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  • Convert.ToSingle() for float data Type

    - by Asim Sajjad
    I have used many of the Convert.To..... functions for conversion , but I didn't understand one thing that for every datatype they have provide a Convert.To function but not for float datatype, in order to convert to float you need to use Convert.ToSingle() , why is this so ?

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  • algorithm - How to sort a 0/1 array with 2n/3 comparisons?

    - by Jackson Tale
    In Algorithm Design Manual, there is such an excise 4-26 Consider the problem of sorting a sequence of n 0’s and 1’s using comparisons. For each comparison of two values x and y, the algorithm learns which of x < y, x = y, or x y holds. (a) Give an algorithm to sort in n - 1 comparisons in the worst case. Show that your algorithm is optimal. (b) Give an algorithm to sort in 2n/3 comparisons in the average case (assuming each of the n inputs is 0 or 1 with equal probability). Show that your algorithm is optimal. For (a), I think it is fairly easy. I can choose a[n-1] as pivot, then do something like in quicksort partition, scan 0 to n - 2, find the middle point where left side is all 0 and right side is all 1, this take n - 1 comparisons. But for (b), I can't get a clue. It says "each of the n inputs is 0 or 1 with equal probability", so I guess I can assume the numbers of 0 and 1 equal? But how can I get a result which is related to 1/3? divide the whole array into 3 groups? Thanks

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  • IndexOutOfRangeException when a stream is a multiple of the buffer size

    - by dnord
    I don't have a lot of experience with streams and buffers, but I'm having to do it for a project, and I'm stuck on an exception being thrown when the stream I'm reading is a multiple of the buffer size I've chosen. Let me show you: My code starts by reading bufferSize (100, let's say) bytes from the stream: numberOfBytesRead = DataReader.GetBytes(0, index, output, 0, bufferSize); Then, I loop through a while loop: while (numberOfBytesRead == bufferSize) { BufferWriter.Write(output); BufferWriter.Flush(); index += bufferSize; numberOfBytesRead = DataReader.GetBytes(0, index, output, 0, bufferSize); } ... and, once we get to a non-bufferSize read, we know we've hit the end of the stream and can move on. But if the bufferSize is 100, and the stream is 200, we'll read positions 0-99, 100-199, and then the attempt to read 200-299 errors out. I'd like it if it returned 0, but it throws an error. What I'm doing to handle that is, well, a try-catch: catch (System.IndexOutOfRangeException) numberOfBytesRead = 0; ...which ends the loop, and successfully finishes the thing, but we all know I don't want to control code flow with error handling. Is there a better (more standard?) way to handle stream reading when the stream length is unknown? This seems like a small wrinkle in a fairly reasonable strategy for reading streams, but I just don't know if I've got it wrong or what. The specifics of this (which I've cleaned up a little bit for posting) are a MySqlDataReader hitting a LARGEBLOB column. It's working whenever the buffer is larger than the number of returned bytes, or when the number of returned bytes is not a multiple of bufferSize. Because we don't, in that case, throw an IndexOutOfRangeException.

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  • HTML forms and passing data back

    - by coLOLtip
    My html form is spreading over several pages (steps), and I want to let the use to take step back in case they would like to change something they filled in. So, I don't want to make users re-type all the information they already have typed once. Thus, how would I make it so that all the information would go back, to speak so? (I use PHP on server-side.)

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  • What techniques are available for filtering collections of objects when using zodb?

    - by Omega
    As the title says: What techniques are available for filtering objects when using zodb? The equivalent in SQL terms would be something like filtering results by a date range. Or only returning rows with a particular value set in a column. If I had a series of blog posts and only wanted ones done in the past month, what would I have to do? Is there any way to optimize these kinds of "queries"? My gut tells me iterating over all the objects in a relationship simply to perform a test is less than optimal.

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  • How do I remove the leaves of a binary tree?

    - by flopex
    I'm trying to remove all of the leaves. I know that leaves have no children, this is what I have so far. public void removeLeaves(BinaryTree n){ if (n.left == null && n.right == null){ n = null; } if (n.left != null) removeLeaves(n.left); if (n.right != null) removeLeaves(n.right); }

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  • Iterative printing over two data types in Python

    - by old Ixfoxleigh
    I often browse freely-available art on the web. Actually, I can't think of a better use for the internet than to turn it into a gigantic art gallery. When I encounter a set of pieces I quite like, I download them all to my hard drive. wget makes that easy, especially in combination with Python's print function, and I use this all the time to make a list of URLs that I then wget. Say I need to download a list of jpegs that run from art0 to art100 in the directory 'art,' I just tell python for i in range(0,101): print "http://somegallery/somedirectory/art", i So, this is probably a fairly simple operation in Python, and after a find-and-replace to remove whitespace, it's just a matter of using wget -i, but in days before I knew any Python I'd slavishly right-click and save. Now I've got a bunch of files from Fredericks & Freiser gallery in New York that all go a(1-14), b(1-14), c(1-14), etc., up to the letter g. I could do that in 7 goes, and it would take me less time than it took to write this SO question. That said, I want to deepen my knowledge of Python. So, given the letters a-g, how do I print a mapping of each letter to the integers 1-14?

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  • Pass form data from block to a page view in Drupal

    - by abdesignuk
    I am using the location module and views module for a postcode search, which works fine in a page display using views. However I want the user to be able to enter their postcode into a block on the homepage and clicking submit my module sends them to the page created in views and the postcode is set as a session S_SESSION['postcode'] before sending to this page, next I want the location page to load but using the session to display the locations automatically. Any ideas I am using hook_form_submit() and inside that declaring the $form_state as a session and then using $form_state['redirect'] to sent to the views page path.

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  • MATLAB: draw centroids

    - by Myx
    Hello - my main question is given a feature centroid, how can I draw it in MATLAB? In more detail, I have an NxNx3 image (an rgb image) of which I take 4x4 blocks and compute a 6-dimensional feature vector for each block. I store these feature vectors in an Mx6 matrix on which I run kmeans function and obtain the centroids in a kx6 matrix, where k is the number of clusters and 6 is the number of features for each block. How can I draw these center clusters in my image in order to visualize if the algorithm is performing the way I wish it to perform? Or if anyone has any other way/suggestions on how I can visualize the centroids on my image, I'd greatly appreciate it. Thank you.

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  • Basic data alignment question

    - by Broken Logic
    I've been playing around to see how my computer works under the hood. What I'm interested in is seeing is what happens on the stack inside a function. To do this I've written the following toy program: #include <stdio.h> void __cdecl Test1(char a, unsigned long long b, char c) { char c1; unsigned long long b1; char a1; c1 = 'b'; b1 = 4; a1 = 'r'; printf("%d %d - %d - %d %d Total: %d\n", (long)&b1 - (long)&a1, (long)&c1 - (long)&b1, (long)&a - (long)&c1, (long)&b - (long)&a, (long)&c - (long)&b, (long)&c - (long)&a1 ); }; struct TestStruct { char a; unsigned long long b; char c; }; void __cdecl Test2(char a, unsigned long long b, char c) { TestStruct locals; locals.a = 'b'; locals.b = 4; locals.c = 'r'; printf("%d %d - %d - %d %d Total: %d\n", (long)&locals.b - (long)&locals.a, (long)&locals.c - (long)&locals.b, (long)&a - (long)&locals.c, (long)&b - (long)&a, (long)&c - (long)&b, (long)&c - (long)&locals.a ); }; int main() { Test1('f', 0, 'o'); Test2('f', 0, 'o'); return 0; } And this spits out the following: 9 19 - 13 - 4 8 Total: 53 8 8 - 24 - 4 8 Total: 52 The function args are well behaved but as the calling convention is specified, I'd expect this. But the local variables are a bit wonky. My question is, why wouldn't these be the same? The second call seems to produce a more compact and better aligned stack. Looking at the ASM is unenlightening (at least to me), as the variable addresses are still aliased there. So I guess this is really a question about the assembler itself allocates the stack to local variables. I realise that any specific answer is likely to be platform specific. I'm more interested in a general explanation unless this quirk really is platform specific. For the record though, I'm compiling with VS2010 on a 64bit Intel machine.

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  • Can not issue data manipulation statements with executeQuery in java

    - by user225269
    I'm trying to insert records in mysql database using java, What do I place in this code so that I could insert records: String id; String name; String school; String gender; String lang; Scanner inputs = new Scanner(System.in); System.out.println("Input id:"); id=inputs.next(); System.out.println("Input name:"); name=inputs.next(); System.out.println("Input school:"); school= inputs.next(); System.out.println("Input gender:"); gender= inputs.next(); System.out.println("Input lang:"); lang=inputs.next(); Class.forName("com.mysql.jdbc.Driver"); Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/employee_record", "root", "MyPassword"); PreparedStatement statement = con.prepareStatement("insert into employee values('id', 'name', 'school', 'gender', 'lang');"); statement.executeUpdate();

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  • Tree-like queues

    - by Rehno Lindeque
    I'm implementing a interpreter-like project for which I need a strange little scheduling queue. Since I'd like to try and avoid wheel-reinvention I was hoping someone could give me references to a similar structure or existing work. I know I can simply instantiate multiple queues as I go along, I'm just looking for some perspective by other people who might have better ideas than me ;) I envision that it might work something like this: The structure is a tree with a single root. You get a kind of "insert_iterator" to the root and then push elements onto it (e.g. a and b in the example below). However, at any point you can also split the iterator into multiple iterators, effectively creating branches. The branches cannot merge into a single queue again, but you can start popping elements from the front of the queue (again, using a kind of "visitor_iterator") until empty branches can be discarded (at your discretion). x -> y -> z a -> b -> { g -> h -> i -> j } f -> b Any ideas? Seems like a relatively simple structure to implement myself using a pool of circular buffers but I'm following the "think first, code later" strategy :) Thanks

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  • Re-load Android activity data

    - by rhinds
    Hi, I am writing an Android app, part of which will be a survey involving multiple pages of checkbox question and answers. I have created an activity to display the question and options (from the DB) and what I want to do now is when i press the "Next" button it should just reload the current activity with the next question set from the database. (the activity starts with survey.getNextQuestion() - so its just a case of refreshing the activity so it updates) Im sure this is a simple thing to do -any ideas? Thanks

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  • WP7 listbox binding not working properly

    - by Marco
    A noob error for sure (I started yesterday afternoon developing in WP7), but I'm wasting a lot time on it. I post my class and a little part of my code: public class ChronoLaps : INotifyPropertyChanged { private ObservableCollection<ChronoLap> laps = null; public int CurrentLap { get { return lap; } set { if (value == lap) return; // Some code here .... ChronoLap newlap = new ChronoLap() { // Some code here ... }; Laps.Insert(0, newlap); lap = value; NotifyPropertyChanged("CurrentLap"); NotifyPropertyChanged("Laps"); } } public ObservableCollection<ChronoLap> Laps { get { return laps; } set { if (value == laps) return; laps = value; if (laps != null) { laps.CollectionChanged += delegate { MeanTime = Laps.Sum(p => p.Time.TotalMilliseconds) / (Laps.Count * 1000); NotifyPropertyChanged("MeanTime"); }; } NotifyPropertyChanged("Laps"); } } } MainPage.xaml.cs public partial class MainPage : PhoneApplicationPage { public ChronoLaps History { get; private set; } private void butStart_Click(object sender, EventArgs e) { History = new ChronoLaps(); // History.Laps.Add(new ChronoLap() { Distance = 0 }); LayoutRoot.DataContext = History; } } MainPage.xaml <phone:PhoneApplicationPage> <Grid x:Name="LayoutRoot" Background="Transparent"> <Grid Grid.Row="2"> <ScrollViewer Margin="-5,13,3,36" Height="758"> <ListBox Name="lbHistory" ItemContainerStyle="{StaticResource ListBoxStyle}" ItemsSource="{Binding Laps}" HorizontalAlignment="Left" Margin="5,25,0,0" VerticalAlignment="Top" Width="444"> <ListBox.ItemTemplate> <DataTemplate> <StackPanel Orientation="Horizontal"> <TextBlock Text="{Binding Lap}" Width="40" /> <TextBlock Text="{Binding Time}" Width="140" /> <TextBlock Text="{Binding TotalTime}" Width="140" /> <TextBlock Text="{Binding Distance}" /> </StackPanel> </DataTemplate> </ListBox.ItemTemplate> </ListBox> </ScrollViewer> </Grid> </Grid> </phone:PhoneApplicationPage> Problem is that when I add one or more items to History.Laps collection, my listbox is not refreshed and these items don't appear. But if I remove comment on // History.Laps.Add(new ChronoLap()... line, this item appear and so every other inserted later. More: if I remove that comment and then write History.Laps.Clear() (before or after setting binding) binding is not working anymore. It's like it gets crazy if collection is empty. I really don't understand the reason... UPDATE AND SOLUTION: If i move History = new ChronoLaps(); LayoutRoot.DataContext = History; from butStart_Click to public MainPage() everything works as expected. Can someone explain me the reason?

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  • CoreData is saving model without the save: method being called

    - by chris
    I have a list of items with a plus button in the navigation bar that opens up a modal window containing a table of the models attributes, that displays a form when the table items are clicked (pretty standard form style). For some reason if I click the plus button to open the form to create a new model, then immediately click the done button, the person model is saved. The action linked to the done button does nothing but call on a delegate method notifying the personListViewController to close the window. The apple docs do state that the model is not saved after calling the insertNewObjectForEntityName: ... Simply creating a managed object does not cause it to be saved to a persistent store. The managed object context acts as a scratchpad. I am at a lost to why this is happening, but every time I click the done button I have a new blank item in the original tableView. I am using SDK v3.1.3 // PersonListViewController - open modal window - (void)addPerson { // Load the new form PersonNewViewController *newController = [[PersonNewViewController alloc] init]; newController.modalFormDelegate = self; [self presentModalViewController:newController animated:YES]; [newController release]; } // PersonFormViewController - (void)viewDidLoad { [super viewDidLoad]; if ( person == nil ) { MyAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate]; self.person = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:appDelegate.managedObjectContext]; } ... UIBarButtonItem *doneButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(done)]; self.navigationItem.rightBarButtonItem = doneButton; [doneButton release]; } - (IBAction) done { [self.modalFormDelegate didCancel]; } // delegate method in the original listViewController - (void) didCancel { [self dismissModalViewControllerAnimated:YES]; }

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  • get data from a querystring

    - by regwe
    i have this querystring that shall open up my page. http://www.a1-one.com/[email protected]&stuid=123456 Now when this page loads, on page_load, I want to pick up email and stuid in two different variables. So I can use them to insert into my database (sql server) how can this be done in vb.net

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  • Remove objects from different environments

    - by Fred
    I have an R script file that executes a second R script via: source("../scripts/second_file.R") That second file has the following lines: myfiles <- list.files(".",pattern = "*.csv") ... rm(myfiles) When I run the master R file I get: > source("../scripts/second_file.R") Error in file.remove(myfiles) : object 'myfiles' not found and the program aborts. I think this has something to do with the environment. I looked at ?rm() pages but less than illuminating. I figure I have to give it a position argument, but not sure which.

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  • Building a NSPredicate for a filter

    - by John
    Hi, Just wondering what the best way to build a NSPredicate is if some filters are optional? This is basically for a filter, so if some options aren't selected I don't to filter by them eg. If I have option1 and option2 set for the filter. NSPredicate* predicate = [NSPredicate predicateWithFormat:@"option1 = %@ AND option2 = %@] .... otherwise if just option1 NSPredicate* predicate = [NSPredicate predicateWithFormat:@"option1 = %@] .... The key being there are 10 different options to filter, so I don't want to have to code for the 10x10 possible combinations. Thanks

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  • Django form and User data

    - by Dean
    I have a model that looks like this: class Client(models.Model): name = models.CharField(max_length=100, primary_key=True) user = models.ForeignKey(User) class Contract(models.Model): title = models.CharField(max_length=100, primary_key=True) start_date = models.DateField() end_date = models.DateField() description = models.TextField() client = models.ForeignKey(Client) user = models.ForeignKey(User) How can i configure a django form so that only clients associated with that user show in the field in the form? My initial thought was this in my forms.py: client = forms.ModelChoiceField(queryset=Client.objects.filter(user__username = User.username)) But it didn't work. So how else would I go about it?

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  • Tag Cloud Data Backend

    - by Waldron
    I want to be able to generate tag clouds from free text that comes from any number of different sources. For clarity, I'm not talking about how to display a tag cloud once the critical tags/phrases are already discovered, I'm hoping to be able to discover the meaningful phrases themselves... preferable on a PHP/MySQL stack. If I had to do this myself, I'd start by establishing some kind of index for words/phrases that gives a "normal" frequency for any word/phrase. eg "Constantinople" occurs once in every 1,000,000 words on average (normal frequency "0.000001"). Then as I analyze a body of text, I'd find the individual words/phrases (another challenge!), find frequencies of each within the input, and measure against the expected freqeuncy. Words that have the highest ratio against expected frequency get boosted priority in the cloud. I'd like to believe someone else has already done this, WAY better than I could hope to, but I'll be damned if I can find it. Any recommendations??

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  • Mysql: create index on 1.4 billion records

    - by SiLent SoNG
    I have a table with 1.4 billion records. The table structure is as follows: CREATE TABLE text_page ( text VARCHAR(255), page_id INT UNSIGNED ) ENGINE=MYISAM DEFAULT CHARSET=ascii The requirement is to create an index over the column text. The table size is about 34G. I have tried to create the index by the following statement: ALTER TABLE text_page ADD KEY ix_text (text) After 10 hours' waiting I finally give up this approach. Is there any workable solution on this problem? UPDATE: the table is unlikely to be updated or inserted or deleted. The reason why to create index on the column text is because this kind of sql query would be frequently executed: SELECT page_id FROM text_page WHERE text = ?

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  • If attacker has original data, and encrypted data, can they determine the passphrase?

    - by Brad Cupit
    If an attacker has several distinct items (for example: e-mail addresses) and knows the encrypted value of each item, can the attacker more easily determine the secret passphrase used to encrypt those items? Meaning, can they determine the passphrase without resorting to brute force? This question may sound strange, so let me provide a use-case: User signs up to a site with their e-mail address Server sends that e-mail address a confirmation URL (for example: https://my.app.com/confirmEmailAddress/bill%40yahoo.com) Attacker can guess the confirmation URL and therefore can sign up with someone else's e-mail address, and 'confirm' it without ever having to sign in to that person's e-mail account and see the confirmation URL. This is a problem. Instead of sending the e-mail address plain text in the URL, we'll send it encrypted by a secret passphrase. (I know the attacker could still intercept the e-mail sent by the server, since e-mail are plain text, but bear with me here.) If an attacker then signs up with multiple free e-mail accounts and sees multiple URLs, each with the corresponding encrypted e-mail address, could the attacker more easily determine the passphrase used for encryption? Alternative Solution I could instead send a random number or one-way hash of their e-mail address (plus random salt). This eliminates storing the secret passphrase, but it means I need to store that random number/hash in the database. The original approach above does not require this extra table. I'm leaning towards the the one-way hash + extra table solution, but I still would like to know the answer: does having multiple unencrypted e-mail addresses and their encrypted counterparts make it easier to determine the passphrase used?

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  • Best way to model Customer <--> Address

    - by Jen
    Every Customer has a physical address and an optional mailing address. What is your preferred way to model this? Option 1. Customer has foreign key to Address Customer (id, phys_address_id, mail_address_id) Address (id, street, city, etc.) Option 2. Customer has one-to-many relationship to Address, which contains a field to describe the address type Customer (id) Address (id, customer_id, address_type, street, city, etc.) Option 3. Address information is de-normalized and stored in Customer Customer (id, phys_street, phys_city, etc. mail_street, mail_city, etc.) One of my overriding goals is to simplify the object-relational mappings, so I'm leaning towards the first approach. What are your thoughts?

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