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  • .net runtime type casting when using reflection

    - by Mike
    I have need to cast a generic list of a concrete type to a generic list of an interface that the concrete types implement. This interface list is a property on an object and I am assigning the value using reflection. I only know the value at runtime. Below is a simple code example of what I am trying to accomplish: public void EmployeeTest() { IList<Employee> initialStaff = new List<Employee> { new Employee("John Smith"), new Employee("Jane Doe") }; Company testCompany = new Company("Acme Inc"); //testCompany.Staff = initialStaff; PropertyInfo staffProperty = testCompany.GetType().GetProperty("Staff"); staffProperty.SetValue(testCompany, (staffProperty.PropertyType)initialStaff, null); } Classes are defined like so: public class Company { private string _name; public string Name { get { return _name; } set { _name = value; } } private IList<IEmployee> _staff; public IList<IEmployee> Staff { get { return _staff; } set { _staff = value; } } public Company(string name) { _name = name; } } public class Employee : IEmployee { private string _name; public string Name { get { return _name; } set { _name = value; } } public Employee(string name) { _name = name; } } public interface IEmployee { string Name { get; set; } } Any thoughts? I am using .NET 4.0. Would the new covariant or contravariant features help? Thanks in advance.

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  • C++ boost mpl vector

    - by Gokul
    I understand that the following code won't work, as i is a runtime parameter and not a compile time parameter. But i want to know, whether there is a way to achieve the same. i have a list of classes and i need to call a template function, with each of these classes. void GucTable::refreshSessionParams() { typedef boost::mpl::vector< SessionXactDetails, SessionSchemaInfo > SessionParams; for( int i = 0; i < boost::mpl::size<SessionParams>::value; ++i ) boost::mpl::at<SessionParams, i>::type* sparam = g_getSessionParam< boost::mpl::at<SessionParams, i>::type >(); sparam->updateFromGucTable(this); } } Can someone suggest me a easy and elegant way to perform the same? i need to iterate through the mpl::vector and use the type to call a global function and then use that parameter to do some run-time operations. Thanks in advance, Gokul. Working code typedef boost::mpl::vector< SessionXactDetails, SessionSchemaInfo > SessionParams; class GucSessionIterator { private: GucTable& m_table; public: GucSessionIterator(GucTable& table) :m_table(table) { } template< typename U > void operator()(const U& ) { g_getSessionParam<U>()->updateFromGucTable(m_table); } }; void GucTable::refreshSessionParams() { boost::mpl::for_each< SessionParams >( GucSessionIterator(*this) ); return; }

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  • Using different numeric variable types

    - by DataPimp
    Im still pretty new so bear with me on this one, my question(s) are not meant to be argumentative or petty but during some reading something struck me as odd. Im under the assumption that when computers were slow and memory was expensive using the correct variable type was much more of a necessity than it is today. Now that memory is a bit easier to come by people seem to have relaxed a bit. For example, you see this sample code everywhere: for (int i = 0; i < length; i++) int? (-2,147,483,648 to 2,147,483,648) for length? Isnt byte (0-255) a better choice? So Im curious of your opinion and what you believe to be best practice, I hate to think this would be used only because the acronym "int" is more intuitive for a beginner...or has memory just become so cheap that we really dont need to concern ourselves with such petty things and therefore we should just use long so we can be sure any other numbers/types(within reason) used can be cast automagically? ...or am Im just being silly by concerning myself with such things?

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  • Need feedback on two member functions of a Table class in C++

    - by George
    int Table::addPlayer(Player player, int position) { deque<Player>::iterator it = playerList.begin()+position; deque<Player>::iterator itStart = playerList.begin()+postion; while(*it != "(empty seat)") { it++; if (it == playerList.end()) { it = playerList.begin(); } if (it == itStart) { cout << "Table full" << endl; return -1; } } //TODO overload Player assignment, << operator *it = player; cout << "Player " << player << " sits at position " << it - playerList.begin() << endl; return it - playerList.begin(); } } int Table::removePlayer(Player player) { deque<Player>::iterator it = playerList.begin(); //TODO Do I need to overload != in Player? while(*it != player) { it++; if (it == playerList.end()) { cout << "Player " << player << " not found" << endl; return -1; } } *it = "(empty seat)"; cout << "Player " << player << " stands up from position " << it - playerList.begin() << endl; return it - playerList.begin(); } Would like some feedback on these two member functions of a Table class for Texas Hold Em Poker simulation. Any information syntax, efficiency or even common practices would be much appreciated.

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  • Trouble with custom WPF Panel-derived class

    - by chaiguy
    I'm trying to write a custom Panel class for WPF, by overriding MeasureOverride and ArrangeOverride but, while it's mostly working I'm experiencing one strange problem I can't explain. In particular, after I call Arrange on my child items in ArrangeOverride after figuring out what their sizes should be, they aren't sizing to the size I give to them, and appear to be sizing to the size passed to their Measure method inside MeasureOverride. Am I missing something in how this system is supposed to work? My understanding is that calling Measure simply causes the child to evaluate its DesiredSize based on the supplied availableSize, and shouldn't affect its actual final size. Here is my full code (the Panel, btw, is intended to arrange children in the most space-efficient manner, giving less space to rows that don't need it and splitting remaining space up evenly among the rest--it currently only supports vertical orientation but I plan on adding horizontal once I get it working properly): protected override Size MeasureOverride( Size availableSize ) { foreach ( UIElement child in Children ) child.Measure( availableSize ); return availableSize; } protected override System.Windows.Size ArrangeOverride( System.Windows.Size finalSize ) { double extraSpace = 0.0; var sortedChildren = Children.Cast<UIElement>().OrderBy<UIElement, double>( new Func<UIElement, double>( delegate( UIElement child ) { return child.DesiredSize.Height; } ) ); double remainingSpace = finalSize.Height; double normalSpace = 0.0; int remainingChildren = Children.Count; foreach ( UIElement child in sortedChildren ) { normalSpace = remainingSpace / remainingChildren; if ( child.DesiredSize.Height < normalSpace ) // if == there would be no point continuing as there would be no remaining space remainingSpace -= child.DesiredSize.Height; else { remainingSpace = 0; break; } remainingChildren--; } extraSpace = remainingSpace / Children.Count; double offset = 0.0; foreach ( UIElement child in Children ) { //child.Measure( new Size( finalSize.Width, normalSpace ) ); double value = Math.Min( child.DesiredSize.Height, normalSpace ) + extraSpace; child.Arrange( new Rect( 0, offset, finalSize.Width, value ) ); offset += value; } return finalSize; }

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  • What's the best way to resolve this scope problem?

    - by Peter Stewart
    I'm writing a program in python that uses genetic techniques to optimize expressions. Constructing and evaluating the expression tree is the time consumer as it can happen billions of times per run. So I thought I'd learn enough c++ to write it and then incorporate it in python using cython or ctypes. I've done some searching on stackoverflow and learned a lot. This code compiles, but leaves the pointers dangling. I tried 'this_node = new Node(...' . It didn't seem to work. And I'm not at all sure how I'd delete all the references as there would be hundreds. I'd like to use variables that stay in scope, but maybe that's not the c++ way. What is the c++ way? class Node { public: char *cargo; int depth; Node *left; Node *right; } Node make_tree(int depth) { depth--; if(depth <= 0) { Node tthis_node("value",depth,NULL,NULL); return tthis_node; } else { Node this_node("operator" depth, &make_tree(depth), &make_tree(depth)); return this_node; } };

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  • Android - Read PNG image without alpha and decode as ARGB_8888

    - by loki666
    I try to read an image from sdcard (in emulator) and then create a Bitmap image with the BitmapFactory.decodeByteArray method. I set the options: options.inPrefferedConfig = Bitmap.Config.ARGB_8888 options.inDither = false Then I extract the pixels into a ByteBuffer. ByteBuffer buffer = ByteBuffer.allocateDirect(width*height*4) bitmap.copyPixelsToBuffer(buffer) I use this ByteBuffer then in the JNI to convert it into RGB format and want to calculate on it. But always I get false data - I test without modifying the ByteBuffer. Only thing I do is to put it into the native method into JNI. Then cast it into a unsigned char* and convert it back into a ByteBuffer before returning it back to Java. unsigned char* buffer = (unsinged char*)(env->GetDirectBufferAddress(byteBuffer)) jobject returnByteBuffer = env->NewDirectByteBuffer(buffer, length) Before displaying the image I get data back with bitmap.copyPixelsFromBuffer( buffer ) But then it has wrong data in it. My Question is if this is because the image is internally converted into RGB 565 or what is wrong here? ..... Have an answer for it: - yes, it is converted internally to RGB565. Does anybody know how to create such an bitmap image from PNG with ARGB8888 pixel format? If anybody has an idea, it would be great!

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  • Am I mocking this helper function right in my Django test?

    - by CppLearner
    lib.py from django.core.urlresolvers import reverse def render_reverse(f, kwargs): """ kwargs is a dictionary, usually of the form {'args': [cbid]} """ return reverse(f, **kwargs) tests.py from lib import render_reverse, print_ls class LibTest(unittest.TestCase): def test_render_reverse_is_correct(self): #with patch('webclient.apps.codebundles.lib.reverse') as mock_reverse: with patch('django.core.urlresolvers.reverse') as mock_reverse: from lib import render_reverse mock_f = MagicMock(name='f', return_value='dummy_views') mock_kwargs = MagicMock(name='kwargs',return_value={'args':['123']}) mock_reverse.return_value = '/natrium/cb/details/123' response = render_reverse(mock_f(), mock_kwargs()) self.assertTrue('/natrium/cb/details/' in response) But instead, I get File "/var/lib/graphyte-webclient/graphyte-webenv/lib/python2.6/site-packages/django/core/urlresolvers.py", line 296, in reverse "arguments '%s' not found." % (lookup_view_s, args, kwargs)) NoReverseMatch: Reverse for 'dummy_readfile' with arguments '('123',)' and keyword arguments '{}' not found. Why is it calling reverse instead of my mock_reverse (it is looking up my urls.py!!) The author of Mock library Michael Foord did a video cast here (around 9:17), and in the example he passed the mock object request to the view function index. Furthermore, he patched POll and assigned an expected return value. Isn't that what I am doing here? I patched reverse? Thanks.

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  • InvalidCastException when getting Text from a Label referenced by dynamicaly built String, Fix?

    - by Chris
    NET Version: 3.5 Ok, I recieve an error (System.InvalidCastException was unhandled. Message="Unable to cast object of type 'System.Windows.Forms.Control[]' to type 'System.Windows.Forms.Label'.") when trying to get Text from a Label referenced by a dynamicly built string. Here's my situation; I have an array of 250 labels named l1 - l250. What I want to do is loop through them using this while statement: int c = 1; while (c < 251) { string k = "l" + c.ToString(); //dynamic name of Control(Label) object ka = Controls.Find(k, true); string ct = ((Label)ka).Text; //<<Error Occurs Here build = build + ct; c++; } and get the text value of each to build a string named build. I don't get any build errors, just this while debuging. While debuging I can go down to view my local variables. When looking through these, I can view the contents of object ka; it does contain the correct Text value of the correct Label I want to "access". I just don't understand how to get there. The text value is listed under "[0]" which is the only subcatagory for "ka".

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  • Scala and Java BigDecimal

    - by geejay
    I want to switch from Java to a scripting language for the Math based modules in my app. This is due to the readability, and functional limitations of mathy Java. For e.g, in Java I have this: BigDecimal x = new BigDecimal("1.1"); BigDecimal y = new BigDecimal("1.1"); BigDecimal z = x.multiply(y.exp(new BigDecimal("2")); As you can see, without BigDecimal operator overloading, simple formulas get complicated real quick. With doubles, this looks fine, but I need the precision. I was hoping in Scala I could do this: var x = 1.1; var y = 0.1; print(x + y); And by default I would get decimal-like behaviour, alas Scala doesn't use decimal calculation by default. Then I do this in Scala: var x = BigDecimal(1.1); var y = BigDecimal(0.1); println(x + y); And I still get an imprecise result. Is there something I am not doing right in Scala? Maybe I should use Groovy to maximise readability (it uses decimals by default)?

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  • invasive vs non-invasive ref-counted pointers in C++

    - by anon
    For the past few years, I've generally accepted that if I am going to use ref-counted smart pointers invasive smart pointers is the way to go -- However, I'm starting to like non-invasive smart pointers due to the following: I only use smart pointers (so no Foo* lying around, only Ptr) I'm starting to build custom allocators for each class. (So Foo would overload operator new). Now, if Foo has a list of all Ptr (as it easily can with non-invasive smart pointers). Then, I can avoid memory fragmentation issues since class Foo move the objects around (and just update the corresponding Ptr). The only reason why this Foo moving objects around in non-invasive smart pointers being easier than invasive smart pointers is: In non-invasive smart pointers, there is only one pointer that points to each Foo. In invasive smart pointers, I have no idea how many objects point to each Foo. Now, the only cost of non-invasive smart pointers ... is the double indirection. [Perhaps this screws up the caches]. Does anyone have a good study of expensive this extra layer of indirection is?

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  • How do I return an array from a method?

    - by dwwilson66
    I'm trying to create a deck of cards for my homework. Code is posted below. I need to create four sets of cards (the four suits) and am create a multidimensional array. When I print the results instead of trying to pass the array, I can see that the data in the array is as expected. However, when I try to pass the array card, I get an error cannot find symbol. I've got this modeled after texbook and Java tutorial examples, and I need some help figuring out what I'm missing. I've over-documented to give an idea of how I'm thinking this SHOULD work...please let me know where I've gone horribly wrong in my understanding. import java.util.*; import java.lang.*; // public class CardGame { public static int[][] main(String[] args) { int[][] startDeck = deckOfCards(); /* cast new deck as int[][], calling method deckOfCards System.out.println(" /// from array: " + Arrays.deepToString(startDeck)); } public static int[][] deckOfCards() /* method to return a multi-dimensional array */ { int rank; int suit; for(rank=1;rank<14;rank++) /* cards 1 - 13 .... */ { for(suit=1;suit<5;suit++) /* suits 1 - 4 .... */ { int[][] card = new int[][] /* define a new card... */ { {rank,suit} /* with rank/suit from for... loops */ }; System.out.println(" /// from array: " + Arrays.deepToString(card)); } } return card; /* Error: cannot find symbol } }

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  • Creating a Function in SQL Server with a Phone Number as a parameter and returns a Random Number

    - by Emer
    Hi Guys, I am hoping someone can help me here as google is not being as forthcoming as I would have liked. I am relatively new to SQL Server and so this is the first function I have set myself to do. The outline of the function is that it has a Phone number varchar(15) as a parameter, it checks that this number is a proper number, i.e. it is 8 digits long and contains only numbers. The main character I am trying to avoid is '+'. Good Number = 12345678 Bad Number = +12345678. Once the number is checked I would like to produce a random number for each phone number that is passed in. I have looked at substrings, the like operator, Rand(), left(), Right() in order to search through the number and then produce a random number. I understand that Rand() will produce the same random number unless alterations are done to it but right now it is about actually getting some working code. Any hints on this would be great or even point me towards some more documentation. I have read books online and they haven't helped me, maybe I am not looking in the right places. Here is a snippet of code I was working on the Rand declare @Phone Varchar (15) declare @Counter Varchar (1) declare @NewNumber Varchar(15) set @Phone = '12345678' set @Counter = len(@Phone) while @Counter > 0 begin select case when @Phone like '%[0-9]%' then cast(rand()*100000000 as int) else 'Bad Number' end set @counter = @counter - 1 end return Thanks for the help in advance Emer

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  • Oracle ODBC x64 - getting 0 when selecting a number(9) column

    - by MatsL
    I'm having a really weird problem with a third party web service that uses an ODBC connection to Oracle 10.2.0.3.0. I've written a .NET client that generates the same SQL as the web service so I can find out what's going on. The web service is hosted by IIS 6 that's in x64 mode so we use Oracle x64 client. The oracle client version is 10.2.0.1.0. I have a table that looks like this (I've removed some columns and names): SQL> describe tablename; Name Null? Type ----------------------------------------- -------- ---------------------------- KOD VARCHAR2(30) ORDNING NUMBER(5) AVGIFT NUMBER(9) I then in SQL*Plus issue the following statement: SELECT KOD as kod, AVGIFT as riskPoang FROM tablename Where upper(KODTYP) = 'OBJLIVSV_RISKVERKSAMTYP' ORDER BY ORDNING And I get the following result: KOD RISKPOANG ------------------------------ ---------- Hög risk 55 Mellan risk 35 Låg risk 15 Mycket låg risk 5 But when I execute the exact same SQL using the same DSN on the same machine I get this: Values Kod: Hög risk RiskPoäng: 0 Kod: Mellan risk RiskPoäng: 0 Kod: Låg risk RiskPoäng: 0 Kod: Mycket låg risk RiskPoäng: 0 If I first cast the number to varchar and then back again to number, like this: SELECT KOD as kod, to_number(to_char(AVGIFT, '99'), '9999999999') as riskPoang FROM tablename Where upper(KODTYP) = 'OBJLIVSV_RISKVERKSAMTYP' ORDER BY ORDNING I get the correct result: Values Kod: Hög risk RiskPoäng: 55 Kod: Mellan risk RiskPoäng: 35 Kod: Låg risk RiskPoäng: 15 Kod: Mycket låg risk RiskPoäng: 5 Has anyone else experiences this? It's incredibly annoying and I'm completely stuck and not sure what to do next. We have a third party web service that use these tables so I must get the original SQL-statement to work since I can't modify its code. And pointers are greatly appreciated! :-) Best regards, Mats

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  • Concise C# code for gathering several properties with a non-null value into a collection?

    - by stakx
    A fairly basic problem for a change. Given a class such as this: public class X { public T A; public T B; public T C; ... // (other fields, properties, and methods are not of interest here) } I am looking for a concise way to code a method that will return all A, B, C, ... that are not null in an enumerable collection. (Assume that declaring these fields as an array is not an option.) public IEnumerable<T> GetAllNonNullAs(this X x) { // ? } The obvious implementation of this method would be: public IEnumerable<T> GetAllNonNullAs(this X x) { var resultSet = new List<T>(); if (x.A != null) resultSet.Add(x.A); if (x.B != null) resultSet.Add(x.B); if (x.C != null) resultSet.Add(x.C); ... return resultSet; } What's bothering me here in particular is that the code looks verbose and repetitive, and that I don't know the initial List capacity in advance. It's my hope that there is a more clever way, probably something involving the ?? operator? Any ideas?

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  • Objective-C subclass and base class casting

    - by ryanjm.mp
    I'm going to create a base class that implements very similar functions for all of the subclasses. This was answered in a different question. But what I need to know now is if/how I can cast various functions (in the base class) to return the subclass object. This is both for a given function but also a function call in it. (I'm working with CoreData by the way) As a function within the base class (this is from a class that is going to become my subclass) +(Structure *)fetchStructureByID:(NSNumber *)structureID inContext:(NSManagedObjectContext *)managedObjectContext {...} And as a function call within a given function: Structure *newStructure = [Structure fetchStructureByID:[currentDictionary objectForKey:@"myId"]]; inContext:managedObjectContext]; Structure is one of my subclasses, so I need to rewrite both of these so that they are "generic" and can be applied to other subclasses (whoever is calling the function). How do I do that? Update: I just realized that in the second part there are actually two issues. You can't change [Structure fetch...] to [self fetch...] because it is a class method, not an instance method. How do I get around that too?

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  • R: manipulating data.frames containing strings and booleans.

    - by Mike Dewar
    Hello. I have a data.frame in R; it's called p. Each element in the data.frame is either True or False. My variable p has, say, m rows and n columns. For every row there is strictly only one TRUE element. It also has column names, which are strings. What I would like to do is the following: For every row in p I see a TRUE I would like to replace with the name of the corresponding column I would then like to collapse the data.frame, which now contains FALSEs and column names, to a single vector, which will have m elements. I would like to do this in an R-thonic manner, so as to continue my enlightenment in R and contribute to a world without for-loops. I can do step 1 using the following for loop: for (i in seq(length(colnames(p)))) { p[p[,i]==TRUE,i]=colnames(p)[i] } but theres's no beauty here and I have totally subscribed to this for-loops-in-R-are-probably-wrong mentality. Maybe wrong is too strong but they're certainly not great. I don't really know how to do step 2. I kind of hoped that the sum of a string and FALSE would return the string but it doesn't. I kind of hoped I could use an OR operator of some kind but can't quite figure that out (Python responds to False or 'bob' with 'bob'). Hence, yet again, I appeal to you beautiful Rstats people for help!

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  • Is there really such a thing as a char or short in modern programming?

    - by Dean P
    Howdy all, I've been learning to program for a Mac over the past few months (I have experience in other languages). Obviously that has meant learning the Objective C language and thus the plainer C it is predicated on. So I have stumbles on this quote, which refers to the C/C++ language in general, not just the Mac platform. With C and C++ prefer use of int over char and short. The main reason behind this is that C and C++ perform arithmetic operations and parameter passing at integer level, If you have an integer value that can fit in a byte, you should still consider using an int to hold the number. If you use a char, the compiler will first convert the values into integer, perform the operations and then convert back the result to char. So my question, is this the case in the Mac Desktop and IPhone OS environments? I understand when talking about theses environments we're actually talking about 3-4 different architectures (PPC, i386, Arm and the A4 Arm variant) so there may not be a single answer. Nevertheless does the general principle hold that in modern 32 bit / 64 bit systems using 1-2 byte variables that don't align with the machine's natural 4 byte words doesn't provide much of the efficiency we may expect. For instance, a plain old C-Array of 100,000 chars is smaller than the same 100,000 ints by a factor of four, but if during an enumeration, reading out each index involves a cast/boxing/unboxing of sorts, will we see overall lower 'performance' despite the saved memory overhead?

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  • Syntactical analysis with Flex/Bison part 2

    - by Imran
    Hallo, I need help in Lex/Yacc Programming. I wrote a compiler for a syntactical analysis for inputs of many statements. Now i have a special problem. In case of an Input the compiler gives the right output, which statement is uses, constant operator or a jmp instructor to which label, now i have to write so, if now a if statement comes, first the first command (before the else) must be give out when the assignment of the if is yes then it must jump to the end because the command after the else isnt needed, so after this jmp then the second command must be give out. I show it in an example maybe you understand what i mean. Input adr. Output if(x==0) 10 if(x==0) Wait 5 20 WAIT 5 else 30 JMP 50 Wait 1 40 WAIT 1 end 50 END like so. I have an idea, maybe i can do it whith a special if statement like IF exp jmp_stmt_end stmt_seq END when the if statement is given in the input the compiler has to recognize the end ofthe statement and like my jmp_stmt in my compiler ( you have to download the files from http://bitbucket.org/matrix/changed-tiny) only to jump to the end. I hope you understand my problem.thanks.

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  • Reading Unicode files line by line C++

    - by Roger Nelson
    What is the correct way to read Unicode files line by line in C++? I am trying to read a file saved as Unicode (LE) by Windows Notepad. Suppose the file contains simply the characters A and B on separate lines. In reading the file byte by byte, I see the following byte sequence (hex) : FE FF 41 00 0D 00 0A 00 42 00 0D 00 0A 00 So 2 byte BOM, 2 byte 'A', 2byte CR , 2byte LF, 2 byte 'B', 2 byte CR, 2 byte LF . I tried reading the text file using the following code: std::wifstream file("test.txt"); file.seekg(2); // skip BOM std::wstring A_line; std::wstring B_line; getline(file,A_line); // I get "A" getline(file,B_line); // I get "\0B" I get the same results using operator instead of getline file >> A_line; file >> B_line; It appears that the single byte CR character is is being consumed only as the single byte. or CR NULL LF is being consumed but not the high byte NULL. I would expect wifstream in text mode would read the 2byte CR and 2byte LF. What am I doing wrong? It does not seem right that one should have to read a text file byte by byte in binary mode just to parse the new lines.

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  • Counting entries in a list of dictionaries: for loop vs. list comprehension with map(itemgetter)

    - by Dennis Williamson
    In a Python program I'm writing I've compared using a for loop and increment variables versus list comprehension with map(itemgetter) and len() when counting entries in dictionaries which are in a list. It takes the same time using a each method. Am I doing something wrong or is there a better approach? Here is a greatly simplified and shortened data structure: list = [ {'key1': True, 'dontcare': False, 'ignoreme': False, 'key2': True, 'filenotfound': 'biscuits and gravy'}, {'key1': False, 'dontcare': False, 'ignoreme': False, 'key2': True, 'filenotfound': 'peaches and cream'}, {'key1': True, 'dontcare': False, 'ignoreme': False, 'key2': False, 'filenotfound': 'Abbott and Costello'}, {'key1': False, 'dontcare': False, 'ignoreme': True, 'key2': False, 'filenotfound': 'over and under'}, {'key1': True, 'dontcare': True, 'ignoreme': False, 'key2': True, 'filenotfound': 'Scotch and... well... neat, thanks'} ] Here is the for loop version: #!/usr/bin/env python # Python 2.6 # count the entries where key1 is True # keep a separate count for the subset that also have key2 True key1 = key2 = 0 for dictionary in list: if dictionary["key1"]: key1 += 1 if dictionary["key2"]: key2 += 1 print "Counts: key1: " + str(key1) + ", subset key2: " + str(key2) Output for the data above: Counts: key1: 3, subset key2: 2 Here is the other, perhaps more Pythonic, version: #!/usr/bin/env python # Python 2.6 # count the entries where key1 is True # keep a separate count for the subset that also have key2 True from operator import itemgetter KEY1 = 0 KEY2 = 1 getentries = itemgetter("key1", "key2") entries = map(getentries, list) key1 = len([x for x in entries if x[KEY1]]) key2 = len([x for x in entries if x[KEY1] and x[KEY2]]) print "Counts: key1: " + str(key1) + ", subset key2: " + str(key2) Output for the data above (same as before): Counts: key1: 3, subset key2: 2 I'm a tiny bit surprised these take the same amount of time. I wonder if there's something faster. I'm sure I'm overlooking something simple. One alternative I've considered is loading the data into a database and doing SQL queries, but the data doesn't need to persist and I'd have to profile the overhead of the data transfer, etc., and a database may not always be available. I have no control over the original form of the data. The code above is not going for style points.

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  • Function with parameter type that has a copy-constructor with non-const ref chosen?

    - by Johannes Schaub - litb
    Some time ago I was confused by the following behavior of some code when I wanted to write a is_callable<F, Args...> trait. Overload resolution won't call functions accepting arguments by non-const ref, right? Why doesn't it reject in the following because the constructor wants a Test&? I expected it to take f(int)! struct Test { Test() { } // I want Test not be copyable from rvalues! Test(Test&) { } // But it's convertible to int operator int() { return 0; } }; void f(int) { } void f(Test) { } struct WorksFine { }; struct Slurper { Slurper(WorksFine&) { } }; struct Eater { Eater(WorksFine) { } }; void g(Slurper) { } void g(Eater) { } // chooses this, as expected int main() { // Error, why? f(Test()); // But this works, why? g(WorksFine()); } Error message is m.cpp: In function 'int main()': m.cpp:33:11: error: no matching function for call to 'Test::Test(Test)' m.cpp:5:3: note: candidates are: Test::Test(Test&) m.cpp:2:3: note: Test::Test() m.cpp:33:11: error: initializing argument 1 of 'void f(Test)' Can you please explain why one works but the other doesn't?

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  • DRYing out implementation of ICloneable in several classes

    - by Sarah Vessels
    I have several different classes that I want to be cloneable: GenericRow, GenericRows, ParticularRow, and ParticularRows. There is the following class hierarchy: GenericRow is the parent of ParticularRow, and GenericRows is the parent of ParticularRows. Each class implements ICloneable because I want to be able to create deep copies of instances of each. I find myself writing the exact same code for Clone() in each class: object ICloneable.Clone() { object clone; using (var stream = new MemoryStream()) { var formatter = new BinaryFormatter(); // Serialize this object formatter.Serialize(stream, this); stream.Position = 0; // Deserialize to another object clone = formatter.Deserialize(stream); } return clone; } I then provide a convenience wrapper method, for example in GenericRows: public GenericRows Clone() { return (GenericRows)((ICloneable)this).Clone(); } I am fine with the convenience wrapper methods looking about the same in each class because it's very little code and it does differ from class to class by return type, cast, etc. However, ICloneable.Clone() is identical in all four classes. Can I abstract this somehow so it is only defined in one place? My concern was that if I made some utility class/object extension method, it would not correctly make a deep copy of the particular instance I want copied. Is this a good idea anyway?

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  • Casting to specify unknown object type?

    - by fuzzygoat
    In the following code I have a view object that is an instance of UIScrollView, if I run the code below I get warnings saying that "UIView might not respond to -setContentSize etc." UIImage *image = [UIImage imageNamed:@"Snowy_UK.jpg"]; imageView = [[UIImageView alloc] initWithImage:image]; [[self view] addSubview:imageView]; [[self view] setContentSize:[image size]]; [[self view] setMaximumZoomScale:2.0]; [[self view] setMinimumZoomScale: [[self view] bounds].size.width / [image size].width]; I have checked the type of the object and [self view] is indeed a UIScrollView. I am guessing that this is just the compiler making a bad guess as to the type and the solution is simply to cast the object to the correct type manually, am I getting this right? UIScrollView *scrollView = (UIScrollView *)[self view]; UIImage *image = [UIImage imageNamed:@"Snowy_UK.jpg"]; imageView = [[UIImageView alloc] initWithImage:image]; [[self view] addSubview:imageView]; [scrollView setContentSize:[image size]]; [scrollView setMaximumZoomScale:2.0]; [scrollView setMinimumZoomScale: [scrollView bounds].size.width / [image size].width]; cheers Gary.

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  • Scala type inference failure on "? extends" in Java code

    - by oxbow_lakes
    I have the following simple Java code: package testj; import java.util.*; public class Query<T> { private static List<Object> l = Arrays.<Object>asList(1, "Hello", 3.0); private final Class<? extends T> clazz; public static Query<Object> newQuery() { return new Query<Object>(Object.class); } public Query(Class<? extends T> clazz) { this.clazz = clazz; } public <S extends T> Query<S> refine(Class<? extends S> clazz) { return new Query<S>(clazz); } public List<T> run() { List<T> r = new LinkedList<T>(); for (Object o : l) { if (clazz.isInstance(o)) r.add(clazz.cast(o)); } return r; } } I can call this from Java as follows: Query<String> sq = Query.newQuery().refine(String.class); //NOTE NO <String> But if I try and do the same from Scala: val sq = Query.newQuery().refine(classOf[String]) I get the following error: error: type mismatch found :lang.this.class[scala.this.Predef.String] required: lang.this.class[?0] forSome{ type ?0 <: ? } val sq = Query.newQuery().refine(classOf[String]) This is only fixed by the insertion of the correct type parameter! val sq = Query.newQuery().refine[String](classOf[String]) Why can't scala infer this from my argument? Note I am using Scala 2.7

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