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• How do I get rid of these warnings?

  - by Brian Postow

  This is really several questions, but anyway... I'm working with a big project in XCode, relatively recently ported from MetroWorks (Yes, really) and there's a bunch of warnings that I want to get rid of. Every so often an IMPORTANT warning comes up, but I never look at them because there's too many garbage ones. So, if I can either figure out how to get XCode to stop giving the warning, or actually fix the problem, that would be great. Here are the warnings: It claims that <map.h> is antiquated. However, when I replace it with <map> my files don't compile. Evidently, there's something in map.h that isn't in map... this decimal constant is unsigned only in ISO C90 This is a large number being compared to an unsigned long. I have even cast it, with no effect. enumeral mismatch in conditional expression: <anonymous enum> vs <anonymous enum> This appears to be from a ?: operator. Possibly that the then and else branches don't evaluate to the same type? Except that in at least one case, it's (matchVp == NULL ? noErr : dupFNErr) And since those are both of type OSErr, which is mac defined... I'm not sure what's up. It also seems to come up when I have other pairs of mac constants... multi-character character constant This one is obvious. The problem is that I actually NEED multi-character constants... -fwritable-strings not compatible with literal CF/NSString I unchecked the "Strings are Read-Only" box in both the project and target settings... and it seems to have had no effect...

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• Specializing a class template constructor

  - by SilverSun

  I'm messing around with template specialization and I ran into a problem with trying to specialize the constructor based on what policy is used. Here is the code I am trying to get to work. #include <cstdlib> #include <ctime> class DiePolicies { public: class RollOnConstruction { }; class CallMethod { }; }; #include <boost/static_assert.hpp> #include <boost/type_traits/is_same.hpp> template<unsigned sides = 6, typename RollPolicy = DiePolicies::RollOnConstruction> class Die { // policy type check BOOST_STATIC_ASSERT(( boost::is_same<RollPolicy, DiePolicies::RollOnConstruction>::value || boost::is_same<RollPolicy, DiePolicies::CallMethod>::value )); unsigned m_die; unsigned random() { return rand() % sides; } public: Die(); void roll() { m_die = random(); } operator unsigned () { return m_die + 1; } }; template<unsigned sides> Die<sides, DiePolicies::RollOnConstruction>::Die() : m_die(random()) { } template<unsigned sides> Die<sides, DiePolicies::CallMethod>::Die() : m_die(0) { } ...\main.cpp(29): error C3860: template argument list following class template name must list parameters in the order used in template parameter list ...\main.cpp(29): error C2976: 'Die' : too few template arguments ...\main.cpp(31): error C3860: template argument list following class template name must list parameters in the order used in template parameter list Those are the errors I get in Microsoft Visual Studio 2010. I'm thinking either I can't figure out the right syntax for the specialization, or maybe it isn't possible to do it this way.

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• Template compiling errors on iPhone SDK 3.2

  - by Didier Malenfant

  I'm porting over some templated code from Windows and I'm hitting some compiler differences on the iPhone 3.2 SDK. Original code inside a class template's member function is: return BinarySearch<uint32, CSimpleKey<T> >(key); where BinarySearch is a method inherited from another template. This produces the following error: csimplekeytable.h:131: error: no matching function for call to 'BinarySearch(NEngine::uint32&)' The visual studio compiler seems to walk up the template hierarchy fine but gcc needs me to fully qualify where the function comes from (I have verified this by fixing the same issues with template member variables that way). So I now need to change this into: return CSimpleTable<CSimpleKey<T> >::BinarySearch<uint32, CSimpleKey<T> >(key); Which now produces the following error: csimplekeytable.h:132: error: expected primary-expression before ',' token csimplekeytable.h:132: error: expected primary-expression before '>' token After some head scratching, I believe what's going on here is that it's trying to resolve the '<' before BinarySearch as a 'Less Than' operator for some reason. So two questions: - Am I on the right path with my interpretation of the error? - How do I fix it? -D

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• How to use multifieldquery and filters in Lucene.net

  - by Khotu Nam

  I want to perform a multi field search on a lucene.net index but filter the results based on one of the fields. Here's what I'm currently doing: To index the fields the definitions are: doc.Add(new Field("id", id.ToString(), Field.Store.YES, Field.Index.UN_TOKENIZED)); doc.Add(new Field("title", title, Field.Store.NO, Field.Index.TOKENIZED)); doc.Add(new Field("summary", summary, Field.Store.NO, Field.Index.TOKENIZED, Field.TermVector.YES)); doc.Add(new Field("description", description, Field.Store.NO, Field.Index.TOKENIZED, Field.TermVector.YES)); doc.Add(new Field("distribution", distribution, Field.Store.NO, Field.Index.UN_TOKENIZED)); When I perform the search I do the following: MultiFieldQueryParser parser = new MultiFieldQueryParser(new string[]{"title", "summary", "description"}, analyzer); parser.SetDefaultOperator(QueryParser.Operator.AND); Query query = parser.Parse(text); BooleanQuery bq = new BooleanQuery(); TermQuery tq = new TermQuery(new Term("distribution", distribution)); bq.Add(tq, BooleanClause.Occur.MUST); Filter filter = new QueryFilter(bq); Hits hits = searcher.Search(query, filter); However, the result is always 0 hits. What am I doing wrong?

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• IEnumerable.Cast not calling cast overload

  - by Martin Neal

  I'm not understanding something about the way .Cast works. I have an explicit (though implicit also fails) cast defined which seems to work when I use it "regularly", but not when I try to use .Cast. Why? Here is some compilable code that demonstrates my problem. public class Class1 { public string prop1 { get; set; } public int prop2 { get; set; } public static explicit operator Class2(Class1 c1) { return new Class2() { prop1 = c1.prop1, prop2 = c1.prop2 }; } } public class Class2 { public string prop1 { get; set; } public int prop2 { get; set; } } void Main() { Class1[] c1 = new Class1[] { new Class1() {prop1 = "asdf",prop2 = 1}}; //works Class2 c2 = (Class2)c1[0]; //doesn't work: Compiles, but throws at run-time //InvalidCastException: Unable to cast object of type 'Class1' to type 'Class2'. Class2 c3 = c1.Cast<Class2>().First(); }

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• How do I construct a more complex single LINQ to XML query?

  - by Cyberherbalist

  I'm a LINQ newbie, so the following might turn out to be very simple and obvious once it's answered, but I have to admit that the question is kicking my arse. Given this XML: <measuresystems> <measuresystem name="SI" attitude="proud"> <dimension name="mass" dim="M" degree="1"> <unit name="kilogram" symbol="kg"> <factor name="hundredweight" foreignsystem="US" value="45.359237" /> <factor name="hundredweight" foreignsystem="Imperial" value="50.80234544" /> </unit> </dimension> </measuresystem> </measuresystems> I can query for the value of the conversion factor between kilogram and US hundredweight using the following LINQ to XML, but surely there is a way to condense the four successive queries into a single complex query? XElement mss = XElement.Load(fileName); IEnumerable<XElement> ms = from el in mss.Elements("measuresystem") where (string)el.Attribute("name") == "SI" select el; IEnumerable<XElement> dim = from e2 in ms.Elements("dimension") where (string)e2.Attribute("name") == "mass" select e2; IEnumerable<XElement> unit = from e3 in dim.Elements("unit") where (string)e3.Attribute("name") == "kilogram" select e3; IEnumerable<XElement> factor = from e4 in unit.Elements("factor") where (string)e4.Attribute("name") == "pound" && (string)e4.Attribute("foreignsystem") == "US" select e4; foreach (XElement ex in factor) { Console.WriteLine ((string)ex.Attribute("value")); }

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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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• 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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• Vehicle License Plate Detection

  - by Ash

  Hey all Basically for my final project at university, I'm developing a vehicle license plate detection application. Now I consider myself an intermediate programmer, however my mathematics knowledge lacks anything above secondary school, therefore producing detection formulae is basically impossible. I've spend a good amount of time looking up academic papers such as: http://www.scribd.com/doc/266575/Detecting-Vehicle-License-Plates-in-Images http://www.cic.unb.br/~mylene/PI_2010_2/ICIP10/pdfs/0003945.pdf http://www.eurasip.org/Proceedings/Eusipco/Eusipco2007/Papers/d3l-b05.pdf When it comes to the maths, I'm lost. Due to this testing various graphic images proved productive, for example: to However this approach is only catered to that particular image, and if the techniques were applied to different images, I'm sure a different, most likely poorer conversion would occur. I've read about a formula called the bottom hat morphology transform, which according to the first does the following: "Basically, the trans- formation keeps all the dark details of the picture, and eliminates everything else (including bigger dark regions and light regions)." Sadly I can't find much information on this, however the image within the documentation near the end of the report shows it's effectiveness. I'm aware this is complicated and vast, I'd just appreciate a little advice, even in terms of what transformation techniques I should focus on developing, or algorithm regarding edge detection or pixel detection. Few things I need to add Developing in C Sharp Confining the project to UK registration plates only I can basically choose the images to convert as a demonstration Thanks

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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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• Generic property- specify the type at runtime

  - by Lirik

  I was reading a question on making a generic property, but I'm a little confused at by the last example from the first answer (I've included the relevant code below): You have to know the type at compile time. If you don't know the type at compile time then you must be storing it in an object, in which case you can add the following property to the Foo class: public object ConvertedValue { get { return Convert.ChangeType(Value, Type); } } That's seems strange: it's converting the value to the specified type, but it's returning it as an object when the value was stored as an object. Doesn't the returned object still require un-boxing? If it does, then why bother with the conversion of the type? I'm also trying to make a generic property whose type will be determined at run time: public class Foo { object Value {get;set;} Type ValType{get;set;} Foo(object value, Type type) { Value = value; ValType = type; } // I need a property that is actually // returned as the specified value type... public object ConvertedValue { get { return Convert.ChangeType(Value, ValType); } } } Is it possible to make a generic property? Does the return property still require unboxing after it's accessed?

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• Trying to use HttpWebRequest to load a page in a file.

  - by Malcolm

  Hi, I have a ASP.NET MVC app that works fine in the browser. I am using the following code to be able to write the html of a retrieved page to a file. (This is to use in a PDF conversion component) But this code errors out continually but not in the browser. I get timeout errors sometimes asn 500 errors. Public Function GetPage(ByVal url As String, ByVal filename As String) As Boolean Dim request As HttpWebRequest Dim username As String Dim password As String Dim docid As String Dim poststring As String Dim bytedata() As Byte Dim requestStream As Stream Try username = "pdfuser" password = "pdfuser" docid = "docid=inv12154" poststring = String.Format("username={0}&password={1}&{2}", username, password, docid) bytedata = Encoding.UTF8.GetBytes(poststring) request = WebRequest.Create(url) request.Method = "Post" request.ContentLength = bytedata.Length request.ContentType = "application/x-www-form-urlencoded" requestStream = request.GetRequestStream() requestStream.Write(bytedata, 0, bytedata.Length) requestStream.Close() request.Timeout = 60000 Dim response As HttpWebResponse Dim responseStream As Stream Dim reader As StreamReader Dim sb As New StringBuilder() Dim line As String = String.Empty response = request.GetResponse() responseStream = response.GetResponseStream() reader = New StreamReader(responseStream, System.Text.Encoding.ASCII) line = reader.ReadLine() While (Not line Is Nothing) sb.Append(line) line = reader.ReadLine() End While File.WriteAllText(filename, sb.ToString()) Catch ex As Exception MsgBox(ex.Message) End Try Return True End Function

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• Flag bit computation and detection

  - by Majid

  Hi all, In some code I'm working on I should take care of ten independent parameters which can take one of two values (0 or 1). This creates 2^10 distinct conditions. Some of the conditions never occur and can be left out, but those which do occur are still A LOT and making a switch to handle all cases is insane. I want to use 10 if statements instead of a huge switch. For this I know I should use flag bits, or rather flag bytes as the language is javascript and its easier to work with a 10 byte string with to represent a 10-bit binary. Now, my problem is, I don't know how to implement this. I have seen this used in APIs where multiple-selectable options are exposed with numbers 1, 2, 4, 8, ... , n^(n-1) which are decimal equivalents of 1, 10, 100, 1000, etc. in binary. So if we make call like bar = foo(7), bar will be an object with whatever options the three rightmost flags enable. I can convert the decimal number into binary and in each if statement check to see if the corresponding digit is set or not. But I wonder, is there a way to determine the n-th digit of a decimal number is zero or one in binary form, without actually doing the conversion?

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• How to use a class's type as the type argument for an inherited collection property in C#

  - by Edelweiss Peimann

  I am trying to create a representation of various types of card that inherit from a generic card class and which all contain references to their owning decks. I tried re-declaring them, as suggested here, but it still won't convert to the specific card type. The code I currently have is as such: public class Deck<T> : List<T> where T : Card { void Shuffle() { throw new NotImplementedException("Shuffle not yet implemented."); } } public class Card { public Deck<Card> OwningDeck { get; set; } } public class FooCard : Card { public Deck<FooCard> OwningDeck { get { return (Deck<FooCard>)base.OwningDeck; } set { OwningDeck = value; } } } The compile-time error I am getting: Error 2 Cannot convert type 'Game.Cards.Deck' to 'Game.Cards.Deck' And a warning suggesting I use a new operator to specify that the hiding is intentional. Would doing so be a violation of convention? Is there a better way? My question to stackoverflow is this: Can what I am trying to do be done elegantly in the .NET type system? If so, can some examples be provided?

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• Problem importing Oracle .dmp file

  - by BitFiddler

  So I have looked at all the suggested ways of importing .dmp files and non of them seem to answer this question: where does the data go once you import it? Context: I created a user like so: SQL> create user IMPORTER identified by "12345"; SQL> grant connect, unlimited tablespace, resource to IMPORTER; I then ran the 'imp' command as follows: C:\>imp system/password FROMUSER=OVIEDOE TOUSER=IMPORTER file=c:\database1.dmp Now there were 9 .dmp files, after each one it asked me for the next one and then I received the message "Import terminated successfully with warnings." The warning was: Warning: the objects were exported by OVIEDOE, not by you import done in WE8MSWIN1252 character set and AL16UTF16 NCHAR character set export client uses WE8ISO8859P1 character set (possible charset conversion) IMP-00046: using FILESIZE value from export file of 2147483648 Now it says it was terminated successfully so my assumption (I am new to oracle so this may be wrong) is that the data was loaded. However, when I use SQL developer to connect to the database and look under the 'tables' node under the IMPORTER user, there is nothing there. What is going on? Did the data load? If so, where can I find it?

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• Why does Tex/Latex not speed up in subsequent runs?

  - by Debilski

  I really wonder, why even recent systems of Tex/Latex do not use any caching to speed up later runs. Every time that I fix a single comma*, calling Latex costs me about the same amount of time, because it needs to load and convert every single picture file. (* I know that even changing a tiny comma could affect the whole structure but of course, a well-written cache format could see the impact of that. Also, there might be situations where 100% correctness is not needed as long as it’s fast.) Is there something in the language of Tex which makes this complicated or impossible to accomplish or is it just that in the original implementation of Tex, there was no need for this (because it would have been slow anyway on those large computers)? But then on the other hand, why doesn’t this annoy other people so much that they’ve started a fork which has some sort of caching (or transparent conversion of Tex files to a format which is faster to parse)? Is there anything I can do to speed up subsequent runs of Latex? Except from putting all the stuff into chapterXX.tex files and then commenting them out?

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• C++0x rvalue references and temporaries

  - by Doug

  (I asked a variation of this question on comp.std.c++ but didn't get an answer.) Why does the call to f(arg) in this code call the const ref overload of f? void f(const std::string &); //less efficient void f(std::string &&); //more efficient void g(const char * arg) { f(arg); } My intuition says that the f(string &&) overload should be chosen, because arg needs to be converted to a temporary no matter what, and the temporary matches the rvalue reference better than the lvalue reference. This is not what happens in GCC and MSVC. In at least G++ and MSVC, any lvalue does not bind to an rvalue reference argument, even if there is an intermediate temporary created. Indeed, if the const ref overload isn't present, the compilers diagnose an error. However, writing f(arg + 0) or f(std::string(arg)) does choose the rvalue reference overload as you would expect. From my reading of the C++0x standard, it seems like the implicit conversion of a const char * to a string should be considered when considering if f(string &&) is viable, just as when passing a const lvalue ref arguments. Section 13.3 (overload resolution) doesn't differentiate between rvalue refs and const references in too many places. Also, it seems that the rule that prevents lvalues from binding to rvalue references (13.3.3.1.4/3) shouldn't apply if there's an intermediate temporary - after all, it's perfectly safe to move from the temporary. Is this: Me misreading/misunderstand the standard, where the implemented behavior is the intended behavior, and there's some good reason why my example should behave the way it does? A mistake that the compiler vendors have somehow all made? Or a mistake based on common implementation strategies? Or a mistake in e.g. GCC (where this lvalue/rvalue reference binding rule was first implemented), that was copied by other vendors? A defect in the standard, or an unintended consequence, or something that should be clarified?

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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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• 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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• Use interface between model and view in ASP.NET MVC

  - by Icerman

  Hi, I am using asp.net MVC 2 to develop a site. IUser is used to be the interface between model and view for better separation of concern. However, things turn to a little messy here. In the controller that handles user sign on: I have the following: IUserBll userBll = new UserBll(); IUser newUser = new User(); newUser.Username = answers[0].ToString(); newUser.Email = answers[1].ToString(); userBll.AddUser(newUser); The User class is defined in web project as a concrete class implementing IUser. There is a similar class in DAL implementing the same interface and used to persist data. However, when the userBll.AddUser is called, the newUser of type User can't be casted to the DAL User class even though both Users class implementing the interface (InvalidCastException). Using conversion operators maybe an option, but it will make the dependency between DAL and web which is against the initial goal of using interface. Any suggestions?

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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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• Get the equivalent time between "dynamic" time zones

  - by doctore

  I have a table providers that has three columns (containing more columns but not important in this case): starttime, start time in which you can contact him. endtime, final hour in which you can contact him. region_id, region where the provider resides. In USA: California, Texas, etc. In UK: England, Scotland, etc starttime and endtime are time without timezone columns, but, "indirectly", their value has time zone of the region in which the provider resides. For example: starttime | endtime | region_id (time zone of region) | "real" st | "real" et ----------|----------|---------------------------------|-----------|----------- 03:00:00 | 17:00:00 | 1 (EGT => -1) | 02:00:00 | 16:00:00 Often I need to get the list of suppliers whose time range is within the current server time (taking into account the time zone conversion). The problem is that the time zones aren't "constant", ie, they may change during the summer time. However, this change is very specific to the region and not always carried out at the same time: EGT <= EGST, ART <= ARST, etc. The question is: 1. Is it necessary to use a webservice to update every so often the time zones in the regions? Does anyone know of a web service that can serve? 2. Is there a better approach to solve this problem? Thanks in advance. UPDATE I will give an example to clarify what I'm trying to get. In the table providers I found this records: idproviders | starttime | endtime | region_id ------------|-----------|----------|----------- 1 | 03:00:00 | 17:00:00 | 23 (Texas) 2 | 04:00:00 | 18:00:00 | 23 (Texas) If I execute the query in January, with this information: Server time (UTC offset) = 0 hours Texas providers (UTC offset) = +1 hour Server time = 02:00:00 I should get the following results: idproviders = 1 If I execute the query in June, with this information: Server time (UTC offset) = 0 hours Texas providers (UTC offset) = +2 hours (their local time has not changed, but their time zone has changed) Server time = 02:00:00 I should get the following results: idproviders = 1 and 2

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• floating point equality in Python and in general

  - by eric.frederich

  I have a piece of code that behaves differently depending on whether I go through a dictionary to get conversion factors or whether I use them directly. The following piece of code will print 1.0 == 1.0 -> False But if you replace factors[units_from] with 10.0 and factors[units_to ] with 1.0 / 2.54 it will print 1.0 == 1.0 -> True #!/usr/bin/env python base = 'cm' factors = { 'cm' : 1.0, 'mm' : 10.0, 'm' : 0.01, 'km' : 1.0e-5, 'in' : 1.0 / 2.54, 'ft' : 1.0 / 2.54 / 12.0, 'yd' : 1.0 / 2.54 / 12.0 / 3.0, 'mile' : 1.0 / 2.54 / 12.0 / 5280, 'lightyear' : 1.0 / 2.54 / 12.0 / 5280 / 5.87849981e12, } # convert 25.4 mm to inches val = 25.4 units_from = 'mm' units_to = 'in' base_value = val / factors[units_from] ret = base_value * factors[units_to ] print ret, '==', 1.0, '->', ret == 1.0 Let me first say that I am pretty sure what is going on here. I have seen it before in C, just never in Python but since Python in implemented in C we're seeing it. I know that floating point numbers will change values going from a CPU register to cache and back. I know that comparing what should be two equal variables will return false if one of them was paged out while the other stayed resident in a register. Questions What is the best way to avoid problems like this?... In Python or in general. Am I doing something completely wrong? Side Note This is obviously part of a stripped down example but what I'm trying to do is come with with classes of length, volume, etc that can compare against other objects of the same class but with different units. Rhetorical Questions If this is a potentially dangerous problem since it makes programs behave in an undetermanistic matter, should compilers warn or error when they detect that you're checking equality of floats Should compilers support an option to replace all float equality checks with a 'close enough' function? Do compilers already do this and I just can't find the information.

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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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• 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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