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  • Problem understanding treesort in Haskell

    - by Jerry
    I am trying to figure out how exactly does treesort from here work (I understand flatten, insert and foldr). I suppose what's being done in treesort is applying insert for each element on the list thus generating a tree and then flattening it. The only problem I can't overcome here is where the list (that is the argument of the function) is hiding (because it is not written anywhere as an argument except for the function type declaration). One more thing: since dot operator is function composition, why is it an error when I change: treesort = flatten . foldr insert Leaf to treesort = flatten( foldr insert Leaf )?

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  • Why does C# not implement GetHashCode for Collections?

    - by Peterdk
    I am porting something from Java to C#. In Java the hashcode of a ArrayList depends on the items in it. In C# I always get the same hashcode from a List... Why is this? For some of my objects the hashcode needs to be different because the objects in their list property make the objects non-equal. I would expect that a hashcode is always unique for the object's state and only equals another hashcode when the object is equal. Am I wrong?

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  • mysql GROUP_CONCAT

    - by user301766
    I want to list all users with their corropsonding user class. Here are simplified versions of my tables CREATE TABLE users ( user_id INT NOT NULL AUTO_INCREMENT, user_class VARCHAR(100), PRIMARY KEY (user_id) ); INSERT INTO users VALUES (1, '1'), (2, '2'), (3, '1,2'); CREATE TABLE classes ( class_id INT NOT NULL AUTO_INCREMENT, class_name VARCHAR(100), PRIMARY KEY (class_id) ); INSERT INTO classes VALUES (1, 'Class 1'), (2, 'Class 2'); And this is the query statement I am trying to use but is only returning the first matching user class and not a concatenated list as hoped. SELECT user_id, GROUP_CONCAT(DISTINCT class_name SEPARATOR ",") AS class_name FROM users, classes WHERE user_class IN (class_id) GROUP BY user_id; Actual Output +---------+------------+ | user_id | class_name | +---------+------------+ | 1 | Class 1 | | 2 | Class 2 | | 3 | Class 1 | +---------+------------+ Wanted Output +---------+---------------------+ | user_id | class_name | +---------+---------------------+ | 1 | Class 1 | | 2 | Class 2 | | 3 | Class 1, Class 2 | +---------+---------------------+ Thanks in advance

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  • Please Help me add up the elements for this structure in Scheme/Lisp

    - by kunjaan
    I have an input which is of this form: (((lady-in-water . 1.25) (snake . 1.75) (run . 2.25) (just-my-luck . 1.5)) ((lady-in-water . 0.8235294117647058) (snake . 0.5882352941176471) (just-my-luck . 0.8235294117647058)) ((lady-in-water . 0.8888888888888888) (snake . 1.5555555555555554) (just-my-luck . 1.3333333333333333))) (context: the word denotes a movie and the number denotes the weighted rating submitted by the user) I need to add all the quantity and return a list which looks something like this ((lady-in-water 2.5) (snake 2.5) (run 2.25) (just-myluck 2.6)) How do I traverse the list and all the quantities? I am really stumped. Please help me. Thanks.

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  • How can one put together multiple arrays into one string?

    - by Noor
    I'm having a hard time describing what I'm looking for. If we pretend that we're pulling an array (I've used the .split to get user input data) where each line represents a link. How can I then add an anchor tagg to that link that I'm pulling? I need to be able to put < a href=" + thearray + "anything< /a. The reason for this is that I'm dynamically creating a list. I think that if I create two variables, one with this part < a href=" one with the closing and then call some sort of function that puts those two and the pulled array in between them until the list is complete. Does this make any sense?

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  • DDD: Trying to code sorting and filtering as it pertains to Poco, Repository, DTO, and DAO using C#?

    - by Dr. Zim
    I get a list of items from my Repository. Now I need to sort and filter them, which I believe would be done in the Repository for efficiency. I think there would be two ways of doing this in a DDD way: Send a filter and a sort object full of conditions to the Repository (What is this called)? Repository result would produce an object with .filter and .sort methods? (This wouldn't be a POJO/POCO because it contains more than one object?). So is the answer 1, 2, or other? Could you explain why? I am leaning toward #1 because the Repository would be able to only send the data I want (or will #2 be able to delay accessing data like a LazyList?) A code example (or website link) would be very helpful. Example: Product product = repo.GetProducts(mySortObject, myFilterObject); // List of Poco product.AddFilter("price", "lessThan", "3.99"); product.AddSort("price", "descending");

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  • Find a base case for a recursive void method

    - by Evan S
    I am doing homework. I would like to build a base case for a recursion where ordering given numbers (list2) in ascending order. Purpose of writing this codes is that when all numbers are in ascending order then should stop calling a method called ascending(list2, list1); and all values in list2 should be shipped to list1. For instance, list2 = 6,5,4,3,2,1 then list2 becomes empty and list1 should be 1,2,3,4,5,6. I am trying to compare result with previous one and if matches then stop. But I can't find the base case to stop it. In addition, Both ascending() and fixedPoint() are void method. Anybody has idea? lol Took me 3 days... When I run my code then 6,5,4,3,2,1 5,6,4,3,2,1 4,5,6,3,2,1 3,4,5,6,2,1 2,3,4,5,6,1 1,2,3,4,5,6 1,2,3,4,5,6 1,2,3,4,5,6 1,2,3,4,5,6 1,2,3,4,5,6 infinite............. public class Flipper { public static void main(String[] args) { Flipper aFlipper = new Flipper(); List<Integer> content = Arrays.asList(6,5,4,3,2,1); ArrayList<Integer> l1 = new ArrayList<Integer>(content); ArrayList<Integer> l2 = new ArrayList<Integer>(); // empty list aFlipper.fixedPoint(l2,l1); System.out.println("fix l1 is "+l1); System.out.println("fix l2 is "+l2); } public void fixedPoint(ArrayList<Integer> list1, ArrayList<Integer> list2) { // data is in list2 ArrayList<Integer> temp1 = new ArrayList<Integer>(); // empty list if (temp1.equals(list2)) { System.out.println("found!!!"); } else { ascending(list2, list1); // data, null temp1 = list1; // store processed value System.out.println("st list1 is "+list1); System.out.println("st list2 is "+list2); } fixedPoint(list2, list1); // null, processed data }

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  • display a confirmation popup on button click based on condition

    - by Raaz
    I have a p:commandButton on click of which I need to add a few values to a list. In my managed bean, I'm validating the value that has to be added, and if it validates to false, I have to display a confirmation popup. This is my code - <p:commandButton id="add" value="Add" type="submit" action="#{bean.doAdd}" ajax="false" update=":List"/> And in the bean, on click of the "Add" button, public String doAdd() throws Exception { if(response != null) { if(keyList.contains(response)) { if(!responseList.contains(response)) { responseList.add(response); } } else { //Have to display confirmation popup. } response = ""; } return response; } I'm using jsf 2.0 and primefaces 3.0. Can someone please tell me how to display the popup from the bean?

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  • Quickly retrieve the subset of properties used in a huge collection in C#

    - by ccornet
    I have a huge Collection (which I can cast as an enumerable using OfType<()) of objects. Each of these objects has a Category property, which is drawn from a list somewhere else in the application. This Collection can reach sizes of hundreds of items, but it is possible that only, say, 6/30 of the possible Categories are actually used. What is the fastest method to find these 6 Categories? The size of the huge Collection discourages me from just iterating across the entire thing and returning all unique values, so is there a faster method of accomplishing this? Ideally I'd collect the categories into a List.

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  • Keeping a large volume of data in Session - Suggestions / alternatives?

    - by Fishcake
    I'm developing a web app for which the client wants us to query their data as little as possible. The data will be coming from a Microsoft CRM instance. So we've agreed that data will only be queried as and when it is needed, therefore if a web user wants to see a list of contacts (for example) that list is fetched into a local DataTable. Then if a new contact is created on the website the new contact is sent to CRM and added to the local DataTable at the same time. Likewise for edits. If the user then looks at their contacts again the data will just come from the local DataTable. At the moment local data is being kept in Session but my concern is that too much memory will start being used up. However traffic is expected to be pretty small, perhaps no more than 20 concurrent users so am I worrying about nothing or is there a better way you can suggest to handle this?

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  • What are Android different screens dimensions in dp for different screens (e.g. xlarge = 960dp x 720dp)?

    - by Zizo
    in this link: Range of screens supported, Android team mentioned that: As you design your UI for different screen sizes, you'll discover that each design requires a minimum amount of space. So, each generalized screen size above has an associated minimum resolution that's defined by the system. These minimum sizes are in "dp" units—the same units you should use when defining your layouts—which allows the system to avoid worrying about changes in screen density. xlarge screens are at least 960dp x 720dp large screens are at least 640dp x 480dp normal screens are at least 470dp x 320dp small screens are at least 426dp x 320dp So, If I want to support all Android screens, can I create images, for full screen view, in those dimensions and that will be sufficient condition to support all available screens? or they are just the minimum sizes, and I need other dimensions? If other dimensions are needed, Please list them as in the list above. Thanks in Advance.

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  • JSF inner datatable not respecting rendered condition of outer table.

    - by Marc
    <h:dataTable cellpadding="0" cellspacing="0" styleClass="list_table" id="OuterItems" value="#{valueList.values}" var="item" border="0"> <h:column rendered="#{item.typeA"> <h:dataTable cellpadding="0" cellspacing="0" styleClass="list_table" id="InnerItems" value="#{item.options}" var="option" border="0"> <h:column > <h:outputText value="Option: #{option.displayValue}"/> </h:column> </h:dataTable> </h:column> <h:column rendered="#{item.typeB"> <h:dataTable cellpadding="0" cellspacing="0" styleClass="list_table" id="InnerItems" value="#{item.demands}" var="demand" border="0"> <h:column > <h:outputText value="Demand: #{demand.displayValue}"/> </h:column> </h:dataTable> </h:column> </h:dataTable> public class Item{ ... public boolean isTypeA(){ return this instanceof TypeA; } public boolean isTypeB(){ return this instanceof TypeB; } ... } public class typeA extends Item(){ ... public List getOptions(){ .... } ... } public class typeB extends Item(){ ... public List getDemands(){ ... } .... } I'm having an issue with JSF. I've abstracted the problem out here, and I'm hoping someone can help me understand how what I'm doing fails. I'm looping over a list of Items. These Items are actually instances of the subclasses TypeA and TypeB. For Type A, I want to display the options, for Type B I want to display the demands. When rendering the page for the first time, this works fine. However, when I post back to the page for some action, I get an error: [3/26/10 12:52:32:781 EST] 0000008c SystemErr R javax.faces.FacesException: Error getting property 'options' from bean of type TypeB at com.sun.faces.lifecycle.ApplyRequestValuesPhase.execute(ApplyRequestValuesPhase.java:89) at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java(Compiled Code)) at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:91) at com.ibm.faces.portlet.FacesPortlet.processAction(FacesPortlet.java:193) My grasp on the JSF lifecyle is very rough. At this point, i understand there is an error in the ApplyRequestValues Phases which is very early and so the previous state is restored and nothing changes. What I don't understand is that in order to fufill the condition for rendering "item.typeA" that object has to be an instance of TypeA. But here, it looks like that object passed the condition even though it was an instance of TypeB. It is like it is evaluating the inner dataTable (InnerItems) before evaluating the outer (outerItems). My working assumption is that I just don't understand how/when the rendered attribute is actually evaluated.

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  • quering an external oracle db in rails application

    - by railscoder
    I have a website which useses a mysql database for its whole operation . But for a new requirement i need to query a external oracle database( used by other component) and compile a list of items and display in a page in the website. How is it possible to connect to a external database just for rendering a single page. And is it possible to cache the queried result for say 1 month before invalidating the cache and get the updated list of items. i dont want query the external oracle db for each request.

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  • Does my Dictionary must use locking mechanism?

    - by theateist
    Many threads have access to summary. Each thread will have an unique key for accessing the dictionary; Dictionary<string, List<Result>> summary; Do I need locking for following operations? summary[key] = new List<Result>() summary[key].Add(new Result()); It seems that I don't need locking because each thread will access dictionary with different key, but won't the (1) be problematic because of adding concurrently new record to dictionary with other treads?

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  • Automatically hyper-link URL's and Email's using C#, whilst leaving bespoke tags in place

    - by marcusstarnes
    I have a site that enables users to post messages to a forum. At present, if a user types a web address or email address and posts it, it's treated the same as any other piece of text. There are tools that enable the user to supply hyper-linked web and email addresses (via some bespoke tags/markup) - these are sometimes used, but not always. In addition, a bespoke 'Image' tag can also be used to reference images that are hosted on the web. My objective is to both cater for those that use these existing tools to generate hyper-linked addresses, but to also cater for those that simply type a web or email address in, and to then automatically convert this to a hyper-linked address for them (as soon as they submit their post). I've found one or two regular expressions that convert a plain string web or email address, however, I obviously don't want to perform any manipulation on addresses that are already being handled via the sites bespoke tagging, and that's where I'm stuck - how to EXCLUDE any web or email addresses that are already catered for via the bespoke tagging - I wan't to leave them as is. Here are some examples of bespoke tagging for the variations that I need to be left alone: [URL=www.msn.com]www.msn.com[/URL] [URL=http://www.msn.com]http://www.msn.com[/URL] [[email protected]][email protected][/EMAIL] [IMG]www.msn.com/images/test.jpg[/IMG] [IMG]http://www.msn.com/images/test.jpg[/IMG] The following examples would however ideally need to be automatically converted into web & email links respectively: www.msn.com http://www.msn.com [email protected] Ideally, the 'converted' links would just have the appropriate bespoke tags applied to them as per the initial examples earlier in this post, so rather than: <a href="..." etc. they'd become: [URL=http://www.. etc.) Unfortunately, we have a LOT of historic data stored with this bespoke tagging throughout, so for now, we'd like to retain that rather than implementing an entirely new way of storing our users posts. Any help would be much appreciated. Thanks.

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  • make tree in scheme

    - by ???
    (define (entry tree) (car tree)) (define (left-branch tree) (cadr tree)) (define (right-branch tree) (caddr tree)) (define (make-tree entry left right) (list entry left right)) (define (mktree order items_list) (cond ((= (length items_list) 1) (make-tree (car items_list) '() '())) (else (insert2 order (car items_list) (mktree order (cdr items_list)))))) (define (insert2 order x t) (cond ((null? t) (make-tree x '() '())) ((order x (entry t)) (make-tree (entry t) (insert2 order x (left-branch t)) (right-branch t))) ((order (entry t) x ) (make-tree (entry t) (left-branch t) (insert2 order x (right-branch t)))) (else t))) The result is: (mktree (lambda (x y) (< x y)) (list 7 3 5 1 9 11)) (11 (9 (1 () (5 (3 () ()) (7 () ()))) ()) ()) But I'm trying to get: (7 (3 (1 () ()) (5 () ())) (9 () (11 () ()))) Where is the problem?

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  • Prolog for beginners about logic and syntax

    - by lnotik
    Hello everybody. I have this question : I need to create a paradict "rightGuesses" which will get 3 arguments , each one of them is a list of letters : 1) The list of guessed letters 2) The word i have to guess 3) The letters that where guessed so far . for example : rightGuesses([n,o,p,q], [p,r,o,l,o,g], Ans). will give us Ans = [p, -, o, -, o, -]. i made: rightGuesses([],T2,[ANS]) rightGuesses([A|T1],T2,[ANS]):- (member(A,T2))=\=true , rightGuesses(T1,T2,[ _ |'-']). rightGuesses([A|T1],T2,[ANS]):- member(A,T2), rightGuesses(T1,T2,[ _ |A]). but i get : ERROR: c:/users/leonid/desktop/file3.pl:5:0: Syntax error: Operator expected Warning: c:/users/leonid/desktop/file3.pl:6: when i trying to compile it what is my problem , and is there is a better way to do it ? thanks in advance.

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  • What can cause my code to run slower when the server JIT is activated?

    - by durandai
    I am doing some optimizations on an MPEG decoder. To ensure my optimizations aren't breaking anything I have a test suite that benchmarks the entire codebase (both optimized and original) as well as verifying that they both produce identical results (basically just feeding a couple of different streams through the decoder and crc32 the outputs). When using the "-server" option with the Sun 1.6.0_18, the test suite runs about 12% slower on the optimized version after warmup (in comparison to the default "-client" setting), while the original codebase gains a good boost running about twice as fast as in client mode. While at first this seemed to be simply a warmup issue to me, I added a loop to repeat the entire test suite multiple times. Then execution times become constant for each pass starting at the 3rd iteration of the test, still the optimized version stays 12% slower than in the client mode. I am also pretty sure its not a garbage collection issue, since the code involves absolutely no object allocations after startup. The code consists mainly of some bit manipulation operations (stream decoding) and lots of basic floating math (generating PCM audio). The only JDK classes involved are ByteArrayInputStream (feeds the stream to the test and excluding disk IO from the tests) and CRC32 (to verify the result). I also observed the same behaviour with Sun JDK 1.7.0_b98 (only that ist 15% instead of 12% there). Oh, and the tests were all done on the same machine (single core) with no other applications running (WinXP). While there is some inevitable variation on the measured execution times (using System.nanoTime btw), the variation between different test runs with the same settings never exceeded 2%, usually less than 1% (after warmup), so I conclude the effect is real and not purely induced by the measuring mechanism/machine. Are there any known coding patterns that perform worse on the server JIT? Failing that, what options are available to "peek" under the hood and observe what the JIT is doing there?

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  • Android: making a custom ListView independent of adapters ?

    - by wei
    I am adding a local database as a cache to a remote web service in my android application to answer queries. I used ArrayAdapters before for list views to display the results from the web service. Now with a database cache, the result could be either a Cursor(from database) or a List(from web), which means the adapter can be CursorAdapter or ArrayAdapter too. Creating two adapters for one query doesn't seem to be a good idea. So I am wondering what would be the best way to refactor my current code to add this database feature? Thanks,

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  • GAE transaction exceptions

    - by bach
    Hi, In this example IS the exception being thrown if ANY of the Table elements are being changed by another client OR only if the element that we changed has been changed by another client? Just to verify - the exception is thrown from the commit() isn't it? PersistenceManager pm = PMF.get().getPersistenceManager(); try { pm.currentTransaction().begin(); List<Row> Table = (List<Row>) pm.newQuery(query).execute(); Table.get(0).setReserved(true); // <----- we change only this element pm.currentTransaction().commit(); } catch (JDOCanRetryException ex) { pm.currentTransaction().rollback() // <----- if Table.get(1) was changed by another client do we get to this point??? }

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  • .NET values lookup

    - by Maciej
    Hi, I have a feeling of missing something obvious. UDP receiver application. It holds a collection of valid UDP sender IPs - only guys with IP on that list will be considered. Since that list must be looked at on every packet and UDPs are so volatile, that operation must be maximum fast. Good choice is Dictionary but it is a key-value structure and what I actually need here is a dictionary-like (hash lookup) key only structure. Is there something like that? Small annoyance rather than a bug but still. I can still use Dictionary Thanks, M.

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  • GAE more than 3 attributes to filter?

    - by Vik
    Hie I am using GAE jdoql and wrote query like: Query query = pm.newQuery(BloodDonor.class); query.setFilter(" state == :stateName && district == :distName &&" + " city == :cityName && bloodGroup == :blood"); @SuppressWarnings("unchecked") List<BloodDonor> donors = (List<BloodDonor>) query.execute(state.toLowerCase(), district.toLowerCase(), city.toLowerCase(), bloodGroup.toLowerCase()); This doesnt work as execute method does not support more than 3 parameters. So how to pass more than 3

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  • Foreach over a collection of IEnumerables

    - by sdr
    I have 3 IEnumerables that I want to iterate over. I want to do something like this: IEnumerable<Car> redCars = GetRedCars(); IEnumerable<Car> greenCars = GetGreenCars(); IEnumerable<Car> blueCars = GetBlueCars(); foreach(Car c in (redCars + greenCars + blueCars)) { c.DoSomething(); } ... The best way I can think of is: ... List<Car> allCars = new List(); allCars.AddRange(redCars); allCars.AddRange(greenCars); allCars.AddRange(blueCars); foreach(car in allCars) { ... } ... Is there a more concise way to do this? Seems like combinding IEnumberables should be trivial.

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  • Is java.util.Scanner that slow?

    - by Cristian Vrabie
    Hi guys, In a Android application I want to use Scanner class to read a list of floats from a text file (it's a list of vertex coordinates for OpenGL). Exact code is: Scanner in = new Scanner(new BufferedInputStream(getAssets().open("vertexes.off"))); final float[] vertexes = new float[nrVertexes]; for(int i=0;i<nrVertexFloats;i++){ vertexes[i] = in.nextFloat(); } It seems however that this is incredibly slow (it took 30 minutes to read 10,000 floats!) - as tested on the 2.1 emulator. What's going on? I don't remember Scanner to be that slow when I used it on the PC (truth be told I never read more than 100 values before). Or is it something else, like reading from an asset input stream? Thanks for the help!

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