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  • Java List with Objects - find and replace (delete) entry if Object with certain attribute already ex

    - by Sophomore
    Hi there I've been working all day and I somehow can't get this probably easy task figured out - probably a lack of coffee... I have a synchronizedList where some Objects are being stored. Those objects have a field which is something like an ID. These objects carry information about a user and his current state (simplified). The point is, that I only want one object for each user. So when the state of this user changes, I'd like to remove the "old" entry and store a new one in the List. protected static class Objects{ ... long time; Object ID; ... } ... if (Objects.contains(ID)) { Objects.remove(ID); Objects.add(newObject); } else { Objects.add(newObject); } Obviously this is not the way to go but should illustrate what I'm looking for... Maybe the data structure is not the best for this purpose but any help is welcome!

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  • Tiered Design With Analytical Widgets - Is This Code Smell?

    - by Repo Man
    The idea I'm playing with right now is having a multi-leveled "tier" system of analytical objects which perform a certain computation on a common object and then create a new set of analytical objects depending on their outcome. The newly created analytical objects will then get their own turn to run and optionally create more analytical objects, and so on and so on. The point being that the child analytical objects will always execute after the objects that created them, which is relatively important. The whole apparatus will be called by a single thread so I'm not concerned with thread safety at the moment. As long as a certain base condition is met, I don't see this being an unstable design but I'm still a little bit queasy about it. Is this some serious code smell or should I go ahead and implement it this way? Is there a better way? Here is a sample implementation: namespace WidgetTier { public class Widget { private string _name; public string Name { get { return _name; } } private TierManager _tm; private static readonly Random random = new Random(); static Widget() { } public Widget(string name, TierManager tm) { _name = name; _tm = tm; } public void DoMyThing() { if (random.Next(1000) > 1) { _tm.Add(); } } } //NOT thread-safe! public class TierManager { private Dictionary<int, List<Widget>> _tiers; private int _tierCount = 0; private int _currentTier = -1; private int _childCount = 0; public TierManager() { _tiers = new Dictionary<int, List<Widget>>(); } public void Add() { if (_currentTier + 1 >= _tierCount) { _tierCount++; _tiers.Add(_currentTier + 1, new List<Widget>()); } _tiers[_currentTier + 1].Add(new Widget(string.Format("({0})", _childCount), this)); _childCount++; } //Dangerous? public void Sweep() { _currentTier = 0; while (_currentTier < _tierCount) //_tierCount will start at 1 but keep increasing because child objects will keep adding more tiers. { foreach (Widget w in _tiers[_currentTier]) { w.DoMyThing(); } _currentTier++; } } public void PrintAll() { for (int t = 0; t < _tierCount; t++) { Console.Write("Tier #{0}: ", t); foreach (Widget w in _tiers[t]) { Console.Write(w.Name + " "); } Console.WriteLine(); } } } class Program { static void Main(string[] args) { TierManager tm = new TierManager(); for (int c = 0; c < 10; c++) { tm.Add(); //create base widgets; } tm.Sweep(); tm.PrintAll(); Console.ReadLine(); } } }

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  • How to use java.Set

    - by owca
    I'm trying to make it working for quite some time,but just can't seem to get it. I have object Tower built of Block's. I've already made it working using arrays, but I wanted to learn Set's. I'd like to get similar functionality to this: public class Tower { public Tower(){ } public Tower add(Block k1){ //(...) //if block already in tower, return "Block already in tower" } public Tower delete(Block k1){ //(...) //if block already dleted, show "No such block in tower" } } Someone gave me some code, but I constantly get errors when trying to use it : Set<Block> tower = new HashSet<Block>(); boolean added = tower.add( k1 ); if( added ) { System.out.println("Added 1 block."); } else { System.out.println("Tower already contains this block."); } How to implement it ?

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  • Return number of matches from c# dictionary

    - by Rickard Haake
    Hello! I have a dictionary with non unique values and I want to count the matches of a string versus the values. Basically I now do dict.ContainsValue(a) to get a bool telling me if the string a exists in dict, but I want to know not only if it exists but how many times it exists (and maybee even get a list of the keys it exists bound to) Is there a way to do this using dictionary, or should I look for a different collection? /Rickard Haake

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  • .NET SortedDictionary But Sorted By Values

    - by Michael Covelli
    I need a data structure that acts like a SortedDictionary<int, double> but is sorted based on the values rather than the keys. I need it to take about 1-2 microseconds to add and remove items when we have about 3000 items in the dictionary. My first thought was simply to switch the keys and values in my code. This very nearly works. I can add and remove elements in about 1.2 microseconds in my testing by doing this. But the keys have to be unique in a SortedDictionary so that means that values in my inverse dictionary would have to be unique. And there are some cases where they may not be. Any ideas of something in the .NET libraries already that would work for me?

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  • How to implement List, Set, and Map in null free design?

    - by Pyrolistical
    Its great when you can return a null/empty object in most cases to avoid nulls, but what about Collection like objects? In Java, Map returns null if key in get(key) is not found in the map. The best way I can think of to avoid nulls in this situation is to return an Entry<T> object, which is either the EmptyEntry<T>, or contains the value T. Sure we avoid the null, but now you can have a class cast exception if you don't check if its an EmptyEntry<T>. Is there a better way to avoid nulls in Map's get(K)? And for argument sake, let's say this language don't even have null, so don't say just use nulls.

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  • Why collection literals ?

    - by Green Hyena
    Hi fellow Java programmers. From the various online articles on Java 7 I have come to know that Java 7 will be having collection literals like the following: List<String> fruits = [ "Apple", "Mango", "Guava" ]; Set<String> flowers = { "Rose", "Daisy", "Chrysanthemum" }; Map<Integer, String> hindiNums = { 1 : "Ek", 2 : "Do", 3 : "Teen" }; My questions are: 1] Wouldn't it have been possible to provide a static method of in all of the collection classes which could be used as follows: List<String> fruits = ArrayList.of("Apple", "Mango", "Guava"); IMO this looks as good as the literal version and is also reasonably concise. Why then did they have to invent a new syntax? 2] When I say List<String> fruits = [ "Apple", "Mango", "Guava" ]; what List would I actually get? Would it be ArrayList or LinkedList or something else? Thanks.

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  • Confused over behavior of List.mapi in F#

    - by James Black
    I am building some equations in F#, and when working on my polynomial class I found some odd behavior using List.mapi Basically, each polynomial has an array, so 3*x^2 + 5*x + 6 would be [|6, 5, 3|] in the array, so, when adding polynomials, if one array is longer than the other, then I just need to append the extra elements to the result, and that is where I ran into a problem. Later I want to generalize it to not always use a float, but that will be after I get more working. So, the problem is that I expected List.mapi to return a List not individual elements, but, in order to put the lists together I had to put [] around my use of mapi, and I am curious why that is the case. This is more complicated than I expected, I thought I should be able to just tell it to make a new List starting at a certain index, but I can't find any function for that. type Polynomial() = let mutable coefficients:float [] = Array.empty member self.Coefficients with get() = coefficients static member (+) (v1:Polynomial, v2:Polynomial) = let ret = List.map2(fun c p -> c + p) (List.ofArray v1.Coefficients) (List.ofArray v2.Coefficients) let a = List.mapi(fun i x -> x) match v1.Coefficients.Length - v2.Coefficients.Length with | x when x < 0 -> ret :: [((List.ofArray v1.Coefficients) |> a)] | x when x > 0 -> ret :: [((List.ofArray v2.Coefficients) |> a)] | _ -> [ret]

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  • Bind ISet in ASP.NET MVC2

    - by Dmitriy Nagirnyak
    Hi, I am trying to find out what would be the best bind first element of ISet (Iesi.Collection) as a first element. So basically I only have to use some kind of collection that has an indexer (and ISet doesn't) then I can write code like this (which works perfectly well): <%: Html.EditorFor(x => x.Company.PrimaryUsers[0].Email) %> But as the ISet has no indexer I cannot use it. So how can I then bind the first element of ISet in MVC2? Thanks, Dmitriy.

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  • Performance for myCollection.Add() vs. myCollection["key"]

    - by Atomiton
    When dealing with a collection of key/value pairs is there any difference between using its Add() method and directly assigning it? For example, a HtmlGenericControl will have an Attributes Collection: var anchor = new HtmlGenericControl("a"); // These both work: anchor.Attributes.Add("class", "xyz"); anchor.Attributes["class"] = "xyz"; Is it purely a matter of preference, or is there a reason for doing one or the other?

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  • How to create a typed stack using Objective-C

    - by Xetius
    I can create a stack class quite easily, using push and pop accessor methods to an NSArray, however. I can make this generic to take any NSObject derived class, however, I want to store only a specific class in this stack. Ideally I want to create something similar to Java's typed lists (List or List) so that I can only store that type in the stack. I can create a different class for each (ProjectStack or ItemStack), but this will lead to a more complicated file structure. Is there a way to do this to restrict the type of class I can add to a container to a specific, configurable type?

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  • Excel VBA: Passing a collection from a class to a module issue

    - by Martin
    Hello, I have been trying to return a collection from a property within a class to a routine in a normal module. The issue I am experiencing is that the collection is getting populated correctly within the property in the class (FetchAll) but when I pass the collection back to the module (Test) all the entries are populated with the last item in the list. This is the Test sub-routine in the standard module: Sub Test() Dim QueryType As New QueryType Dim Item Dim QueryTypes As Collection Set QueryTypes = QueryType.FetchAll For Each Item In QueryTypes Debug.Print Item.QueryTypeID, _ Left(Item.Description, 4) Next Item End Sub This is the FetchAll property in the QueryType class: Public Property Get FetchAll() As Collection Dim RS As Variant Dim Row As Long Dim QTypeList As Collection Set QTypeList = New Collection RS = .Run ' populates RS with a record set from a database (as an array), ' some code removed ' goes through the array and sets up objects for each entry For Row = LBound(RS, 2) To UBound(RS, 2) Dim QType As New QueryType With QType .QueryTypeID = RS(0, Row) .Description = RS(1, Row) .Priority = RS(2, Row) .QueryGroupID = RS(3, Row) .ActiveIND = RS(4, Row) End With ' adds new QType to collection QTypeList.Add Item:=QType, Key:=CStr(RS(0, Row)) Debug.Print QTypeList.Item(QTypeList.Count).QueryTypeID, _ Left(QTypeList.Item(QTypeList.Count).Description, 4) Next Row Set FetchAll = QTypeList End Property This is the output I get from the debug in FetchAll: 1 Numb 2 PBM 3 BPM 4 Bran 5 Claw 6 FA C 7 HNW 8 HNW 9 IFA 10 Manu 11 New 12 Non 13 Numb 14 Repo 15 Sell 16 Sms 17 SMS 18 SWPM This is the output I get from the debug in Test: 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM 18 SWPM Anyone got any ideas? I am probably totally overlooking something! Thanks, Martin

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  • java.lang.ClassNotFoundException using google commons

    - by pie154
    I have two classes inside a package. Both call a method from another class, one works perfectly fine and the other gives the error java.lang.ClassNotFoundException and the error java.lang.NoClassDefFoundError: com/google/common/base/Predicate The class path should be the same for both as they are in he same package so I can't figure out why one has access to the class and the other doesn't? thanks in advance for any help given.

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  • stack overflow on XMLListCollection collectionEvent

    - by reidLinden
    I'm working on a Flex 3 project, and I'm using a pair of XMLListCollection(s) to manage a combobox and a data grid. The combobox piece is working perfectly. The XMLListCollection for this is static. The user picks an item, and, on "change", it fires off an addItem() to the second collection. The second collection's datagrid then displays the updated list, and all is well. The datagrid, however, is editable. A further complication is that I have another event handler bound to the second XMLLIstCollection's "change" event, and in that handler, I do make additional changes to the second list. This essentially causes an infinite loop (a stack overflow :D ), of the second lists "change" handler. I'm not really sure how to handle this. Searching has brought up an idea or two regarding AutoUpdate functionality, but I wasn't able to get much out of them. In particular, the behavior persists, executing the 'updates' as soon as I re-enable, so I imagine I may be doing it wrong. I want the update to run, in general, just not DURING that code block. Thanks for your help!

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  • Is an "infinite" iterator bad design?

    - by Adamski
    Is it generally considered bad practice to provide Iterator implementations that are "infinite"; i.e. where calls to hasNext() always(*) return true? Typically I'd say "yes" because the calling code could behave erratically, but in the below implementation hasNext() will return true unless the caller removes all elements from the List that the iterator was initialised with; i.e. there is a termination condition. Do you think this is a legitimate use of Iterator? It doesn't seem to violate the contract although I suppose one could argue it's unintuitive. public class CyclicIterator<T> implements Iterator<T> { private final List<T> l; private Iterator it; public CyclicIterator<T>(List<T> l) { this.l = l; this.it = l.iterator(); } public boolean hasNext() { return !l.isEmpty(); } public T next() { T ret; if (!hasNext()) { throw new NoSuchElementException(); } else if (it.hasNext()) { ret = it.next(); } else { it = l.iterator(); ret = it.next(); } return ret; } public void remove() { it.remove(); } }

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  • How to sort a Map<Key, Value> on the values in Java?

    - by Abe
    I am relatively new to Java, and often find that I need to sort a Map on the values. Since the values are not unique, I find myself converting the keySet into an array, and sorting that array through array sort with a custom comparator that sorts on the value associated with the key. Is there an easier way?

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  • What is the big deal with IQueryable?

    - by jjr2527
    I've seen a lot of people talking about IQueryable and I haven't quite picked up on what all the buzz is about. I always work with generic List's and find they are very rich in the way you can "query" them and work with them, even run LINQ queries against them. So I'm wondering if there is a good reason to start considering a different default collection in my projects.

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  • Transpose a Collection

    - by Joseph Melettukunnel
    Hello, I've a list of different sizes of a T-Shirt, e.g. S, M, L. Since this might change for T-Shirts (sometimes we just have e.g. M, L), we load this into a List sizes. Since most DataGrids (xamDataGrid, WPF Toolkit DataGrid) need Properties for binding to the Columns, I'd like to transpose somehow my data. Does anyone have an idea how to do this? E.g. Instead of having List where Size { string sizeName, int available, int defect, int ordered} Avail. Defect Ordered [S] 1 2 3 [M] 1 2 3 [L] 1 2 3 I want an Object which has the Properties S, M, L containing the Values like this: [S] [M] [L] Avail. 1 2 3 Defect 1 2 3 Ordered 1 2 3 The problem here is that I don't know how many sizes will be available for the tshirt, it might be 3, 4, or 10. Thanks for any help Cheers PS: Here is a mockup of how the final grid should look like http://img39.imageshack.us/img39/9161/multirowspangridfixedel.png

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  • c# reflection - getting the first item out of a reflected collection without casting to specific col

    - by Andy Clarke
    Hi, I've got a Customer object with a Collection of CustomerContacts IEnumerable Contacts { get; set; } In some other code I'm using Reflection and have the PropertyInfo of Contacts property var contacts = propertyInfo.GetValue(customerObject, null); I know contacts has at least one object in it, but how do I get it out? I don't want to Cast it to IEnumerable because I want to keep my reflection method dynamic. I thought about calling FirstOrDefault() by reflection - but can't do that easily because its an extension method. Does anyone have any ideas? Thanks

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  • How to traverse the item in the collection in a List or Observable collection?

    - by Ashish Ashu
    I have a collection that is binded to my Listview. I have provided options to user to "move up" "move down" the selected item in the list view. I have binded the selected item of the listview to my viewmodel, hence I get the item in the collection on which user want to do the operation. I have attached "move up" "move down" commands in my viewmodel. I want what is the best way to move up and down in the collection in the collection which is reflected in the list view. Please suggest.

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  • Method in ICollection in C# that adds all elements of another ICollection to it

    - by drasto
    Is there some method in ICollection in C# that would add all elements of another collection? Right now I have to always write foreach cycle for this: ICollection<Letter> allLetters = ... //some initalization ICollection<Letter> justWrittenLetters = ... //some initalization ... //some code, adding to elements to those ICollections foreach(Letter newLetter in justWrittenLetters){ allLetters.add(newLetter); } My question is, is there method that can replace that cycle? Like for example the method addAll(Collection c) in Java ? So I would write only something like: allLetters.addAll(justWrittenLetters);

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  • IList<Item> Collection Class accessing database

    - by Mike
    Hi, I have a database with Users. Users have Items. These Items can change actively. How do you access the items in a collection type format? For the user, I fill all the user properties at the time of instantiation. If I load the user's items at the time of the instantiation, and the items change, they will have old data. I was thinking, maybe I need an ItemCollection class and have that a field/property apart of the user class, that way to traverse all the user's items I could use a foreach loop. So, my question is, what is the best practice/best way of accessing the items from a database using some sort of collection? On accessing the particular Item, it needs to get the latest database information, and when the user does do a foreach loop, the latest item information must be available. I.e. What I'm trying to do Console.WriteLine(User.Items[3].ID); returns 5. //this updates the item information and saves it to the database. User.Items[3].ID = 13; //Add a new item to the database. User.Items.Add(new Item { id = 17}); foreach (Item item in User.Items) { //this would traverse all items in the database. //not some cached copy at the time of instantiation of the user. }

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