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  • What is the equivalent of Java's .length for arrays in C#?

    - by Michael Loftus
    I'm new to C#, and I'm trying to convert this code from java into C#. static public double euclidean_2(double[] x, double[] y) { if (x.length != y.length) throw new RuntimeException("Arguments must have same number of dimensions."); double cumssq = 0.0; for (int i = 0; i < x.length; i++) cumssq += (x[i] - y[i]) * (x[i] - y[i]); return cumssq; } I know java uses .length but what is the equivalent in C# since I keep getting an error Thanks

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  • how can I get around no arrays as class constants in php?

    - by user151841
    I have a class with a static method. There is an array to check that a string argument passed is a member of a set. But, with the static method, I can't reference the class property in an uninstantiated class, nor can I have an array as a class constant. I suppose I could hard code the array in the static method, but then if I need to change it, I'd have to remember to change it in two places. I'd like to avoid this.

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  • How to use php variables (arrays) in mysql select statements?

    - by davidconn
    Hi everybody, How do you use a php variable (array) inside a mysql select statement? I am designing an auction site and currently working on a page that lets people view a list of all the current bids for an item. I want to display 3 columns: amountbid - the amount each bidder has bid for the item (held in tblbid) bidderid - the id of each bidder who has bid (found in tbluser) total_positivity_feedback - how many users have left positive feedback for the bidder (calculated from tblfeedback) To find the 'amount' and the 'bidderid' columns i pass the essayid URL parameter from the previous page. This works fine. Despite this, i can't display the total_positivity_feedback column for the various users who have made each bid. My mysql query looks like this: select tblbid.bidderid, tblbid.amount, (select count(tblfeedback.feedbackid) from tblfeedback WHERE tblfeedback.writerid = "ARRAY VARIABLE GOES HERE") AS total_positivity_feedback FROM tblbid WHERE tblbid.essayid = $essayid_bids I assume that the only way to accomplish this is to make the variable contain the bidderid's of those people who bid for that particular essay? I can't seem to work out how to do this tho?!? Many thanks for your help

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  • C++: How to make comparison function for char arrays?

    - by Newbie
    Is this possible? i get weird error message when i put char as the type: inline bool operator==(const char *str1, const char *str2){ // ... } Error message: error C2803: 'operator ==' must have at least one formal parameter of class type ... which i dont understand at all. I was thinking if i could directly compare stuff like: const char *str1 = "something"; const char *str2 = "something else"; const char str3[] = "lol"; // not sure if this is same as above and then compare: if(str1 == str2){ // ... } etc. But i also want it to work with: char *str = new char[100]; and: char *str = (char *)malloc(100); I am assuming every char array i use this way would end in NULL character, so the checking should be possible, but i understand it can be unsafe etc. I just want to know if this is possible to do, and how.

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  • Numpy zero rank array indexing/broadcasting

    - by Lemming
    I'm trying to write a function that supports broadcasting and is fast at the same time. However, numpy's zero-rank arrays are causing trouble as usual. I couldn't find anything useful on google, or by searching here. So, I'm asking you. How should I implement broadcasting efficiently and handle zero-rank arrays at the same time? This whole post became larger than anticipated, sorry. Details: To clarify what I'm talking about I'll give a simple example: Say I want to implement a Heaviside step-function. I.e. a function that acts on the real axis, which is 0 on the negative side, 1 on the positive side, and from case to case either 0, 0.5, or 1 at the point 0. Implementation Masking The most efficient way I found so far is the following. It uses boolean arrays as masks to assign the correct values to the corresponding slots in the output vector. from numpy import * def step_mask(x, limit=+1): """Heaviside step-function. y = 0 if x < 0 y = 1 if x > 0 See below for x == 0. Arguments: x Evaluate the function at these points. limit Which limit at x == 0? limit > 0: y = 1 limit == 0: y = 0.5 limit < 0: y = 0 Return: The values corresponding to x. """ b = broadcast(x, limit) out = zeros(b.shape) out[x>0] = 1 mask = (limit > 0) & (x == 0) out[mask] = 1 mask = (limit == 0) & (x == 0) out[mask] = 0.5 mask = (limit < 0) & (x == 0) out[mask] = 0 return out List Comprehension The following-the-numpy-docs way is to use a list comprehension on the flat iterator of the broadcast object. However, list comprehensions become absolutely unreadable for such complicated functions. def step_comprehension(x, limit=+1): b = broadcast(x, limit) out = empty(b.shape) out.flat = [ ( 1 if x_ > 0 else ( 0 if x_ < 0 else ( 1 if l_ > 0 else ( 0.5 if l_ ==0 else ( 0 ))))) for x_, l_ in b ] return out For Loop And finally, the most naive way is a for loop. It's probably the most readable option. However, Python for-loops are anything but fast. And hence, a really bad idea in numerics. def step_for(x, limit=+1): b = broadcast(x, limit) out = empty(b.shape) for i, (x_, l_) in enumerate(b): if x_ > 0: out[i] = 1 elif x_ < 0: out[i] = 0 elif l_ > 0: out[i] = 1 elif l_ < 0: out[i] = 0 else: out[i] = 0.5 return out Test First of all a brief test to see if the output is correct. >>> x = array([-1, -0.1, 0, 0.1, 1]) >>> step_mask(x, +1) array([ 0., 0., 1., 1., 1.]) >>> step_mask(x, 0) array([ 0. , 0. , 0.5, 1. , 1. ]) >>> step_mask(x, -1) array([ 0., 0., 0., 1., 1.]) It is correct, and the other two functions give the same output. Performance How about efficiency? These are the timings: In [45]: xl = linspace(-2, 2, 500001) In [46]: %timeit step_mask(xl) 10 loops, best of 3: 19.5 ms per loop In [47]: %timeit step_comprehension(xl) 1 loops, best of 3: 1.17 s per loop In [48]: %timeit step_for(xl) 1 loops, best of 3: 1.15 s per loop The masked version performs best as expected. However, I'm surprised that the comprehension is on the same level as the for loop. Zero Rank Arrays But, 0-rank arrays pose a problem. Sometimes you want to use a function scalar input. And preferably not have to worry about wrapping all scalars in at least 1-D arrays. >>> step_mask(1) Traceback (most recent call last): File "<ipython-input-50-91c06aa4487b>", line 1, in <module> step_mask(1) File "script.py", line 22, in step_mask out[x>0] = 1 IndexError: 0-d arrays can't be indexed. >>> step_for(1) Traceback (most recent call last): File "<ipython-input-51-4e0de4fcb197>", line 1, in <module> step_for(1) File "script.py", line 55, in step_for out[i] = 1 IndexError: 0-d arrays can't be indexed. >>> step_comprehension(1) array(1.0) Only the list comprehension can handle 0-rank arrays. The other two versions would need special case handling for 0-rank arrays. Numpy gets a bit messy when you want to use the same code for arrays and scalars. However, I really like to have functions that work on as arbitrary input as possible. Who knows which parameters I'll want to iterate over at some point. Question: What is the best way to implement a function as the one above? Is there a way to avoid if scalar then like special cases? I'm not looking for a built-in Heaviside. It's just a simplified example. In my code the above pattern appears in many places to make parameter iteration as simple as possible without littering the client code with for loops or comprehensions. Furthermore, I'm aware of Cython, or weave & Co., or implementation directly in C. However, the performance of the masked version above is sufficient for the moment. And for the moment I would like to keep things as simple as possible.

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  • Stack overflow while working with CFBuilder plugin

    - by lynxoid
    In the past 30 minutes of working in CFBuilder (I have it as an Eclipse Plug in), I got this error 4 times: A stack overflow has occurred. You are recommended to exit the workbench. Subsequent errors may happen and may terminate the workbench without warning. See the .log file for more details. Do you want to exit workbench?. together with: Unhandled event loop exception java.lang.StackOverflowError The log file had this: !ENTRY org.eclipse.ui 4 0 2010-05-11 09:41:51.951 !MESSAGE Unhandled event loop exception !STACK 0 java.lang.StackOverflowError at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.sort(Unknown Source) at com.adobe.ide.cfml.parser.generated.CFMLParserBase.getVariableInfo(CFMLParserBase.java:1613) at com.adobe.ide.cfml.parser.generated.CFMLParserBase.getVariableInfo(CFMLParserBase.java:1603) at com.adobe.ide.editor.model.CFMLDOMUtils.getVariable(CFMLDOMUtils.java:2375) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromNode(CFMLDOMUtils.java:2484) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromFunctionCall(CFMLDOMUtils.java:2168) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromNode(CFMLDOMUtils.java:2495) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromFunctionCall(CFMLDOMUtils.java:2168) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromNode(CFMLDOMUtils.java:2495) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromFunctionCall(CFMLDOMUtils.java:2168) (and so on - repeat n times) It happens whenever I copy/paste something. Does anyone know what is going on?

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  • How to avoid repetition when working with primitive types?

    - by I82Much
    I have the need to perform algorithms on various primitive types; the algorithm is essentially the same with the exception of which type the variables are. So for instance, /** * Determine if <code>value</code> is the bitwise OR of elements of <code>validValues</code> array. * For instance, our valid choices are 0001, 0010, and 1000. * We are given a value of 1001. This is valid because it can be made from * ORing together 0001 and 1000. * On the other hand, if we are given a value of 1111, this is invalid because * you cannot turn on the second bit from left by ORing together those 3 * valid values. */ public static boolean isValid(long value, long[] validValues) { for (long validOption : validValues) { value &= ~validOption; } return value != 0; } public static boolean isValid(int value, int[] validValues) { for (int validOption : validValues) { value &= ~validOption; } return value != 0; } How can I avoid this repetition? I know there's no way to genericize primitive arrays, so my hands seem tied. I have instances of primitive arrays and not boxed arrays of say Number objects, so I do not want to go that route either. I know there are a lot of questions about primitives with respect to arrays, autoboxing, etc., but I haven't seen it formulated in quite this way, and I haven't seen a decisive answer on how to interact with these arrays. I suppose I could do something like: public static<E extends Number> boolean isValid(E value, List<E> numbers) { long theValue = value.longValue(); for (Number validOption : numbers) { theValue &= ~validOption.longValue(); } return theValue != 0; } and then public static boolean isValid(long value, long[] validValues) { return isValid(value, Arrays.asList(ArrayUtils.toObject(validValues))); } public static boolean isValid(int value, int[] validValues) { return isValid(value, Arrays.asList(ArrayUtils.toObject(validValues))); } Is that really much better though? Any thoughts in this matter would be appreciated.

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  • Microphone array support in Windows. Info on performance and compatible hardware?

    - by exinocactus
    It is officially claimed by Microsoft (Audio Device Technologies for Windows), that Windows Vista has an integrated system-level support of microphone arrays for improved sound capturing by isolating a sound source in target direction and rejecting ambient noise and reverberation. In more technical terms, an implementation of an adaptive beamformer. Theoretically, microphone arrays with 2-4 mics can substantially improve SNR under some conditions like speaker in front of the laptop in noisy environment (airport, cafe). Surprisingly, though, I find very little information about commercially-available products supporting these new features. I mean products like portable usb micropone arrays or laptops or flat screens with integrated mic arrays. I could only find info about two laptop models having "noise cancelling digital array microphone". These are Dell Latitude and Eee PC 1008P-KR. Now my questions: Do you have any experience with the Windows beamformer implementation? For instance, in the above mentioned laptops. How well does it work? Are there any tests results available in the net or in print (papers?)? Do you know about other microphone array hardware? What could be the reason why mic array technology didn't get sucess Is there mic arrays support in 'Windows 7'?

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  • What is the best algorithm for this array-comparison problem?

    - by mark
    What is the most efficient for speed algorithm to solve the following problem? Given 6 arrays, D1,D2,D3,D4,D5 and D6 each containing 6 numbers like: D1[0] = number D2[0] = number ...... D6[0] = number D1[1] = another number D2[1] = another number .... ..... .... ...... .... D1[5] = yet another number .... ...... .... Given a second array ST1, containing 1 number: ST1[0] = 6 Given a third array ans, containing 6 numbers: ans[0] = 3, ans[1] = 4, ans[2] = 5, ......ans[5] = 8 Using as index for the arrays D1,D2,D3,D4,D5 and D6, the number that goes from 0, to the number stored in ST1[0] minus one, in this example 6, so from 0 to 6-1, compare each res array against each D array My algorithm so far is: I tried to keep everything unlooped as much as possible. EML := ST1[0] //number contained in ST1[0] EML1 := 0 //start index for the arrays D While EML1 < EML if D1[ELM1] = ans[0] goto two if D2[ELM1] = ans[0] goto two if D3[ELM1] = ans[0] goto two if D4[ELM1] = ans[0] goto two if D5[ELM1] = ans[0] goto two if D6[ELM1] = ans[0] goto two ELM1 = ELM1 + 1 return 0 //If the ans[0] number is not found in either D1[0-6], D2[0-6].... D6[0-6] return 0 which will then exclude ans[0-6] numbers two: EML1 := 0 start index for arrays Ds While EML1 < EML if D1[ELM1] = ans[1] goto three if D2[ELM1] = ans[1] goto three if D3[ELM1] = ans[1] goto three if D4[ELM1] = ans[1] goto three if D5[ELM1] = ans[1] goto three if D6[ELM1] = ans[1] goto three ELM1 = ELM1 + 1 return 0 //If the ans[1] number is not found in either D1[0-6], D2[0-6].... D6[0-6] return 0 which will then exclude ans[0-6] numbers three: EML1 := 0 start index for arrays Ds While EML1 < EML if D1[ELM1] = ans[2] goto four if D2[ELM1] = ans[2] goto four if D3[ELM1] = ans[2] goto four if D4[ELM1] = ans[2] goto four if D5[ELM1] = ans[2] goto four if D6[ELM1] = ans[2] goto four ELM1 = ELM1 + 1 return 0 //If the ans[2] number is not found in either D1[0-6], D2[0-6].... D6[0-6] return 0 which will then exclude ans[0-6] numbers four: EML1 := 0 start index for arrays Ds While EML1 < EML if D1[ELM1] = ans[3] goto five if D2[ELM1] = ans[3] goto five if D3[ELM1] = ans[3] goto five if D4[ELM1] = ans[3] goto five if D5[ELM1] = ans[3] goto five if D6[ELM1] = ans[3] goto five ELM1 = ELM1 + 1 return 0 //If the ans[3] number is not found in either D1[0-6], D2[0-6].... D6[0-6] return 0 which will then exclude ans[0-6] numbers five: EML1 := 0 start index for arrays Ds While EML1 < EML if D1[ELM1] = ans[4] goto six if D2[ELM1] = ans[4] goto six if D3[ELM1] = ans[4] goto six if D4[ELM1] = ans[4] goto six if D5[ELM1] = ans[4] goto six if D6[ELM1] = ans[4] goto six ELM1 = ELM1 + 1 return 0 //If the ans[4] number is not found in either D1[0-6], D2[0-6].... D6[0-6] return 0 which will then exclude ans[0-6] numbers six: EML1 := 0 start index for arrays Ds While EML1 < EML if D1[ELM1] = ans[5] return 1 ////If the ans[1] number is not found in either D1[0-6]..... if D2[ELM1] = ans[5] return 1 which will then include ans[0-6] numbers return 1 if D3[ELM1] = ans[5] return 1 if D4[ELM1] = ans[5] return 1 if D5[ELM1] = ans[5] return 1 if D6[ELM1] = ans[5] return 1 ELM1 = ELM1 + 1 return 0 As language of choice, it would be pure c

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  • Silverlight 4 Twitter Client &ndash; Part 6

    - by Max
    In this post, we are going to look into implementing lists into our twitter application and also about enhancing the data grid to display the status messages in a pleasing way with the profile images. Twitter lists are really cool feature that they recently added, I love them and I’ve quite a few lists setup one for DOTNET gurus, SQL Server gurus and one for a few celebrities. You can follow them here. Now let us move onto our tutorial. 1) Lists can be subscribed to in two ways, one can be user’s own lists, which he has created and another one is the lists that the user is following. Like for example, I’ve created 3 lists myself and I am following 1 other lists created by another user. Both of them cannot be fetched in the same api call, its a two step process. 2) In the TwitterCredentialsSubmit method we’ve in Home.xaml.cs, let us do the first api call to get the lists that the user has created. For this the call has to be made to https://twitter.com/<TwitterUsername>/lists.xml. The API reference is available here. myService1.AllowReadStreamBuffering = true; myService1.UseDefaultCredentials = false; myService1.Credentials = new NetworkCredential(GlobalVariable.getUserName(), GlobalVariable.getPassword()); myService1.DownloadStringCompleted += new DownloadStringCompletedEventHandler(ListsRequestCompleted); myService1.DownloadStringAsync(new Uri("https://twitter.com/" + GlobalVariable.getUserName() + "/lists.xml")); 3) Now let us look at implementing the event handler – ListRequestCompleted for this. public void ListsRequestCompleted(object sender, System.Net.DownloadStringCompletedEventArgs e) { if (e.Error != null) { StatusMessage.Text = "This application must be installed first."; parseXML(""); } else { //MessageBox.Show(e.Result.ToString()); parseXMLLists(e.Result.ToString()); } } 4) Now let us look at the parseXMLLists in detail xdoc = XDocument.Parse(text); var answer = (from status in xdoc.Descendants("list") select status.Element("name").Value); foreach (var p in answer) { Border bord = new Border(); bord.CornerRadius = new CornerRadius(10, 10, 10, 10); Button b = new Button(); b.MinWidth = 70; b.Background = new SolidColorBrush(Colors.Black); b.Foreground = new SolidColorBrush(Colors.Black); //b.Width = 70; b.Height = 25; b.Click += new RoutedEventHandler(b_Click); b.Content = p.ToString(); bord.Child = b; TwitterListStack.Children.Add(bord); } So here what am I doing, I am just dynamically creating a button for each of the lists and put them within a StackPanel and for each of these buttons, I am creating a event handler b_Click which will be fired on button click. We will look into this method in detail soon. For now let us get the buttons displayed. 5) Now the user might have some lists to which he has subscribed to. We need to create a button for these as well. In the end of TwitterCredentialsSubmit method, we need to make a call to http://api.twitter.com/1/<TwitterUsername>/lists/subscriptions.xml. Reference is available here. The code will look like this below. myService2.AllowReadStreamBuffering = true; myService2.UseDefaultCredentials = false; myService2.Credentials = new NetworkCredential(GlobalVariable.getUserName(), GlobalVariable.getPassword()); myService2.DownloadStringCompleted += new DownloadStringCompletedEventHandler(ListsSubsRequestCompleted); myService2.DownloadStringAsync(new Uri("http://api.twitter.com/1/" + GlobalVariable.getUserName() + "/lists/subscriptions.xml")); 6) In the event handler – ListsSubsRequestCompleted, we need to parse through the xml string and create a button for each of the lists subscribed, let us see how. I’ve taken only the “full_name”, you can choose what you want, refer the documentation here. Note the point that the full_name will have @<UserName>/<ListName> format – this will be useful very soon. xdoc = XDocument.Parse(text); var answer = (from status in xdoc.Descendants("list") select status.Element("full_name").Value); foreach (var p in answer) { Border bord = new Border(); bord.CornerRadius = new CornerRadius(10, 10, 10, 10); Button b = new Button(); b.Background = new SolidColorBrush(Colors.Black); b.Foreground = new SolidColorBrush(Colors.Black); //b.Width = 70; b.MinWidth = 70; b.Height = 25; b.Click += new RoutedEventHandler(b_Click); b.Content = p.ToString(); bord.Child = b; TwitterListStack.Children.Add(bord); } Please note, I am setting the button width to be auto based on the content and also giving it a midwidth value. I wanted to create a rounded corner buttons, but for some reason its not working. Also add this StackPanel – TwitterListStack of the Home.xaml <StackPanel HorizontalAlignment="Center" Orientation="Horizontal" Name="TwitterListStack"></StackPanel> After doing this, you would get a series of buttons in the top of the home page. 7) Now the button click event handler – b_Click, in this method, once the button is clicked, I call another method with the content string of the button which is clicked as the parameter. Button b = (Button)e.OriginalSource; getListStatuses(b.Content.ToString()); 8) Now the getListsStatuses method: toggleProgressBar(true); WebRequest.RegisterPrefix("http://", System.Net.Browser.WebRequestCreator.ClientHttp); WebClient myService = new WebClient(); myService.AllowReadStreamBuffering = true; myService.UseDefaultCredentials = false; myService.DownloadStringCompleted += new DownloadStringCompletedEventHandler(TimelineRequestCompleted); if (listName.IndexOf("@") > -1 && listName.IndexOf("/") > -1) { string[] arrays = null; arrays = listName.Split('/'); arrays[0] = arrays[0].Replace("@", " ").Trim(); //MessageBox.Show(arrays[0]); //MessageBox.Show(arrays[1]); string url = "http://api.twitter.com/1/" + arrays[0] + "/lists/" + arrays[1] + "/statuses.xml"; //MessageBox.Show(url); myService.DownloadStringAsync(new Uri(url)); } else myService.DownloadStringAsync(new Uri("http://api.twitter.com/1/" + GlobalVariable.getUserName() + "/lists/" + listName + "/statuses.xml")); Please note that the url to look at will be different based on the list clicked – if its user created, the url format will be http://api.twitter.com/1/<CurentUser>/lists/<ListName>/statuses.xml But if it is some lists subscribed, it will be http://api.twitter.com/1/<ListOwnerUserName>/lists/<ListName>/statuses.xml The first one is pretty straight forward to implement, but if its a list subscribed, we need to split the listName string to get the list owner and list name and user them to form the string. So that is what I’ve done in this method, if the listName has got “@” and “/” I build the url differently. 9) Until now, we’ve been using only a few nodes of the status message xml string, now we will look to fetch a new field - “profile_image_url”. Images in datagrid – COOL. So for that, we need to modify our Status.cs file to include two more fields one string another BitmapImage with get and set. public string profile_image_url { get; set; } public BitmapImage profileImage { get; set; } 10) Now let us change the generic parseXML method which is used for binding to the datagrid. public void parseXML(string text) { XDocument xdoc; xdoc = XDocument.Parse(text); statusList = new List<Status>(); statusList = (from status in xdoc.Descendants("status") select new Status { ID = status.Element("id").Value, Text = status.Element("text").Value, Source = status.Element("source").Value, UserID = status.Element("user").Element("id").Value, UserName = status.Element("user").Element("screen_name").Value, profile_image_url = status.Element("user").Element("profile_image_url").Value, profileImage = new BitmapImage(new Uri(status.Element("user").Element("profile_image_url").Value)) }).ToList(); DataGridStatus.ItemsSource = statusList; StatusMessage.Text = "Datagrid refreshed."; toggleProgressBar(false); } We are here creating a new bitmap image from the image url and creating a new Status object for every status and binding them to the data grid. Refer to the Twitter API documentation here. You can choose any column you want. 11) Until now, we’ve been using the auto generate columns for the data grid, but if you want it to be really cool, you need to define the columns with templates, etc… <data:DataGrid AutoGenerateColumns="False" Name="DataGridStatus" Height="Auto" MinWidth="400"> <data:DataGrid.Columns> <data:DataGridTemplateColumn Width="50" Header=""> <data:DataGridTemplateColumn.CellTemplate> <DataTemplate> <Image Source="{Binding profileImage}" Width="50" Height="50" Margin="1"/> </DataTemplate> </data:DataGridTemplateColumn.CellTemplate> </data:DataGridTemplateColumn> <data:DataGridTextColumn Width="Auto" Header="User Name" Binding="{Binding UserName}" /> <data:DataGridTemplateColumn MinWidth="300" Width="Auto" Header="Status"> <data:DataGridTemplateColumn.CellTemplate> <DataTemplate> <TextBlock TextWrapping="Wrap" Text="{Binding Text}"/> </DataTemplate> </data:DataGridTemplateColumn.CellTemplate> </data:DataGridTemplateColumn> </data:DataGrid.Columns> </data:DataGrid> I’ve used only three columns – Profile image, Username, Status text. Now our Datagrid will look super cool like this. Coincidentally,  Tim Heuer is on the screenshot , who is a Silverlight Guru and works on SL team in Microsoft. His blog is really super. Here is the zipped file for all the xaml, xaml.cs & class files pages. Ok let us stop here for now, will look into implementing few more features in the next few posts and then I am going to look into developing a ASP.NET MVC 2 application. Hope you all liked this post. If you have any queries / suggestions feel free to comment below or contact me. Cheers! Technorati Tags: Silverlight,LINQ,Twitter API,Twitter,Silverlight 4

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  • Efficient Trie implementation for unicode strings

    - by U Mad
    I have been looking for an efficient String trie implementation. Mostly I have found code like this: Referential implementation in Java (per wikipedia) I dislike these implementations for mostly two reasons: They support only 256 ASCII characters. I need to cover things like cyrillic. They are extremely memory inefficient. Each node contains an array of 256 references, which is 4096 bytes on a 64 bit machine in Java. Each of these nodes can have up to 256 subnodes with 4096 bytes of references each. So a full Trie for every ASCII 2 character string would require a bit over 1MB. Three character strings? 256MB just for arrays in nodes. And so on. Of course I don't intend to have all of 16 million three character strings in my Trie, so a lot of space is just wasted. Most of these arrays are just null references as their capacity far exceeds the actual number of inserted keys. And if I add unicode, the arrays get even larger (char has 64k values instead of 256 in Java). Is there any hope of making an efficient trie for strings? I have considered a couple of improvements over these types of implementations: Instead of using array of references, I could use an array of primitive integer type, which indexes into an array of references to nodes whose size is close to the number of actual nodes. I could break strings into 4 bit parts which would allow for node arrays of size 16 at the cost of a deeper tree.

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  • ECS with Go - circular imports [migrated]

    - by Andreas
    I'm exploring both Go and Entity-Component-Systems. I understand how ECS works, and I'm trying to replicate what seems to be the go-to document of ECS, namely http://cowboyprogramming.com/2007/01/05/evolve-your-heirachy/ For performance, the document recommends to use static arrays of every component type. That is, not arrays of component interfaces (arrays of pointers). The problem with this in Go is circular imports. I have one package, ecs, which contains the definitions for Entity, Component and System types/interfaces as well as an EntityManager. Another package, ecs/components, contains the various components. Obviously, the ecs/components package depends on ecs. But, to declare arrays of specific components in EntityManager, ecs would depend on ecs/components, therefore creating a circular import. Is there any way of avoiding this? I am aware that normally a high level system should not depend on lower systems. I'm also want to point out that using an array of pointers is probably fast enough for my purposes, but I'm interested in possible workarounds (for future reference) Thank you for your help!

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  • ArrayList in Java [on hold]

    - by JNL
    I was implementing a program to remove the duplicates from the 2 character array. I implemented these 2 solutions, Solution 1 worked fine, but Solution 2 given me UnSupportedoperationException. I am wonderring why i sthat so? The two solutions are given below; public void getDiffernce(Character[] inp1, Character[] inp2){ // Solution 1: // ********************************************************************************** List<Character> list1 = new ArrayList<Character>(Arrays.asList(inp1)); List<Character> list2 = new ArrayList<Character>(Arrays.asList(inp2)); list1.removeAll(list2); System.out.println(list1); System.out.println("*********************************************************************************"); // Solution 2: Character a[] = {'f', 'x', 'l', 'b', 'y'}; Character b[] = {'x', 'b','d'}; List<Character> al1 = new ArrayList<Character>(); List<Character> al2 = new ArrayList<Character>(); al1 = (Arrays.asList(a)); System.out.println(al1); al2 = (Arrays.asList(b)); System.out.println(al2); al1.removeAll(al2); // retainAll(al2); System.out.println(al1); }

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  • SPARC T4-4 Beats 8-CPU IBM POWER7 on TPC-H @3000GB Benchmark

    - by Brian
    Oracle's SPARC T4-4 server delivered a world record TPC-H @3000GB benchmark result for systems with four processors. This result beats eight processor results from IBM (POWER7) and HP (x86). The SPARC T4-4 server also delivered better performance per core than these eight processor systems from IBM and HP. Comparisons below are based upon system to system comparisons, highlighting Oracle's complete software and hardware solution. This database world record result used Oracle's Sun Storage 2540-M2 arrays (rotating disk) connected to a SPARC T4-4 server running Oracle Solaris 11 and Oracle Database 11g Release 2 demonstrating the power of Oracle's integrated hardware and software solution. The SPARC T4-4 server based configuration achieved a TPC-H scale factor 3000 world record for four processor systems of 205,792 QphH@3000GB with price/performance of $4.10/QphH@3000GB. The SPARC T4-4 server with four SPARC T4 processors (total of 32 cores) is 7% faster than the IBM Power 780 server with eight POWER7 processors (total of 32 cores) on the TPC-H @3000GB benchmark. The SPARC T4-4 server is 36% better in price performance compared to the IBM Power 780 server on the TPC-H @3000GB Benchmark. The SPARC T4-4 server is 29% faster than the IBM Power 780 for data loading. The SPARC T4-4 server is up to 3.4 times faster than the IBM Power 780 server for the Refresh Function. The SPARC T4-4 server with four SPARC T4 processors is 27% faster than the HP ProLiant DL980 G7 server with eight x86 processors on the TPC-H @3000GB benchmark. The SPARC T4-4 server is 52% faster than the HP ProLiant DL980 G7 server for data loading. The SPARC T4-4 server is up to 3.2 times faster than the HP ProLiant DL980 G7 for the Refresh Function. The SPARC T4-4 server achieved a peak IO rate from the Oracle database of 17 GB/sec. This rate was independent of the storage used, as demonstrated by the TPC-H @3000TB benchmark which used twelve Sun Storage 2540-M2 arrays (rotating disk) and the TPC-H @1000TB benchmark which used four Sun Storage F5100 Flash Array devices (flash storage). [*] The SPARC T4-4 server showed linear scaling from TPC-H @1000GB to TPC-H @3000GB. This demonstrates that the SPARC T4-4 server can handle the increasingly larger databases required of DSS systems. [*] The SPARC T4-4 server benchmark results demonstrate a complete solution of building Decision Support Systems including data loading, business questions and refreshing data. Each phase usually has a time constraint and the SPARC T4-4 server shows superior performance during each phase. [*] The TPC believes that comparisons of results published with different scale factors are misleading and discourages such comparisons. Performance Landscape The table lists the leading TPC-H @3000GB results for non-clustered systems. TPC-H @3000GB, Non-Clustered Systems System Processor P/C/T – Memory Composite(QphH) $/perf($/QphH) Power(QppH) Throughput(QthH) Database Available SPARC Enterprise M9000 3.0 GHz SPARC64 VII+ 64/256/256 – 1024 GB 386,478.3 $18.19 316,835.8 471,428.6 Oracle 11g R2 09/22/11 SPARC T4-4 3.0 GHz SPARC T4 4/32/256 – 1024 GB 205,792.0 $4.10 190,325.1 222,515.9 Oracle 11g R2 05/31/12 SPARC Enterprise M9000 2.88 GHz SPARC64 VII 32/128/256 – 512 GB 198,907.5 $15.27 182,350.7 216,967.7 Oracle 11g R2 12/09/10 IBM Power 780 4.1 GHz POWER7 8/32/128 – 1024 GB 192,001.1 $6.37 210,368.4 175,237.4 Sybase 15.4 11/30/11 HP ProLiant DL980 G7 2.27 GHz Intel Xeon X7560 8/64/128 – 512 GB 162,601.7 $2.68 185,297.7 142,685.6 SQL Server 2008 10/13/10 P/C/T = Processors, Cores, Threads QphH = the Composite Metric (bigger is better) $/QphH = the Price/Performance metric in USD (smaller is better) QppH = the Power Numerical Quantity QthH = the Throughput Numerical Quantity The following table lists data load times and refresh function times during the power run. TPC-H @3000GB, Non-Clustered Systems Database Load & Database Refresh System Processor Data Loading(h:m:s) T4Advan RF1(sec) T4Advan RF2(sec) T4Advan SPARC T4-4 3.0 GHz SPARC T4 04:08:29 1.0x 67.1 1.0x 39.5 1.0x IBM Power 780 4.1 GHz POWER7 05:51:50 1.5x 147.3 2.2x 133.2 3.4x HP ProLiant DL980 G7 2.27 GHz Intel Xeon X7560 08:35:17 2.1x 173.0 2.6x 126.3 3.2x Data Loading = database load time RF1 = power test first refresh transaction RF2 = power test second refresh transaction T4 Advan = the ratio of time to T4 time Complete benchmark results found at the TPC benchmark website http://www.tpc.org. Configuration Summary and Results Hardware Configuration: SPARC T4-4 server 4 x SPARC T4 3.0 GHz processors (total of 32 cores, 128 threads) 1024 GB memory 8 x internal SAS (8 x 300 GB) disk drives External Storage: 12 x Sun Storage 2540-M2 array storage, each with 12 x 15K RPM 300 GB drives, 2 controllers, 2 GB cache Software Configuration: Oracle Solaris 11 11/11 Oracle Database 11g Release 2 Enterprise Edition Audited Results: Database Size: 3000 GB (Scale Factor 3000) TPC-H Composite: 205,792.0 QphH@3000GB Price/performance: $4.10/QphH@3000GB Available: 05/31/2012 Total 3 year Cost: $843,656 TPC-H Power: 190,325.1 TPC-H Throughput: 222,515.9 Database Load Time: 4:08:29 Benchmark Description The TPC-H benchmark is a performance benchmark established by the Transaction Processing Council (TPC) to demonstrate Data Warehousing/Decision Support Systems (DSS). TPC-H measurements are produced for customers to evaluate the performance of various DSS systems. These queries and updates are executed against a standard database under controlled conditions. Performance projections and comparisons between different TPC-H Database sizes (100GB, 300GB, 1000GB, 3000GB, 10000GB, 30000GB and 100000GB) are not allowed by the TPC. TPC-H is a data warehousing-oriented, non-industry-specific benchmark that consists of a large number of complex queries typical of decision support applications. It also includes some insert and delete activity that is intended to simulate loading and purging data from a warehouse. TPC-H measures the combined performance of a particular database manager on a specific computer system. The main performance metric reported by TPC-H is called the TPC-H Composite Query-per-Hour Performance Metric (QphH@SF, where SF is the number of GB of raw data, referred to as the scale factor). QphH@SF is intended to summarize the ability of the system to process queries in both single and multiple user modes. The benchmark requires reporting of price/performance, which is the ratio of the total HW/SW cost plus 3 years maintenance to the QphH. A secondary metric is the storage efficiency, which is the ratio of total configured disk space in GB to the scale factor. Key Points and Best Practices Twelve Sun Storage 2540-M2 arrays were used for the benchmark. Each Sun Storage 2540-M2 array contains 12 15K RPM drives and is connected to a single dual port 8Gb FC HBA using 2 ports. Each Sun Storage 2540-M2 array showed 1.5 GB/sec for sequential read operations and showed linear scaling, achieving 18 GB/sec with twelve Sun Storage 2540-M2 arrays. These were stand alone IO tests. The peak IO rate measured from the Oracle database was 17 GB/sec. Oracle Solaris 11 11/11 required very little system tuning. Some vendors try to make the point that storage ratios are of customer concern. However, storage ratio size has more to do with disk layout and the increasing capacities of disks – so this is not an important metric in which to compare systems. The SPARC T4-4 server and Oracle Solaris efficiently managed the system load of over one thousand Oracle Database parallel processes. Six Sun Storage 2540-M2 arrays were mirrored to another six Sun Storage 2540-M2 arrays on which all of the Oracle database files were placed. IO performance was high and balanced across all the arrays. The TPC-H Refresh Function (RF) simulates periodical refresh portion of Data Warehouse by adding new sales and deleting old sales data. Parallel DML (parallel insert and delete in this case) and database log performance are a key for this function and the SPARC T4-4 server outperformed both the IBM POWER7 server and HP ProLiant DL980 G7 server. (See the RF columns above.) See Also Transaction Processing Performance Council (TPC) Home Page Ideas International Benchmark Page SPARC T4-4 Server oracle.com OTN Oracle Solaris oracle.com OTN Oracle Database 11g Release 2 Enterprise Edition oracle.com OTN Sun Storage 2540-M2 Array oracle.com OTN Disclosure Statement TPC-H, QphH, $/QphH are trademarks of Transaction Processing Performance Council (TPC). For more information, see www.tpc.org. SPARC T4-4 205,792.0 QphH@3000GB, $4.10/QphH@3000GB, available 5/31/12, 4 processors, 32 cores, 256 threads; IBM Power 780 QphH@3000GB, 192,001.1 QphH@3000GB, $6.37/QphH@3000GB, available 11/30/11, 8 processors, 32 cores, 128 threads; HP ProLiant DL980 G7 162,601.7 QphH@3000GB, $2.68/QphH@3000GB available 10/13/10, 8 processors, 64 cores, 128 threads.

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  • Subterranean IL: Generics and array covariance

    - by Simon Cooper
    Arrays in .NET are curious beasts. They are the only built-in collection types in the CLR, and SZ-arrays (single dimension, zero-indexed) have their own commands and IL syntax. One of their stranger properties is they have a kind of built-in covariance long before generic variance was added in .NET 4. However, this causes a subtle but important problem with generics. First of all, we need to briefly recap on array covariance. SZ-array covariance To demonstrate, I'll tweak the classes I introduced in my previous posts: public class IncrementableClass { public int Value; public virtual void Increment(int incrementBy) { Value += incrementBy; } } public class IncrementableClassx2 : IncrementableClass { public override void Increment(int incrementBy) { base.Increment(incrementBy); base.Increment(incrementBy); } } In the CLR, SZ-arrays of reference types are implicitly convertible to arrays of the element's supertypes, all the way up to object (note that this does not apply to value types). That is, an instance of IncrementableClassx2[] can be used wherever a IncrementableClass[] or object[] is required. When an SZ-array could be used in this fashion, a run-time type check is performed when you try to insert an object into the array to make sure you're not trying to insert an instance of IncrementableClass into an IncrementableClassx2[]. This check means that the following code will compile fine but will fail at run-time: IncrementableClass[] array = new IncrementableClassx2[1]; array[0] = new IncrementableClass(); // throws ArrayTypeMismatchException These checks are enforced by the various stelem* and ldelem* il instructions in such a way as to ensure you can't insert a IncrementableClass into a IncrementableClassx2[]. For the rest of this post, however, I'm going to concentrate on the ldelema instruction. ldelema This instruction pops the array index (int32) and array reference (O) off the stack, and pushes a pointer (&) to the corresponding array element. However, unlike the ldelem instruction, the instruction's type argument must match the run-time array type exactly. This is because, once you've got a managed pointer, you can use that pointer to both load and store values in that array element using the ldind* and stind* (load/store indirect) instructions. As the same pointer can be used for both input and output to the array, the type argument to ldelema must be invariant. At the time, this was a perfectly reasonable restriction, and maintained array type-safety within managed code. However, along came generics, and with it the constrained callvirt instruction. So, what happens when we combine array covariance and constrained callvirt? .method public static void CallIncrementArrayValue() { // IncrementableClassx2[] arr = new IncrementableClassx2[1] ldc.i4.1 newarr IncrementableClassx2 // arr[0] = new IncrementableClassx2(); dup newobj instance void IncrementableClassx2::.ctor() ldc.i4.0 stelem.ref // IncrementArrayValue<IncrementableClass>(arr, 0) // here, we're treating an IncrementableClassx2[] as IncrementableClass[] dup ldc.i4.0 call void IncrementArrayValue<class IncrementableClass>(!!0[],int32) // ... ret } .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } And the result: Unhandled Exception: System.ArrayTypeMismatchException: Attempted to access an element as a type incompatible with the array. at IncrementArrayValue[T](T[] arr, Int32 index) at CallIncrementArrayValue() Hmm. We're instantiating the generic method as IncrementArrayValue<IncrementableClass>, but passing in an IncrementableClassx2[], hence the ldelema instruction is failing as it's expecting an IncrementableClass[]. On features and feature conflicts What we've got here is a conflict between existing behaviour (ldelema ensuring type safety on covariant arrays) and new behaviour (managed pointers to object references used for every constrained callvirt on generic type instances). And, although this is an edge case, there is no general workaround. The generic method could be hidden behind several layers of assemblies, wrappers and interfaces that make it a requirement to use array covariance when calling the generic method. Furthermore, this will only fail at runtime, whereas compile-time safety is what generics were designed for! The solution is the readonly. prefix instruction. This modifies the ldelema instruction to ignore the exact type check for arrays of reference types, and so it lets us take the address of array elements using a covariant type to the actual run-time type of the array: .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 readonly. ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } But what about type safety? In return for ignoring the type check, the resulting controlled mutability pointer can only be used in the following situations: As the object parameter to ldfld, ldflda, stfld, call and constrained callvirt instructions As the pointer parameter to ldobj or ldind* As the source parameter to cpobj In other words, the only operations allowed are those that read from the pointer; stind* and similar that alter the pointer itself are banned. This ensures that the array element we're pointing to won't be changed to anything untoward, and so type safety within the array is maintained. This is a typical example of the maxim that whenever you add a feature to a program, you have to consider how that feature interacts with every single one of the existing features. Although an edge case, the readonly. prefix instruction ensures that generics and array covariance work together and that compile-time type safety is maintained. Tune in next time for a look at the .ctor generic type constraint, and what it means.

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  • When to use an Array vs When to use a Vector, when dealing with GameObjects?

    - by user32465
    I understand that from other answers, Arrays and Vectors are the best choices. Many on SE claim that Linked Lists and Maps are bad for video game programming. I understand that for the most part, I can use Arrays. However, I don't really understand exactly when to use Vectors over Arrays. Why even use Vectors? Wouldn't it be best if I simply always used an Array, that way I know how much memory my game needs? Specifically my game would only ever load a single "Map" area of tiles, such as Map[100][100], so I could very easily have an array of GameObjectContainer GameObjects[100][100], which would reserve an entire map's worth of possible gameobjects, correct? So why use a Vector instead? Memory is quite large on modern hardware.

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  • Looking for feedback on design pattern for simple 2D environment

    - by Le Mot Juiced
    I'm working in iOS. I am trying to make a very simple 2D environment where there are some basic shapes you can drag around with your finger. These shapes should interact in various ways when dropped on each other, or when single-tapped versus double-tapped, etc. I don't know the name for the design pattern I'm thinking of. Basically, you have a bunch of arrays named after attributes, such as "double-tappable" or "draggable" or "stackable". You assign these attributes to the shapes by putting the shapes in the arrays. So, if there's a double-tap event, the code gets the location of it, then iterates through the "double-tappable" array to see if any of its members are in that location. And so on: every interactive event causes a scan through the appropriate array or arrays. It seems like that should work, but I'm wondering if there's a better pattern for the purpose.

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  • Is sstable2json broken in Cassandra 0.6.0-beta3?

    - by knorv
    I'm getting NullPointerException:s when using sstable2json in Cassandra 0.6.0-beta3: $ bin/sstable2json .../cassandra/data/system/LocationInfo-1-Data.db Exception in thread "main" java.lang.NullPointerException at java.util.Arrays$ArrayList.<init>(Arrays.java:3357) at java.util.Arrays.asList(Arrays.java:3343) at org.apache.cassandra.tools.SSTableExport.export(SSTableExport.java:255) at org.apache.cassandra.tools.SSTableExport.export(SSTableExport.java:299) at org.apache.cassandra.tools.SSTableExport.export(SSTableExport.java:323) at org.apache.cassandra.tools.SSTableExport.main(SSTableExport.java:367) I've had no problems with sstable2json when using Cassandra 0.5. Is sstable2json broken in Cassandra 0.6.0-beta3 or am I doing something wrong?

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  • Does the dealloc in Appdelegate calls or not?

    - by monish
    Hi guys, I the allocated arrays in the didFinishLaunching of my appdelegate.And I released those arrays in the dealloc of the appdelegate. My doubt here is does the dealloc of appdelegate calls?and does the arrays in the appdelegate releases or not? Anyone's help will be much appreciated. Thank you, Monish Kumar.

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  • Java webservice does not return all struct array

    - by Aykut
    Hi I wrote a webservice which runs correctly. In the webservice, there is a class which contains other classes' arrays and the webservice returns this class's instance. for example public class cls1 implements Serializable{ cls2[] cls2Arr; cls3[] cls3Arr; } I fill this arrays (cls2Arr and cls3Arr) correctly in service side. When I read this arrays from client, I see only last item of arrays. I checked on the service side before the webservice returns, and the cls1 instance and everything else looked good. What can be a reason ? Thx

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  • Optimizing sparse dot-product in C#

    - by Haggai
    Hello. I'm trying to calculate the dot-product of two very sparse associative arrays. The arrays contain an ID and a value, so the calculation should be done only on those IDs that are common to both arrays, e.g. <(1, 0.5), (3, 0.7), (12, 1.3) * <(2, 0.4), (3, 2.3), (12, 4.7) = 0.7*2.3 + 1.3*4.7 . My implementation (call it dict) currently uses Dictionaries, but it is too slow to my taste. double dot_product(IDictionary<int, double> arr1, IDictionary<int, double> arr2) { double res = 0; double val2; foreach (KeyValuePair<int, double> p in arr1) if (arr2.TryGetValue(p.Key, out val2)) res += p.Value * val2; return res; } The full arrays have about 500,000 entries each, while the sparse ones are only tens to hundreds entries each. I did some experiments with toy versions of dot products. First I tried to multiply just two double arrays to see the ultimate speed I can get (let's call this "flat"). Then I tried to change the implementation of the associative array multiplication using an int[] ID array and a double[] values array, walking together on both ID arrays and multiplying when they are equal (let's call this "double"). I then tried to run all three versions with debug or release, with F5 or Ctrl-F5. The results are as follows: debug F5: dict: 5.29s double: 4.18s (79% of dict) flat: 0.99s (19% of dict, 24% of double) debug ^F5: dict: 5.23s double: 4.19s (80% of dict) flat: 0.98s (19% of dict, 23% of double) release F5: dict: 5.29s double: 3.08s (58% of dict) flat: 0.81s (15% of dict, 26% of double) release ^F5: dict: 4.62s double: 1.22s (26% of dict) flat: 0.29s ( 6% of dict, 24% of double) I don't understand these results. Why isn't the dictionary version optimized in release F5 as do the double and flat versions? Why is it only slightly optimized in the release ^F5 version while the other two are heavily optimized? Also, since converting my code into the "double" scheme would mean lots of work - do you have any suggestions how to optimize the dictionary one? Thanks! Haggai

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  • dynimically using pointer

    - by gcc
    Input: 3 1 2 n 4 5 d 1 21 30 x Output: 2: 4 5 21 30 Input: 3 j 3 34 6 22 10 51 n 1 2 j 1 3 4 5 n 6 7 x Output: 1: 1 2 3 4 5 2: 6 7 3: 34 6 22 10 51 'j': (Jump to array# command) 'd': (Delete array# command) 'n': (Next array command) 'x': (Exit command) #: (Integer number) int num_arrays; /* maximum number of arrays */ int **arrays; /* array of array pointers */ int *l_arrays; /* actual lengths of arrays */ int *c_arrays; /* actual capacities of arrays */ how can we write that code

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