I am doing a project in Apache hama to implement breadth first search and am facing trouble in partitioning the input graph.can anybody suggest a method to do the same?
public static class MinIntCombiner extends Combiner<IntWritable> {
#Override
public IntWritable combine(Iterable<IntWritable> messages) {
int visited = Integer.MAX_VALUE;
Iterator<IntWritable> it = messages.iterator();
// int msgValue = it.next().get();
while (it.hasNext()== true) {
int msgValue = it.next().get();
if (visited > msgValue)
visited = msgValue;
// msgValue = it.next().get();
}
return new IntWritable(visited);
}
The partitioner used here is
ssspJob.setPartitioner(HashPartitioner.class);
As we cannot use Hashpartitioner for bfs, can anyone suggest an alternative method?
Related
I have a Blazor server app. Some variables on a specific razor page (main.razor) are defined as static because I want that these variables keep their values when the client navigates to other pages in the same project and comes back again to main.razor. So far it is working good.
But when I refresh the complete page, or even close the tab and reopen my app (login again), I see that the static variables still keep their values. How can prevent this? Of course I want that the values return to their default values (like 0 or ""), when the client makes a login or refreshes the page with F5. How can I do that?
I have defined the related variables in the following way:
private static StringBuilder log = new StringBuilder();
public static string testvar1= "";
public static int testvar2= 0;
Statics exist for the lifetime of the application instance which explains the behaviour you see.
You need to be maintaining state. At one end of the spectrum you can implement a State Management system such as Fluxor. At the other just create a user class, set it up as a service and inject it as a Scoped Service. Or you can build a middle-of-the-road solution.
This is mine.
A generic UIStateService that maintains a Dictionary of (state)objects against a Guid.
public class UIStateService
{
private Dictionary<Guid, object> _stateItems = new Dictionary<Guid, object>();
public void AddStateData(Guid Id, object value)
{
if (_stateItems.ContainsKey(Id))
_stateItems[Id] = value;
else
_stateItems.Add(Id, value);
}
public void ClearStateData(Guid Id)
{
if (_stateItems.ContainsKey(Id))
_stateItems.Remove(Id);
}
public bool TryGetStateData<T>(Guid Id, out T? value)
{
value = default;
if (Id == Guid.Empty)
return false;
var isdata = _stateItems.ContainsKey(Id);
var val = isdata
? _stateItems[Id]
: default;
if (val is T)
{
value = (T)val;
return true;
}
return false;
}
}
Set it up as a service:
builder.Services.AddScoped<UIStateService>();
Next define a simple template ComponentBase page that contains the common page code:
using Blazr.UI;
using Microsoft.AspNetCore.Components;
namespace BlazorApp2.Pages
{
public class StatePage : ComponentBase
{
// this provides a guid for this specific page during the lifetime of the application runtime
// we use this as the reference to store the state data against
private static Guid RouteId = Guid.NewGuid();
[Inject] protected UIStateService UIStateService { get; set; } = default!;
protected void SaveState<T>(T state) where T : class, new()
{
if (RouteId != Guid.Empty)
this.UIStateService.AddStateData(RouteId, state);
}
protected bool GetState<T>( out T value) where T : class, new()
{
value = new T();
if (RouteId != Guid.Empty && this.UIStateService.TryGetStateData<T>(RouteId, out T? returnedState))
{
value = returnedState ?? new T();
return true;
}
else
return false;
}
}
}
And use it in a page:
#page "/"
#inherits StatePage
<PageTitle>Index</PageTitle>
<h1>Hello, world!</h1>
Welcome to your new app.
<SurveyPrompt Title="How is Blazor working for you?" />
<div class="p-2">
<button class="btn btn-primary" #onclick=SetData>Set Data</button>
</div>
<div class="p-3 text-primary">
State Time : #stateData.StateTime;
</div>
#code {
private MyStateData stateData = new MyStateData();
protected override void OnInitialized()
{
if (this.GetState<MyStateData>(out MyStateData value))
this.stateData = value;
else
this.SaveState<MyStateData>(this.stateData);
}
private void SetData()
{
this.stateData.StateTime = DateTime.Now.ToLongTimeString();
SaveState<MyStateData>(this.stateData);
}
public class MyStateData
{
public string StateTime { get; set; } = DateTime.Now.ToLongTimeString();
}
}
You can now navigate around the application and the state will be maintained for the page.
You can apply an observer/notification pattern to the state object to trigger automatic state updates if you wish.
I have some code that generates answers based on the user input. But in somecases i need to update the values later by calling SetAnswers But when i compile my code i get the following error:
NullReferenceException: Object reference not set to an instance of an object
I get this error on the line marked by the arrow.
See below for my code:
public class Generate_Questions : MonoBehaviour{
public Question q5, q4;
void Start(){
q4 = create_question("Select object to edit", EXTERNAL);
Visual_Question vq1 = new Visual_Question(1, q4, new vector(1,1,1), Ui, Canvas);
vq1.draw_question();
}
void Update(){
}
public class Visual_Question : Generate_Questions{
public Visual_Question(int order_id, Question q, Vector2 loc, Dictionary<string, RectTransform> ui, RectTransform canvas){
}
public void draw_question(){
q4.SetAnswers(new Answer[]{ <--------- this generates the error.
new Answer(null, "Select an option")
});
}
}
public class Question{
public string text;
public int answers_loc;
public List<Answer> answers;
public Question(string q_text, int answers_loc){
answers = new List<Answer>();
this.text = q_text;
this.answers_loc = answers_loc;
}
public void SetAnswers(Answer[] c_answers){
foreach(Answer answer in c_answers){
this.answers.Add(answer);
}
}
public bool CheckIfAnswersAvailable(){
if(answers.Count > 0){
return true;
}else{
return false;
}
}
public int QuestionLocation(){
return answers_loc;
}
}
public Question create_question(string text, int a_type){
Question Q = new Question(text, a_type);
return Q;
}
public interface IAnswer{
string GetText();
string GetDataType();
object GetValue();
Question GetNextQuestion();
}
public class Answer : IAnswer{
public string text;
public Question next = null;
public int? action = null;
public Element obj = null;
public string property = null;
public float? value = null;
public Answer(Question next, string text){
this.text = text;
this.next = next;
}
public Answer(Question next, string text, Element obj, int? action){
this.action = action;
this.text = text;
this.next = next;
this.obj = obj;
}
public Answer(Question next, string text, Element obj, int? action, string property, float? value){
this.action = action;
this.next = next;
this.text = text;
this.obj = obj;
this.property = property;
this.value = value;
}
public string GetText(){
return text;
}
public string GetDataType(){
throw new System.NotImplementedException();
}
public object GetValue(){
return value;
}
public Question GetNextQuestion(){
return next;
}
}
}
how would i go about fixing this problem? I am a complete newbie to c#. So my question may be already answered but i just dont know what i am looking for.
I assume that IAnswer[] is an interface and since you are trying to initialize an abstract object you get that runtime exception
NullReferenceException: Object reference not set to an instance of an object
if you want to create instance of IAnswer object you have to restructure it like class or structure.
Your class Visual_Question derives from Generate_Questions, so the member q4 that you use en draw_question is not initialized. This is not the member of Generated_Questions but a member of Visual_Question that is not initialized.
In Generate_Questions you are creating a new instance of Visual_Question and then immediately calling draw_question on that new instance. You now have 2 instances of a question (both derive from Generate_Questions), but only one of them has had the Start method, which initializes q4 called. If, however, you attempt to call Start from your second instance, you're going to find yourself in an infinite series of recursive calls and quickly crash with a different error (a stack overflow in this case).
One issue with the current code is that Generate_Questions sounds more like an action than a class. I'd suggest removing the inheritance from Visual_Question and make that an interface that you would implement on Question. Question should probably have the create_question method removed. That probably belongs in a MonoBehavior script (technically it's a factory method -- look up the factory pattern -- I'm not going to go into it here since this is a beginner topic).
Something like (obviously not complete):
public class Generate_Questions : MonoBehaviour
{
private IVisualQuestion q4;
void Start()
{
q4 = new Question("Select object to edit", EXTERNAL);
q4.DrawQuestion(new vector(1,1,1), Ui, Canvas)
}
void Update() {}
}
public interface IVisualQuestion
{
void DrawQuestion(Vector2 loc, Dictionary<string, RectTransform> ui, RectTransform canvas);
}
public class Question : IVisualQuestion
{
// ... insert the Question constructor and code here ...
// Implement VisualQuestion interface
public void DrawQuestion(Vector2 loc, Dictionary<string, RectTransform> ui, RectTransform canvas)
{
this.SetAnswers(new Answer[]{new Answer(null, "Select an option")});
}
}
In general, you probably don't need inheritance. As you learn more C#, you'll discover that when inheritance is going to help it will be clear. More often than not, using an interface is a far better and flexible approach. As a commenter noted, you probably don't want to inherit from MonoBehavior. You really only need that for classes that the Unity Engine is going to directly handle.
Another note: the convention in C# is to name methods, variables, etc. in PascalCase, not using underscores to separate words.
Although I'm relatively new to AutoMapper I'm using it in a small project I'm developing. I've never had problems using it before but now I'm facing some weird behavior passing parameters to a Custom Resolver.
Here's the scenario: I get a list of messages from my repository and then map those to a frontend friendly version of it. Nothing fancy, just some normal mapping between objects. I have a field in that frontend object that tells if a certain user already voted for that message and that's what I'm using the Custom Resolver for (it's that second "ForMember"):
public List<SupportMessageUi> GetAllVisible(string userId)
{
Mapper.CreateMap<SupportMessage, SupportMessageUi>()
.ForMember(dest => dest.Votes,
opt => opt.ResolveUsing<SupportMessageVotesResolver>())
.ForMember(dest => dest.UserVoted,
opt => opt.ResolveUsing<SupportMessagesUserVotedResolver>()
.ConstructedBy(() => new SupportMessagesUserVotedResolver(userId)));
var messages = _unitOfWork.MessagesRepository.Get(m => m.Visible);
var messagesUi = Mapper.Map<List<SupportMessageUi>>(messages);
return messagesUi;
}
I'm calling this method on a web service and the problem is: the first time I call the webservice (using the webservice console) it all runs perfectly. For example, if I pass '555' as the userId I get to this method with the correct value:
And in the Custom Resolver the value was correctly passed to the constructor:
The results returned are correct. The problem comes next. The second time I call the service, passing a different argument ('666' this time) the argument that gets to the constructor of the Custom Resolver is the old one ('555'). Here's what I mean:
Right before mapping the objects we can see that the value passed to the constructor was correct ('666'):
But when it gets to the constructor of the Resolver the value is wrong, and is the old one ('555'):
All subsequent calls to the service use the original value in the Custom Resolver constructor ('555'), independently of the value I pass to the service (also happens if I make the call from another browser). If I shut down the server and relaunch it I can pass a new parameter (that will be used in all other calls until I shut it down again).
Any idea on why this is happening?
It's happening because AutoMapper.CreateMap is a static method, and only needs to be called once. With the CreateMap code in your web method, you're trying to call it every time you call that method on your web service. Since the web server process stays alive between calls (unless you restart it, like you said) then the static mappings stay in place. Hence, the necessity of calling AutoMapper.Reset, as you said in your answer.
But it's recommended that you put your mapping creation in AppStart or Global or a static constructor or whatever, so you only call it once. There are ways to call Map that allow you to pass in values, so you don't need to try to finesse things with the constructor of your ValueResolver.
Here's an example using a ValueResolver (note the change to implementing IValueResolver instead of inheriting ValueResolver<TSource, TDestination>):
[Test]
public void ValueTranslator_ExtraMapParameters()
{
const int multiplier = 2;
ValueTranslator translator = new ValueTranslator();
Mapper.AssertConfigurationIsValid();
ValueSource source = new ValueSource { Value = 4 };
ValueDest dest = translator.Translate(source, multiplier);
Assert.That(dest.Value, Is.EqualTo(8));
source = new ValueSource { Value = 5 };
dest = translator.Translate(source, multiplier);
Assert.That(dest.Value, Is.EqualTo(10));
}
private class ValueTranslator
{
static ValueTranslator()
{
Mapper.CreateMap<ValueSource, ValueDest>()
.ForMember(dest => dest.Value, opt => opt.ResolveUsing<ValueResolver>().FromMember(src => src.Value));
}
public ValueDest Translate(ValueSource source, int multiplier)
{
return Mapper.Map<ValueDest>(source, opt => opt.Items.Add("multiplier", multiplier));
}
private class ValueResolver : IValueResolver
{
public ResolutionResult Resolve(ResolutionResult source)
{
return source.New((int)source.Value * (int)source.Context.Options.Items["multiplier"]);
}
}
}
private class ValueSource { public int Value { get; set; } }
private class ValueDest { public int Value { get; set; } }
And here's an example using a TypeConverter:
[Test]
public void TypeTranslator_ExtraMapParameters()
{
const int multiplier = 3;
TypeTranslator translator = new TypeTranslator();
Mapper.AssertConfigurationIsValid();
TypeSource source = new TypeSource { Value = 10 };
TypeDest dest = translator.Translate(source, multiplier);
Assert.That(dest.Value, Is.EqualTo(30));
source = new TypeSource { Value = 15 };
dest = translator.Translate(source, multiplier);
Assert.That(dest.Value, Is.EqualTo(45));
}
private class TypeTranslator
{
static TypeTranslator()
{
Mapper.CreateMap<TypeSource, TypeDest>()
.ConvertUsing<TypeConverter>();
}
public TypeDest Translate(TypeSource source, int multiplier)
{
return Mapper.Map<TypeDest>(source, opt => opt.Items.Add("multiplier", multiplier));
}
private class TypeConverter : ITypeConverter<TypeSource, TypeDest>
{
public TypeDest Convert(ResolutionContext context)
{
TypeSource source = (TypeSource)context.SourceValue;
int multiplier = (int)context.Options.Items["multiplier"];
return new TypeDest { Value = source.Value * multiplier };
}
}
}
private class TypeSource { public int Value { get; set; } }
private class TypeDest { public int Value { get; set; } }
Answering myself: I was not using AutoMapper.Reset(). Once I did that everything started working properly.
Helpful reading: http://www.markhneedham.com/blog/2010/01/27/automapper-dont-forget-mapper-reset-at-the-start/
The architecture: Win8 app + local Web API Self-Host share a common "Contracts" project.
The Web API returns very general contract types (IEnumerable etc.).
Within the Win8 app I want to convert these contracts to concrete MVVM compatible model objects which use ObservableCollection for example instead of IEnumerables.
I would have loved to use AutoMapper for this task but it is not compatible with the WinRT.
I used AutoMapper some time ago, but now I generally use a specific class to do this work so I can test it and implement "strange" logic. This class is responsible for the mapping in the 2 direction (if both are needed).
Sometimes, because I'm lazy ;-), I have used an implicit conversion operator to simplify the conversion, but I think that conceptually a constructor for the dto could be better:
public class ItemDto
{
public Int32 Id { get; set; }
public String Description { get; set; }
public static implicit operator ItemDto (Item item)
{
var dto = new ItemDto()
{
Id = item.Id,
Description = item.LongDescription
};
return dto;
}
In all these cases, I think that the possibility to test your mapping has a great value.
You can to use reflection ( System.Reflection) for mapper yours DTOs by yourself, in a loop by the properties and mapping using the portable CLR types.
Thank you for your suggestions.
I solved it in a non-generic fashion, for every model I do have a specific converter that does the job. What do you think?
using Project.Contracts;
using Project.Models;
namespace Project.Converters.Contracts
{
public static class ProductConverter
{
public static ProductContract ToContract(this Product model)
{
if (model == null)
{
return new ProductContract();
}
return new ProductContract
{
Id = model.Id,
Name = mode.Name,
Tags = model.Tags.ToContracts()
};
}
public static ICollection<ProductContract> ToContracts(this IEnumerable<Product> models)
{
if (models == null)
{
return new Collection<ProductContract>();
}
return models.Select(m => m.ToContract()).ToList();
}
public static Product ToModel(this ProductContract contract)
{
if (contract == null)
{
return new Product();
}
return new Product
{
Id = contract.Id,
Name = contract.Name,
Tags = contract.Tags.ToModels()
};
}
public static ObservableCollection<Product> ToModels(this IEnumerable<ProductContract> contracts)
{
if (contracts == null)
{
return new ObservableCollection<Product>();
}
return new ObservableCollection<Product>(contracts.Select(c => c.ToModel()));
}
}
}
public class A
{
public X x { get; set; }
}
public class B
{
public X x { get; set; }
}
public class X
{
public X(object owner) { /* ... */ }
}
Basically if classes A and B are registered in Windsor I want to be able to resolve X dependency in such a way that it gets instance of the class it was required for.
In plain code it would look like that:
var a = new A();
var x = new X(a);
a.X = x;
Is there a way to do this in Windsor, maybe through some extensibility mechanism?
It looks like some crazy question even for me, so here is some motivation behind it:
The X in the example above is ITracer which is a proxy for TraceSource that is adding some bits of info to each traced message, namely, unique ID of the owner and its type (now it is only ID - that's why the question - I can't get to the instance and call GetType() on it).
A brief example to make it more clear. Suppose you have some service IService and want to add traces to it in the most non-intrusive way. But in the application could be dozen of instances of this service, so in traces you want to distinguish them by ID/type. It would be good if class received its tracer from the container and just wrote messages there when needed, without thinking of IDs, concrete TraceSource etc.
I already have some infrastructure that allows me to write like that:
[TracedTo("NameOfTheTraceSource")]
public class Service : IService
{
public ITracer Tracer { get; set; }
}
And Windsor correctly resolves Tracer to be its own (non-shared with other objects) instance of ITracer pointing to TraceSource with name NameOfTheTraceSource. Moreover, if I add traceAllMethods = true to the attribute - Windsor will automatically add interceptor which will write down each method call on this instance via the same Tracer (and only does this if corresponding TraceSource has some listeners configured - we don't have to support adding them on the fly). This is just awesome because it doesn't require anything from the developer of Service and it doesn't suffer performance degradation when it is not needed, not a bit. And so I'm working to make this even more convenient :)
OK, I think what you want here is a facility. Here's a simple one (with no error checking) that may be what you're looking for (or at least point you in the right direction):
public class XFacility : AbstractFacility
{
protected override void Init()
{
this.Kernel.ComponentCreated += KernelOnComponentCreated;
}
private void KernelOnComponentCreated(ComponentModel model, object instance)
{
var props =
instance.GetType().GetProperties().Where(p => p.CanWrite && p.PropertyType == typeof (X));
if (props.Any())
{
var pi = props.First();
pi.SetValue(instance, new X(instance), null);
}
}
}
Now make sure you add the facility to the container before you do any resolving:
var container = new WindsorContainer();
container.AddFacility<XFacility>();
container.Register(Component.For<A>(),
Component.For<B>()
);
var a = container.Resolve<A>();