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• R: What are the best functions to deal with concatenating and averaging values in a data.frame?

  - by John

  I have a data.frame from this code: my_df = data.frame("read_time" = c("2010-02-15", "2010-02-15", "2010-02-16", "2010-02-16", "2010-02-16", "2010-02-17"), "OD" = c(0.1, 0.2, 0.1, 0.2, 0.4, 0.5) ) which produces this: > my_df read_time OD 1 2010-02-15 0.1 2 2010-02-15 0.2 3 2010-02-16 0.1 4 2010-02-16 0.2 5 2010-02-16 0.4 6 2010-02-17 0.5 I want to average the OD column over each distinct read_time (notice some are replicated others are not) and I also would like to calculate the standard deviation, producing a table like this: > my_df read_time OD stdev 1 2010-02-15 0.15 0.05 5 2010-02-16 0.3 0.1 6 2010-02-17 0.5 0 Which are the best functions to deal with concatenating such values in a data.frame?

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• Why are my JavaScript variables not persisting across functions?

  - by Eric Belair

  I have the following JavaScript in my HTML page referencing an HTML form on the page: <script type="text/javascript"> <!-- var myForm = document.myForm; function validateForm() { if (myForm.myInput == "") alert("Please input some text."); return false; } myForm.submit(); } function showFormInput() { myForm.reset(); document.getElementById('myInput').style.display = 'inline'; } //--> </script> ... <form name="myForm" id="myForm" action="..." method="post"> <input id="myInput" name="myInput" type="text" value="" style="display:none;" /> </form> Both functions are throwing an exception when trying to access the variable myForm, saying that "myForm is null or not an object". Why is this occurring?

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• PHP multiple __autoload functions *without* the use of spl_register_autoload?

  - by Keith Palmer

  I'm an author of a growing library of PHP + QuickBooks related code. I'd like to utilize PHPs __autoload() function, however my code is a library that other people can include() into their own applications, so I can't rely on __autoload() being not already defined. Is there a way to have multiple __autoload() functions? I saw spl_autoload_register() in the PHP manual, but not all of my users have the SPL extension installed, so I can't rely on that. If there was a way to fall-back to using this and use normal require/include statements by default, I might consider that. Does anyone else have any other clever solutions to this issue? It seems like a glaring oversight to only be able to have a single __autoload() function...

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• Practise Questions for Templates,Functors,CallBack functions in c++?

  - by Eternal Learner

  Hi, I have been reading templates,functors,callback function for the past week and have referred some good books and articles. I however feel that, unless I can get good practice - programming in templates and use functors-callbacks there is no way I can really understand all the concepts or fluently use them while coding. Could anyone suggest some articles or books or websites where , there is a definition of the problem and also a solution to the same. I could just write code for the problem and check later on if my solution is good enough.. I am also aware that some of our stack-overflow members are experts in templates and callback functions. It would be great if they could design a problem and also post a solution , where a lot of template beginners like me could benefit.

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• How to execute unknown functions from dynamic load libraries?

  - by activenightly

  It's easy to load functions from dynamic libraries when you know this function in design time. just do something like this: int (*fn)(int); l0 = dlopen("./libfoo.so", RTLD_LAZY); if (!l0) { fprintf(stderr, "l0 %s\n", dlerror()); return 1; } fn = (int (*)(int))dlsym(l0, "foo"); if ((error = dlerror()) != NULL) { fprintf(stderr, "fn:%s\n", error); return 1; } x=(*fn)(y); ... How to execute library function when it's unknown in design time? In runtime you have a function name and array of arguments pointers and array of arguments sizes: char* fn_name="foo"; int foo_argc; void* foo_argv[]; int foo_argv_size[]; In scripting language it's a piece a cake task, but how to implement this nicely in c++?

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• How do I bind functions to all input elements using jQuery?

  - by bakkelun

  Hi, let's say I have this set of HTML-markup and CSS #CSS .inputhelp_text { background: #000; color: #fff; } .nodisplay { display: none; } <input class="inputhelp" id="firstname" /><span class="inputhelp_text nodisplay" id="help_firstname">Write in your firstname</span> <input class="inputhelp" id="lastname" /><span class="inputhelp_text nodisplay" id="help_lastname">Write in your lastname</span> Using jQuery, I need to bind a function to all input fields (I guess using jQuery's EACH function) so that when I click the input field, it should switch the class of each span to only "inputhelp_text". I've gotten this to work in two separate functions for each field, but since I have alot of fields, I know there's a better way to solve it. Any suggestions?

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• Is it possible to access JSON properties with relative syntax when using JSON defined functions?

  - by Justin Vincent

  // JavaScript JSON var myCode = { message : "Hello World", helloWorld : function() { alert(this.message); } }; myCode.helloWorld(); The above JavaScript code will alert 'undefined'. To make it work for real the code would need to look like the following... (note the literal path to myCode.message) // JavaScript JSON var myCode = { message : "Hello World", helloWorld : function() { alert(myCode.message); } }; myCode.helloWorld(); My question is... if I declare functions using json in this way, is there some "relative" way to get access to myCode.message or is it only possible to do so using the literal namespace path myCode.message?

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• how to go through a string array and apply functions for different strings?

  - by Newbie

  Ok, this may be really noobish question, but i am wishing there is something i dont know yet. I go through a file, and check which string each line has, depending on the string value i execute a different function for it (or functions). This is how i do it now: if(str == "something"){ // do stuff }else if(str == "something else"){ // do stuff }else if(str == "something more"){ // do stuff }else if(str == "something again"){ // do stuff }else if(str == "something different"){ // do stuff }else if(str == "something really different"){ // do stuff } I am afraid this will become "slow" after i have to repeat those else if lines a lot... I tried to use switch() statement, but obviously it doesnt work here, is there something similar to switch() to use here?

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• Function to register functions to be called if event invoked.

  - by zaidwaqi

  Hi, I have a Panel which contains 20 PictureBox controls. If a user clicks on any of the controls, I want a method within the Panel to be called. How do I do this? public class MyPanel : Panel { public MyPanel() { for(int i = 0; i < 20; i++) { Controls.Add(new PictureBox()); } } // DOESN'T WORK. // function to register functions to be called if the pictureboxes are clicked. public void RegisterFunction( <function pointer> func ) { foreach ( Control c in Controls ) { c.Click += new EventHandler( func ); } } } How do I implement RegisterFunction()? Also, if there are cool C# features that can make the code more elegant, please share. Thanks.

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• How to access constant defined in child class from parent class functions?

  - by kavoir.com

  I saw this example from php.net: <?php class MyClass { const MY_CONST = "yonder"; public function __construct() { $c = get_class( $this ); echo $c::MY_CONST; } } class ChildClass extends MyClass { const MY_CONST = "bar"; } $x = new ChildClass(); // prints 'bar' $y = new MyClass(); // prints 'yonder' ?> But $c::MY_CONST is only recognized in version 5.3.0 or later. The class I'm writing may be distributed a lot. Basically, I have defined a constant in ChildClass and one of the functions in MyClass (father class) needs to use the constant. Any idea?

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• C++ OOP: Which functions to put into the class?

  - by oh boy

  Assume I have a class a: class a { public: void load_data( ); private: void check_data( ); void work_data( ); void analyze_data( ); } Those functions all do something with the class or one of its members. However this function: bool validate_something( myType myData ) { if ( myData.blah > 0 && myData.blah < 100 ) { return true; } return false; } Is related to the class and will only be called by it, so it won't be needed anywhere else Doesn't do anything with the class or its members - just a small "utility" function Where to put validate_something? Inside or outside the class?

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• Are static members of a generic class tied to the specific instance?

  - by mafutrct

  This is more of a documentation than a real question. I noticed the principle it is not described on SO yet (did I miss it?), so here goes: Imagine a generic class that contains a static member: class Foo<T> { public static int member; } Is there a new instance of the member for each specific class, or is there only a single instance for all Foo-type classes? It can easily be verified by code like this: Foo<int>.member = 1; Foo<string>.member = 2; Console.WriteLine (Foo<int>.member); What is the result, and where is this behavior documented?

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• JavaScript: One ID, two functions. How can I do this with minimal code duplication?

  - by user1775598

  I've got an ID and I'd like to assign two functions to it. Here's what it currently looks like: document.getElementById(this.config.dragArea).addEventListener("drop", this._dropFiles, false); document.getElementById(this.config.dragArea).addEventListener("drop", this._handleFileDrop, false); How can I rewrite this file without so much duplication? I tried doing document.getElementById(this.config.dragArea).addEventListener("drop", this._dropFiles, this._handleFileDrop, false); and document.getElementById(this.config.dragArea).addEventListener("drop", function(){this._dropFiles; this._handleFileDrop}, false); All to no avail :(

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• Does F# documentation have a way to search for functions by their types?

  - by Nathan Sanders

  Say I want to know if F# has a library function of type ('T -> bool) -> 'T list -> int ie, something that counts how many items of a list that a function returns true for. (or returns the index of the first item that returns true) I used to use the big list at the MSR site for F# before the documentation on MSDN was ready. I could just search the page for the above text because the types were listed. But now the MSDN documentation only lists types on the individual pages--the module page is a mush of descriptive text. Google kinda-sorta works, but it can't help with // compatible interfaces ('T -> bool) -> Seq<'T> -> int // argument-swaps Seq<'T> -> ('T -> bool) -> int // type-variable names ('a -> bool) -> Seq<'a> -> int // wrappers ('a -> bool) -> 'a list -> option<int> // uncurried versions ('T -> bool) * 'T list -> int // .NET generic syntax ('T -> bool) -> List<'T> -> int // methods List<'T> member : ('T -> bool) -> int Haskell has a standalone program for this called Hoogle. Does F# have an equivalent, like Fing or something?

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• How do I access abstract private data from derived class without friend or 'getter' functions in C++?

  - by John

  So, I am caught up in a dilemma right now. How am I suppose to access a pure abstract base class private member variable from a derived class? I have heard from a friend that it is possible to access it through the base constructor, but he didn't explain. How is it possible? There are some inherited classes from base class. Is there any way to gain access to the private variables ? class Base_button { private: bool is_vis; Rect rButton; public: // Constructors Base_button(); Base_button( const Point &corner, double height, double width ); // Destructor virtual ~ Base_button(); // Accessors virtual void draw() const = 0; bool clicked( const Point &click ) const; bool is_visible() const; // Mutators virtual void show(); virtual void hide(); void move( const Point &loc ); }; class Button : public Base_button { private: Message mButton; public: // Constructors Button(); Button( const Point &corner, const string &label ); // Acessors virtual void draw() const; // Mutators virtual void show(); virtual void hide(); }; I want to be able access Rect and bool in the base class from the subclass

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• Overhead of calling tiny functions from a tight inner loop? [C++]

  - by John

  Say you see a loop like this one: for(int i=0; i<thing.getParent().getObjectModel().getElements(SOME_TYPE).count(); ++i) { thing.getData().insert( thing.GetData().Count(), thing.getParent().getObjectModel().getElements(SOME_TYPE)[i].getName() ); } if this was Java I'd probably not think twice. But in performance-critical sections of C++, it makes me want to tinker with it... however I don't know if the compiler is smart enough to make it futile. This is a made up example but all it's doing is inserting strings into a container. Please don't assume any of these are STL types, think in general terms about the following: Is having a messy condition in the for loop going to get evaluated each time, or only once? If those get methods are simply returning references to member variables on the objects, will they be inlined away? Would you expect custom [] operators to get optimized at all? In other words is it worth the time (in performance only, not readability) to convert it to something like: ElementContainer &source = thing.getParent().getObjectModel().getElements(SOME_TYPE); int num = source.count(); Store &destination = thing.getData(); for(int i=0;i<num;++i) { destination.insert(thing.GetData().Count(), source[i].getName(); } Remember, this is a tight loop, called millions of times a second. What I wonder is if all this will shave a couple of cycles per loop or something more substantial? Yes I know the quote about "premature optimisation". And I know that profiling is important. But this is a more general question about modern compilers, Visual Studio in particular.

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• Is there some file browser that uses low level functions to browse hard disk?

  - by watbywbarif

  I have Windows 7, NTFS hard disk. I have detected rootkit files but can't delete them through Windows explorer, obviously because they are not visible. Is there some other file browser that is using low level function calls, lower that win api, so that I can try to see and study these files before removal. I know the exact locations. I know that I can load some live CD and delete them, but I wonder about the first possible solution.

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• 'hijacking' gui and mapping certain controls to certain functions. VNC. TouchOSC

  - by Nick

  I need a VNC LIKE application which rather than sharing the screen, can take control of a specific application and then share that functionality across a network to multiple clients. Obviously, VNC requires use of the mouse and therefore only one user can do something at one time, this is NOT what I am after. I am after something that can hijack the graphic user interface, map certain controls, and then display them in another piece of software (perhaps like TOUCHOSC) The software I would like to map and share is called YAMAHA STUDIO MANAGER and is used to control certain Yamaha audio hardware, and in my case a Yamaha LS9 and M7CL mixing console. Its free.

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• How to visualize the design of a program in order to communicate it to others

  - by Joris Meys

  I am (re-)designing some packages for R, and I am currently working out the necessary functions, objects, both internal and for the interface with the user. I have documented the individual functions and objects. So I have the description of all the little parts. Now I need to give an overview of how the parts fit together. The scheme of the motor so to say. I've started with making some flowchart-like graphs in Visio, but that quickly became a clumsy and useless collection of boxes, arrrows and-what-not. So hence the question: Is there specific software you can use for vizualizing the design of your program If so, care to share some tips on how to do this most efficiently If not, how do other designers create the scheme of their programs and communicate that to others? Edit: I am NOT asking how to explain complex processes to somebody, nor asking how to illustrate programming logic. I am asking how to communicate the design of a program/package, i.e.: the objects (with key features and representation if possible) the related functions (with arguments and function if possible) the interrelation between the functions at the interface and the internal functions (I'm talking about an extension package for a scripting language, keep that in mind) So something like this : But better. This is (part of) the interrelations between functions in the old package that I'm now redesigning for obvious reasons :-) PS : I made that graph myself, using code extraction tools on the source and feeding the interrelation matrix to yEd Graph Editor.

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• Effective handling of variables in non-object oriented programming

  - by srnka

  What is the best method to use and share variables between functions in non object-oriented program languages? Let's say that I use 10 parameters from DB, ID and 9 other values linked to it. I need to work with all 10 parameters in many functions. I can do it next ways: 1. call functions only with using ID and in every function get the other parameters from DB. Advantage: local variables are clear visible, there is only one input parameter to function Disadvantage: it's slow and there are the same rows for getting parameters in every function, which makes function longer and not so clear 2. call functions with all 10 parameters Advantage: working with local variables, clear function code Disadvantage: many input parameters, what is not nice 3. getting parameters as global variables once and using them everywhere Advantage - clearer code, shorter functions, faster processing Disadvantage - global variables - loosing control of them, possibility of unwanted overwriting (Especially when some functions should change their values) Maybe there is some another way how to implement this and make program cleaner and more effective. Can you say which way is the best for solving this issue?

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• Chaining functions in jQuery. I cannot find an explanation anywhere.

  - by Marius

  Hello there, I have no idea how to do this. My markup: <table> <tr> <td id="colLeft"> Lorem ipsum dolor<br/> Lorem ipsum dolor<br/> Lorem ipsum dolor<br/> Lorem ipsum dolor<br/> Lorem ipsum dolor<br/> Lorem ipsum dolor. </td> <td id="colRight"> <div>1</div> <div>2</div> </td> </tr> </table> $(document).ready(function() { $('#colRight > div').each(function() { // I try to: select all divs in #colRight $(this).height(function(){ // I try to: sets the height of each div to: $('#colLeft').height() / $('#colRight > div').length(); // the height of #colLeft divided by the number of divs in colRight. }); }); }); What I am trying to do is to change the height of each div to the height of #colLeft divided by the number of divs in #colRight. However, it doesnt work. I've never understood how to chain functions, and never found anyone to teach me. So I would like to ask two favours of you. Why doesnt my above jQuery code. Does anyone know of a tutorial that explains it more detailed than in the tutorials on the jQuery website? Thank you for your time. Kind regards, Marius

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• How can I use "Dependency Injection" in simple php functions, and should I bother?

  - by Tchalvak

  I hear people talking about dependency injection and the benefit of it all the time, but I don't really understand it. I'm wondering if it's a solution to the "I pass database connections as arguments all the time" problem. I tried reading wikipedia's entry on it, but the example is written in Java so I don't solidly understand the difference it is trying to make clear. ( http://en.wikipedia.org/wiki/Dependency_injection ). I read this dependency-injection-in-php article ( http://www.potstuck.com/2009/01/08/php-dependency-injection/ ), and it seems like the objective is to not pass dependencies to an object directly, but to cordon off the creation of an object along with the creation of it's dependencies. I'm not sure how to apply that in a using php functions context, though. Additionally, is the following Dependency Injection, and should I bother trying to do dependency injection in a functional context? Version 1: (the kind of code that I create, but don't like, every day) function get_data_from_database($database_connection){ $data = $database_connection->query('blah'); return $data; } Version 2: (don't have to pass a database connection, but perhaps not dependency injection?) function get_database_connection(){ static $db_connection; if($db_connection){ return $db_connection; } else { // create db_connection ... } } function get_data_from_database(){ $conn = get_database_connection(); $data = $conn->query('blah'); return $data; } $data = get_data_from_database(); Version 3: (the creation of the "object"/data is separate, and the database code is still, so perhaps this would count as dependency injection?) function factory_of_data_set(){ static $db_connection; $data_set = null; $db_connection = get_database_connection(); $data_set = $db_connection->query('blah'); return $data_set; } $data = factory_of_data_set(); Anyone have a good resource or just insight that makes the method and benefit -crystal- clear?

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• Qt Socket blocking functions required to run in QThread where created. Any way past this?

  - by Alexander Kondratskiy

  The title is very cryptic, so here goes! I am writing a client that behaves in a very synchronous manner. Due to the design of the protocol and the server, everything has to happen sequentially (send request, wait for reply, service reply etc.), so I am using blocking sockets. Here is where Qt comes in. In my application I have a GUI thread, a command processing thread and a scripting engine thread. I create the QTcpSocket in the command processing thread, as part of my Client class. The Client class has various methods that boil down to writing to the socket, reading back a specific number of bytes, and returning a result. The problem comes when I try to directly call Client methods from the scripting engine thread. The Qt sockets randomly time out and when using a debug build of Qt, I get these warnings: QSocketNotifier: socket notifiers cannot be enabled from another thread QSocketNotifier: socket notifiers cannot be disabled from another thread Anytime I call these methods from the command processing thread (where Client was created), I do not get these problems. To simply phrase the situation: Calling blocking functions of QAbstractSocket, like waitForReadyRead(), from a thread other than the one where the socket was created (dynamically allocated), causes random behaviour and debug asserts/warnings. Anyone else experienced this? Ways around it? Thanks in advance.

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• Can I combine two functions into one using Javascript?

  - by Melissa

  I have the following code that I would like to simplify. With javascript and jQuery is there an easy way that I could combine these two functions? Most of the code is the same but I am not sure how I could create a single function that works differently depending on what is clicked. $(document).ready(function () { $('#ListBooks').click(ListBooks); $('#Create').click(Create); }); function Create() { var dataSourceID = $('#DataSourceID').val(); var subjectID = $('#SubjectID').val(); var contentID = $('#ContentID').val(); if (dataSourceID && dataSourceID != '00' && subjectID && subjectID != "00" && contentID && contentID != "00") { var e = encodeURIComponent, arr = ["dataSourceID=" + e(dataSourceID), "subjectID=" + e(subjectID), "contentID=" + e(contentID)]; window.location.href = '/Administration/Books/Create?' + arr.join("&"); } else { alert('Datasource, Subject and Content must be selected.'); } return false; } function ListBooks() { var dataSourceID = $('#DataSourceID').val(); var subjectID = $('#SubjectID').val(); var contentID = $('#ContentID').val(); if (dataSourceID && dataSourceID != '00' && subjectID && subjectID != "00" && contentID && contentID != "00") { var e = encodeURIComponent, arr = ["dataSourceID=" + e(dataSourceID), "subjectID=" + e(subjectID), "contentID=" + e(contentID)]; window.location.href = '/Administration/Books/ListBooks?' + arr.join("&"); } else { alert('Datasource, Subject and Content must be selected.'); } return false; }

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• What is the cleanest way to use anonymous functions?

  - by Fletcher Moore

  I've started to use Javascript a lot more, and as a result I am writing things complex enough that organization is becoming a concern. However, this question applies to any language that allows you to nest functions. Essentially, when should you use an anonymous function over a named global or inner function? At first I thought it was the coolest feature ever, but I think I am going overboard. Here's an example I wrote recently, ommiting all the variable delcarations and conditionals so that you can see the structure. function printStream() { return fold(function (elem, acc) { ... var comments = (function () { return fold(function (comment, out) { ... return out + ...; }, '', elem.comments); return acc + ... + comments; }, '', data.stream); } I realized though (I think) there's some kind of beauty in being so compact, it is probably isn't a good idea to do this in the same way you wouldn't want a ton of code in a double for loop.

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