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  • which collection should I use

    - by Masna
    Hello, I have a number of custom objects of type X. X has a number of parameters and must be unique in the collection. (I created my own equals method based on the custom parameters to examine this) In each object of type x, I have a list of objects y. I want to add/remove/modify easily an object y. For example: To write the add method, it would be something like add(objTypeX, objTypeY) I would check or the collections already has a objTypeX. If so: i would add the objTypeY to the already existing objTypeX else: i would create objTypeX and add objTypeY to this object. To modify an objTypeY, it would be something like(objTypeX, objTypeY, newobjTypeY) I would get objTypeX out of the collections and modify objTypeY to newobjTypeY Which collections should I use? I tried with hashset but i can get a specific object out of the list, without run down the list till I find that object. I develop this in vb.net 3.5

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  • Direct comparator in Java out of the box

    - by KARASZI István
    I have a method which needs a Comparator for one of its parameters. I would like to pass a Comparator which does a normal comparison and a reverse comparator which does in reverse. java.util.Collections provides a reverseOrder() this is good for the reverse comparison, but I could not find any normal Comparator. The only solution what came into my mind is Collections.reverseOrder(Collections.reverseOrder()). but I don't like it because the double method calling inside. Of course I could write a NormalComparator like this: public class NormalComparator<T extends Comparable> implements Comparator<T> { public int compare(T o1, T o2) { return o1.compareTo(o2); } } But I'm really surprised that Java doesn't have a solution for this out of the box.

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  • How do you get an object associated with a Future Actor?

    - by Bruce Ferguson
    I would like to be able to get access to the object that is being returned from spawning a future import scala.actors.Future import scala.actors.Futures._ class Object1(i:Int) { def getAValue(): Int = {i} } object Test { def main( args: Array[String] ) = { var tests = List[Future[Object1]]() for(i <- 0 until 10) { val test = future { val obj1 = new Object1(i) println("Processing " + i + "...") Thread.sleep(1000) println("Processed " + i) obj1 } tests = tests ::: List(test) } val timeout = 1000 * 60 * 5 // wait up to 5 minutes val futureTests = awaitAll(timeout,tests: _*) futureTests.foreach(test => println("result: " + future())) } } The output from one run of this code is: Processing 0... Processing 1... Processing 2... Processing 3... Processed 0 Processing 4... Processed 1 Processing 5... Processed 2 Processing 6... Processed 3 Processing 7... Processed 4 Processing 8... Processed 6 Processing 9... Processed 5 Processed 7 Processed 8 Processed 9 result: <function0> result: <function0> result: <function0> result: <function0> result: <function0> result: <function0> result: <function0> result: <function0> result: <function0> result: <function0> I've tried future().getClass(), and the output is result: class scala.actors.FutureActor What I'm looking to be able to access is the obj1 objects. Thanks Bruce

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  • is it possible to write data to a collection in wpf?

    - by randyc
    Hello. In looking through samples I have seen a number of examples where it is possible to present data within a wpf applicaiton by binding to collections. However I was wondering is it possible to write to a collection from an applicaiton. Say for example i have 2 or more fields such as names and I wanted to have hte ability to add up to three names in my application ( all stored in memory). Will collections serve this purpose. In the past with asp.net I have done this by creating data tables and storing values on the fly or during the session. I am trying to learn WPF and I was wondering if collections work in the same fashion? If so could you please post an example or point me to references that show examples of this? Thank you in advance.

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  • Can I transform this asynchronous java network API into a monadic representation (or something else

    - by AlecZorab
    I've been given a java api for connecting to and communicating over a proprietary bus using a callback based style. I'm currently implementing a proof-of-concept application in scala, and I'm trying to work out how I might produce a slightly more idiomatic scala interface. A typical (simplified) application might look something like this in Java: DataType type = new DataType(); BusConnector con = new BusConnector(); con.waitForData(type.getClass()).addListener(new IListener<DataType>() { public void onEvent(DataType t) { //some stuff happens in here, and then we need some more data con.waitForData(anotherType.getClass()).addListener(new IListener<anotherType>() { public void onEvent(anotherType t) { //we do more stuff in here, and so on } }); } }); //now we've got the behaviours set up we call con.start(); In scala I can obviously define an implicit conversion from (T = Unit) into an IListener, which certainly makes things a bit simpler to read: implicit def func2Ilistener[T](f: (T => Unit)) : IListener[T] = new IListener[T]{ def onEvent(t:T) = f } val con = new BusConnector con.waitForData(DataType.getClass).addListener( (d:DataType) => { //some stuff, then another wait for stuff con.waitForData(OtherType.getClass).addListener( (o:OtherType) => { //etc }) }) Looking at this reminded me of both scalaz promises and f# async workflows. My question is this: Can I convert this into either a for comprehension or something similarly idiomatic (I feel like this should map to actors reasonably well too) Ideally I'd like to see something like: for( d <- con.waitForData(DataType.getClass); val _ = doSomethingWith(d); o <- con.waitForData(OtherType.getClass) //etc )

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  • What are the requirements of a collection type when model binding?

    - by Richard Ev
    I have been reviewing model binding with collections, specifically going through this article http://weblogs.asp.net/nmarun/archive/2010/03/13/asp-net-mvc-2-model-binding-for-a-collection.aspx However, the model I would like to use in my code does not implement collections using generic lists. Instead it uses its own collection classes, which inherit from a custom generic collection base class, the declaration of which is public abstract class CollectionBase<T> : IEnumerable<T> The collections in my POSTed action method are all non-null, but contain no elements. Can anyone advise?

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  • GAE JCache NumberFormatException, will I need to write Java to avoid?

    - by Jasper
    This code below produces a NumberFormatException in this line: val cache = cf.createCache(Collections.emptyMap()) Do you see any errors? Will I need to write a Java version to avoid this, or is there a Scala way? ... import java.util.Collections import net.sf.jsr107cache._ object QueryGenerator extends ServerResource { private val log = Logger.getLogger(classOf[QueryGenerator].getName) } class QueryGenerator extends ServerResource { def getCounter(cache:Cache):long = { if (cache.containsKey("counter")) { cache.get("counter").asInstanceOf[long] } else { 0l } } @Get("html") def getHtml(): Representation = { val cf = CacheManager.getInstance().getCacheFactory() val cache = cf.createCache(Collections.emptyMap()) val counter = getCounter(cache) cache.put("counter", counter + 1) val q = QueueFactory.getQueue("query-generator") q.add(TaskOptions.Builder.url("/tasks/query-generator").method(Method.GET).countdownMillis(1000L)) QueryGenerator.log.warning(counter.toString) new StringRepresentation("QueryGenerator started!", MediaType.TEXT_HTML) } } Thanks!

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  • Fluent NHibernate Automap does not take into account IList<T> collections as indexed

    - by Francisco Lozano
    I am using automap to map a domain model (simplified version): public class AppUser : Entity { [Required] public virtual string NickName { get; set; } [Required] [DataType(DataType.Password)] public virtual string PassKey { get; set; } [Required] [DataType(DataType.EmailAddress)] public virtual string EmailAddress { get; set; } public virtual IList<PreferencesDescription> PreferencesDescriptions { get; set; } } public class PreferencesDescription : Entity { public virtual AppUser AppUser { get; set; } public virtual string Content{ get; set; } } The PreferencesDescriptions collection is mapped as an IList, so is an indexed collection (when I require standard unindexed collections I use ICollection). The fact is that fluent nhibernate's automap facilities map my domain model as an unindexed collection (so there's no "position" property in the DDL generated by SchemaExport). ¿How can I make it without having to override this very case - I mean, how can I make Fluent nhibernate's automap make always indexed collections for IList but not for ICollection

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  • Render multiple control collections in ASP.NET custom control

    - by Monty
    I've build a custom WebControl, which has the following structure: <gws:ModalBox ID="ModalBox1" HeaderText="Title" runat="server"> <Contents>(controls...)</Contents> <Footer>(controls...)</Footer> </gws:ModalBox> The control contains two ControlCollection properties, 'Contents' and 'Footer'. Never tried to build a control with multiple control collections, but solved it like this (simplified): [PersistChildren(false), ParseChildren(true)] public class ModalBox : WebControl { private ControlCollection _contents; private ControlCollection _footer; public ModalBox() : base() { this._contents = base.CreateControlCollection(); this._footer = base.CreateControlCollection(); } [PersistenceMode(PersistenceMode.InnerProperty)] public ControlCollection Contents { get { return this._contents; } } [PersistenceMode(PersistenceMode.InnerProperty)] public ControlCollection Footer { get { return this._footer; } } protected override void RenderContents(HtmlTextWriter output) { // Render content controls. foreach (Control control in this.Contents) { control.RenderControl(output); } // Render footer controls. foreach (Control control in this.Footer) { control.RenderControl(output); } } } However it seems to render properly, it doesn't work anymore if I add some asp.net labels and input controls inside the property. I'll get the HttpException: Unable to find control with id 'KeywordTextBox' that is associated with the Label 'KeywordLabel'. Somewhat understandable, because the label appears before the textbox in the controlcollection. However, with default asp.net controls it does work, so why doesn't this work? What am I doing wrong? Is it even possible to have two control collections in one control? Should I render it differently? Thanks for replies.

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  • Load collections eagerly in NHibernate using Criteria API

    - by Zuber
    I have an entity A which HasMany entities B and entities C. All entities A, B and C have some references x,y and z which should be loaded eagerly. I want to read from the database all entities A, and load the collections of B and C eagerly using criteria API. So far, I am able to fetch the references in 'A' eagerly. But when the collections are loaded, the references within them are lazily loaded. Here is how I do it AllEntities_A = _session.CreateCriteria(typeof(A)) .SetFetchMode("x", FetchMode.Eager) .SetFetchMode("y", FetchMode.Eager) .List<A>().AsQueryable(); The mapping of entity A using Fluent is as shown below. _B and _C are private ILists for B & C respectively in A. Id(c => c.SystemId); Version(c => c.Version); References(c => c.x).Cascade.All(); References(c => c.y).Cascade.All(); HasMany<B>(Reveal.Property<A>("_B")) .AsBag() .Cascade.AllDeleteOrphan() .Not.LazyLoad() .Inverse() .Cache.ReadWrite().IncludeAll(); HasMany<C>(Reveal.Property<A>("_C")) .AsBag() .Cascade.AllDeleteOrphan() .LazyLoad() .Inverse() .Cache.ReadWrite().IncludeAll(); I don't want to make changes to the mapping file, and would like to load the entire entity A eagerly. i.e. I should get a List of A's where there will be List of B's and C's whose reference properties will also be loaded eagerly

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  • Writing lambda functions in Scala

    - by user2433237
    I'm aware that you can write anonymous functions in Scala but I'm having trouble trying to convert a piece of code from Scheme. Could anyone help me convert this to Scala? (define apply-env (lambda (env search-sym) (cases environment env (empty-env () (eopl:error 'apply-env "No binding for ~s" search-sym)) (extend-env (var val saved-env) (if (eqv? search-sym var) val (apply-env saved-env search-sym))) (extend-env-rec (p-name b-var p-body saved-env) (if (eqv? search-sym p-name) (proc-val (procedure b-var p-body env)) (apply-env saved-env search-sym)))))) Thanks in advance

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  • More nest Python nested dictionaries.

    - by clutch
    After reading http://stackoverflow.com/questions/635483/what-is-the-best-way-to-implement-nested-dictionaries-in-python why is it wrong to do: c = collections.defaultdict(collections.defaultdict(int)) in python? I would think this would work to produce {key:{key:1}} or am I thinking about it wrong?

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  • What Are Collections Implemented As In VB6?

    - by Tom Tresansky
    So a collection in VB6 keeps track of a key for each object, and you can look up the object by its key. Does that mean collections are implemented as some sort of hashtable under the hood? I realize you can have multiple items with the same key in a collection, hence the SOME SORT. Anybody know what type data structure a VB6 collection is supposed to represent?

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  • Javacing code in terminal havivng a Jar in CLASSPATH

    - by Masi
    How can you javac the code in terminal by using google-collections in CLASSPATH? Example of code trying to javac in terminal (works in Eclipse) import com.google.common.collect.BiMap; import com.google.common.collect.HashBiMap; public class Locate { ... BiMap<MyFile, Integer> rankingToResult = HashBiMap.create(); ... } Javacing in terminaling src 288 % javac Locate.java Locate.java:14: package com.google.common.collect does not exist import com.google.common.collect.BiMap; ^ Locate.java:15: package com.google.common.collect does not exist import com.google.common.collect.HashBiMap; ^ Locate.java:153: cannot find symbol symbol : class BiMap location: class Locate BiMap<MyFile, Integer> rankingToResult = HashBiMap.create(); ^ Locate.java:153: cannot find symbol symbol : variable HashBiMap location: class Locate BiMap<MyFile, Integer> rankingToResult = HashBiMap.create(); ^ 4 errors My CLASSPATH src 289 % echo $CLASSPATH /u/1/bin/javaLibraries/google-collect-1.0.jar

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  • Unit testing several implementation of the same trait/interface

    - by paradigmatic
    I program mostly in scala and java, using scalatest in scala and junit for unit testing. I would like to apply the very same tests to several implementations of the same interface/trait. The idea is to verify that the interface contract is enforced and to check Liskov substitution principle. For instance, when testing implementations of lists, tests could include: An instance should be empty, if and only if and only if it has zero size. After calling clear, the size sould be zero. Adding an element in the middle of a list, will increment by one the index of rhs elements. etc. What are the best practices ?

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  • http(/* argument here */) How is this Object (Http) being used without an explicit or implicit meth

    - by Randin
    In the example for coding with Json using Databinder Dispatch Nathan uses an Object (Http) without a method, shown here: import dispatch._ import Http._ Http("http://www.fox.com/dollhouse/" >>> System.out ) How is he doing this? Thank you for all of the answers unfortunatly I was not specific enough... It looks like it is simply passing an argument to a constructor of class or companion object Http. In another example, I've seen another form: http = new Http http(/* argument here */) Is this valid Scala? I guess it must be, because the author is a Scala expert. But it makes no sense to me. Actions are usually performed by invoking methods on objects, whether explicitly as object.doSomething() or implicitly as object = something (using the apply() method underneath the syntactic sugar). All I can think of is that a constructor is being used to do something in addition to constructing an object. In other words, it is having side effects, such as in this case going off and doing something on the web.

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  • Cost of using repeated parameters

    - by Palimondo
    I consider refactoring few method signatures that currently take parameter of type List or Set of concrete classes --List[Foo]-- to use repeated parameters instead: Foo*. This would allow me to use the same method name and overload it based on the parameter type. This was not possible using List or Set, because List[Foo] and List[Bar] have same type after erasure: List[Object]. In my case the refactored methods work fine with scala.Seq[Foo] that results from the repeated parameter. I would have to change all the invocations and add a sequence argument type annotation to all collection parameters: baz.doStuffWith(foos:_*). Given that switching from collection parameter to repeated parameter is semantically equivalent, does this change have some performance impact that I should be aware of? Is the answer same for scala 2.7._ and 2.8?

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  • Migrating from Maven to SBT

    - by Vasil Remeniuk
    Hi people, As you know, SBT is compatible with Maven in some way -- SBT recognizes simple Maven POMs and can use dependencies and repositories specified in them. However, SBT wiki says that, if inline dependency is specified in SBT project definition, POM will be ignored (so using both in this case is impossible): Maven and Ivy configurations (pom.xml and ivy.xml) are ignored when inline dependency declarations are present. Does anyone know, if any kind of converter from Maven POM to SBT project definition exists (translating POM's XML into project definition Scala code)? I'm considering writing such script (that will help to migrate my old Scala/Maven projects to SBT), but want to know first, if this functionality already exists. Thanks in advance.

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  • Discovering a functional algorithm from a mutable one

    - by Garrett Rowe
    This isn't necessarily a Scala question, it's a design question that has to do with avoiding mutable state, functional thinking and that sort. It just happens that I'm using Scala. Given this set of requirements: Input comes from an essentially infinite stream of random numbers between 1 and 10 Final output is either SUCCEED or FAIL There can be multiple objects 'listening' to the stream at any particular time, and they can begin listening at different times so they all may have a different concept of the 'first' number; therefore listeners to the stream need to be decoupled from the stream itself. Pseudocode: if (first number == 1) SUCCEED else if (first number >= 9) FAIL else { first = first number rest = rest of stream for each (n in rest) { if (n == 1) FAIL else if (n == first) SUCCEED else continue } } Here is a possible mutable implementation: sealed trait Result case object Fail extends Result case object Succeed extends Result case object NoResult extends Result class StreamListener { private var target: Option[Int] = None def evaluate(n: Int): Result = target match { case None => if (n == 1) Succeed else if (n >= 9) Fail else { target = Some(n) NoResult } case Some(t) => if (n == t) Succeed else if (n == 1) Fail else NoResult } } This will work but smells to me. StreamListener.evaluate is not referentially transparent. And the use of the NoResult token just doesn't feel right. It does have the advantage though of being clear and easy to use/code. Besides there has to be a functional solution to this right? I've come up with 2 other possible options: Having evaluate return a (possibly new) StreamListener, but this means I would have to make Result a subtype of StreamListener which doesn't feel right. Letting evaluate take a Stream[Int] as a parameter and letting the StreamListener be in charge of consuming as much of the Stream as it needs to determine failure or success. The problem I see with this approach is that the class that registers the listeners should query each listener after each number is generated and take appropriate action immediately upon failure or success. With this approach, I don't see how that could happen since each listener is forcing evaluation of the Stream until it completes evaluation. There is no concept here of a single number generation. Is there any standard scala/fp idiom I'm overlooking here?

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  • Implicit parameter in Scalaz

    - by Thomas Jung
    I try to find out why the call Ø in scalaz.ListW.<^> works def <^>[B: Zero](f: NonEmptyList[A] => B): B = value match { case Nil => Ø case h :: t => f(Scalaz.nel(h, t)) } My minimal theory is: trait X[T]{ def y : T } object X{ implicit object IntX extends X[Int]{ def y = 42 } implicit object StringX extends X[String]{ def y = "y" } } trait Xs{ def ys[T](implicit x : X[T]) = x.y } class A extends Xs{ def z[B](implicit x : X[B]) : B = ys //the call Ø } Which produces: import X._ scala> new A().z[Int] res0: Int = 42 scala> new A().z[String] res1: String = y Is this valid? Can I achieve the same result with fewer steps?

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  • IntelliJ doesn't seem to pickup certain sbt libraries, no code completion

    - by Blankman
    I am using sbt console in my terminal to compile my scala/play project. I am using intellij to edit my source code, basically using it just for getting some code completion and navigation etc. For some reason certain libraries don't seem to load correctly. For example, I added elastic search to my Dependancies.scala file, reloaded sbt and everything compiles fine but for some reason IntelliJ doesn't pickup the jars correctly i.e. they are in red and there is no syntax completion. How can I fix this? I tried shutting intellij down and restarting it but the problem remains. I am using Intelli 13.1.3 (ultimate)

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  • Misc. Naming: Can I place underscores instead of camel casing in modern languages?

    - by Bubba88
    Hi! I would like to ask some kind of permission (I hope that doesn't sound strange) from the people who have influence on the naming conventions in modern languages like F#, Scala, etc. My problem is - I just can't read camelCased code and wish I could write underscored_names at least in my internal implementations (not in API interface). This applies to just everything - local var names, method names, params.. (Not class names I think) It seems that now the camel-casing is preferred for example for the names of object methods, but could that be not the only way? What would you say; Can I go with underscored names in languages like I mentioned (F#, Scala)?

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  • How can I run a package created with Simple Build Tool?

    - by Lukasz Lew
    I run: $ echo 'object Hi { def main(args: Array[String]) { println("Hi!") } }' > hw.scala $ sbt > warn Set log level to warn > run Hi! > package $ java -jar target/scala_2.7.7/test_2.7.7-1.0.jar Exception in thread "main" java.lang.NoClassDefFoundError: scala/ScalaObject at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:621) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124) at java.net.URLClassLoader.defineClass(URLClassLoader.java:260) Why can't I run this jar package this way?

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