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  • Shall I optimize or let compiler to do that?

    - by Knowing me knowing you
    What is the preferred method of writing loops according to efficiency: Way a) /*here I'm hoping that compiler will optimize this code and won't be calling size every time it iterates through this loop*/ for (unsigned i = firstString.size(); i < anotherString.size(), ++i) { //do something } or maybe should I do it this way: Way b) unsigned first = firstString.size(); unsigned second = anotherString.size(); and now I can write: for (unsigned i = first; i < second, ++i) { //do something } the second way seems to me like worse option for two reasons: scope polluting and verbosity but it has the advantage of being sure that size() will be invoked once for each object. Looking forward to your answers.

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  • Scala updating/creating value in a hashmap

    - by user1672739
    I don't understand this with Scala hasmaps: How do I create a value or update one if it does not exist? I am tryng to count the number of characters in a list of Strings. I've tried this code but it doesn't work : def times(chars: List[Char]): List[(Char, Int)] = { val map = new HashMap[Char, Int]() chars.foreach( (c : Char) => { map.update(c, map.get(c) + 1) }) } I understand the returning type isn't correct. But is my foreach loop wrong? Is there a prettier way to write it?

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  • dabbledb + iPhone

    - by user193545
    I have been using DabbbleDB online database for storing/retrieving values for one of my iPhone applications. I am using their JSON response for retrieving the records. The problem that I am facing is that if there are a large number of records in the database, it takes a long time to get the response from the server and then to parse the JSON response. Instead I would like to to get a set of records at a time and run a loop to fetch all the records in background. I do not know whether we can query for a set of records at a time from online databases like DabbleDB. Anybody having an idea, please help.

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  • Birthday effect - clarification needed plz.

    - by Mark
    Please help interpret the Birthday effect as described in Wikipedia: A birthday attack works as follows: 1) Pick any message m and compute h(m). 2) Update list L. Check if h(m) is in the list L. 3) if (h(m),m) is already in L, a colliding message pair has been found. else save the pair (h(m),m) in the list L and go back to step 1. From the birthday paradox we know that we can expect to find a matching entry, after performing about 2^(n/2) hash evaluations. Does the above mean 2^(n/2) iterations through the above entire loop (i.e. 2^(n/2) returns to step 1), OR does it mean 2^(n/2) comparisons to individual items already in L.

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  • Minimizing distance to a weighted grid

    - by Andrew Tomazos - Fathomling
    Lets suppose you have a 1000x1000 grid of positive integer weights W. We want to find the cell that minimizes the average weighted distance.to each cell. The brute force way to do this would be to loop over each candidate cell and calculate the distance: int best_x, best_y, best_dist; for x0 = 1:1000, for y0 = 1:1000, int total_dist = 0; for x1 = 1:1000, for y1 = 1:1000, total_dist += W[x1,y1] * sqrt((x0-x1)^2 + (y0-y1)^2); if (total_dist < best_dist) best_x = x0; best_y = y0; best_dist = total_dist; This takes ~10^12 operations, which is too long. Is there a way to do this in or near ~10^8 or so operations?

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  • Finding employees specific to department in SQL SERVER 2000(SET BASED)

    - by xyz
    Suppose I have a table (tblEmp) whose structure is like as under Dept Emp d1 e1 d1 e2 d1 e3 d2 e4 d2 e5 d3 e6 If I need to bring the output as Dept DepartmentSpecificEmployees d1 e1,e2,e3 d2 e4,e5 d3 e6 I will write the query as select Dept, stuff((select Emp + ',' from tblEmp t2 where t1.Dept = t2.Dept for xml path(''),1,1,'')DepartmentSpecificEmployees from tblEmp t1 group by Dept But this will work in Sql Server 2005+. How can I achieve the same in Sql Server 2000 without any variable declaration or loop or cursor? If I use COALESCE as an alternative, then I need to use a variable which will defeat the purpose Please help

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  • Strange macro declaration in C

    - by Andrey Atapin
    Exploring libusb-1.0.9 source code, I have found such line (./os/poll_windows.c:78): #define CHECK_INIT_POLLING do {if(!is_polling_set) init_polling();} while(0) As for me this is the same like: #define CHECK_INIT_POLLING if(!is_polling_set) init_polling(); Is there any reason to loop that expression? UPDATE: I couldn't still realize what'd be wrong after the answers, and the following example helped: #include <stdio.h> #define TEST if(test) foo(); #define TEST_DO do { if(test) foo(); } while(0) int test = 1; void foo() { printf("%s", "Foo called"); } int main(int argc, char** argv) { if(argc > 1) TEST_DO; /* LINE 12 */ else printf("%s", "skipping..."); return 0; } If you put TEST at line 12, a compiler will give an error "error: ‘else’ without a previous ‘if’". Hope, this will help someone.

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  • How to do something after effect animation ends in Flex?

    - by Chobicus
    I'm a beginner in Flex so there must be more elegant way of doing this. //move effect private var m:Move = new Move(); //this function creates labels with some text and starts move effect on them public function moveText(i:int):void { var myLabel:Label = new Label(); myLabel.text = "some text"; m.target = myLabel; ... m.play(); } Method moveText is called in a loop so I guess that labels don't get "garbage collected". What I want to do is to remove Labels created in moveText method after play animation ends. Another way of doing this is maybe creating some kind of "pool" of labels which I would use to move arround text. I don't know how would I return labels in to "pool". The question is how to do something after effect animation ends?

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  • Any way to break if statement in PHP?

    - by Usman
    Is there any command in PHP to stop executing the current or parent if statement, same as break or break(1) for switch/loop. For example $arr=array('a','b'); foreach($arr as $val) { break; echo "test"; } echo "finish"; in the above code PHP will not do echo "test"; and will go to echo "finish"; I need this for if $a="test"; if("test"==$a) { break; echo "yes"; // I don't want this line or lines after to be executed, without using another if } echo "finish"; I want to break the if statement above and stop executing echo "yes"; or such codes which are no longer necessary to be executed, there may be or may not be an additional condition, is there way to do this?

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  • RoR: Condition Always False - Why?

    - by Matt Hollingsworth
    Working in RoR 2.3.x. My quiz_results table has a row for user_id (3907) and result (0.1), and two users I'm looking at with no rows in the quiz_results table. This line keeps returining false: -if QuizResult.find_by_user_id(@user_id).present? But if I change it to anything that returns true, the next line reports an error on the * method: ="#{(QuizResult.average('score', :conditions => 'user_id = #{@user.id}') * 100).round}%" The beginning of the code is a loop: [email protected] do |user| Any ideas how to fix? Have tried unsuccessfully all day.

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  • sound not playing when i press the button and how to fix overlapping sounds

    - by alfredjunco
    the code is giving me an error"Unused variable'path'" and when i press a button there is no sound playing how do i fix this the aSound is in the h file - (void)playOnce:(NSString *)aSound; - (IBAction) beatButton50 { [self playOnce:@"racecars"]; } - (void)playOnce:(NSString *)aSound { NSString *path = [[NSBundle mainBundle] pathForResource:aSound ofType:@"caf"]; if([theAudio isPlaying]) { [theAudio stop]; } } - (void)playLooped:(NSString *)aSound { NSString *path = [[NSBundle mainBundle] pathForResource:aSound ofType:@"caf"]; if (!theAudio) { theAudio = [[AVAudioPlayer alloc] initWithContentsOfURL: [NSURL fileURLWithPath: path] error: NULL]; } [theAudio setDelegate: self]; // loop indefinitely [theAudio setNumberOfLoops: -1]; [theAudio setVolume: 1.0]; [theAudio play]; } - (void)stopAudio { [theAudio stop]; [theAudio setCurrentTime:0]; }

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  • Ojective C Class or struct?

    - by Scott Pendleton
    I have a class Song with properties Title, Key, Artist, etc. There are no methods. I loop through a database of song information and create a Song object for each, populating the properties, and then store the Song objects in an NSArray. Then I thought, why not just have a struct Song with all those same properties instead of a class Song. Doing so would eliminate the class files, the #import Song line in the using class's .m file, and the need to alloc, init, release. On the other hand, I'd have to put the struct definition in every class that might need it. (Unless there's some globally accessible location -- is there?) Also, can a struct be stored in an NSArray?

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  • Adding characters to string

    - by Jamza
    I am currently trying to build a very basic serial shell with my arduino. I am able to get an output from the device using Serial.read() and can get the character it has outputted, but I cannot work out how to then add that character to a longer to form the full command. I tried the logical thing but it doesn't work: char Command[]; void loop(){ if(Serial.available() > 0){ int clinput = Serial.read(); Command = Command + char(clinput); } Can anybody help? Thank You.

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  • for (Object object : list) [java] construction

    - by EugeneP
    My question, is, whether the sequence of elements picked from a list will always be the same, is this construction behaviour is deterministic for java "List"s - descendants of java.util.List 2) question, if I use for(Object o: list) construction and inside the loop's body increment a variable, will it be the index of list's elements? So, how it goes through list's elements, from 0 to size()-1 or chaotically? List.get(i) will always return this element? 3) question ( I suppose for the 2-nd question the answer will be negative, so:) for (int i=0; i < list.size(); i++) { } is the best way if I need to save the index of an element and later get it back from a list by its id?

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  • how divide herader from binary data

    - by fixo2020
    Hi, I have this code: ofstream dest("test.txt",ios::binary); while (true){ size_t retval = recv (sd, buffer, sizeof(buffer), 0); dest.write(buffer,retval); if(retval <= 0) { delete[] buffer; break;} } Now, the recv() function return 4 bytes each loop right? and buffer contain it, this return all data so, pseudo-header and binary data (image), but I want know how capture only binary data, I know that the end of header are "\n\r" right? but what's are the solution better for make this? I make a function that detect when are "\n\r"? and after how capture binary data? Or, I put all data in memory, and after parse it? but how? I'm desperate :(

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  • How to identify each parameter type in a C# method?

    - by user465876
    I have a C# method say: MyMethod(int num, string name, Color color, MyComplexType complex) Using reflection, how can I distinctly identify each of the parameter types of any method? I want to perform some task by parameter type. If the type is simple int, string or boolean then I do something, if it is Color, XMLDocument, etc I do something else and if it is user defined type like MyComplexType or MyCalci etc then I want to do certain task. I am able to retrieve all the parameters of a method using ParameterInfo and can loop through each parameter and get their types. But how can I identify each data type? foreach (var parameter in parameters) { //identify primitive types?? //identify value types //identify reference types } Edit: this is apart of my code to create a propert grid sort of page where I want to show the parameter list with data types for the selected method. If the parameter has any userdefined type/reference type then I want to expand it further to show all the elements under it with datatypes.

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  • JQuery get height of each previous element

    - by Jk_
    I'm trying to find a good solution to get the height of all the element above my target. So loop the prev() function ! Any ideas on how I could deal with that ? <div> <div style="height:50px;width:100%"></div> <div style="height:12px;width:100%"></div> <div style="height:23px;width:100%"></div> <div style="height:56px;width:100%"></div> <div id="#mytarget"><p>HERE</p></div> </div> $('#mytarget').prev().each(function() { alert($(this).outerHeight()); }); and it will fires ["56","23","12","50"].

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  • Difference between local and instance variables in ruby

    - by fflyer05
    I am working on a script that creates several fairly complex nested hash datastructures and then iterates through them conditionally creating database records. This is a standalone script using active record. After several minutes of running I noticed a significant lag in server responsiveness and discovered that the script, while being set to be nice +19, was enjoying a steady %85 - %90 total server memory. In this case I am using instance variables simply for readability. It helps knowing what is going to be re-used outside of the loop vs. what won't. Is there a reason to not use instance variables when they are not needed? Are there differences in memory allocation and management between local and instance variables? Would it help setting @variable = nil when its no longer needed?

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  • Create MVC 5 Combo Box from CRM Entities?

    - by SpaceCowboy74
    I am working on an MVC 5 App that pulls data from Dynamics CRM 5. The Data I am getting back is an IQueryable of type Account (The CRM Entity class auto generated by CrmSvcUtil). I am retrieving all of the items and can loop through them with code like this: @foreach (var item in Model.ToList()) { <tr> <td> @item.AccountId </td> <td> @Html.DisplayFor(modelItem => item.Name) </td> </tr> } The problem is, I would like to instead put them in a drop down list. I can't figure out what the syntax is to put these in a DropDown is. Any suggestions?

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  • Search box inside a div. Django

    - by Juliette Dupuis
    In my django app I display a list of elements (friends name) thanks to a loop: <div> {% for friend in group %} <p>{{ friend.name }} <p> {% endfor %} </div> I would like to create a search box on the top of my list in order to be able to find only the friends the user wants. I would like the search bar does not need to click to send the request (an example is the Airtime searchbox on top of the facebook friends list). I have absolutely no idea on how to do that, and I'm looking for hints or tips to start. Thank you very much for your help.

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  • How to initialize std::vector from C-style array?

    - by dehmann
    What is the cheapest way to initialize a std::vector from a C-style array? Example: In the following class, I have a vector, but due to outside restrictions, the data will be passed in as C-style array: class Foo { std::vector<double> w_; public: void set_data(double* w, int len){ // how to cheaply initialize the std::vector? } Obviously, I can call w_.resize() and then loop over the elements, or call std::copy(). Are there any better methods?

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  • PHP arrays & keys - fetching particular ones

    - by Rohan
    Hi Lets say I have an array with a structure like this: $arr= Array( array( "id"=>"a" "type">"apple"), array( "id"=>"b"), array( "id"=>"c"), array( "id"=>"c" "type"=>"banana") ); now I want to have a foreach loop which fetches all the array elements which have a key in them named "type". Something like foreach(all arrays which have type in them as $item) How would I do that? many thanks.

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  • How to get the set events of a control?

    - by Jack
    It's possible via C# code get an list of methods/delegates that was set to Control? let me explain better.. For example. Assuming some definitions like this: foo.Click += (a, b) => { ... } //.. foo.Click += (A,B) => { ... } And a megic method: var baa = foo.GetEvents("Click"); Returns baa[0] points to (a, b) => { ... } baa[1] points to (A,B) => { ... } My scenery: I make and add dynamically event to some controls inside a loop. I want depending to a boolean value a event of control of index one,will removed by using control.Click -= baa[1] or something like this. I hope this is clear for your. Thanks in advance.

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  • Can someone please clarify the Birthday Effect for me?

    - by Mark
    Please help interpret the Birthday effect as described in Wikipedia: A birthday attack works as follows: Pick any message m and compute h(m). Update list L. Check if h(m) is in the list L. if (h(m),m) is already in L, a colliding message pair has been found. else save the pair (h(m),m) in the list L and go back to step 1. From the birthday paradox we know that we can expect to find a matching entry, after performing about 2^(n/2) hash evaluations. Does the above mean 2^(n/2) iterations through the above entire loop (i.e. 2^(n/2) returns to step 1), OR does it mean 2^(n/2) comparisons to individual items already in L.

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  • Help needed in pivoting (SQL Server 2005)

    - by Newbie
    I have a table like ID Grps Vals --- ---- ----- 1 1 1 1 1 3 1 1 45 1 2 23 1 2 34 1 2 66 1 3 10 1 3 17 1 3 77 2 1 144 2 1 344 2 1 555 2 2 11 2 2 22 2 2 33 2 3 55 2 3 67 2 3 77 The desired output being ID Record1 Record2 Record3 --- ------- ------- ------- 1 1 23 10 1 3 34 17 1 45 66 77 2 144 11 55 2 344 22 67 2 555 33 77 I have tried(using while loop) but the program is running slow. I have been asked to do so by using SET based approach. My approach so far is SELECT ID,[1] AS [Record1], [2] AS [Record2], [3] as [Record3] FROM ( Select Row_Number() Over(Partition By ID Order By Vals) records ,* From myTable)x PIVOT (MAX(vals) FOR Grps IN ([1],[2],[3])) p But it is not working. Can any one please help to solve this.(SQL SERVER 2005)

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