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• F# in ASP.NET, mathematics and testing

  - by DigiMortal

  Starting from Visual Studio 2010 F# is full member of .NET Framework languages family. It is functional language with syntax specific to functional languages but I think it is time for us also notice and study functional languages. In this posting I will show you some examples about cool things other people have done using F#. F# and ASP.NET As I am ASP/ASP.NET MVP I am – of course – interested in how people use different languages and technologies with ASP.NET. C# MVP Tomáš Petrícek writes about developing ASP.NET MVC applications using F#. He also shows how to use LINQ To SQL in F# (using F# PowerPack) and provides sample solution and Visual Studio 2010 template for F# MVC web applications. You may also find interesting how you can create controllers in F#. Excellent work, Tomáš! Vladimir Matveev has interesting example about how to use F# and ApplicationHost class to process ASP.NET requests ouside of IIS. This is simple and very straight-forward example and I strongly suggest you to take a look at it. Very cool example is project Strom in Codeplex. Storm is web services testing tool that is fully written on F#. Take a look at this site because Codeplex offers also source code besides binaries. Math Functional languages are strong in fields like mathematics and physics. When I wrote my C# example about BigInteger class I found out that recursive version of Fibonacci algorithm in C# is not performing well. In same time I made same experiment on F# and in F# there were no performance problems with recursive version. You can find F# version of Fibonacci algorithm from Bob Palmer’s blog posting Fibonacci numbers in F#. Although golden spiral is useful for solving many problems I looked for some practical code example and found one. Kean Walmsley published in his Through the Interface blog very interesting posting Creating Fibonacci spirals in AutoCAD using F#. There are also other cool examples you may be interested in. Using numerical components by Extreme Optimization  it is possible to make some numerical integration (quadrature method) using F# (also C# example is available). fsharp.it introduces factorials calculation on F#. Robert Pickering has made very good work on programming The Game of Life in Silverlight and F# – I definitely suggest you to try out this example as it is very illustrative too. Who wants something more complex may take a look at Newton basin fractal example in F# by Jonathan Birge. Testing After some searching and surfing I found out that there is almost everything available for F# to write tests and test your F# code. FsCheck - FsCheck is a port of Haskell's QuickCheck. Important parts of the manual for using FsCheck is almost literally "adapted" from the QuickCheck manual and paper. Any errors and omissions are entirely my responsibility. FsTest - This project is designed to Language Oriented Programming constructs around unit testing and behavior testing in F#. The goal of this project is to create a Domain Specific Language for testing F# code in a way that makes sense for functional programming. FsUnit - FsUnit makes unit-testing with F# more enjoyable. It adds a special syntax to your favorite .NET testing framework. xUnit.NET - xUnit.net is a developer testing framework, built to support Test Driven Development, with a design goal of extreme simplicity and alignment with framework features. It is compatible with .NET Framework 2.0 and later, and offers several runners: console, GUI, MSBuild, and Visual Studio integration via TestDriven.net, CodeRush Test Runner and Resharper. It also offers test project integration for ASP.NET MVC. Getting started Well, as a first thing you need Visual Studio 2010. Then take a look at these resources: F# samples @ MSDN Microsoft F# Developer Center @ MSDN F# Language Reference @ MSDN F# blog F# forums Real World Functional Programming: With Examples in F# and C# (Amazon) Happy F#-ing! :)

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• Information I need to know as a Java Developer [on hold]

  - by Woy

  I'm a java developer. I'm trying to get more knowledge to become a better programmer. I've listed a number of technologies to learn. Instead of what I've listed, what technologies would you suggest to learn as well for a Junior Java Developer? I realize, there's a lot of things to study. Java: - how a garbage collector works - resource management - network programming - TCP/IP HTTP - transactions, - consistency: interfaces, classes collections, hash codes, algorithms, comp. complexity concurrent programming: synchronizing, semafores steam management metability: thread-safety byte code manipulations, reflections, Aspect-Oriented Programming as base to understand frameworks such as Spring etc. Web stack: servlets, filters, socket programming Libraries: JDK, GWT, Apache Commons, Joda-Time, Dependency Injections: Spring, Nano Tools: IDE: very good knowledge - debugger - profiler - web analyzers: Wireshark, firebugs - unit testing SQL/Databases: Basics SELECTing columns from a table Aggregates Part 1: COUNT, SUM, MAX/MIN Aggregates Part 2: DISTINCT, GROUP BY, HAVING + Intermediate JOINs, ANSI-89 and ANSI-92 syntax + UNION vs UNION ALL x NULL handling: COALESCE & Native NULL handling Subqueries: IN, EXISTS, and inline views Subqueries: Correlated ITH syntax: Subquery Factoring/CTE Views Advanced Topics Functions, Stored Procedures, Packages Pivoting data: CASE & PIVOT syntax Hierarchical Queries Cursors: Implicit and Explicit Triggers Dynamic SQL Materialized Views Query Optimization: Indexes Query Optimization: Explain Plans Query Optimization: Profiling Data Modelling: Normal Forms, 1 through 3 Data Modelling: Primary & Foreign Keys Data Modelling: Table Constraints Data Modelling: Link/Corrollary Tables Full Text Searching XML Isolation Levels Entity Relationship Diagrams (ERDs), Logical and Physical Transactions: COMMIT, ROLLBACK, Error Handling

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• Improving long-polling Ajax performance

  - by Bears will eat you

  I'm writing a webapp (Firefox-compatible only) which uses long polling (via jQuery's ajax abilities) to send more-or-less constant updates from the server to the client. I'm concerned about the effects of leaving this running for long periods of time, say, all day or overnight. The basic code skeleton is this: function processResults(xml) { // do stuff with the xml from the server } function fetch() { setTimeout(function () { $.ajax({ type: 'GET', url: 'foo/bar/baz', dataType: 'xml', success: function (xml) { processResults(xml); fetch(); }, error: function (xhr, type, exception) { if (xhr.status === 0) { console.log('XMLHttpRequest cancelled'); } else { console.debug(xhr); fetch(); } } }); }, 500); } (The half-second "sleep" is so that the client doesn't hammer the server if the updates are coming back to the client quickly - which they usually are.) After leaving this running overnight, it tends to make Firefox crawl. I'd been thinking that this could be partially caused by a large stack depth since I've basically written an infinitely recursive function. However, if I use Firebug and throw a breakpoint into fetch, it looks like this is not the case. The stack that Firebug shows me is only about 4 or 5 frames deep, even after an hour. One of the solutions I'm considering is changing my recursive function to an iterative one, but I can't figure out how I would insert the delay in between Ajax requests without spinning. I've looked at the JS 1.7 "yield" keyword but I can't quite wrap my head around it, to figure out if it's what I need here. Is the best solution just to do a hard refresh on the page periodically, say, once every hour? Is there a better/leaner long-polling design pattern that won't put a hurt on the browser even after running for 8 or 12 hours? Or should I just skip the long polling altogether and use a different "constant update" pattern since I usually know how frequently the server will have a response for me?

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• Xapian gem failed to install on Mac OS X Snow Leopard + macports

  - by goodwill

  I have installed xapian-core + xapian-bindings with macports on snow leopard, then trying to install xapian gem fails: Building native extensions. This could take a while... ERROR: Error installing xapian: ERROR: Failed to build gem native extension. /opt/ruby-enterprise/bin/ruby extconf.rb ./configure --with-ruby checking for a BSD-compatible install... /usr/bin/install -c checking whether build environment is sane... yes checking for a thread-safe mkdir -p... ./install-sh -c -d checking for gawk... no checking for mawk... no checking for nawk... no checking for awk... awk checking whether make sets $(MAKE)... yes checking how to create a ustar tar archive... gnutar checking build system type... i386-apple-darwin10.3.0 checking host system type... i386-apple-darwin10.3.0 checking for style of include used by make... GNU checking for gcc... gcc checking for C compiler default output file name... a.out checking whether the C compiler works... yes checking whether we are cross compiling... no checking for suffix of executables... checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ISO C89... none needed checking dependency style of gcc... gcc3 checking for a sed that does not truncate output... /usr/bin/sed checking for grep that handles long lines and -e... /usr/bin/grep checking for egrep... /usr/bin/grep -E checking for ld used by gcc... /usr/libexec/gcc/i686-apple-darwin10/4.2.1/ld checking if the linker (/usr/libexec/gcc/i686-apple-darwin10/4.2.1/ld) is GNU ld... no checking for /usr/libexec/gcc/i686-apple-darwin10/4.2.1/ld option to reload object files... -r checking for BSD-compatible nm... /usr/bin/nm checking whether ln -s works... yes checking how to recognize dependent libraries... pass_all checking how to run the C preprocessor... gcc -E checking for ANSI C header files... yes checking for sys/types.h... yes checking for sys/stat.h... yes checking for stdlib.h... yes checking for string.h... yes checking for memory.h... yes checking for strings.h... yes checking for inttypes.h... yes checking for stdint.h... yes checking for unistd.h... yes checking dlfcn.h usability... yes checking dlfcn.h presence... yes checking for dlfcn.h... yes checking for g++... g++ checking whether we are using the GNU C++ compiler... yes checking whether g++ accepts -g... yes checking dependency style of g++... gcc3 checking how to run the C++ preprocessor... g++ -E checking the maximum length of command line arguments... 196608 checking command to parse /usr/bin/nm output from gcc object... ok checking for objdir... .libs checking for ar... ar checking for ranlib... ranlib checking for strip... strip checking for dsymutil... dsymutil checking for nmedit... nmedit checking for -single_module linker flag... yes checking for -exported_symbols_list linker flag... yes checking if gcc supports -fno-rtti -fno-exceptions... no checking for gcc option to produce PIC... -fno-common checking if gcc PIC flag -fno-common works... yes checking if gcc static flag -static works... no checking if gcc supports -c -o file.o... yes checking whether the gcc linker (/usr/libexec/gcc/i686-apple-darwin10/4.2.1/ld) supports shared libraries... yes checking dynamic linker characteristics... darwin10.3.0 dyld checking how to hardcode library paths into programs... immediate checking whether stripping libraries is possible... yes checking if libtool supports shared libraries... yes checking whether to build shared libraries... yes checking whether to build static libraries... no checking whether we are using the GNU C++ compiler... (cached) yes checking whether g++ accepts -g... (cached) yes checking dependency style of g++... (cached) gcc3 checking for xapian-config... /opt/local/bin/xapian-config checking /opt/local/bin/xapian-config works... yes checking whether to enable maintainer-specific portions of Makefiles... no checking for ruby1.8... no checking for ruby... /opt/ruby-enterprise/bin/ruby checking /opt/ruby-enterprise/bin/ruby version... ruby 1.8.7 (2009-06-12 patchlevel 174) [i686-darwin10.2.0], MBARI 0x6770, Ruby Enterprise Edition 2009.10 checking for /opt/ruby-enterprise/lib/ruby/1.8/i686-darwin10.2.0/ruby.h... yes checking ruby/io.h... no checking whether to use -fvisibility=hidden... yes configure: creating ./config.status config.status: creating Makefile config.status: creating xapian-version.h config.status: creating python/Makefile config.status: creating python/docs/Makefile config.status: creating php/Makefile config.status: creating php/docs/Makefile config.status: creating java/Makefile config.status: creating java/native/Makefile config.status: creating java/org/xapian/Makefile config.status: creating java/org/xapian/errors/Makefile config.status: creating java/org/xapian/examples/Makefile config.status: creating java-swig/Makefile config.status: creating tcl8/Makefile config.status: creating tcl8/docs/Makefile config.status: creating tcl8/pkgIndex.tcl config.status: creating csharp/Makefile config.status: creating csharp/docs/Makefile config.status: creating csharp/AssemblyInfo.cs config.status: creating ruby/Makefile config.status: creating ruby/docs/Makefile config.status: creating xapian-bindings.spec config.status: creating python/generate-python-exceptions config.status: creating config.h config.status: config.h is unchanged config.status: executing depfiles commands *** Building bindings for languages: ruby make make all-recursive Making all in ruby make all-recursive Making all in docs make all-am make[5]: Nothing to be done for `all-am'. /bin/sh ../libtool --tag=CXX --mode=compile g++ -DHAVE_CONFIG_H -I. -I.. -I/opt/ruby-enterprise/lib/ruby/1.8/i686-darwin10.2.0 -I/opt/ruby-enterprise/lib/ruby/1.8/i686-darwin10.2.0 -fno-strict-aliasing -Wall -Wno-unused -Wno-uninitialized -fvisibility=hidden -I/opt/local/include -g -O2 -MT xapian_wrap.lo -MD -MP -MF .deps/xapian_wrap.Tpo -c -o xapian_wrap.lo xapian_wrap.cc ../libtool: line 393: /bin/sed: No such file or directory ../libtool: line 393: /bin/sed: No such file or directory ../libtool: line 792: /bin/sed: No such file or directory : ignoring unknown tag ../libtool: line 792: /bin/sed: No such file or directory *** Warning: inferring the mode of operation is deprecated. *** Future versions of Libtool will require --mode=MODE be specified. ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1103: /bin/sed: No such file or directory ../libtool: line 1156: /bin/sed: No such file or directory : compile: cannot determine name of library object from `' make[4]: *** [xapian_wrap.lo] Error 1 make[3]: *** [all-recursive] Error 1 make[2]: *** [all] Error 2 make[1]: *** [all-recursive] Error 1 make: *** [all] Error 2 extconf.rb:3:in `system!': unhandled exception from extconf.rb:6 Gem files will remain installed in /opt/ruby-enterprise/lib/ruby/gems/1.8/gems/xapian-1.0.15 for inspection. Results logged to /opt/ruby-enterprise/lib/ruby/gems/1.8/gems/xapian-1.0.15/gem_make.out Any idea pal?

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• How to make xml in C#?

  - by kacalapy

  i have not worked with XML in a while can someone post the syntax needed to build and save an xml node structure that resembles that of a tree structure that is created by a recursive function. basically i have a recursive function that saves data found an a page(url) and then follows each URL found on that page recursivley and does the same to it. to audit this i want an output as a xml file to disk so i can see how it is doing its recursion and parsing. the code i have is below. please add to it the needed xml calls needed to create a xml structure like the one i show below. (please include the full name space so i can see where the objects i need in .net are for this.) page1.htm has 2 links on it: <a href=page1_1.htm> <a href=page1_2.htm> page1_1.htm has 2 links on it <a href=page1_1_a.htm> (this then will have some links also) <a href=page1_1_b.htm> (this then will have no more links on it - dead end) the xml should do something like this: <node url=page1.htm> ...<node url=page1_1_a.htm> ...... <node url="xxx.htm"/> ...... <node url="yyy.htm".> ... </node> ...<node url=page1_1_b.htm /> </node>

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• How to use Common Table Expression and check no duplication in SQL Server

  - by vodkhang

  I have a table references to itself. User table: id, username, managerid and managerid links back to id Now, I want to get all the managers including direct manager, manager of direct manager, so on and so forth... The problem is that I do not want to have a unstop recursive sql. So, I want to check if an id alreay in a list, I will not include it anymore. Here is my sql for that: with all_managers (id, username, managerid, idlist) as ( select u1.id, u1.username, u1.managerid, ' ' from users u1, users u2 where u1.id = u2.managerid and u2.id = 6 UNION ALL select u.id, u.username, u.managerid, idlist + ' ' + u.id from all_managers a, users u where a.managerid = u.id and charindex(cast(u.id as nvarchar(5)), idlist) != 0 ) select id, username from all_managers; The problem is that in this line: select u1.id, u1.username, u1.managerid, ' ' The SQL Server complains with me that I can not put ' ' as the initialized for idlist. nvarchar(40) does not work as well. I do not know how to declare it inside a common table expression like this one. Usually, in db2, I can just put varchar(40) My sample data: ID UserName ManagerID 1 admin 1 2 a 1 3 b 1 4 c 2 What I want to do is that I want to find all managers of c guy. The result should be: admin, a, b. Some of the user can be his manager (like admin) because the ManagerID does not allow NULL and some does not have direct manager. With common table expression, it can lead to an infinite recursive. So, I am also trying to avoid that situation by trying to not include the id twice. For example, in the 1st iteration, we already have id : 1, so, in the 2nd iteration and later on, 1 should never be allowed. I also want to ask if my current approach is good or not and any other solutions? Because if I have a big database with a deep hierarchy, I will have to initialize a big varchar to keep it and it consumes memory, right?

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• Regex For Finding Ctypes with Int32

  - by Stefan H

  (Hey all, I am looking for a little regex help... I am trying to find all CType(expression,Int32) s and replace them with CInt(expression) This, however, is proving quite difficult, considering there could be a nested Ctype(expression, Int32) within the regex match. Does anyone have any ideas for how to best go about doing this? Here is what I have now: Dim str As String = "CType((original.Width * CType((targetSize / CType(original.Height, Single)), Single)), Int32)" Dim exp As New Regex("CType\((.+), Int32\)") str = exp.Replace(str, "CInt($1)") But this will match the entire string and replace it. I was thinking of doing a recursive function to find the outer most match, and then work inwards, but that still presents a problem with things like CType(replaceChars(I), Int32)), Chr(CType(replacementChars(I), Int32) Any tips would be appreciated. Input returnString.Replace(Chr(CType(replaceChars(I), Int32)), Chr(CType(replacementChars(I), Int32))) Output: returnString.Replace(Chr(CInt(replaceChars(I))),Chr(CInt(replacementChars(I)))) Edit: Been working on it a little more and have a recursive function that I'm still working out the kinks in. Recursion + regex. it kinda hurts. Private Function FindReplaceCInts(ByVal strAs As String) As String System.Console.WriteLine(String.Format("Testing : {0}", strAs)) Dim exp As New Regex("CType\((.+), Int32\)") If exp.Match(strAs).Success Then For Each match As Match In exp.Matches(strAs) If exp.Match(match.Value.Substring(2)).Success Then Dim replaceT As String = match.Value.Substring(2) Dim Witht As String = FindReplaceCInts(match.Value.Substring(2)) System.Console.WriteLine(strAs.IndexOf(replaceT)) strAs.Replace(replaceT, Witht) End If Next strAs = exp.Replace(strAs, "CInt($1)") End If Return strAs End Function Cheers,

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• Using hash tables in racket

  - by user2963128

  Im working on an Ngrams program and im having trouble filling out my hash table. i want to write out a recursive function that will take the words and add them to the hash table. The way its supposed to work is given the data set 1 2 3 4 5 6 7 the first entry in the hash table should have a key of [1 2] and the data should be 3. The second entry should be: [2 3] and its data should be 4 and continuing on until the end of the text file. we are given a predefined function called readword that will simply return 1 word from the text. But im not sure how to make these calls overlap each other. The calls would look something like this if the data was hard coded in. (hash-set! (list "1" "2") 3 (hash-set! (list "2" "3") 4 2 calls that ive tried look like this (hash-set! Ngram-table(list((word1) (word2)) readword in))) (hash-set! Ngram-table(append((cdr data) word1)) readword in) apparently the in after readword is supposed to tell the computer that this is and input instead of an output or something like that. How would I call this to make the data in the key of the hashtable overlap like this? And what would the recursive call look like? edit: also we are not allowed to use assigment statements in this program.

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• stdexcept On Android

  - by David R.

  I'm trying to compile SoundTouch on Android. I started with this configure line: ./configure CPPFLAGS="-I/Volumes/android-build/mydroid/development/ndk/build/platforms/android-3/arch-arm/usr/include/" LDFLAGS="-Wl,-rpath-link=/Volumes/android-build/mydroid/development/ndk/build/platforms/android-3/arch-arm/usr/lib -L/Volumes/android-build/mydroid/development/ndk/build/platforms/android-3/arch-arm/usr/lib -nostdlib -lc" --host=arm-eabi --enable-shared=yes CFLAGS="-nostdlib -O3 -mandroid" host_alias=arm-eabi --no-create --no-recursion Because the Android NDK targets ARM, I also had to change the Makefile to remove the -msse2 flags to progress. When I run 'make', I get: /bin/sh ../../libtool --tag=CXX --mode=compile arm-eabi-g++ -DHAVE_CONFIG_H -I. -I../../include -I../../include -I/Volumes/android-build/mydroid/development/ndk/build/platforms/android-3/arch-arm/usr/include/ -O3 -fcheck-new -I../../include -g -O2 -MT FIRFilter.lo -MD -MP -MF .deps/FIRFilter.Tpo -c -o FIRFilter.lo FIRFilter.cpp libtool: compile: arm-eabi-g++ -DHAVE_CONFIG_H -I. -I../../include -I../../include -I/Volumes/android-build/mydroid/development/ndk/build/platforms/android-3/arch-arm/usr/include/ -O3 -fcheck-new -I../../include -g -O2 -MT FIRFilter.lo -MD -MP -MF .deps/FIRFilter.Tpo -c FIRFilter.cpp -o FIRFilter.o FIRFilter.cpp:46:21: error: stdexcept: No such file or directory FIRFilter.cpp: In member function 'virtual void soundtouch::FIRFilter::setCoefficients(const soundtouch::SAMPLETYPE*, uint, uint)': FIRFilter.cpp:177: error: 'runtime_error' is not a member of 'std' FIRFilter.cpp: In static member function 'static void* soundtouch::FIRFilter::operator new(size_t)': FIRFilter.cpp:225: error: 'runtime_error' is not a member of 'std' make[2]: *** [FIRFilter.lo] Error 1 make[1]: *** [all-recursive] Error 1 make: *** [all-recursive] Error 1 This isn't very surprising, since the -nostdlib flag was required. Android seems to have neither stdexcept nor stdlib. How can I get past this block of compiling SoundTouch? At a guess, there may be some flag I don't know about that I should use. I could refactor the code not to use stdexcept. There may be a way to pull in the original stdexcept source and reference that. I might be able to link to a precompiled stdexcept library.

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• Invert linear linked list

  - by ArtWorkAD

  Hi, a linear linked list is a set of nodes. This is how a node is defined (to keep it easy we do not distinguish between node an list): class Node{ Object data; Node link; public Node(Object pData, Node pLink){ this.data = pData; this.link = pLink; } public String toString(){ if(this.link != null){ return this.data.toString() + this.link.toString(); }else{ return this.data.toString() ; } } public void inc(){ this.data = new Integer((Integer)this.data + 1); } public void lappend(Node list){ Node child = this.link; while(child != null){ child = child.link; } child.link = list; } public Node copy(){ if(this.link != null){ return new Node(new Integer((Integer)this.data), this.link.copy()); }else{ return new Node(new Integer((Integer)this.data), null); } } public Node invert(){ Node child = this.link; while(child != null){ child = child.link; } child.link = this;.... } } I am able to make a deep copy of the list. Now I want to invert the list so that the first node is the last and the last the first. The inverted list has to be a deep copy. I started developing the invert function but I am not sure. Any Ideas? Update: Maybe there is a recursive way since the linear linked list is a recursive data structure. I would take the first element, iterate through the list until I get to a node that has no child and append the first element, I would repeat this for the second, third....

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• More FP-correct way to create an update sql query

  - by James Black

  I am working on access a database using F# and my initial attempt at creating a function to create the update query is flawed. let BuildUserUpdateQuery (oldUser:UserType) (newUser:UserType) = let buf = new System.Text.StringBuilder("UPDATE users SET "); if (oldUser.FirstName.Equals(newUser.FirstName) = false) then buf.Append("SET first_name='").Append(newUser.FirstName).Append("'" ) |> ignore if (oldUser.LastName.Equals(newUser.LastName) = false) then buf.Append("SET last_name='").Append(newUser.LastName).Append("'" ) |> ignore if (oldUser.UserName.Equals(newUser.UserName) = false) then buf.Append("SET username='").Append(newUser.UserName).Append("'" ) |> ignore buf.Append(" WHERE id=").Append(newUser.Id).ToString() This doesn't properly put a , between any update parts after the first, for example: UPDATE users SET first_name='Firstname', last_name='lastname' WHERE id=... I could put in a mutable variable to keep track when the first part of the set clause is appended, but that seems wrong. I could just create an list of tuples, where each tuple is oldtext, newtext, columnname, so that I could then loop through the list and build up the query, but it seems that I should be passing in a StringBuilder to a recursive function, returning back a boolean which is then passed as a parameter to the recursive function. Does this seem to be the best approach, or is there a better one?

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• Recursively MySQL Query

  - by Rachel

  How can I implement recursive MySQL Queries. I am trying to look for it but resources are not very helpful. Trying to implement similar logic. public function initiateInserts() { //Open Large CSV File(min 100K rows) for parsing. $this->fin = fopen($file,'r') or die('Cannot open file'); //Parsing Large CSV file to get data and initiate insertion into schema. $query = ""; while (($data=fgetcsv($this->fin,5000,";"))!==FALSE) { $query = $query + "INSERT INTO dt_table (id, code, connectid, connectcode) VALUES (" + $data[0] + ", " + $data[1] + ", " + $data[2] + ", " + $data[3] + ")"; } $stmt = $this->prepare($query); // Execute the statement $stmt->execute(); $this->checkForErrors($stmt); } @Author: Numenor Error Message: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '0' at line 1 This Approach inspired to look for an MySQL recursive query approach.

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• postgres stored procedure problem

  - by easyrider

  Hi all, Ich have a problem in postgres function: CREATE OR REPLACE FUNCTION getVar(id bigint) RETURNS TABLE (repoid bigint, suf VARCHAR, nam VARCHAR) AS $$ declare rec record; BEGIN FOR rec IN (WITH RECURSIVE children(repoobjectid,variant_of_object_fk, suffix, variantname) AS ( SELECT repoobjectid, variant_of_object_fk, '' as suffix,variantname FROM b2m.repoobject_tab WHERE repoobjectid = id UNION ALL SELECT repo.repoobjectid, repo.variant_of_object_fk, suffix || '..' , repo.variantname FROM b2m.repoobject_tab repo, children WHERE children.repoobjectid = repo.variant_of_object_fk) SELECT repoobjectid,suffix,variantname FROM children) LOOP RETURN next; END LOOP; RETURN; END; It can be compiled, but if y try to call it select * from getVar(18) I got 8 empty rows with 3 columns. If i execute the following part of procedure with hard-coded id parameter: WITH RECURSIVE children(repoobjectid,variant_of_object_fk, suffix, variantname) AS ( SELECT repoobjectid, variant_of_object_fk, '' as suffix,variantname FROM b2m.repoobject_tab WHERE repoobjectid = 18 UNION ALL SELECT repo.repoobjectid, repo.variant_of_object_fk, suffix || '..' , repo.variantname FROM b2m.repoobject_tab repo, children WHERE children.repoobjectid = repo.variant_of_object_fk) SELECT repoobjectid,suffix,variantname FROM children I got exactly, what i need 8 rows with data: repoobjectid suffix variantname 18 19 .. for IPhone 22 .. for Nokia 23 .... OS 1.0 and so on. What is going wrong ? Please help. Thanx in advance

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• Recursion in prepared statements

  - by Rob

  I've been using PDO and preparing all my statements primarily for security reasons. However, I have a part of my code that does execute the same statement many times with different parameters, and I thought this would be where the prepared statements really shine. But they actually break the code... The basic logic of the code is this. function someFunction($something) { global $pdo; $array = array(); static $handle = null; if (!$handle) { $handle = $pdo->prepare("A STATEMENT WITH :a_param"); } $handle->bindValue(":a_param", $something); if ($handle->execute()) { while ($row = $handle->fetch()) { $array[] = someFunction($row['blah']); } } return $array; } It looked fine to me, but it was missing out a lot of rows. Eventually I realised that the statement handle was being changed (executed with different param), which means the call to fetch in the while loop will only ever work once, then the function calls itself again, and the result set is changed. So I am wondering what's the best way of using PDO prepared statements in a recursive way. One way could be to use fetchAll(), but it says in the manual that has a substantial overhead. The whole point of this is to make it more efficient. The other thing I could do is not reuse a static handle, and instead make a new one every time. I believe that since the query string is the same, internally the MySQL driver will be using a prepared statement anyway, so there is just the small overhead of creating a new handle on each recursive call. Personally I think that defeats the point. Or is there some way of rewriting this?

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• [CODE GENERATION] How to generate DELETE statements in PL/SQL, based on the tables FK relations?

  - by The chicken in the kitchen

  Is it possible via script/tool to generate authomatically many delete statements based on the tables fk relations, using Oracle PL/SQL? In example: I have the table: CHICKEN (CHICKEN_CODE NUMBER) and there are 30 tables with fk references to its CHICKEN_CODE that I need to delete; there are also other 150 tables foreign-key-linked to that 30 tables that I need to delete first. Is there some tool/script PL/SQL that I can run in order to generate all the necessary delete statements based on the FK relations for me? (by the way, I know about cascade delete on the relations, but please pay attention: I CAN'T USE IT IN MY PRODUCTION DATABASE, because it's dangerous!) I'm using Oracle DataBase 10G R2. This is the result I've written, but it is not recursive: This is a view I have previously written, but of course it is not recursive! CREATE OR REPLACE FORCE VIEW RUN ( OWNER_1, CONSTRAINT_NAME_1, TABLE_NAME_1, TABLE_NAME, VINCOLO ) AS SELECT OWNER_1, CONSTRAINT_NAME_1, TABLE_NAME_1, TABLE_NAME, '(' || LTRIM ( EXTRACT (XMLAGG (XMLELEMENT ("x", ',' || COLUMN_NAME)), '/x/text()'), ',') || ')' VINCOLO FROM ( SELECT CON1.OWNER OWNER_1, CON1.TABLE_NAME TABLE_NAME_1, CON1.CONSTRAINT_NAME CONSTRAINT_NAME_1, CON1.DELETE_RULE, CON1.STATUS, CON.TABLE_NAME, CON.CONSTRAINT_NAME, COL.POSITION, COL.COLUMN_NAME FROM DBA_CONSTRAINTS CON, DBA_CONS_COLUMNS COL, DBA_CONSTRAINTS CON1 WHERE CON.OWNER = 'TABLE_OWNER' AND CON.TABLE_NAME = 'TABLE_OWNED' AND ( (CON.CONSTRAINT_TYPE = 'P') OR (CON.CONSTRAINT_TYPE = 'U')) AND COL.TABLE_NAME = CON1.TABLE_NAME AND COL.CONSTRAINT_NAME = CON1.CONSTRAINT_NAME --AND CON1.OWNER = CON.OWNER AND CON1.R_CONSTRAINT_NAME = CON.CONSTRAINT_NAME AND CON1.CONSTRAINT_TYPE = 'R' GROUP BY CON1.OWNER, CON1.TABLE_NAME, CON1.CONSTRAINT_NAME, CON1.DELETE_RULE, CON1.STATUS, CON.TABLE_NAME, CON.CONSTRAINT_NAME, COL.POSITION, COL.COLUMN_NAME) GROUP BY OWNER_1, CONSTRAINT_NAME_1, TABLE_NAME_1, TABLE_NAME; ... and it contains the error of using DBA_CONSTRAINTS instead of ALL_CONSTRAINTS...

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• Tail recursion and memoization with C#

  - by Jay

  I'm writing a function that finds the full path of a directory based on a database table of entries. Each record contains a key, the directory's name, and the key of the parent directory (it's the Directory table in an MSI if you're familiar). I had an iterative solution, but it started looking a little nasty. I thought I could write an elegant tail recursive solution, but I'm not sure anymore. I'll show you my code and then explain the issues I'm facing. Dictionary<string, string> m_directoryKeyToFullPathDictionary = new Dictionary<string, string>(); ... private string ExpandDirectoryKey(Database database, string directoryKey) { // check for terminating condition string fullPath; if (m_directoryKeyToFullPathDictionary.TryGetValue(directoryKey, out fullPath)) { return fullPath; } // inductive step Record record = ExecuteQuery(database, "SELECT DefaultDir, Directory_Parent FROM Directory where Directory.Directory='{0}'", directoryKey); // null check string directoryName = record.GetString("DefaultDir"); string parentDirectoryKey = record.GetString("Directory_Parent"); return Path.Combine(ExpandDirectoryKey(database, parentDirectoryKey), directoryName); } This is how the code looked when I realized I had a problem (with some minor validation/massaging removed). I want to use memoization to short circuit whenever possible, but that requires me to make a function call to the dictionary to store the output of the recursive ExpandDirectoryKey call. I realize that I also have a Path.Combine call there, but I think that can be circumvented with a ... + Path.DirectorySeparatorChar + .... I thought about using a helper method that would memoize the directory and return the value so that I could call it like this at the end of the function above: return MemoizeHelper( m_directoryKeyToFullPathDictionary, Path.Combine(ExpandDirectoryKey(database, parentDirectoryKey)), directoryName); But I feel like that's cheating and not going to be optimized as tail recursion. Any ideas? Should I be using a completely different strategy? This doesn't need to be a super efficient algorithm at all, I'm just really curious. I'm using .NET 4.0, btw. Thanks!

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• No idea how to solve SICP exercise 1.11

  - by Javier Badia

  This is not homework. Exercise 1.11: A function f is defined by the rule that f(n) = n if n<3 and f(n) = f(n - 1) + 2f(n - 2) + 3f(n - 3) if n 3. Write a procedure that computes f by means of a recursive process. Write a procedure that computes f by means of an iterative process. Implementing it recursively is simple enough. But I couldn't figure out how to do it iteratively. I tried comparing with the Fibonacci example given, but I didn't know how to use it as an analogy. So I gave up (shame on me) and Googled for an explanation, and I found this: (define (f n) (if (< n 3) n (f-iter 2 1 0 n))) (define (f-iter a b c count) (if (< count 3) a (f-iter (+ a (* 2 b) (* 3 c)) a b (- count 1)))) After reading it, I understand the code and how it works. But what I don't understand is the process needed to get from the recursive defintion of the function to this. I don't get how the code formed in someone's head. Could you explain the thought process needed to arrive at the solution?

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• What exactly is a reentrant function?

  - by eSKay

  Most of the times, the definition of reentrance is quoted from Wikipedia: A computer program or routine is described as reentrant if it can be safely called again before its previous invocation has been completed (i.e it can be safely executed concurrently). To be reentrant, a computer program or routine: Must hold no static (or global) non-constant data. Must not return the address to static (or global) non-constant data. Must work only on the data provided to it by the caller. Must not rely on locks to singleton resources. Must not modify its own code (unless executing in its own unique thread storage) Must not call non-reentrant computer programs or routines. How is safely defined? If a program can be safely executed concurrently, does it always mean that it is reentrant? What exactly is the common thread between the six points mentioned that I should keep in mind while checking my code for reentrant capabilities? Also, Are all recursive functions reentrant? Are all thread-safe functions reentrant? Are all recursive and thread-safe functions reentrant? While writing this question, one thing comes to mind: Are the terms like reentrance and thread safety absolute at all i.e. do they have fixed concrete definations? For, if they are not, this question is not very meaningful. Thanks!

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• Running a Model::find in for loop in cakephp v1.3

  - by Gaurav Sharma

  Hi all, How can I achieve the following result in cakephp: In my application a Topic is related to category, category is related to city and city is finally related to state in other words: topic belongs to category, category belongs to city , city belongs to state.. Now in the Topic controller's index action I want to find out all the topics and it's city and state. How can I do this. I can easily do this using a custom query ($this-Model-query() function ) but then I will be facing pagination difficulties. I tried doing like this function index() { $this->Topic->recursive = 0; $topics = $this->paginate(); for($i=0; $i<count($topics);$i++) { $topics[$i]['City'] = $this->Topic->Category->City->find('all', array('conditions' => array('City.id' => $topics[$i]['Category']['city_id']))); } $this->set(compact('messages')); } The method that I have adopted is not a good one (running query in a loop) Using the recursive property and setting it to highest value (2) will degrade performance and is not going to yield me state information. How shall I solve this ? Please help Thanks

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• string comparision and counting the key in target [closed]

  - by mesun

  Suppose we want to count the number of times that a key string appears in a target string. We are going to create two different functions to accomplish this task: one iterative, and one recursive. For both functions, you can rely on Python's find function - you should read up on its specifications to see how to provide optional arguments to start the search for a match at a location other than the beginning of the string. For example, find("atgacatgcacaagtatgcat","atgc") #returns the value 5, while find("atgacatgcacaagtatgcat","atgc",6) #returns the value 15, meaning that by starting the search at index 6, #the next match is found at location 15. For the recursive version, you will want to think about how to use your function on a smaller version of the same problem (e.g., on a smaller target string) and then how to combine the result of that computation to solve the original problem. For example, given you can find the first instance of a key string in a target string, how would you combine that result with invocation of the same function on a smaller target string? You may find the string slicing operation useful in getting substrings of string.

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• C# Recursion SumOfOnlyNeg Elements

  - by Chris

  Hello, A array gets filled up with random elements (negative and positive). Now i want to calculate the sum of ONLY the postive elements. Iterative there is no problem, but in the recursion version i can only get the sum of both negative and postive. How can i "check" in the recursive version that it only sums up the Postive elements? Best Regards. Iterative version: public int IterSomPosElem(int[] tabel, int n) { n = 0; for (int i = 0; i < tabel.Length; i++) { if (tabel[i] >= 0) { n += tabel[i]; } } return n; } Recursive version atm (sums up all the elements insteed, of only the positive) public int RecuSomPosElem(int[] tabel, int n) { if(n == 1) return tabel[0]; //stopCriterium else { return (tabel[n - 1] + RecuSomPosElem(tabel, n - 1)); // how to check, so it only sums up the postive elements and "ignores" the negative elements. } }

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• Efficient Multiplication of Varying-Length #s [Conceptual]

  - by Milan Patel

  Write the pseudocode of an algorithm that takes in two arbitrary length numbers (provided as strings), and computes the product of these numbers. Use an efficient procedure for multiplication of large numbers of arbitrary length. Analyze the efficiency of your algorithm. I decided to take the (semi) easy way out and use the Russian Peasant Algorithm. It works like this: a * b = a/2 * 2b if a is even a * b = (a-1)/2 * 2b + a if a is odd My pseudocode is: rpa(x, y){ if x is 1 return y if x is even return rpa(x/2, 2y) if x is odd return rpa((x-1)/2, 2y) + y } I have 3 questions: Is this efficient for arbitrary length numbers? I implemented it in C and tried varying length numbers. The run-time in was near-instant in all cases so it's hard to tell empirically... Can I apply the Master's Theorem to understand the complexity...? a = # subproblems in recursion = 1 (max 1 recursive call across all states) n / b = size of each subproblem = n / 1 - b = 1 (problem doesn't change size...?) f(n^d) = work done outside recursive calls = 1 - d = 0 (the addition when a is odd) a = 1, b^d = 1, a = b^d - complexity is in n^d*log(n) = log(n) this makes sense logically since we are halving the problem at each step, right? What might my professor mean by providing arbitrary length numbers "as strings". Why do that? Many thanks in advance

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• git submodule pull and commit automatically on webserver

  - by Lukas Oppermann

  I have the following setup, I am working on a project project with the submodule submodule. Whenever I push changes to github it sends a post request to update.php on the server. This php file executes a git command. Without submodules I can just do a git pull and everything is fine but with submodules it is much more difficult. I have this at the moment, but it does not do what I want. I should git pull the repo and update and pull the latest version of each submodule. <?php echo `git submodule foreach 'git checkout master; git pull; git submodule update --init --recursive; git commit -m "updating"' && git pull && git submodule foreach 'git add -A .' && git commit -m "updating to latest version including submodules" 2>&1s`; EDIT// Okay, I got it half way done. <?php echo `git submodule foreach 'git checkout master; git pull; git submodule update --init --recursive; git commit -am "updating"; echo "updated"' && git pull && git commit -am "updating to latest version including submodules" && echo 'updated'`; The echo prevents the script to stop because of non-zero returned. It works 100% fine when I run it from the console using php update.php. When github initialized the file, or I run it from the browser it still does not work. Any ideas?

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• Top n items in a List ( including duplicates )

  - by Krishnan

  Trying to find an efficient way to obtain the top N items in a very large list, possibly containing duplicates. I first tried sorting & slicing, which works. But this seems unnnecessary. You shouldn't need to sort a very large list if you just want the top 20 members. So I wrote a recursive routine which builds the top-n list. This also works, but is very much slower than the non-recursive one! Question: Which is my second routine (elite2) so much slower than elite, and how do I make it faster ? My code is attached below. Thanks. import scala.collection.SeqView import scala.math.min object X { def elite(s: SeqView[Int, List[Int]], k:Int):List[Int] = { s.sorted.reverse.force.slice(0,min(k,s.size)) } def elite2(s: SeqView[Int, List[Int]], k:Int, s2:List[Int]=Nil):List[Int] = { if( k == 0 || s.size == 0) s2.reverse else { val m = s.max val parts = s.force.partition(_==m) val whole = if( parts._1.size > 1) parts._1.tail:::parts._2 else parts._2 elite2( whole.view, k-1, m::s2 ) } } def main(args:Array[String]) = { val N = 1000000/3 val x = List(N to 1 by -1).flatten.map(x=>List(x,x,x)).flatten.view println(elite2(x,20)) println(elite(x,20)) } }

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• Insertion into BST without header Node JAVA

  - by Petiatil

  I am working on a recursive insertion method for a BST. This function is suppose to be a recursive helper method and is in a private class called Node. The Node class is in a class called BinarySearchTree which contains an instance variable for the root. When I am trying to insert an element, I get a NullPointerException at : this.left = insert(((Node)left).element); I am unsure about why this occurs. If I understand correctly, in a BST, I am suppose to insert the item at the last spot on the path transversed. Any help is appreciated! private class Node implements BinaryNode<E> { E item; BinaryNode<E> left, right; public BinaryNode<E> insert(E item) { int compare = item.compareTo(((Node)root).item); if(root == null) { root = new Node(); ((Node)root).item = item; } else if(compare < 0) { this.left = insert(((Node)left).item); } else if(compare > 0) { this.right = insert(((Node)right).item); } return root; } }

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