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• Optimizing sparse dot-product in C#

  - by Haggai

  Hello. I'm trying to calculate the dot-product of two very sparse associative arrays. The arrays contain an ID and a value, so the calculation should be done only on those IDs that are common to both arrays, e.g. <(1, 0.5), (3, 0.7), (12, 1.3) * <(2, 0.4), (3, 2.3), (12, 4.7) = 0.7*2.3 + 1.3*4.7 . My implementation (call it dict) currently uses Dictionaries, but it is too slow to my taste. double dot_product(IDictionary<int, double> arr1, IDictionary<int, double> arr2) { double res = 0; double val2; foreach (KeyValuePair<int, double> p in arr1) if (arr2.TryGetValue(p.Key, out val2)) res += p.Value * val2; return res; } The full arrays have about 500,000 entries each, while the sparse ones are only tens to hundreds entries each. I did some experiments with toy versions of dot products. First I tried to multiply just two double arrays to see the ultimate speed I can get (let's call this "flat"). Then I tried to change the implementation of the associative array multiplication using an int[] ID array and a double[] values array, walking together on both ID arrays and multiplying when they are equal (let's call this "double"). I then tried to run all three versions with debug or release, with F5 or Ctrl-F5. The results are as follows: debug F5: dict: 5.29s double: 4.18s (79% of dict) flat: 0.99s (19% of dict, 24% of double) debug ^F5: dict: 5.23s double: 4.19s (80% of dict) flat: 0.98s (19% of dict, 23% of double) release F5: dict: 5.29s double: 3.08s (58% of dict) flat: 0.81s (15% of dict, 26% of double) release ^F5: dict: 4.62s double: 1.22s (26% of dict) flat: 0.29s ( 6% of dict, 24% of double) I don't understand these results. Why isn't the dictionary version optimized in release F5 as do the double and flat versions? Why is it only slightly optimized in the release ^F5 version while the other two are heavily optimized? Also, since converting my code into the "double" scheme would mean lots of work - do you have any suggestions how to optimize the dictionary one? Thanks! Haggai

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• In Java how does one turn a String into a char or a char into a String?

  - by David

  Is there a way to turn a char into a String or a String with one letter into a char (like how you can turn an int into a double and a double into an int)? (please link to the relevant documentation if you can). How do I go about finding something like this that I'm only vaguely aware of in the documentation?

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• Focus process window, ShowWindow vs System Tray

  - by ais

  I try open process window, this code work if window state is minimize, but if program in system tray window isn't opened. [DllImport("User32")] private static extern int SetForegroundWindow(IntPtr hwnd); [DllImport("User32")] private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow); private static void ShowWindow(Process process) { ShowWindow(process.MainWindowHandle, SW_RESTORE); SetForegroundWindow(process.MainWindowHandle); }

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• Convert multiquery to a query using group by and so on

  - by ffffff

  -schema CREATE TABLE `ratings` ( `id` int(11) NOT NULL default '0', `rating` int(11) NOT NULL default '1', `rating_start` datetime NOT NULL default '0000-00-00 00:00:00', PRIMARY KEY (`id`) ) TYPE=MyISAM -myprogram.php foreach($ids as $id){ $sql = "SELECT rating FROM ratings WHERE id = '$id' AND rating_start >= NOW()"; $sql .= "ORDER BY rating_start DESC LIMIT 1;" $ret = $db->execute($id); } Can I teke same date from a Query? by using id IN (".implode(",",$ids).") and GROUP BY id

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• T-SQL get SELECTed value of stored procedure

  - by David

  In T-SQL, this is allowed: DECLARE @SelectedValue int SELECT @SelectedValue = MyIntField FROM MyTable WHERE MyPrimaryKeyField = 1 So, it's possible to get the value of a SELECT and stuff it in a variable (provided it's scalar, obviously). If I put the same select logic in a stored procedure: CREATE PROCEDURE GetMyInt AS SELECT MyIntField FROM MyTable WHERE MyPrimaryKeyField = 1 Can I get the output of this stored procedure and stuff it in a variable? Something like: DECLARE @SelectedValue int SELECT @SelectedValue = EXEC GetMyInt (I know the syntax above is not allowed because I tried it!)

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• c++/boost: use tuple ctors when subclassing

  - by bbb

  Hi there, is there some way to use a boost tuple's ctors as an addition to the subclass methods (and ctors) like here? // typedef boost::tuple<int, SomeId, SomeStatus> Conn; // Conn(1); // works and initializes using default ctors of Some* struct Conn : boost::tuple<int, AsynchId, AccDevRetStatus> {}; Conn(1); // "no matching function call" (but i want it so much) T.H.X.

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• C/C++ pragma in define macro

  - by aaa

  is there some way to embed pragma statement in macro with other statements? I am trying to achieve something like: #define DEFINE_DELETE_OBJECT(type) \ void delete_ ## type_(int handle); \ void delete_ ## type(int handle); \ #pragma weak delete_ ## type_ = delete_ ## type I am okay with boost solutions (save for wave) if one exists. thank you

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• MySQL function to compare values in a db table against the previous

  - by Stuart

  Iam quite new to functions in SQL and I would like to create a function to compare values in a MySQL table against previous and I am not sure how to do this. For example (iId is the input value) DECLARE pVal INT(20); DECLARE val INT(20); SELECT price INTO pVal FROM products WHERE Id=iId; SELECT price FROM products; IF price == pVal THEN SET val = price; END IF; Thanks

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• How do I output installation status using gtk in c?

  - by Runner

  int main( int argc, char *argv[] ) { GtkWidget *window; gtk_init (&argc, &argv); window = gtk_window_new (GTK_WINDOW_TOPLEVEL); gtk_widget_show (window); gtk_main (); return 0; } The above is just a empty winform,I want to output dynamic information in it(not editable), how should I do that?

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• converting python list of strings to their type

  - by user248237

  given a list of python strings, how can I automatically convert them to their correct type? Meaning, if I have: ["hello", "3", "3.64", "-1"] I'd like this to be converted to the list ["hello", 3, 3.64, -1] where the first element is a stirng, the second an int, the third a float and the fourth an int. how can I do this? thanks.

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• Why does this programe require MSVCR80.dll?

  - by Runner

  #include <gtk/gtk.h> int main( int argc, char *argv[] ) { GtkWidget *window; gtk_init (&argc, &argv); window = gtk_window_new (GTK_WINDOW_TOPLEVEL); gtk_widget_show (window); gtk_main (); return 0; } I tried putting various versions of MSVCR80.dll under the same directory as the generated executable(via cmake),but none matched.

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• Java serialization problem

  - by stefan89

  I have two classes X and Y, like this: class X implements Serializable { int val1; Y val2; } class Y implements Serializable { int val; } I want to transmit an object of type X from a client to server but i can't because the class X has a field of type Y. I replaced the field of type Y with a field of type X in class X and it works.

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• Get rid of Trailing Numbers in C

  - by Tech163

  For example, #include <stdio.h> int main (int argc, const char * argv[]) { char out = printf("teststring"); printf("%d\n", out); return 0; } will return teststring10. Anyone has an idea how to get rid of the 10? Thanks in advance.

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• IList<T> and IReadOnlyList<T>

  - by Safak Gür

  My problem is that I have a method that can take a collection as parameter that, Has a Count property Has an integer indexer (get-only) And I don't know what type should this parameter be. I would choose IList<T> before .NET 4.5 since there is no other indexable collection interface for this and arrays implement it, which is a big plus. But .NET 4.5 introduces the new IReadOnlyList<T> interface and I want my method to support that, too. How can I write this method to support both IList<T> and IReadOnlyList<T> without violating the basic principles like DRY? Can I convert IList<T> to IReadOnlyList<T> somehow in an overload? What is the way to go here? Edit: Daniel's answer gave me some pretty ideas, I guess I'll go with this: public void Do<T>(IList<T> collection) { DoInternal(collection, collection.Count, i => collection[i]); } public void Do<T>(IReadOnlyList<T> collection) { DoInternal(collection, collection.Count, i => collection[i]); } private void DoInternal<T>(IEnumerable<T> collection, int count, Func<int, T> indexer) { // Stuff } Or I could just accept a ReadOnlyList<T> and provide an helper like this: public static class CollectionEx { public static IReadOnlyList<T> AsReadOnly<T>(this IList<T> collection) { if (collection == null) throw new ArgumentNullException("collection"); return new ReadOnlyWrapper<T>(collection); } private sealed class ReadOnlyWrapper<T> : IReadOnlyList<T> { private readonly IList<T> _Source; public int Count { get { return _Source.Count; } } public T this[int index] { get { return _Source[index]; } } public ReadOnlyWrapper(IList<T> source) { _Source = source; } public IEnumerator<T> GetEnumerator() { return _Source.GetEnumerator(); } IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); } } } Then I could call Do(array.AsReadOnly())

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• Android OnKeyListener

  - by user346665

  Why I can't implement OnKeyListener with parameter View such as on example where parameters are (View v, int keyCode, KeyEvent event) I'm forced to use parameters (DialogInterface dialog, int keyCode, KeyEvent event) but not the View as I want.

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• Why does a programming language need keywords?

  - by eSKay

  For example (in C): int break = 1; int for = 2; Why will the compiler have any problems at all in deducing that break and for are variables here?

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• How many additional function calls does fib(n) require if "LINE 3" is removed?

  - by BROCK

  I just got this question on a interview and had no idea how to calculate the answer. How many additional function calls does fib(n) require if "LINE 3" is removed? The answer should be in terms on n. int fib(int n) { if(n == 0) return 0; if(n == 1) return 1; if(n == 2) return 1; //LINE 3 HERE <--- return fib(n - 1) + fib(n - 2); }

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• nhibernate activerecord lazy collection with custom query

  - by George Polevoy

  What i'm trying to accomplish, is having a temporal soft delete table. table Project(ID int) table ProjectActual(ProjectID int, IsActual bit, ActualAt datetime) Now is it possible to map a collection of actual projects, where project is actual when there is no record in ProjectActual.ProjectID = ID, or the last record sorted by ActualAt descending has IsActual set to 1 (true)?

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• Use of const in a method

  - by kouPhax

  In the following method, public void InspectList(IList<int> values) { if(values != null) { const string format = "Element At {0}"; foreach(int i in values) { Log(string.Format(format, i)); } } } Does the use of const provide any benefit over just declaring the string as a string? Woudl it not be interned anyway?

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• How to check total cache size using a program

  - by user1888541

  so I'm having some trouble creating a program to measure cache size in C. I understand the basic concept of going about this but I'm still having trouble figuring out exactly what I am doing wrong. Basically, I create an array of varying length (going by power of 2s) and access each element in the array and put it in a dummy variable. I go through the array and do this around 1000 times to negate the "noise" that would otherwise occur if I only did it once to get an accurate measurement for time. Then, I look for the size that causes a big jump in access time. Unfortunately, this is where I am having my problem, I don't see this jump using my code and clearly I am doing something wrong. Another thing is that I used /proc/cpuinfo to check the cache and it said the size was 6114 but that was not a power of 2. I was told to go by powers of 2 to figure out the cache can anyone explain why this is? Here is the just of my code...I will post the rest if need be { struct timeval start; struct timeval end; // int n = 1; // change this to test different sizes int array_size = 1048576*n; // I'm trying to check the time "manually" first before creating a loop for the program to do it by itself this is why I have a separate "n" variable to increase the size char x = 0; int i =0, j=0; char *a; a =malloc(sizeof(char) * (array_size)); gettimeofday(&start,NULL); for(i=0; i<1000; i++) { for(j=0; j < array_size; j += 1) { x = a[j]; } } gettimeofday(&end,NULL); int timeTaken = (end.tv_sec * 1000000 + end.tv_usec) - (start.tv_sec *1000000 + start.tv_usec); printf("Time Taken: %d \n", timeTaken); printf("Average: %f \n", (double)timeTaken/((double)array_size); }

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• Dividing a double with integer

  - by hardcoder

  I am facing an issue while dividing a double with an int. Code snippet is : double db = 10; int fac = 100; double res = db / fac; The value of res is 0.10000000000000001 instead of 0.10. Does anyone know what is the reason for this? I am using cc to compile the code.

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• Refactor the following two C++ methods to move out duplicate code

  - by ossandcad

  I have the following two methods that (as you can see) are similar in most of its statements except for one (see below for details) unsigned int CSWX::getLineParameters(const SURFACE & surface, vector<double> & params) { VARIANT varParams; surface->getPlaneParams(varParams); // this is the line of code that is different SafeDoubleArray sdParams(varParams); for( int i = 0 ; i < sdParams.getSize() ; ++i ) { params.push_back(sdParams[i]); } if( params.size() > 0 ) return 0; return 1; } unsigned int CSWX::getPlaneParameters(const CURVE & curve, vector<double> & params) { VARIANT varParams; curve->get_LineParams(varParams); // this is the line of code that is different SafeDoubleArray sdParams(varParams); for( int i = 0 ; i < sdParams.getSize() ; ++i ) { params.push_back(sdParams[i]); } if( params.size() > 0 ) return 0; return 1; } Is there any technique that I can use to move the common lines of code of the two methods out to a separate method, that could be called from the two variations - OR - possibly combine the two methods to a single method? The following are the restrictions: The classes SURFACE and CURVE are from 3rd party libraries and hence unmodifiable. (If it helps they are both derived from IDispatch) There are even more similar classes (e.g. FACE) that could fit into this "template" (not C++ template, just the flow of lines of code) I know the following could (possibly?) be implemented as solutions but am really hoping there is a better solution: I could add a 3rd parameter to the 2 methods - e.g. an enum - that identifies the 1st parameter (e.g. enum::input_type_surface, enum::input_type_curve) I could pass in an IDispatch and try dynamic_cast< and test which cast is NON_NULL and do an if-else to call the right method (e.g. getPlaneParams() vs. get_LineParams()) The following is not a restriction but would be a requirement because of my teammates resistance: Not implement a new class that inherits from SURFACE/CURVE etc. (They would much prefer to solve it using the enum solution I stated above)

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• Inlining an array of non-default constructible objects in a C++ class

  - by porgarmingduod

  C++ doesn't allow a class containing an array of items that are not default constructible: class Gordian { public: int member; Gordian(int must_have_variable) : member(must_have_variable) {} }; class Knot { Gordian* pointer_array[8]; // Sure, this works. Gordian inlined_array[8]; // Won't compile. Can't be initialized. }; As even beginner C++ users know, the language guarantees that all members are initialized when constructing a class. And it doesn't trust the user to initialize everything in the constructor - one has to provide valid arguments to the constructors of all members before the body of the constructor even starts. Generally, that's a great idea as far as I'm concerned, but I've come across a situation where it would be a lot easier if I could actually have an array of non-default constructible objects. The obvious solution: Have an array of pointers to the objects. This is not optimal in my case, as I am using shared memory. It would force me to do extra allocation from an already contended resource (that is, the shared memory). The entire reason I want to have the array inlined in the object is to reduce the number of allocations. This is a situation where I would be willing to use a hack, even an ugly one, provided it works. One possible hack I am thinking about would be: class Knot { public: struct dummy { char padding[sizeof(Gordian)]; }; dummy inlined_array[8]; Gordian* get(int index) { return reinterpret_cast<Gordian*>(&inlined_array[index]); } Knot() { for (int x = 0; x != 8; x++) { new (get(x)) Gordian(x*x); } } }; Sure, it compiles, but I'm not exactly an experienced C++ programmer. That is, I couldn't possibly trust my hacks less. So, the questions: 1) Does the hack I came up with seem workable? What are the issues? (I'm mainly concerned with C++0x on newer versions of GCC). 2) Is there a better way to inline an array of non-default constructible objects in a class?

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• Advanced Model Binding vs 2010

  - by user281180

  Can I have an example of advanced model binding using ajaxpost? I have two classes Person and Test as follows: public class person{ public ArrayList Name = new ArrayList(); public Test []test {get;set;} } public class Test { public int ID{get;set;} public int mark{get;set;} } My Controller could be [HttpPost] public EmptyResult CaseTest(Person person) { return new EmptyResult(); } How do I post the values from the view?

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• Xerces conflicts string.h

  - by Velthune

  Compiling my program I have this error: /usr/include/xercesc/util/Compilers/GCCDefs.hpp:133:60: error: declaration of ‘int strcasecmp(const char*, const char*)’ has a different exception specifier /usr/include/string.h:536:12: error: from previous declaration ‘int strcasecmp(const char*, const char*) throw ()’ make: *** [src/test/VFTImageMaterial.o] Error 1 Any idea about this conflict with string.h?

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