foreign key not working in MySQL: Why can I INSERT a value that's not in the foreign column?

  - by stalepretzel

  I've created a table in MySQL: CREATE TABLE actions ( A_id int NOT NULL AUTO_INCREMENT, type ENUM('rate','report','submit','edit','delete') NOT NULL, Q_id int NOT NULL, U_id int NOT NULL, date DATE NOT NULL, time TIME NOT NULL, rate tinyint(1), PRIMARY KEY (A_id), CONSTRAINT fk_Question FOREIGN KEY (Q_id) REFERENCES questions(P_id), CONSTRAINT fk_User FOREIGN KEY (U_id) REFERENCES users(P_id)); This created the table I wanted just fine (although a "DESCRIBE actions;" command showed me that the foreign keys were keys of type MUL, and I'm not sure what this means). However, when I try to enter a Q_id or a U_id that does not exist in the questions or users tables, MySQL still allows these values. What did I do wrong? How can I prevent a table with a foreign key from accepting invalid data? If I add TYPE=InnoDB to the end, I get an error: ERROR 1005 (HY000): Can't create table './quotes/actions.frm' (errno: 150) Why might that happen? I'm told that it's important to enforce data integrity with functional foreign keys, but also that InnoDB should not be used with MySQL. What do you recommend?

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• Do complex JOINs cause high coupling and maintenance problems ?

  - by ashkan.kh.nazary

  Our project has ~40 tables with complex relations.A colleague believes in using long join queries which enforces me to learn about tables outside of my module but I think I should not concern about tables not directly related to my module and use data access functions (written by those responsible for other modules) when I need data from them. Let me clarify: I am responsible for the ContactVendor module which enables the customers to contact the vendor and start a conversation about some specific product. Products module has it's own complex tables and relations with functions that encapsulate details (for example i18n, activation, product availability etc ...). Now I need to show the product title of some product related to some conversation between the vendor and customers. I may either write a long query that retrieves the product info along with conversation stuff in one shot (which enforces me to learn about Product tables) OR I may pass the relevant product_id to the get_product_info(int) function. First approach is obviously demanding and introduces many bad practices and things I normally consider fault in programming. The problem with the second approach seems to be the countless mini queries these access functions cause and performance loss is a concern when a loop tries to fetch product titles for 100 products using functions that each perform a separate query. So I'm stuck between "don't code to the implementation, code to interface" and performance. What is the right way of doing things ? UPDATE: I'm specially concerned about possible future modifications to those tables outside of my module. What if the Products module decided to change the way they are doing things? or for some reason modify the schema? It means some other modules would break or malfunction until the change is integrated to them. The usual ripple effect problem.

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• Ranking/ weighing search result

  - by biso

  I am trying to build an application that has a smart adaptive search engine (lets say for cars). If I search for for 4x4 then the DB will return all the 4x4 cars I have (100 cars) - but as time goes by and I start checking out cars, liking them, commenting on them, etc the order of the search result should be the different. That means 1 month later when searching for 4x4, I should get the same result set ordered differently as per my previous interaction with the site. If I was mainly liking and commenting on German cars, BMW should be on the top and Land cruiser should be further down. This ranking should be based on attributes that I captureduring user interaction (eg: car origin, user age, user location, car type[4x4, coupe, hatchback], price range). So for each car result I get, I will be weighing it based on how well it is performing on the 5 attributes above. I intend to use the DB just as a repository and do the ranking and the thinking on the server. My question is, what kind of algorithm should I be using to weigh/rank my search result? Thanks.

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• Parse usable Street Address, City, State, Zip from a string

  - by Rob Allen

  Problem: I have an address field from an Access database which has been converted to Sql Server 2005. This field has everything all in one field. I need to parse out the individual sections of the address into their appropriate fields in a normalized table. I need to do this for approximately 4,000 records and it needs to be repeatable. Here are the rules for this exercise: 1 - no whining about how this should have been separate fields in the first place, we are often confronted with less than ideal situations and have to make the best of them 2- for this post, use any language you want 3- feel free to play code golf 4 - Assume an address in the US (for now) 5 - assume that the input string will sometimes contain an addressee (the person being addressed) and/or a second street address (i.e. Suite B) 6 - states may be abbreviated 7 - zip code could be standard 5 digit or zip+4 8 - there are typos in some instances UPDATE: In response to the questions posed, standards were not universally followed, I need need to store the individual values, not just geocode and errors means typo (corrected above) Sample Data: A. P. Croll & Son 2299 Lewes-Georgetown Hwy, Georgetown, DE 19947 11522 Shawnee Road, Greenwood DE 19950 144 Kings Highway, S.W. Dover, DE 19901 Intergrated Const. Services 2 Penns Way Suite 405 New Castle, DE 19720 Humes Realty 33 Bridle Ridge Court, Lewes, DE 19958 Nichols Excavation 2742 Pulaski Hwy Newark, DE 19711 2284 Bryn Zion Road, Smyrna, DE 19904 VEI Dover Crossroads, LLC 1500 Serpentine Road, Suite 100 Baltimore MD 21 580 North Dupont Highway Dover, DE 19901 P.O. Box 778 Dover, DE 19903

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• Java: Initializing a public static field in superclass that needs a different value in every subclas

  - by BinaryMuse

  Good evening, I am developing a set of Java classes so that a container class Box contains a List of a contained class Widget. A Widget needs to be able to specify relationships with other Widgets. I figured a good way to do this would be to do something like this: public abstract class Widget { public static class WidgetID { // implementation stolen from Google's GWT private static int nextHashCode; private final int index; public WidgetID() { index = ++nextHashCode; } public final int hashCode() { return index; } } public abstract WidgetID getWidgetID(); } so sublcasses of Widget could: public class BlueWidget extends Widget { public static final WidgetID WIDGETID = new WidgetID(); @Override public WidgetID getWidgetID() { return WIDGETID; } } Now, BlueWidget can do getBox().addWidgetRelationship(RelationshipTypes.SomeType, RedWidget.WIDGETID, and Box can iterate through it's list comparing the second parameter to iter.next().getWidgetID(). Now, all this works great so far. What I'm trying to do is keep from having to declare the public static final WidgetID WIDGETID in all the subclasses and implement it instead in the parent Widget class. The problem is, if I move that line of code into Widget, then every instance of a subclass of Widget appears to get the same static final WidgetID for their Subclassname.WIDGETID. However, making it non-static means I can no longer even call Subclassname.WIDGETID. So: how do I create a static WidgetID in the parent Widget class while ensuring it is different for every instance of Widget and subclasses of Widget? Or am I using the wrong tool for the job here? Thanks!

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• Java map with values limited by key's type parameter

  - by Ashley Mercer

  Is there a way in Java to have a map where the type parameter of a value is tied to the type parameter of a key? What I want to write is something like the following: public class Foo { // This declaration won't compile - what should it be? private static Map<Class<T>, T> defaultValues; // These two methods are just fine public static <T> void setDefaultValue(Class<T> clazz, T value) { defaultValues.put(clazz, value); } public static <T> T getDefaultValue(Class<T> clazz) { return defaultValues.get(clazz); } } That is, I can store any default value against a Class object, provided the value's type matches that of the Class object. I don't see why this shouldn't be allowed since I can ensure when setting/getting values that the types are correct. EDIT: Thanks to cletus for his answer. I don't actually need the type parameters on the map itself since I can ensure consistency in the methods which get/set values, even if it means using some slightly ugly casts.

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• Access/Download server files, not in site root, with PHP

  - by user271619

  Usually I save documents (images, mpegs, excel, word docs, etc...) for my friends or family on my website's root, inside a directory called /files/ or something similar. Nothing too uncommon. But, I have been playing with user session control, and allowing users to upload files to the dedicated /files/ directory. (the file names are saved in a db, with that user's ID) But, that means other people could try to guess and locate other people's files. I do randomize the file names, upon upload. And I stop the apache from displaying the /files/ directory content. However, I'd like to start saving the files outside of the website's root. This way it can't be accessible via the browser. I don't have any code to show, but I didn't want to even start on this endeavor if it's not able to be accomplished. I did find this snippet that shows how to display an image, from outside your website root: $file = $_GET['file']; $fileDir = '/path/to/files/'; if (file_exists($fileDir . $file)) { // Note: You should probably do some more checks // on the filetype, size, etc. $contents = file_get_contents($fileDir . $file); // Note: You should probably implement some kind // of check on filetype header('Content-type: image/jpeg'); echo $contents; } ? Maybe I can use this for any file type, but has anyone heard of a better way to allow users (logged in) to access their files from online, but not letting other users has similar access?

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• Clustered index - multi-part vs single-part index and effects of inserts/deletes

  - by Anssssss

  This question is about what happens with the reorganizing of data in a clustered index when an insert is done. I assume that it should be more expensive to do inserts on a table which has a clustered index than one that does not because reorganizing the data in a clustered index involves changing the physical layout of the data on the disk. I'm not sure how to phrase my question except through an example I came across at work. Assume there is a table (Junk) and there are two queries that are done on the table, the first query searches by Name and the second query searches by Name and Something. As I'm working on the database I discovered that the table has been created with two indexes, one to support each query, like so: --drop table Junk1 CREATE TABLE Junk1 ( Name char(5), Something char(5), WhoCares int ) CREATE CLUSTERED INDEX IX_Name ON Junk1 ( Name ) CREATE NONCLUSTERED INDEX IX_Name_Something ON Junk1 ( Name, Something ) Now when I looked at the two indexes, it seems that IX_Name is redundant since IX_Name_Something can be used by any query that desires to search by Name. So I would eliminate IX_Name and make IX_Name_Something the clustered index instead: --drop table Junk2 CREATE TABLE Junk2 ( Name char(5), Something char(5), WhoCares int ) CREATE CLUSTERED INDEX IX_Name_Something ON Junk2 ( Name, Something ) Someone suggested that the first indexing scheme should be kept since it would result in more efficient inserts/deletes (assume that there is no need to worry about updates for Name and Something). Would that make sense? I think the second indexing method would be better since it means one less index needs to be maintained. I would appreciate any insight into this specific example or directing me to more info on maintenance of clustered indexes.

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• How to handle dates that repeat indefinitely

  - by Addsy

  I am implementing a fairly simple calendar on a website using PHP and MySQL. I want to be able to handle dates that repeat indefinitely and am not sure of the best way to do it. For a time limited repeating event it seems to make sense to just add each event within the timeframe into my db table and group them with some form of recursion id. But when there is no limit to how often the event repeats, is it better to a) put records in the db for a specific time frame (eg the next 2 years) and then periodically check and add new records as time goes by - The problem with this is that if someone is looking 3 years ahead, the event won't show up b) not actually have records for each event but instead when i check in my php code for events within a specified time period, calculate wether a repeated event will occur within this time period - The problem with this is that it means there isn't a specific record for each event which i can see being a pain when i then want to associate other info (attendance etc) with that event. It also seems like it might be a bit slow Has anyone tried either of these methods? If so how did it work out? Or is there some other ingenious crafty method i'm missing?

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