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• Best approach to synchronising properties across threads

  - by user290796

  Hi, I'm looking for some advice on the best approach to synchronising access to properties of an object in C++. The application has an internal cache of objects which have 10 properties. These objects are to be requested in sets which can then have their properties modified and be re-saved. They can be accessed by 2-4 threads at any given time but access is not intense so my options are: Lock the property accessors for each object using a critical section. This means lots of critical sections - one for each object. Return copies of the objects when requested and have an update function which locks a single critical section to update the object properties when appropriate. I think option 2 seems the most efficient but I just want to see if I'm missing a hidden 3rd option which would be more appropriate. Thanks, J

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• grouping objects to achieve a similar mean property for all groups

  - by cytochrome

  I have a collection of objects, each of which has a numerical 'weight'. I would like to create groups of these objects such that each group has approximately the same arithmetic mean of object weights. The groups won't necessarily have the same number of members, but the size of groups will be within one of each other. In terms of numbers, there will be between 50 and 100 objects and the maximum group size will be about 5. Is this a well-known type of problem? It seems a bit like a knapsack or partition problem. Are efficient algorithms known to solve it? As a first step, I created a python script that achieves very crude equivalence of mean weights by sorting the objects by weight, subgrouping these objects, and then distributing a member of each subgroup to one of the final groups. I am comfortable programming in python, so if existing packages or modules exist to achieve part of this functionality, I'd appreciate hearing about them. Thank you for your help and suggestions.

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• Generating Fibonacci series in F#

  - by photo_tom

  I'm just starting to learn F# using VS2010 and below is my first attempt at generating the Fibonacci series. What I'm trying to do is to build a list of all numbers less than 400. let fabList = let l = [1;2;] let mutable a = 1 let mutable b = 2 while l.Tail < 400 do let c = a + b l.Add(c) let a = b let b = c My first problem is that on the last statement, I'm getting an error message "Incomplete structured construct at or before this point in expression" on the last line. I don't understand what I'm doing wrong here. While this seems to be an obvious way to build the list in a fairly efficient way (from a c++/C# programmer), from what little I know of f#, this doesn't seem to feel to be the right way to do the program. Am I correct in this feeling?

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• C#, Fastest (Best?) Method of Identifying Duplicate Files in an Array of Directories

  - by Nate Greenwood

  I want to recurse several directories and find duplicate files between the n number of directories. My knee-jerk idea at this is to have a global hashtable or some other data structure to hold each file I find; then check each subsequent file to determine if it's in the "master" list of files. Obviously, I don't think this would be very efficient and the "there's got to be a better way!" keeps ringing in my brain. Any advice on a better way to handle this situation would be appreciated.

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• Is there any declare for toggle() that if its open do this, closed to that?

  - by Dejan.S

  Im doing some jquery stuff with toggle(), I'm doing different actions depending on if the current div is closing or showing, i know i can easy check if a div hasClass() or is(':visible') for what i want to do, but I'm thinking maybe there is somehow that i can reduce the amount of code or just do it more efficient? like declare the toggle() with two functions that this is for when its showing and this is for when its closing, is this possible? hope you get what i mean? like this, or check a jsfiddle $('#click_me').on('click', function() { $('#contain').toogle('blind', 300, function (){ alert('open'); }, function (){ alert('close'); }); });

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• Algorithm to Group All the Cycles Together

  - by Ngu Soon Hui

  I have a lot of cycles ( indicated by numeric values, for example, 1-2-3-4 corresponds to a cycle, with 4 edges, edge 1 is {1:2}, edge 2 is {2:3}, edge 3 is {3,4}, edge 4 is {4,1}, and so on). A cycle is said to be connected to another cycle if they share one and only one edge. For example, let's say I have two cycles 1-2-3-4 and 5-6-7-8, then there are two cycle groups because these two cycles are not connecting to each other. If I have two cycles 1-2-3-4 and 3-4-5-6, then I have only one cycle group because these two cycles share the same edge. What is the most efficient way to find all the cycle groups?

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• ColdFusion Timeout Error

  - by Jason

  I have a scheduled task that runs once a day that builds an XML file that I pass off to another group. Recently the amount of data has greatly increased and is now causing the task to time out (I think). I have tried to optimize my script as much as possible but with no luck. It times out long before an hour and I don't get any kind of ColdFusion error. Instead I get a "This page cannot be found" after it runs. Could this be a timeout someplace other than Coldfusion? Is there a more efficient way to build this XML file? select PersonID, FirstName, LastName from People select d.DepartmentID, DepartmentName, pd.PersonID from Department d inner join PersonDepartment pd on d.DepartmentID = pd.DepartmentID select PaperID, PaperTitle, PaperDescription, pp.PersonID from Paper p inner join PersonPaper pp on p.PaperID = pp.PaperID select DepartmentID, DepartmentName from getDepartments where PersonID = #getPeople.PersonID# select PaperID, PaperDescription from getpapers where PersonID = #getPeople.PersonID# #getPeople.PersonID# #getPeople.Firstname# #getPeople.LastName# #getPersonDepartments.DepartmentID# #getPersonDepartments.DepartmentName# #getPersonPapers.PaperID# #getPersonPapers.PaperDescription# Done!

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• Creating a page selector with JSP/JSTL

  - by zakSyed

  I am working on a project where I am required to build a page somewhat similar to the one you see when you visit a website like blockbuster. When you click on browse more you are taken to a page with a bar on top with different page numbers and a drop down to select the number of pages you want to view on that page. I want to include a feature like that on my page but I am not sure where to start. In my page I have list of 200 items which I want to display page by page. I was suggested to use custom tags, but is there a more simpler or efficient way to create that functionality. My web application uses Spring MVC framework and is coded entirely in Java. Any suggestions will be appreciated.

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• C# remove duplicates from List<List<int>>

  - by marseilles84

  I'm having trouble coming up with the most efficient algorithm to remove duplicates from List<List<int>>, for example (I know this looks like a list of int[], but just doing it that way for visual purposes: my_list[0]= {1, 2, 3}; my_list[1]= {1, 2, 3}; my_list[2]= {9, 10, 11}; my_list[3]= {1, 2, 3}; So the output would just be new_list[0]= {1, 2, 3}; new_list[1]= {9, 10, 11}; Let me know if you have any ideas. I would really appreciate it.

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• How do I ensure data consistency in this concurrent situation?

  - by MalcomTucker

  The problem is this: I have multiple competing threads (100+) that need to access one database table Each thread will pass a String name - where that name exists in the table, the database should return the id for the row, where the name doesn't already exist, the name should be inserted and the id returned. There can only ever be one instance of name in the database - ie. name must be unique How do I ensure that thread one doesn't insert name1 at the same time as thread two also tries to insert name1? In other words, how do I guarantee the uniqueness of name in a concurrent environment? This also needs to be as efficient as possible - this has the potential to be a serious bottleneck. I am using MySQL and Java. Thanks

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• More intelligent Context Menus in Visual Studio 2008 Database Projects

  - by Mike C.

  I'm using a SQL Server 2008 Database Project, and I'm finding it's very cumbersome to add certain items. For example, if I right click on Tables = Keys and navigate to the Add item, I'd expect to see the different kinds of keys that I can add. Instead, I see the stock items that don't apply, and I'm forced to navigate the Add New Item screen to find Primary Key. Is there a way to make this more efficient? I have Resharper; can I leverage templates somehow (kind of a noob with these). Thanks!

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• Override onDraw to change how the drawing occurs (Android)

  - by Casebash

  I want to change how my UI elements display, so I am overriding onDraw. The following code allows me to change a View to be drawn using PorterDuff.Mode.DARKEN. Unfortunately, this method involves creating a bitmap the size of the entire screen, then drawing to it then drawing this large bitmap the main screen again, for each UI element. This isn't at all efficient. Is it possible to achieve this in a more effecient way? @Override protected void onDraw(Canvas canvas) { //TODO: Reduce the burden from multiple drawing Bitmap bitmap=Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Config.ARGB_8888); Log.e("tmp",canvas.getClipBounds().toString()); Canvas offscreen=new Canvas(bitmap); super.onDraw(offscreen); //Then draw onscreen Paint p=new Paint(); p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DARKEN)); canvas.drawBitmap(bitmap, 0, 0, p); }

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• Pre-loading external files (CSS, JavaScript) for other pages

  - by Jason Young

  I'm curious if there is an efficient way to wait for the front page of a site to load, and then pre-load CSS and script files that I know will likely be needed for the other pages on the site. I want the front page of the site to be as fast as possible (lean and mean). It's likely that the user will not immediately click on a link. Since there will likely be some idle time, this seems like an opportune time to pre-load some of the external assets. Pre-loading should cause them to become cached. When the user does click on another page, the only request needed will be for the content and possibly some images, etc. Has anyone done this? Is it a bad idea? Is there an elegant way to implement it?

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• JavaScript BubbleSort

  - by Alyn

  Hi, Have a bubblesort routine similar the this. I need to make it more efficient by stopping the loop when the array is sorted or if the array is already sorted. function sortNumbers(listbox) { var x, y, holder; // The Bubble Sort method. for(x = 0; x < ranarray.length; x++) { for(y = 0; y < (ranarray.length-1); y++) { if(ranarray[y] > ranarray[y+1]) { holder = ranarray[y+1]; ranarray[y+1] = ranarray[y]; ranarray[y] = holder; } } }

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• Appengine backreferences - need composite index?

  - by davezor

  I have a query that is very recently starting to throw: "The built-in indices are not efficient enough for this query and your data. Please add a composite index for this query." I checked the line on which this exception is being thrown, and the problem query is this one: count = self.vote_set.filter("direction =", 1).count() This is literally a one-filter operation using appengine's built-in backreferences. I have no idea how to optimize this query...anyone have any suggestions? I tried to add this index: - kind: Vote properties: - name: direction direction: desc - kind: Vote properties: - name: direction And I got a message (obviously) saying this was an unnecessary index. Thanks for your help in advance.

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• Building a custom iterator.

  - by Isai

  I am making this class which is a custom Map based off a hash map. I have an add method where if you add an object the object will be the key, and its value will be 1 if the object is not currently in the list. However if you add object that is currently in the list its value will be bumped up by 1. So if I added 10 strings which were all the same, the key would be that string and the value will be 10. I understand in practice when I iterate through the map, there is actually only one object to iterate, however, I am trying to create a inner class that will define an iterator that will iterate the same object however many times its value is. I can do this by simply using for loops to construct an appropriate ArrayList and just create an iterator for that, but that is too inefficient. Is there an easy or more efficient way of doing this?

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• What are the disadvantages of using a StringBuilder?

  - by stickman

  I know that StringBuilder is more efficient than a normal string when processing code which modifies the string value a lot because although strings act like value types, they are actually reference, which makes them immutable so every time we change it, we need to create a new reference in memory. My question is that, why doesn't .NET just use stringBuilder by default? There must be some disadvantages of it over just using String. Can anyone tell me what they are? The only thing I can think of is perhaps it is a heavier object and it takes more time to instantiate so if you aren't changing the string too much, this would override the benefits of StringBuilder

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• Awk or Sed: File Annotation

  - by lukmac

  Hallo, my SO friend, my question is: Specification: annotate the fields of FILE_2 to the corresponding position of FILE_1. A field is marked, and hence identified, by a delimiter pair. I did this job in python before I knew awk and sed, with a couple hundred lines of code. Now I want to see how powerful and efficient awk and sed can be. Show me some masterpiece of awk or sed, please! The delimiter pairs can be configured in FILE_3, but let's assume the first delimiter in a pair is 'Marker (number i) start', the other one is 'Marker (number i) done' Example: |-----------------FILE_1------------------| text text text text blabla Marker_1_start Marker_1_done any text in between blabla Marker_2_start Marker_2_done text text |-----------------FILE_2------------------| Marker_1_start 11 1111 Marker_1_done Marker_2_start 2222 22 Marker_2_done Expected Output: |-----------------FILE_Out------------------| text text text text blabla Marker_1_start 11 1111 Marker_1_done any text in between blabla Marker_2_start 2222 22 Marker_2_done text text

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• How to find and update the next record in a linking table

  - by someoneinomaha

  I have a classifieds system I'm working on. People are able to add photos to a classified, but I only display one when displaying the list of classifieds. To do that, I have a linking table between classifieds and photos that has a "is_main" boolean field. When someone deletes one of their classified photos, I want to: 1) See if there is more than that photo tied to the classified. 2) If there is, update the next photo and set that "is_main" field to TRUE. Just trying to find out the most efficient way to do this.

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• Help with algorithm to determine phrase occurrence in string in PHP

  - by Will M.

  I have an array of phrases (max 2 words) like $words = array('barack obama', 'chicago', 'united states'); and then I have a string like: $sentence = "Barack Obama is from Chicago. Barack Obama's favorite food it pizza."; I want to find/create an efficient algorithm that would return the number of occurrences of the words in the array $words in the string $sentence. In this case it would be: 'barack obama' => 2 'chicago' => 0 How can I built this?

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• MySQL "IS IN" equivalent?

  - by nute

  A while ago I worked on a MS-SQL project and I remember a "IS IN" thing. I tried it on a MySQL project and it did not work. Is there an equivalent? Workaround? Here is the full query I am trying to run: SELECT * FROM product_product, product_viewhistory, product_xref WHERE ( (product_viewhistory.productId = product_xref.product_id_1 AND product_xref.product_id_2 = product_product.id) OR (product_viewhistory.productId = product_xref.product_id_2 AND product_xref.product_id_1 = product_product.id) ) AND product_product.id IS IN (SELECT DISTINCT pvh.productId FROM product_viewhistory AS pvh WHERE pvh.cookieId = :cookieId ORDER BY pvh.viewTime DESC LIMIT 10) AND product_viewhistory.cookieId = :cookieId AND product_product.outofstock='N' ORDER BY product_xref.hits DESC LIMIT 10 It's pretty big ... but the part I am interested in is: AND product_product.id IS IN (SELECT DISTINCT pvh.productId FROM product_viewhistory AS pvh WHERE pvh.cookieId = :cookieId ORDER BY pvh.viewTime DESC LIMIT 10) Which basically says I want the products to be in the "top 10" of that sub-query. How would you achieve that with MySQL (while trying to be efficient)?

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• Retrieving a single Guid in CRM 4.0

  - by user1746560

  I'm new to CRM (version 4.0) and i'm trying to return a 'yearid' guide based on a given year (which is also stored in the entity).So far i've got: public static Guid GetYearID(string yearName) { ICrmService service = CrmServiceFactory.GetCrmService(); // Create the query object. QueryExpression query = new QueryExpression("year"); ColumnSet columns = new ColumnSet(); columns.AddColumn("yearid"); query.ColumnSet = columns; FilterExpression filter = new FilterExpression(); filter.FilterOperator = LogicalOperator.And; filter.AddCondition(new ConditionExpression { AttributeName = "yearName", Operator = ConditionOperator.Equal, Values = new object[] { yearName} }); query.Criteria = filter; } But my questions are: A) What code do in addition to this to actually store the Guid? B) Is using a QueryExpression the most efficient way to do this?

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• Explanation of NSMutableURLRequest : setHTTPMethod

  - by kkmoslehpour

  I am new to objective c programming. I am currently trying to insert data into mysql database. I have read a couple links on this and could not find the exact answer I am looking for. Here is what I am trying to do: I have my app that user inputs a name in a text field and once the press the add button, it makes a connection to my php file and my php file does the rest of the work (using POST method) and adds the name to the mysql dataase. I have seen a lot of people use NSMutableURLRequest : setHTTPMethod :POST`` in their code (in my case my php file does that and I don't haveNSMutableURLRequest` included in my code and it works perfectly fine.) My questions are: Are there any benefits of including NSMutableURLRequest in your code when you can just call your php code to take care of the POST for you? What does NSMutableURLRequest exactly do and which way is more efficient?

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• Is select() Ok to implemnet single socket read/write timeout ?

  - by chmike

  I have an application processing network communication with blocking calls. Each thread manages a single connection. I've added a timeout on the read and write operation by using select prior to read or write on the socket. Select is known to be inefficient when dealing with large number of sockets. But is it ok, in term of performance to use it with a single socket or are there more efficient methods to add timeout support on single sockets calls ? The benefit of select is to be portable.

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• Who owes who money optimisation problem

  - by Francis

  Say you have n people, each who owe each other money. In general it should be possible to reduce the amount of transactions that need to take place. i.e. if X owes Y £4 and Y owes X £8, then Y only needs to pay X £4 (1 transaction instead of 2). This becomes harder when X owes Y, but Y owes Z who owes X as well. I can see that you can easily calculate one particular cycle. It helps for me when I think of it as a fully connected graph, with the nodes being the amount each person owes. Problem seems to be NP-complete, but what kind of optimisation algorithm could I make, nevertheless, to reduce the total amount of transactions? Doesn't have to be that efficient, as N is quite small for me.

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