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• Want to add a functional language to my toolchest. Haskell or Erlang?

  - by sean.johnson

  I've been an OO/procedural guy my whole career except in school where I did a lot of logic programming (Prolog). I work on an amazing variety of projects (freelancer) and so I don't want the tools I know and understand to hold me back from using the right tool for the job. I've decided I should know a functional programming language. I've narrowed the field to Haskell and Erlang. What are the pros and cons, advantages and disadvantages, and major trade offs of Haskell and Erlang? How do I decide in a rational way, which is the better path? This is a big time investment, so I'd like to chose wisely. Is there a good case to be made for something else entirely? F#, Scala Ocaml? (BTW, I'm normally a Ruby/C/Obj.C guy, so I'm not terribly impressed or dependent on the JVM as a runtime. It's completely neutral to me. It's a fine runtime, I don't hold it for or against a language. I don't use Microsoft products though, so a .NET runtime would be a negative.)

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• Sorting arrays in java

  - by user360706

  Write a static method in Java : public static void sortByFour (int[] arr) That receives as a paramater an array full of non-negative numbers (zero or positive) and sorts the array in the following way : In the beginning of the array all the numbers that devide by four without a remainder will appear. After them all the numbers in the array that devide by 4 with a remainder of 1 will appear. After them all the numbers in the array that devide by 4 with a remainder of 2 will appear. In the end of the array all the rest numbers (those who divide by 4 with the remainder 3) will appear. (The order of the numbers in each group doesn't matter) The method must be the most efficient it can. This is what I wrote but unfortunately it doesn't work well... :( public static void swap( int[] arr, int left, int right ) { int temp = arr[left]; arr[left] = arr[right]; arr[right] = temp; } public static void sortByFour( int[] arr ) { int left = 0; int right = ( arr.length - 1 ); int mid = ( arr.length / 2 ); while ( left < right ) { if ( ( arr[left] % 4 ) > ( arr[right] % 4 ) ) { swap( arr, left, right ); right--; } if ( ( arr[left] % 4 ) == ( arr[right] % 4 ) ) left++; else left++; } } Can someone please help me by fixing my code so that it will work well or rewriting it?

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• How do you unit-test a method with complex input-output

  - by Dan

  When you have a simple method, like for example sum(int x, int y), it is easy to write unit tests. You can check that method will sum correctly two sample integers, for example 2 + 3 should return 5, then you will check the same for some "extraordinary" numbers, for example negative values and zero. Each of these should be separate unit test, as a single unit test should contain single assert. What do you do when you have a complex input-output? Take a Xml parser for example. You can have a single method parse(String xml) that receives the String and returns a Dom object. You can write separate tests that will check that certain text node is parsed correctly, that attributes are parsed OK, that child node belongs to parent etc. For all these I can write a simple input, for example <root><child/></root> that will be used to check parent-child relationships between nodes and so on for the rest of expectations. Now, take a look at follwing Xml: <root> <child1 attribute11="attribute 11 value" attribute12="attribute 12 value">Text 1</child1> <child2 attribute21="attribute 21 value" attribute22="attribute 22 value">Text 2</child2> </root> In order to check that method worked correctly, I need to check many complex conditions, like that attribute11 and attribute12 belong to element1, that Text 1 belongs to child1 etc. I do not want to put more than one assert in my unit-test. How can I accomplish that?

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• Finding missing files by checksum

  - by grw

  Hi there, I'm doing a large data migration between two file systems (let's call them F1 and F2) on a Linux system which will necessarily involve copying the data verbatim into a differently-structured hierarchy on F2 and changing the file names. I'd like to write a script to generate a list of files which are in F1 but not in F2, i.e. the ones which weren't copied by the migration script into the new hierarchy, so that I can go back and migrate them manually. Unfortunately for reasons not worth going into, the migration script can't be modified to list files that it doesn't migrate. My question differs from this previously answered one because of the fact that I cannot rely on filenames as a comparison. I know the basic outline of the process would be: Generate a list of checksums for all files, recursing through F1 Do the same for F2 Compare the lists and generate a negative intersection of the checksums, ignoring the file names, to find files which are in F1 but not in F2. I'm kind of stuck getting past that stage, so I'd appreciate any pointers on which tools to use. I think I need to use the 'comm' command to compare the list of file checksums, but since md5sum, sha512sum and the like put the file name next to the checksum, I can't see a way to get it to bring me a useful comparison. Maybe awk is the way to go? I'm using Red Hat Enterprise Linux 5.x. Thanks.

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• Variable not accessible within an if statment

  - by Chris

  I have a variable which holds a score for a game. My variable is accessible and correct outside of an if statement but not inside as shown below score is declared at the top of the main.cpp and calculated in the display function which also contains the code below cout << score << endl; //works if(!justFinished){ cout << score << endl; // doesn't work prints a large negative number endTime = time(NULL); ifstream highscoreFile; highscoreFile.open("highscores.txt"); if(highscoreFile.good()){ highscoreFile.close(); }else{ std::ofstream outfile ("highscores.txt"); cout << score << endl; outfile << score << std::endl; outfile.close(); } justFinished = true; } cout << score << endl;//works

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• WPF: How do I bind a Control to a formula composed of several dependency properties?

  - by Pablo

  Hi all, I'm working on Expression Blend and I'm currently designing a custom control which has a Grid with 5 rows inside, and also has two Dependency properties: "Value", and "Maximum". Three of the rows have fixed height, and what I'm trying to do is set the remaining rows height to "Value/Maximum" and "1-Value/Maximum" respectively. How do I go and do that? When I set the height to "Value" it seems to react, but when I go and set it to "Value/Maximum" it stops working. I'm still a bit new around WPF, so there must be another way to achieve what I'm intending, but after searching I couln't find my problem elsewhere. Code: <Grid x:Name="LayoutRoot" Width="Auto" Background="Transparent"> <Grid.RowDefinitions> <RowDefinition Height="32"/> <RowDefinition Height="{Binding Path=(Value/Maximum), ElementName=UserControl, Mode=Default}"/> <RowDefinition Height="16"/> <RowDefinition Height="{Binding Path=(1-Value/Maximum), ElementName=UserControl, Mode=Default}"/> <RowDefinition Height="32"/> </Grid.RowDefinitions> (...) By the way, Value is always a not negative double less than or equal to Maximum; so the result of the division will be number between 0.0 a 1.0. I want a "star" instead of "pixel" row height.

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• Factorial function - design and test.

  - by lukas

  I'm trying to nail down some interview questions, so I stared with a simple one. Design the factorial function. This function is a leaf (no dependencies - easly testable), so I made it static inside the helper class. public static class MathHelper { public static int Factorial(int n) { Debug.Assert(n >= 0); if (n < 0) { throw new ArgumentException("n cannot be lower that 0"); } Debug.Assert(n <= 12); if (n > 12) { throw new OverflowException("Overflow occurs above 12 factorial"); } //by definition if (n == 0) { return 1; } int factorialOfN = 1; for (int i = 1; i <= n; ++i) { //checked //{ factorialOfN *= i; //} } return factorialOfN; } } Testing: [TestMethod] [ExpectedException(typeof(OverflowException))] public void Overflow() { int temp = FactorialHelper.MathHelper.Factorial(40); } [TestMethod] public void ZeroTest() { int factorialOfZero = FactorialHelper.MathHelper.Factorial(0); Assert.AreEqual(1, factorialOfZero); } [TestMethod] public void FactorialOf5() { int factOf5 = FactorialHelper.MathHelper.Factorial(5); Assert.AreEqual(120,factOf5); } [TestMethod] [ExpectedException(typeof(ArgumentException))] public void NegativeTest() { int factOfMinus5 = FactorialHelper.MathHelper.Factorial(-5); } I have a few questions: Is it correct? (I hope so ;) ) Does it throw right exceptions? Should I use checked context or this trick ( n 12 ) is ok? Is it better to use uint istead of checking for negative values? Future improving: Overload for long, decimal, BigInteger or maybe generic method? Thank you

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• How do I do a count on that meet a specific condition, dependent on several has_many relationships i

  - by Angela

  I have a Model Campaign. A Campaign has many Events. Each Event has an attribute :days. A Campaign also has_many Contacts. Each Contact as a :date_entered attribute. The from_today(contact,event) method returns a number, which is the number of days from the contact's :date_entered till today minus the event's :days. In other words, a positive number shows the number of days from today till the :days of the event is elapsed. If it is negative, if means that the number of days that has elapsed since the :date_entered is greater than the :days attribute of an event. In other words, the event is overdue. What I would like to be able to do is do campaign.overdue and this would result in a total number of contacts that have an overdue event. It shouldn't count multiple events for a single contact, just one contact. How do I do that? It seems like I would need to cycle through all the events for every contact and keep a counter but I'm assuming that there is a better way.

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• ArgumentOutOfRangeException was unhandled by user code - (ASP .net)

  - by ASr..

  I use a GridView to display the records from the database. Also i've attached a Hyperlink to the GridView using TemplateField. When I try to add "onclick" attribute to the HyperLink inside the RowDateBound event, I get the following error.. GridView1.DataKeys[e.Row.RowIndex].Value = 'GridView1.DataKeys[e.Row.RowIndex]' threw an exception of type 'System.ArgumentOutOfRangeException' Message = "Index was out of range. Must be non-negative and less than the size of the collection.\r\nParameter name: index" This is the coding inside the RowDataBound mentod.. protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e) { if (e.Row.RowType == DataControlRowType.DataRow) { HyperLink HyperLink1 = (HyperLink)e.Row.FindControl("HyperLink1"); //The following line makes the error HyperLink1.Attributes.Add("onclick", "ShowMyModalPopup('" + GridView1.DataKeys[e.Row.RowIndex].Value + "')"); } } This is "ShowMyModalPopup" function in javascript <script type="text/javascript"> function ShowMyModalPopup(userpk) { var modal = $find('ModalPopupExtender1'); modal.show(); WebService.FetchOneUser(userpk,DisplayResult); } </script> Can anyone please explain me why this error occurs.. Many thanks in advance..

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• Error in bisection method code in Matlab

  - by Amanda Collins

  I need to write a proper implementation of the bisection method, which means I must address all possible user input errors. Here is my code: function [x_sol, f_at_x_sol, N_iterations] = bisection(f, xn, xp, eps_f, eps_x) % solving f(x)=0 with bisection method % f is the function handle to the desired function, % xn and xp are borders of search, % f(xn)<0 and f(xp)>0 required, % eps_f defines how close f(x) should be to zero, % eps_x defines uncertainty of solution x if(f(xp) < 0) error('xp must be positive') end; if(f(xn)>0) error('xn must be negative') end; if (xn >= xp) error ('xn must be less than xp') end; xg=(xp+xn)/2; %initial guess fg=f(xg); % initial function evaluation N_iterations=1; while ( (abs(fg) > eps_f) & (abs(xg-xp) > eps_x) ) if (fg>0) xp=xg; else xn=xg; end xg=(xp+xn)/2; %update guess fg=f(xg); %update function evaluation N_iterations=N_iterations+1; end x_sol=xg; %solution is ready f_at_x_sol=fg; if (f_at_x_sol > eps_f) error('No convergence') end and here is the error message I receive when I try to test this in Matlab: >> bisection(x.^2, 2, -1, 1e-8, 1e-10) Attempted to access f(-1); index must be a positive integer or logical. Error in bisection (line 9) if(f(xp)<0) I was attempting to see if my error codes worked, but it doesn't look like they do. I get the same error when I try to test it on a function that should work.

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• F# How to tokenise user input: separating numbers, units, words?

  - by David White

  I am fairly new to F#, but have spent the last few weeks reading reference materials. I wish to process a user-supplied input string, identifying and separating the constituent elements. For example, for this input: XYZ Hotel: 6 nights at 220EUR / night plus 17.5% tax the output should resemble something like a list of tuples: [ ("XYZ", Word); ("Hotel:", Word); ("6", Number); ("nights", Word); ("at", Operator); ("220", Number); ("EUR", CurrencyCode); ("/", Operator); ("night", Word); ("plus", Operator); ("17.5", Number); ("%", PerCent); ("tax", Word) ] Since I'm dealing with user input, it could be anything. Thus, expecting users to comply with a grammar is out of the question. I want to identify the numbers (could be integers, floats, negative...), the units of measure (optional, but could include SI or Imperial physical units, currency codes, counts such as "night/s" in my example), mathematical operators (as math symbols or as words including "at" "per", "of", "discount", etc), and all other words. I have the impression that I should use active pattern matching -- is that correct? -- but I'm not exactly sure how to start. Any pointers to appropriate reference material or similar examples would be great.

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• Ruby integer to string key

  - by Gene

  A system I'm building needs to convert non-negative Ruby integers into shortest-possible UTF-8 string values. The only requirement on the strings is that their lexicographic order be identical to the natural order on integers. What's the best Ruby way to do this? We can assume the integers are 32 bits and the sign bit is 0. This is successful: (i >> 24).chr + ((i >> 16) & 0xff).chr + ((i >> 8) & 0xff).chr + (i & 0xff).chr But it appears to be 1) garbage-intense and 2) ugly. I've also looked at pack solutions, but these don't seem portable due to byte order. FWIW, the application is Redis hash field names. Building keys may be a performance bottleneck, but probably not. This question is mostly about the "Ruby way".

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• What data stucture should I use for BigInt class

  - by user1086004

  I would like to implement a BigInt class which will be able to handle really big numbers. I want only to add and multiply numbers, however the class should also handle negative numbers. I wanted to represent the number as a string, but there is a big overhead with converting string to int and back for adding. I want to implement addition as on the high school, add corresponding order and if the result is bigger than 10, add the carry to next order. Then I thought that it would be better to handle it as a array of unsigned long long int and keep the sign separated by bool. With this I'm afraid of size of the int, as C++ standard as far as I know guarantees only that int < float < double. Correct me if I'm wrong. So when I reach some number I should move in array forward and start adding number to the next array position. Is there any data structure that is appropriate or better for this? Thanks in advance.

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• 2-column table with two foreign keys. Performance/design question.

  - by Emanuel

  Hello everyone! I recently ran into a quite complex problem and after looking around a lot I couldn't find a solution to it. I've found answers to my questions many times before on stackoverflow.com, so I decided to post here. So I'm making a user/group managment system for a web-based project, and I'm storing all related data into a postgreSQL database. This system relies on three tables: USERS GROUPS GROUP_USERS The two first tables simply define all the users and all the groups on the site, and the last table, GROUP_USERS, stores the groups every user is part of. It only has two columns: USER_ID GROUP_ID Since every user can be a member of several groups, I decided to make a separate table for this purpose, rather than storing a comma separated column in the USERS-table. Now, both columns are foreign keys, and I want to make them both primary keys as well, this since each combination of USER_ID and GROUP_ID has to be unique, and if I give them the constraint UNIQUE pgAdmin tells me that each table should have at least one Primary key. But now I am stuck with what seems to be a lot of indexes and relations to a very small table only containing numbers. In the end, I want this table to be as fast as possible, even if containing tens of thousands of rows. Size on disk shouldn't be a problem since its just all numbers anyway, but it feels quite stupid to have a full-sized index refering to a smaller table. Should I stick with my current solution, store comma-separated values in a column in the USERS-table or is there any other solution I should be aware of. PS. I don't want to use an array-column, even if they are supported by postgreSQL. I want to be as generic as possible so I can switch database later on, if necessary. EDIT: I other words, will using a compound primary key and two foreign keys in one table with only two columns have a negative impact on performance rather than the opposite due to the size of the generated index? Thank you!

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• How do i find if an object is before or after a waypoint?

  - by BoMann Andersen

  Im working on a racing game for a school project. Using Visual studio 10 pro, and Irrlicht. Sorry for bad grammar ., and its my first question so not sure if its done right. How i want it to work is that i make waypoints at different points on the track, and then i run my waypoint check to see if a car is past its next waypoint (the next it "needs" to go past), if yes then it updates the next waypoint, else nothing. The way i hope this will work is, i make a vector from n to n+1, then find the vector that is perpendicular to the first vector at n. Then i see if the object is in front or behind that vector. I found a Gamedev.net forumpost that helped me make this function: void Engine::checkWaypoint(Vehicle* vehicle) { btVector3 vector = waypoints[vehicle->nextWaypoint]; // n btVector3 nextVector = waypoints[vehicle->nextWaypoint + 1]; // n+1 vector = nextVector - vector; // First vector btVector3 pos = btVector3(vehicle->position.X,vehicle->position.Y,vehicle->position.Z); float product = vector.dot(pos - waypoints[vehicle->nextWaypoint]); // positiv = before, negative = behind if(product < 0) vehicle->nextWaypoint += 1; } Current bugs with this is: Updates the nextwaypoint more then ones without going past a new point. When it gets to the end and resets, it stops triggering on the first waypoints. So my questions: Is this an good way to do this? Did i do it right?

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• Replace duplicate values in array with new randomly generated values

  - by RussellDias

  I have below a function (created by Gordon in a previous question that went unanswered) that creates an array with n amount of values. The sum of the array is equal to $max. function randomDistinctPartition($n, $max) { $partition= array(); for($i=1; $i < $n; $i++) { $maxSingleNumber = $max - $n; $partition[] = $number = rand(1, $maxSingleNumber); } $max -= $number; } $partition[] = $max; return $partition; } For example: If I set $n = 4 and $max = 30. Then I should get the following. array(5, 7, 10, 8); However, this function does not take into account duplicates and 0s. What I would like - and have been trying to accomplish - is to generate an array with unique numbers that add up to my predetermined variable $max. No Duplicate numbers and No 0 and/or negative integers.

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• Variable not accessible within and if statment

  - by Chris

  I have a variable which holds a score for a game. My variable is accessible and correct outside of an if statement but not inside as shown below cout << score << endl; //works if(!justFinished){ cout << score << endl; // doesn't work prints a large negative number endTime = time(NULL); ifstream highscoreFile; highscoreFile.open("highscores.txt"); if(highscoreFile.good()){ highscoreFile.close(); }else{ std::ofstream outfile ("highscores.txt"); cout << score << endl; outfile << score << std::endl; outfile.close(); } justFinished = true; } cout << score << endl;//works

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• How to style "form" field labels in Windows Phone 7?

  - by Jeremy Bell

  Is there any standards guidance on how to style field labels next to form fields in windows phone 7 silverlight applications? For example, let's say I have a StackPanel with the TextBlock label and a TextBox for data entry. Currently I am using the default TextBlock Margin included in the PhoneTextSubtleStyle ("12,0,12,0"), and using a Margin of "0,-12,0,0" to push the TextBox up closer to the label: <StackPanel HorizontalAlignment="Left"> <TextBlock VerticalAlignment="Center" Text="Name" Style="{StaticResource PhoneTextSubtleStyle}" /> <TextBox Text="{Binding ItemName, Mode=TwoWay}" TextChanged="TextBox_TextChanged" VerticalAlignment="Center" Width="433" Margin="0,-12,0,0" /> </StackPanel> Note that the TextBox seems to have some internal padding of 12 pixels to the left and right, so that the TextBlock label and the TextBox control visually line up perfectly on the left. The problem is, I see existing apps with widely varying conventions for field label styling. Some do not do the negative margin adjustment, like I have above. Some don't. Some appear to override the label TextBlock Margin so that it is indented an additional 12 pixels on the left (i.e. "24,0,12,0" instead of the default "12,0,12,0"). Some apps put the labels to the left of the fields themselves (I hate that). Is there some standard design guidance on field labels in Windows Phone 7? I read through the design template PDF and could only determine that the field labels should be upper case on the first word (preferably only one word labels), and should NOT have a colon at the end. I didn't see anything with regards to margins or alignment between the label and the field.

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• C++ gdb GUI

  - by HappyDude

  Briefly: Does anyone know of a GUI for gdb that brings it on par or close to the feature set you get in the more recent version of Visual C++? In detail: As someone who has spent a lot of time programming in Windows, one of the larger stumbling blocks I've found whenever I have to code C++ in Linux is that debugging anything using commandline gdb takes me several times longer than it does in Visual Studio, and it does not seem to be getting better with practice. Some things are just easier or faster to express graphically. Specifically, I'm looking for a GUI that: Handles all the basics like stepping over & into code, watch variables and breakpoints Understands and can display the contents of complex & nested C++ data types Doesn't get confused by and preferably can intelligently step through templated code and data structures while displaying relevant information such as the parameter types Can handle threaded applications and switch between different threads to step through or view the state of Can handle attaching to an already-started process or reading a core dump, in addition to starting the program up in gdb If such a program does not exist, then I'd like to hear about experiences people have had with programs that meet at least some of the bullet points. Does anyone have any recommendations? Edit: Listing out the possibilities is great, and I'll take what I can get, but it would be even more helpful if you could include in your responses: (a) Whether or not you've actually used this GUI and if so, what positive/negative feedback you have about it. (b) If you know, which of the above-mentioned features are/aren't supported Lists are easy to come by, sites like this are great because you can get an idea of people's personal experiences with applications.

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• new to lists on python

  - by user1762229

  This is my current code: while True: try: mylist = [0] * 7 for x in range(7): sales = float(input("Sales for day:")) mylist[x] = sales if sales < 0: print ("Sorry,invalid. Try again.") except: print ("Sorry, invalid. Try again.") else: break print (mylist) best = max(sales) worst = min(sales) print ("Your best day had", best, "in sales.") print ("Your worst day had", worst, "in sales.") When I run it I get this: Sales for day:-5 Sorry,invalid. Try again. Sales for day:-6 Sorry,invalid. Try again. Sales for day:-7 Sorry,invalid. Try again. Sales for day:-8 Sorry,invalid. Try again. Sales for day:-9 Sorry,invalid. Try again. Sales for day:-2 Sorry,invalid. Try again. Sales for day:-5 Sorry,invalid. Try again. [-5.0, -6.0, -7.0, -8.0, -9.0, -2.0, -5.0] Traceback (most recent call last): File "C:/Users/Si Hong/Desktop/HuangSiHong_assign9_part.py", line 45, in <module> best = max(sales) TypeError: 'float' object is not iterable I am not quite sure how to code it so that, the lists do NOT take in negative values, because I only want values 0 or greater. I am not sure how to solve the TypeError issue so that the min and max values will print as in my code My last issue is, if I want to find the average value of the seven inputs that an user puts in, how should I go about this in pulling the values out of the lists Thank you so much

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• IDENTITY_INSERT ON inside of cursor does not allow inserted id

  - by Mac

  I am trying to set some id's for a bunch of rows in a database where the id column is an identity. I've created a cursor to loop through the rows and update the ids with incrementing negative numbers (-1,-2,-3 etc). When I updated just one row turning on the IDENTITY_INSERT it worked fine but as soon as I try and use it in a cursor, it throws the following error. Msg 8102, Level 16, State 1, Line 22 Cannot update identity column 'myRowID'. DECLARE @MinId INT; SET @MinId = (SELECT MIN(myRowId) FROM myTable)-1; DECLARE myCursor CURSOR FOR SELECT myRowId FROM dbo.myTable WHERE myRowId > 17095 OPEN myCursor DECLARE @myRowId INT FETCH NEXT FROM myCursor INTO @myRowId WHILE (@@FETCH_STATUS <> -1) BEGIN SET IDENTITY_INSERT dbo.myTable ON; --UPDATE dbo.myTable --SET myRowId = @MinId --WHERE myRowId = @myRowId; PRINT (N'ID: ' + CAST(@myRowId AS VARCHAR(10)) + N' NewID: ' + CAST(@MinId AS VARCHAR(4))); SET @MinId = @MinId - 1; FETCH NEXT FROM myCursor INTO @myRowId END CLOSE myCursor DEALLOCATE myCursor GO SET IDENTITY_INSERT dbo.myTable OFF; GO Does anyone know what I'm doing wrong?

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• How to map string keys to unique integer IDs?

  - by Marek

  I have some data that comes regularily as a dump from a data souce with a string natural key that is long (up to 60 characters) and not relevant to the end user. I am using this key in a url. This makes urls too long and user unfriendly. I would like to transform the string keys into integers with the following requirements: The source dataset will change over time. The ID should be: non negative integer unique and constant even if the set of input keys changes preferrably reversible back to key (not a strong requirement) The database is rebuilt from scratch every time so I can not remember the already assigned IDs and match the new data set to existing IDs and generate sequential IDs for the added keys. There are currently around 30000 distinct keys and the set is constantly growing. How to implement a function that will map string keys to integer IDs? What I have thought about: 1. Built-in string.GetHashCode: ID(key) = Math.Abs(key.GetHashCode()) is not guaranteed to be unique (not reversible) 1.1 "Re-hashing" the built-in GetHashCode until a unique ID is generated to prevent collisions. existing IDs may change if something colliding is added to the beginning of the input data set 2. a perfect hashing function I am not sure if this can generate constant IDs if the set of inputs changes (not reversible) 3. translate to base 36/64/?? does not shorten the long keys enough What are the other options?

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• Changing direction of rotation Pygame

  - by czl

  How would you change the direction of a rotating image/rect in Pygame? Applying positive and negative degree values works but it seems to only be able to rotate one direction throughout my window. Is there a way to ensure a change in direction of rotation? Perhaps change up rotation of a spinning image every 5 seconds, or if able to change the direction of the spin when hitting a X or Y axis. I've added some code below. It seems like switching movement directions is easy with rect.move_ip as long as I specify a speed and have location clause, it does what I want. Unfortunately rotation is't like that. Here I'l adding angles to make sure it spins, but no matter what I try, I'm unable to negate the rotation. def rotate_image(self): #rotate image orig_rect = self.image.get_rect() rot_image = pygame.transform.rotate(self.image, self.angle) rot_rect = orig_rect.copy() rot_rect.center = rot_image.get_rect().center rot_image = rot_image.subsurface(rot_rect).copy() return rot_image def render(self): self.screen.fill(self.bg_color) self.rect.move_ip(0,5) #Y axis movement at 5 px per frame self.angle += 5 #add 5 anglewhen the rect has not hit one of the window self.angle %= 360 if self.rect.left < 0 or self.rect.right > self.width: self.speed[0] = -self.speed[0] self.angle = -self.angle #tried to invert the angle self.angle -= 5 #trying to negate the angle rotation self.angle %= 360 self.screen.blit(self.rotate_image(),self.rect) pygame.display.flip() I would really like to know how to invert rotation of a image. You may provide your own examples.

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• Practice of checking 'trueness' or 'equality' of conditional statements - does it really make sense?

  - by senthilkumar1033

  I remember many years back, when I was in school, one of my computer science teachers taught us that it was better to check for 'trueness' or 'equality' of a condition and not the negative stuff like 'inequality'. Let me elaborate - If a piece of conditional code can be written by checking whether an expression is true or false, we should check the 'trueness'. Example: Finding out whether a number is odd - it can be done in two ways: if ( num % 2 != 0 ) { // Number is odd } or if ( num % 2 == 1 ) { // Number is odd } When I was beginning to code, I knew that num % 2 == 0 implies the number is even, so I just put a ! there to check if it is odd. But he was like 'Don't check NOT conditions. Have the practice of checking the 'trueness' or 'equality' of conditions whenever possible.' And he recommended that I use the second piece of code. I am not for or against either but I just wanted to know - what difference does it make? Please don't reply 'Technically the output will be the same' - we ALL know that. Is it a general programming practice or is it his own programming practice that he is preaching to others?

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• Reverse wildcard search in codeigniter

  - by Andy Platt

  I am implementing a snippet-based content management system into my current project. Snippets can be associated with a page either by exact match of the full url falling back to a wildcard match on a partial url or finally a default snippet. To implement this I have a created table of page associations with a wildcard flag, the system first checks the current url against the non-wildcard associations and if it doesn't find a match it checks against the partial url's where the wildcard flag is set. In order to achieve this I am getting all the partial url's from the database and putting them into an array then walking the array to check for a match against the current url: protected function _check_wildcard($url = NULL) { if($url) { $q = $this->db->where('wildcard' ,'Y') ->from('content') ->get(); $wildcards = $q->result_array(); foreach($wildcards AS $wildcard) { if(strpos($url,$wildcard['url']) > 0) { return $wildcard['snipppet_id']; } } } else { return NULL; } } Can anyone suggest a better way to do this - preferably one that doesn't involve having to constantly download the full list of all the wildcards each time I load a page as I am afraid that this will have a negative effect on the scalability of the system down the line?

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