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  • Can hash tables really be O(1)

    - by drawnonward
    It seems to be common knowledge that hash tables can achieve O(1) but that has never made sense to me. Can someone please explain it? A. The value is an int smaller than the size of the hash table, so the value is its own hash, so there is no hash table but if there was it would be O(1) and still be inefficient. B. You have to calculate the hash, so the order is O(n) for the size of the data being looked up. The lookup might be O(1) after you do O(n) work, but that still comes out to O(n) in my eyes. And unless you have a perfect hash or a large hash table there are probably several items per bucket so it devolves into a small linear search at some point anyway. I think hash tables are awesome, but I do not get the O(1) designation unless it is just supposed to be theoretical.

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  • Python: What's a correct and good way to implement __hash__()?

    - by random-name
    What's a correct and good way to implement hash()? I am talking about the function that returns a hashcode that is then used to insert objects into hashtables aka dictionaries. As hash() returns an integer and is used for "binning" objects into hashtables I assume that the values of the returned integer should be uniformly distributed for common data (to minimize collisions). What's a good practice to get such values? Are collisions a problem? In my case I have a small class which acts as a container class holding some ints, some floats and a string.

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  • hash table with chaining method program freezing

    - by Justin Carrey
    I am implementing hash table in C using linked list chaining method. The program compiles but when inserting a string in hash table, the program freezes and gets stuck. The program is below: struct llist{ char *s; struct llist *next; }; struct llist *a[100]; void hinsert(char *str){ int strint, hashinp; strint = 0; hashinp = 0; while(*str){ strint = strint+(*str); } hashinp = (strint%100); if(a[hashinp] == NULL){ struct llist *node; node = (struct llist *)malloc(sizeof(struct llist)); node->s = str; node->next = NULL; a[hashinp] = node; } else{ struct llist *node, *ptr; node = (struct llist *)malloc(sizeof(struct llist)); node->s = str; node->next = NULL; ptr = a[hashinp]; while(ptr->next != NULL){ ptr = ptr->next; } ptr->next = node; } } void hsearch(char *strsrch){ int strint1, hashinp1; strint1 = 0; hashinp1 = 0; while(*strsrch){ strint1 = strint1+(*strsrch); } hashinp1 = (strint1%100); struct llist *ptr1; ptr1 = a[hashinp1]; while(ptr1 != NULL){ if(ptr1->s == strsrch){ cout << "Element Found\n"; break; } else{ ptr1 = ptr1->next; } } if(ptr1 == NULL){ cout << "Element Not Found\n"; } } hinsert() is to insert elements into hash and hsearch is to search an element in the hash. Hash function is written inside hinsert() itself. In the main(), what i am initializing all the elements in a[] to be NULL like this: for(int i = 0;i < 100; i++){ a[i] = NULL; } Help is very much appreciated. Thanks !

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  • What would a compress method do in a hash table?

    - by Bradley Oesch
    For an assignment I have to write the code for a generic Hash Table. In an example Put method, there are two lines: int hash = key.hashCode(); // get the hashcode of the key int index = compress(hash); // compress it to an index I was of the understanding that the hashCode method used the key to return an index, and you would place the key/value pair in the array at that index. But here we "compress" the hash code to get the index. What does this method do? How does it "compress" the hash code? Is it necessary and/or preferred?

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  • hash tables and 2d vectors

    - by Sunil
    I want to push a 2d vector into a hash table row by row and later search for a row (vector) in the hash table and want to be able to find it. I want to do something like #include <iostream> #include <set> #include <vector> using namespace std; int main(){ std::set < vector<int> > myset; vector< vector<int> > v; int k = 0; for ( int i = 0; i < 5; i++ ) { v.push_back ( vector<int>() ); for ( int j = 0; j < 5; j++ ) v[i].push_back ( k++ ); } for ( int i = 0; i < 5; i++ ) { std::copy(v[i].begin(),v[i].end(),std::inserter(myset)); // This is not correct but what is the right way ? // and also here, I want to search for a particular vector if it exists in the table. for ex. the second row of vector v. } return 0; } I'm not sure how to insert and look up a vector in a set. So if nybody could guide me, it will be helpful. Thanks

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  • What exactly are hashtables?

    - by keg
    What are they and how do they work? Where are they used? When should I (not) use them? I've heard the word over and over again, yet I don't know its exact meaning. What I heard is that they allow associative arrays by sending the array key through a hash function that converts it into an int and then uses a regular array. Am I right with that? (Notice: This is not my homework; I go too school but they teach us only the BASICs in informatics)

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  • 'table' undeclared (first use this in a function)

    - by user2318083
    So I'm not sure why this isn't working, I'm creating a new table and setting it to the variable 'table' Is there something I'm doing wrong? This is the error I get when trying to run it: src/simpleshell.c:19:3: error: ‘table’ undeclared (first use in this function) src/simpleshell.c:19:3: note: each undeclared identifier is reported only once for each function it appears in My code is as follows: #include "parser.h" #include "hash_table.h" #include "variables.h" #include "shell.h" #include <stdio.h> int main(void) { char input[MAXINPUTLINE]; table = Table_create(); signal_c_init(); printf("\nhlsh$ "); while(fgets(input, sizeof(input), stdin)){ stripcrlf(input); parse(input); printf("\nhlsh$ "); } Table_free(table); return 0; } Then this is my create a table in the hash_table file: struct Table *Table_create(void){ struct Table *t; t = (struct Table*)calloc(1, sizeof(struct Table)); return t; } From the hash_table.c: #include "hash_table.h" #include "parser.h" #include "shell.h" #include "variables.h" #include <stdio.h> #include <sys/resource.h> #include <sys/wait.h> #include <sys/types.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <pwd.h> #include <fcntl.h> #include <limits.h> #include <signal.h> struct Table *table; unsigned int hash(const char *x){ int i; unsigned int h = 0U; for (i=0; x[i]!='\0'; i++){ h = h * 65599 + (unsigned char)x[i]; } return h % 1024; }

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  • Generating an identifier for objects so that they can be added to a hashtable I have created

    - by dukenukem
    I have a hashtable base class and I am creating different type of hashtable by deriving from it. I only allow it to accept objects that implement my IHashable interface.For example - class LinearProbingHashTable<T> : HashTableBase<T> where T: IHashable { ... ... ... } interface IHashable { /** * Every IHashable implementation should provide an indentfying value for use in generating a hash key. */ int getIdentifier(); } class Car : IHashable { public String Make { get; set; } public String Model { get; set; } public String Color { get; set; } public int Year { get; set; } public int getIdentifier() { /// ??? } } Can anyone suggest a good method for generating an identifier for the car that can be used by the hash function to place it in the hash table? I am actually really looking for a general purpose solution to generating an id for any given class. I would like to have a base class for all classes, HashableObject, that implements IHashable and its getIdentifier method. So then I could just derive from HashableObject which would automatically provide an identifier for any instances. Which means I wouldn't have to write a different getIdentifier method for every object I add to the hashtable. public class HashableObject : IHashable { public int getIdentifier() { // Looking for code here that would generate an id for any object... } } public class Dog : HashableObject { // Dont need to implement getIdentifier because the parent class does it for me }

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  • Glib segfault g_free hash table

    - by Mike
    I'm not quite sure why if I try to free the data I get segfault. Any help will be appreciate it. static GHashTable *hashtable; static void add_inv(char *q) { gpointer old_key, old_value; if(!g_hash_table_lookup_extended(hashtable, q, &old_key, &old_value)){ g_hash_table_insert(hashtable, g_strdup(q), GINT_TO_POINTER(10)); }else{ (old_value)++; g_hash_table_insert(hashtable, g_strdup(q), old_value); g_hash_table_remove (hashtable, q); // segfault g_free(old_key); // segfault g_free(old_value); // segfault } } ... int main(int argc, char *argv[]){ hashtable = g_hash_table_new(g_str_hash, g_str_equal); ... g_hash_table_destroy(hashtable); }

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  • simple C++ hash_set example

    - by celil
    I am new to C++ and STL. I am stuck with the following simple example of a hash set storing custom data structures: #include <iostream> #include <ext/hash_set> using namespace std; using namespace __gnu_cxx; struct trip { int trip_id; int delta_n; int delta_secs; trip(int trip_id, int delta_n, int delta_secs){ this->trip_id = trip_id; this->delta_n = delta_n; this->delta_secs = delta_secs; } }; struct hash_trip { size_t operator()(const trip t) { hash<int> H; return H(t.trip_id); } }; struct eq_trip { bool operator()(const trip t1, const trip t2) { return (t1.trip_id==t2.trip_id) && (t1.delta_n==t2.delta_n) && (t1.delta_secs==t2.delta_secs); } }; int main() { hash_set<trip, hash_trip, eq_trip> trips; trip t = trip(3,2,-1); trip t1 = trip(3,2,0); trips.insert(t); } when I try to compile it, I get the following error message: /usr/include/c++/4.2.1/ext/hashtable.h: In member function ‘size_t __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::_M_bkt_num_key(const _Key&, size_t) const [with _Val = trip, _Key = trip, _HashFcn = hash_trip, _ExtractKey = std::_Identity<trip>, _EqualKey = eq_trip, _Alloc = std::allocator<trip>]’: /usr/include/c++/4.2.1/ext/hashtable.h:599: instantiated from ‘size_t __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::_M_bkt_num(const _Val&, size_t) const [with _Val = trip, _Key = trip, _HashFcn = hash_trip, _ExtractKey = std::_Identity<trip>, _EqualKey = eq_trip, _Alloc = std::allocator<trip>]’ /usr/include/c++/4.2.1/ext/hashtable.h:1006: instantiated from ‘void __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::resize(size_t) [with _Val = trip, _Key = trip, _HashFcn = hash_trip, _ExtractKey = std::_Identity<trip>, _EqualKey = eq_trip, _Alloc = std::allocator<trip>]’ /usr/include/c++/4.2.1/ext/hashtable.h:437: instantiated from ‘std::pair<__gnu_cxx::_Hashtable_iterator<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>, bool> __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::insert_unique(const _Val&) [with _Val = trip, _Key = trip, _HashFcn = hash_trip, _ExtractKey = std::_Identity<trip>, _EqualKey = eq_trip, _Alloc = std::allocator<trip>]’ /usr/include/c++/4.2.1/ext/hash_set:197: instantiated from ‘std::pair<typename __gnu_cxx::hashtable<_Value, _Value, _HashFcn, std::_Identity<_Value>, _EqualKey, _Alloc>::const_iterator, bool> __gnu_cxx::hash_set<_Value, _HashFcn, _EqualKey, _Alloc>::insert(const typename __gnu_cxx::hashtable<_Value, _Value, _HashFcn, std::_Identity<_Value>, _EqualKey, _Alloc>::value_type&) [with _Value = trip, _HashFcn = hash_trip, _EqualKey = eq_trip, _Alloc = std::allocator<trip>]’ try.cpp:45: instantiated from here /usr/include/c++/4.2.1/ext/hashtable.h:595: error: passing ‘const hash_trip’ as ‘this’ argument of ‘size_t hash_trip::operator()(trip)’ discards qualifiers What am I doing wrong?

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  • Use ASP.NET 4 Browser Definitions with ASP.NET 3.5

    - by Stephen Walther
    We updated the browser definitions files included with ASP.NET 4 to include information on recent browsers and devices such as Google Chrome and the iPhone. You can use these browser definition files with earlier versions of ASP.NET such as ASP.NET 3.5. The updated browser definition files, and instructions for installing them, can be found here: http://aspnet.codeplex.com/releases/view/41420 The changes in the browser definition files can cause backwards compatibility issues when you upgrade an ASP.NET 3.5 web application to ASP.NET 4. If you encounter compatibility issues, you can install the old browser definition files in your ASP.NET 4 application. The old browser definition files are included in the download file referenced above. What’s New in the ASP.NET 4 Browser Definition Files The complete set of browsers supported by the new ASP.NET 4 browser definition files is represented by the following figure:     If you look carefully at the figure, you’ll notice that we added browser definitions for several types of recent browsers such as Internet Explorer 8, Firefox 3.5, Google Chrome, Opera 10, and Safari 4. Furthermore, notice that we now include browser definitions for several of the most popular mobile devices: BlackBerry, IPhone, IPod, and Windows Mobile (IEMobile). The mobile devices appear in the figure with a purple background color. To improve performance, we removed a whole lot of outdated browser definitions for old cell phones and mobile devices. We also cleaned up the information contained in the browser files. Here are some of the browser features that you can detect: Are you a mobile device? <%=Request.Browser.IsMobileDevice %> Are you an IPhone? <%=Request.Browser.MobileDeviceModel == "IPhone" %> What version of JavaScript do you support? <%=Request.Browser["javascriptversion"] %> What layout engine do you use? <%=Request.Browser["layoutEngine"] %>   Here’s what you would get if you displayed the value of these properties using Internet Explorer 8: Here’s what you get when you use Google Chrome: Testing Browser Settings When working with browser definition files, it is useful to have some way to test the capability information returned when you request a page with different browsers. You can use the following method to return the HttpBrowserCapabilities the corresponds to a particular user agent string and set of browser headers: public HttpBrowserCapabilities GetBrowserCapabilities(string userAgent, NameValueCollection headers) { HttpBrowserCapabilities browserCaps = new HttpBrowserCapabilities(); Hashtable hashtable = new Hashtable(180, StringComparer.OrdinalIgnoreCase); hashtable[string.Empty] = userAgent; // The actual method uses client target browserCaps.Capabilities = hashtable; var capsFactory = new System.Web.Configuration.BrowserCapabilitiesFactory(); capsFactory.ConfigureBrowserCapabilities(headers, browserCaps); capsFactory.ConfigureCustomCapabilities(headers, browserCaps); return browserCaps; } At the end of this blog entry, there is a link to download a simple Visual Studio 2008 project – named Browser Definition Test -- that uses this method to display capability information for arbitrary user agent strings. For example, if you enter the user agent string for an iPhone then you get the results in the following figure: The Browser Definition Test application enables you to submit a user-agent string and display a table of browser capabilities information. The browser definition files contain sample user-agent strings for each browser definition. I got the iPhone user-agent string from the comments in the iphone.browser file. Enumerating Browser Definitions Someone asked in the comments whether or not there is a way to enumerate all of the browser definitions. You can do this if you ware willing to use a little reflection and read a private property. The browser definition files in the config\browsers folder get parsed into a class named BrowserCapabilitesFactory. After you run the aspnet_regbrowsers tool, you can see the source for this class in the config\browser folder by opening a file named BrowserCapsFactory.cs. The BrowserCapabilitiesFactoryBase class has a protected property named BrowserElements that represents a Hashtable of all of the browser definitions. Here's how you can read this protected property and display the ID for all of the browser definitions: var propInfo = typeof(BrowserCapabilitiesFactory).GetProperty("BrowserElements", BindingFlags.NonPublic | BindingFlags.Instance); Hashtable browserDefinitions = (Hashtable)propInfo.GetValue(new BrowserCapabilitiesFactory(), null); foreach (var key in browserDefinitions.Keys) { Response.Write("" + key); } If you run this code using Visual Studio 2008 then you get the following results: You get a huge number of outdated browsers and devices. In all, 449 browser definitions are listed. If you run this code using Visual Studio 2010 then you get the following results: In the case of Visual Studio 2010, all the old browsers and devices have been removed and you get only 19 browser definitions. Conclusion The updated browser definition files included in ASP.NET 4 provide more accurate information for recent browsers and devices. If you would like to test the new browser definitions with different user-agent strings then I recommend that you download the Browser Definition Test project: Browser Definition Test Project

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  • Some non-generic collections

    - by Simon Cooper
    Although the collections classes introduced in .NET 2, 3.5 and 4 cover most scenarios, there are still some .NET 1 collections that don't have generic counterparts. In this post, I'll be examining what they do, why you might use them, and some things you'll need to bear in mind when doing so. BitArray System.Collections.BitArray is conceptually the same as a List<bool>, but whereas List<bool> stores each boolean in a single byte (as that's what the backing bool[] does), BitArray uses a single bit to store each value, and uses various bitmasks to access each bit individually. This means that BitArray is eight times smaller than a List<bool>. Furthermore, BitArray has some useful functions for bitmasks, like And, Xor and Not, and it's not limited to 32 or 64 bits; a BitArray can hold as many bits as you need. However, it's not all roses and kittens. There are some fundamental limitations you have to bear in mind when using BitArray: It's a non-generic collection. The enumerator returns object (a boxed boolean), rather than an unboxed bool. This means that if you do this: foreach (bool b in bitArray) { ... } Every single boolean value will be boxed, then unboxed. And if you do this: foreach (var b in bitArray) { ... } you'll have to manually unbox b on every iteration, as it'll come out of the enumerator an object. Instead, you should manually iterate over the collection using a for loop: for (int i=0; i<bitArray.Length; i++) { bool b = bitArray[i]; ... } Following on from that, if you want to use BitArray in the context of an IEnumerable<bool>, ICollection<bool> or IList<bool>, you'll need to write a wrapper class, or use the Enumerable.Cast<bool> extension method (although Cast would box and unbox every value you get out of it). There is no Add or Remove method. You specify the number of bits you need in the constructor, and that's what you get. You can change the length yourself using the Length property setter though. It doesn't implement IList. Although not really important if you're writing a generic wrapper around it, it is something to bear in mind if you're using it with pre-generic code. However, if you use BitArray carefully, it can provide significant gains over a List<bool> for functionality and efficiency of space. OrderedDictionary System.Collections.Specialized.OrderedDictionary does exactly what you would expect - it's an IDictionary that maintains items in the order they are added. It does this by storing key/value pairs in a Hashtable (to get O(1) key lookup) and an ArrayList (to maintain the order). You can access values by key or index, and insert or remove items at a particular index. The enumerator returns items in index order. However, the Keys and Values properties return ICollection, not IList, as you might expect; CopyTo doesn't maintain the same ordering, as it copies from the backing Hashtable, not ArrayList; and any operations that insert or remove items from the middle of the collection are O(n), just like a normal list. In short; don't use this class. If you need some sort of ordered dictionary, it would be better to write your own generic dictionary combining a Dictionary<TKey, TValue> and List<KeyValuePair<TKey, TValue>> or List<TKey> for your specific situation. ListDictionary and HybridDictionary To look at why you might want to use ListDictionary or HybridDictionary, we need to examine the performance of these dictionaries compared to Hashtable and Dictionary<object, object>. For this test, I added n items to each collection, then randomly accessed n/2 items: So, what's going on here? Well, ListDictionary is implemented as a linked list of key/value pairs; all operations on the dictionary require an O(n) search through the list. However, for small n, the constant factor that big-o notation doesn't measure is much lower than the hashing overhead of Hashtable or Dictionary. HybridDictionary combines a Hashtable and ListDictionary; for small n, it uses a backing ListDictionary, but switches to a Hashtable when it gets to 9 items (you can see the point it switches from a ListDictionary to Hashtable in the graph). Apart from that, it's got very similar performance to Hashtable. So why would you want to use either of these? In short, you wouldn't. Any gain in performance by using ListDictionary over Dictionary<TKey, TValue> would be offset by the generic dictionary not having to cast or box the items you store, something the graphs above don't measure. Only if the performance of the dictionary is vital, the dictionary will hold less than 30 items, and you don't need type safety, would you use ListDictionary over the generic Dictionary. And even then, there's probably more useful performance gains you can make elsewhere.

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  • How would you implement a hashtable in language x?

    - by mk
    The point of this question is to collect a list of examples of hashtable implementations using arrays in different languages. It would also be nice if someone could throw in a pretty detailed overview of how they work, and what is happening with each example. Edit: Why not just use the built in hash functions in your specific language? Because we should know how hash tables work and be able to implement them. This may not seem like a super important topic, but knowing how one of the most used data structures works seems pretty important to me. If this is to become the wikipedia of programming, then these are some of the types of questions that I will come here for. I'm not looking for a CS book to be written here. I could go pull Intro to Algorithms off the shelf and read up on the chapter on hash tables and get that type of info. More specifically what I am looking for are code examples. Not only for me in particular, but also for others who would maybe one day be searching for similar info and stumble across this page. To be more specific: If you had to implement them, and could not use built-in functions, how would you do it? You don't need to put the code here. Put it in pastebin and just link it.

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  • Goodbye XML&hellip; Hello YAML (part 2)

    - by Brian Genisio's House Of Bilz
    Part 1 After I explained my motivation for using YAML instead of XML for my data, I got a lot of people asking me what type of tooling is available in the .Net space for consuming YAML.  In this post, I will discuss a nice tooling option as well as describe some small modifications to leverage the extremely powerful dynamic capabilities of C# 4.0.  I will be referring to the following YAML file throughout this post Recipe: Title: Macaroni and Cheese Description: My favorite comfort food. Author: Brian Genisio TimeToPrepare: 30 Minutes Ingredients: - Name: Cheese Quantity: 3 Units: cups - Name: Macaroni Quantity: 16 Units: oz Steps: - Number: 1 Description: Cook the macaroni - Number: 2 Description: Melt the cheese - Number: 3 Description: Mix the cooked macaroni with the melted cheese Tooling It turns out that there are several implementations of YAML tools out there.  The neatest one, in my opinion, is YAML for .NET, Visual Studio and Powershell.  It includes a great editor plug-in for Visual Studio as well as YamlCore, which is a parsing engine for .Net.  It is in active development still, but it is certainly enough to get you going with YAML in .Net.  Start by referenceing YamlCore.dll, load your document, and you are on your way.  Here is an example of using the parser to get the title of the Recipe: var yaml = YamlLanguage.FileTo("Data.yaml") as Hashtable; var recipe = yaml["Recipe"] as Hashtable; var title = recipe["Title"] as string; In a similar way, you can access data in the Ingredients set: var yaml = YamlLanguage.FileTo("Data.yaml") as Hashtable; var recipe = yaml["Recipe"] as Hashtable; var ingredients = recipe["Ingredients"] as ArrayList; foreach (Hashtable ingredient in ingredients) { var name = ingredient["Name"] as string; } You may have noticed that YamlCore uses non-generic Hashtables and ArrayLists.  This is because YamlCore was designed to work in all .Net versions, including 1.0.  Everything in the parsed tree is one of two things: Hashtable, ArrayList or Value type (usually String).  This translates well to the YAML structure where everything is either a Map, a Set or a Value.  Taking it further Personally, I really dislike writing code like this.  Years ago, I promised myself to never write the words Hashtable or ArrayList in my .Net code again.  They are ugly, mostly depreciated collections that existed before we got generics in C# 2.0.  Now, especially that we have dynamic capabilities in C# 4.0, we can do a lot better than this.  With a relatively small amount of code, you can wrap the Hashtables and Array lists with a dynamic wrapper (wrapper code at the bottom of this post).  The same code can be re-written to look like this: dynamic doc = YamlDoc.Load("Data.yaml"); var title = doc.Recipe.Title; And dynamic doc = YamlDoc.Load("Data.yaml"); foreach (dynamic ingredient in doc.Recipe.Ingredients) { var name = ingredient.Name; } I significantly prefer this code over the previous.  That’s not all… the magic really happens when we take this concept into WPF.  With a single line of code, you can bind to the data dynamically in the view: DataContext = YamlDoc.Load("Data.yaml"); Then, your XAML is extremely straight-forward (Nothing else.  No static types, no adapter code.  Nothing): <StackPanel> <TextBlock Text="{Binding Recipe.Title}" /> <TextBlock Text="{Binding Recipe.Description}" /> <TextBlock Text="{Binding Recipe.Author}" /> <TextBlock Text="{Binding Recipe.TimeToPrepare}" /> <TextBlock Text="Ingredients:" FontWeight="Bold" /> <ItemsControl ItemsSource="{Binding Recipe.Ingredients}" Margin="10,0,0,0"> <ItemsControl.ItemTemplate> <DataTemplate> <StackPanel Orientation="Horizontal"> <TextBlock Text="{Binding Quantity}" /> <TextBlock Text=" " /> <TextBlock Text="{Binding Units}" /> <TextBlock Text=" of " /> <TextBlock Text="{Binding Name}" /> </StackPanel> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> <TextBlock Text="Steps:" FontWeight="Bold" /> <ItemsControl ItemsSource="{Binding Recipe.Steps}" Margin="10,0,0,0"> <ItemsControl.ItemTemplate> <DataTemplate> <StackPanel Orientation="Horizontal"> <TextBlock Text="{Binding Number}" /> <TextBlock Text=": " /> <TextBlock Text="{Binding Description}" /> </StackPanel> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> </StackPanel> This nifty XAML binding trick only works in WPF, unfortunately.  Silverlight handles binding differently, so they don’t support binding to dynamic objects as of late (March 2010).  This, in my opinion, is a major lacking feature in Silverlight and I really hope we will see this feature available to us in Silverlight 4 Release.  (I am not very optimistic for Silverlight 4, but I can hope for the feature in Silverlight 5, can’t I?) Conclusion I still have a few things I want to say about using YAML in the .Net space including de-serialization and using IronRuby for your YAML parser, but this post is hopefully enough to see how easy it is to incorporate YAML documents in your code. Codeplex Site for YAML tools Dynamic wrapper for YamlCore

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  • resizing arrays when close to memory capacity

    - by user548928
    So I am implementing my own hashtable in java, since the built in hashtable has ridiculous memory overhead per entry. I'm making an open-addressed table with a variant of quadratic hashing, which is backed internally by two arrays, one for keys and one for values. I don't have the ability to resize though. The obvious way to do it is to create larger arrays and then hash all of the (key, value) pairs into the new arrays from the old ones. This falls apart though when my old arrays take up over 50% of my current memory, since I can't fit both the old and new arrays in memory at the same time. Is there any way to resize my hashtable in this situation Edit: the info I got for current hashtable memory overheads is from here How much memory does a Hashtable use? Also, for my current application, my values are ints, so rather than store references to Integers, I have an array of ints as my values.

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  • Query about running a program through valgrind and getting false results comparing to other systems.

    - by FILIaS
    Yesterday i posted this: What's the problem with this code? [hashtable in C] and paxdiablo offered to help me. He posted a sample of code and asked me to run it through valgrind on my machine. This code normally generates: 12,4 But on my machine, i get 24,8. The doubled! I'm just curious why is that happening. Hope sb has a good explaination. I post also paxdiablo's code (for anyone who cant find it.) #include <stdio.h> #include <stdlib.h> typedef struct HashTable { int size ; struct List *head; struct List *tail; } HashTable; typedef struct List { char *number; char *name; int time; struct List *next; } List; #define size_of_table 211 HashTable *createHashTable(void) { HashTable *new_table = malloc(sizeof(*new_table)*size_of_table); //line 606 printf ("%d\n", sizeof(*new_table)); printf ("%d\n", sizeof(new_table)); if (new_table == NULL) { return NULL; } int i=0; for(i; i<size_of_table; i++) { new_table[i].size=0; new_table[i].head=NULL; new_table[i].tail=NULL; } return new_table; } int main(void) { HashTable *x = createHashTable(); free (x); return 0; }

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  • XML-RPC with java

    - by Mona
    hi, I'm developing a server in XML-RPC using Java , but when i compile it , i get this error ServeurSomDiff.java:33: cannot find symbol symbol : method addHandler(java.lang.String,java.lang.String) location: class org.apache.xmlrpc.webserver.WebServer server.addHandler("SOMDIFF",new ServeurSomDiff ()); here 's my server : import java.util.Hashtable; import org.apache.xmlrpc.webserver.*; public class ServeurSomDiff { public ServeurSomDiff (){ } public Hashtable sumAndDifference (int x, int y) { Hashtable result = new Hashtable(); result.put("somme", new Integer(x + y)); result.put("difference", new Integer(x - y)); return result; } public static void main (String [] args) { try { WebServer server = new WebServer(8000); server.addHandler("SOMDIFF",new ServeurSomDiff()); server.start(); System.out.println("Serveur lance sur http://localhost:8000/RPC2"); } catch (Exception exception) {System.err.println("JavaServer: " + exception.toString()); } } } any ideas on how to fix this . thanks

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  • Cannot we pass Hash table in WCF services?

    - by Thinking
    I have just odne something like [ServiceContract] public interface IService1 { [OperationContract] Hashtable MyHashTable(); // TODO: Add your service operations here } and implemented as public Hashtable MyHashTable() { Hashtable h = new Hashtable(); for (int i = 0; i < 10; i++) h.Add(i, "val" + i.ToString()); return h; } When I am trying to run the service , I am getting the error "This operation is not supported in WCF test client" Why so? Thanks

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  • Implements an Undo/Redo in MVC

    - by bnabilos
    Hello, I have a Java application and I want to implement an Undo/Redo option. the value that I want to stock and that I want to be able to recover is an integer. My Class Model implements the interface StateEditable and I have to redefine the 2 functions restoreState(Hashtable<?, ?> state) and storeState(Hashtable<Object, Object> state) but I don't know what to put on them. It will be really great if somebody can help me to do that. These are the first lines of my Model class, the value that I want to do an undo/redo on it is value public class Model extends Observable implements StateEditable { private int value = 5; private UndoManager undoRedo = new UndoManager(); final UndoableEditListener editListener = new UndoableEditListener() { public void undoableEditHappened(UndoableEditEvent evt) { undoRedo.addEdit(evt.getEdit()); } }; @Override public void restoreState(Hashtable<?, ?> state) { } @Override public void storeState(Hashtable<Object, Object> state) { } }

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  • Error while reading custom configuration file(app.config)

    - by Newbie
    I am making a custom configuration in my winform application. (It will represent a country-corrency list) First the CountryList class namespace UtilityMethods { public class CountryList : ConfigurationSection { public CountryList() { // // TODO: Add constructor logic here // } [ConfigurationProperty("CountryCurrency", IsRequired = true)] public Hashtable CountryCurrencies { get { return CountryCurrency.GetCountryCurrency(); } } } } The GetCountryCurrency() method is defined in CountryCurrency class as under namespace UtilityMethods { public static class CountryCurrency { public static Hashtable GetCountryCurrency() { Hashtable ht = new Hashtable(); ht.Add("India", "Rupees"); ht.Add("USA", "Dollar"); return ht; } } } The app.config file looks like <?xml version="1.0" encoding="utf-8" ?> <configuration> <configSections> <section name ="CountryList1" type ="UtilityMethods.CountryList,CountryList,Version=2.0.0.0, Culture=neutral"/> </configSections> <appSettings /> </configuration> And I am calling this from a button_click's event as try { CountryList cList = ConfigurationManager.GetSection("CountryList") as CountryList; Hashtable ht = cList.CountryCurrencies; } catch (Exception ex) { string h = ex.Message; } Upon running the application and clicking on the button I am getting this error Could not load type 'UtilityMethods.CountryList' from assembly 'System.Configuration, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' Please help (dotnet framework : 3.5 Language: C#)

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  • Animation using AniMate with Unity3D doesn't interact with physical objects

    - by Albz
    I'm designing a maze with Unity3D. The maze has a number of bifurcations and the player will stop before each bifurcation and simply choose left or right. Then an automatic animation will move the player through the next bifurcation till the end of the maze (or till a dead end). To animate the player I'm using AniMate and C# in my Unity project. Using AniMate I'm simply creating a point-to-point animation for each bifurcation (e.g. mage below: from the start/red arrow to point 5) My problem is that my animation script (associated to the "First Person Controller") is not working properly since physics is not respected (the player passes through walls). If in the same project I enable the standard character controls in Unity, then I can navigate in the maze with the physical contrains of walls etc... (i.e. I have colliders). This is an example of the code I'm using when I press left to pass from starting point, trough point 1 to point 2: void FixedUpdate () { if (Input.GetKey(KeyCode.LeftArrow)) { //To point 1 Hashtable props = new Hashtable(); props.Add("position", new Vector3(756f,112f,1124f)); props.Add("physics", true); Ani.Mate.To(transform, 2, props); //To point 2 Hashtable props2 = new Hashtable(); props2.Add("position", new Vector3(731f,112f,1124f)); props2.Add("physics", true); Ani.Mate.To(transform, 2, props2); } } What happens practically when I press the left arrow button is that the player moves directly to point 2 using a straight line passing through the wall. I tried to pass to AniMate "Physics = true" but it doesn't seem to help. Any idea on how to solve this issue? Alternatively... any hint on how to have a more optimized code and just use a series of vector3 coordinates (one for each point) to obtain the simple animation I want without having to declare new Hashtable(); etc... every time? I chose AniMate simply because 1. I'm a beginner with Unity 2. I don't need complex animations (e.g. I don't need to use iTween), just fixed animations along straight lines and I need something really simple and quick to implement in a script. However, if someone has an equally simple solution it will be welcome. thank you in advance for your help

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  • when get pagecontent from URL the connect alway return nopermistion ?

    - by tiendv
    I have a methor to return pagecontent of link but when it run, alway return "Do not perrmisson ", plesea check it here is code to return string pagecontent public static String getPageContent(String targetURL) throws Exception { Hashtable contentHash = new Hashtable(); URL url; URLConnection conn; // The data streams used to read from and write to the URL connection. DataOutputStream out; DataInputStream in; // String returned as the result . String returnString = ""; // Create the URL object and make a connection to it. url = new URL(targetURL); conn = url.openConnection(); // check out permission of acess URL if (conn.getPermission() != null) { returnString = "Do not Permission access URL "; } else { // Set connection parameters. We need to perform input and output, // so set both as true. conn.setDoInput(true); conn.setDoOutput(true); // Disable use of caches. conn.setUseCaches(false); // Set the content type we are POSTing. We impersonate it as // encoded form data conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); // get the output stream . out = new DataOutputStream(conn.getOutputStream()); String content = ""; // Create a single String value pairs for all the keys // in the Hashtable passed to us. Enumeration e = contentHash.keys(); boolean first = true; while (e.hasMoreElements()) { // For each key and value pair in the hashtable Object key = e.nextElement(); Object value = contentHash.get(key); // If this is not the first key-value pair in the hashtable, // concantenate an "&" sign to the constructed String if (!first) content += "&"; // append to a single string. Encode the value portion content += (String) key + "=" + URLEncoder.encode((String) value); first = false; } // Write out the bytes of the content string to the stream. out.writeBytes(content); out.flush(); out.close(); // check if can't read from URL // Read input from the input stream. in = new DataInputStream(conn.getInputStream()); String str; while (null != ((str = in.readLine()))) { returnString += str + "\n"; } in.close(); } // return the string that was read. return returnString; }

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