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  • Why can a List(Of SomeObject) not be converted to an IEnumerable(Of ISomeInterface) while SomeObject

    - by ropstah
    Please see the last comment in GetListChildren() function. "Why can a List(Of Page) not be converted to an IEnumerable(Of IListHasChildren) ?" Interface IListHasChildren Function GetListChildren() as IEnumerable(Of IListHasChildren) End Interface Public Class Page : Implements IListHasChildren Public Function GetChildren() As List(Of Page) //'return List(Of Page) with children End Function Public Function GetListChildren() : Implements IListHasChildren.GetListChildren Return Me.GetChildren() //'This cannot be converted to IEnumerable(Of IListHasChildren) ?? End Function End Class

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  • Return an empty collection when Linq where returns nothing

    - by ahsteele
    I am using the below statement with the intent of getting all of the machine objects from the MachineList collection (type IEnumerable) that have a MachineStatus of i. The MachineList collection will not always contain machines with a status of i. At times when no machines have a MachineStatus of i I'd like to return an empty collection. My call to ActiveMachines (which is used first) works but InactiveMachines does not. public IEnumerable<Machine> ActiveMachines { get { return Customer.MachineList .Where(m => m.MachineStatus == "a"); } } public IEnumerable<Machine> InactiveMachines { get { return Customer.MachineList .Where(m => m.MachineStatus == "i"); } } Edit Upon further examination it appears that any enumeration of MachineList will cause subsequent enumerations of MachineList to throw an exeception: Object reference not set to an instance of an object. Therefore, it doesn't matter if a call is made to ActiveMachines or InactiveMachines as its an issue with the MachineList collection. This is especially troubling because I can break calls to MachineList simply by enumerating it in a Watch before it is called in code. At its lowest level MachineList implements NHibernate.IQuery being returned as an IEnumerable. What's causing MachineList to lose its contents after an initial enumeration?

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  • StructureMap and injecting IEnumerable<T>

    - by GiddyUpHorsey
    I'm new to StructureMap and have some existing code that I'm working with that uses StructureMap 2.5.4. There is a class that is constructed using StructureMap that has a constructor that takes IEnumerable<TCar> as a parameter. The registry has the following code. Scan(x => { x.TheCallingAssembly(); x.WithDefaultConventions(); x.AddAllTypesOf<ICar>(); } ); ForRequestedType<IEnumerable<ICar>>().TheDefault.Is.ConstructedBy( x => ObjectFactory.GetAllInstances<ICar>()); I'm writing a unit test and have obtained a nested container off the ObjectFactory and have injected an instance using the Inject method. One of the instances of ICar should receive the injected type in its constructor. However it wasn't working and I tracked that down to the ObjectFactory.GetAllInstances() call which doesn't use my nested container. How can I get this to work? I also read about StructureMap autowiring arrays and IEnumerable instances but I couldn't get it to work. Is there a better way to rewrite the above registry code so that an instance of IEnumerable<TCar> will be created and use the injected type from my nested container?

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  • C# iterator is executed twice when composing two IEnumerable methods

    - by achristoph
    I just started learning about C# iterator but got confused with the flow of the program after reading the output of the program. The foreach with uniqueVals seems to be executed twice. My understanding is that the first few lines up to the line before "Nums in Square: 3" should not be there. Can anyone help to explain why this happens? The output is: Unique: 1 Adding to uniqueVals: 1 Unique: 2 Adding to uniqueVals: 2 Unique: 2 Unique: 3 Adding to uniqueVals: 3 Nums in Square: 3 Unique: 1 Adding to uniqueVals: 1 Square: 1 Number returned from Unique: 1 Unique: 2 Adding to uniqueVals: 2 Square: 2 Number returned from Unique: 4 Unique: 2 Unique: 3 Adding to uniqueVals: 3 Square: 3 Number returned from Unique: 9 static class Program { public static IEnumerable<T> Unique<T>(IEnumerable<T> sequence) { Dictionary<T, T> uniqueVals = new Dictionary<T, T>(); foreach (T item in sequence) { Console.WriteLine("Unique: {0}", item); if (!uniqueVals.ContainsKey(item)) { Console.WriteLine("Adding to uniqueVals: {0}", item); uniqueVals.Add(item, item); yield return item; Console.WriteLine("After Unique yield: {0}", item); } } } public static IEnumerable<int> Square(IEnumerable<int> nums) { Console.WriteLine("Nums in Square: {0}", nums.Count()); foreach (int num in nums) { Console.WriteLine("Square: {0}", num); yield return num * num; Console.WriteLine("After Square yield: {0}", num); } } static void Main(string[] args) { var nums = new int[] { 1, 2, 2, 3 }; foreach (int num in Square(Unique(nums))) Console.WriteLine("Number returned from Unique: {0}", num); Console.Read(); } }

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  • How to Implement an Interface that Requires Duplicate Member Names?

    - by Will Marcouiller
    I often have to implement some interfaces such as IEnumerable<T> in my code. Each time, when implementing automatically, I encounter the following: public IEnumerator<T> GetEnumerator() { // Code here... } public IEnumerator GetEnumerator1() { // Code here... } Though I have to implement both GetEnumerator() methods, they impossibly can have the same name, even if we understand that they do the same, somehow. The compiler can't treat them as one being the overload of the other, because only the return type differs. When doing so, I manage to set the GetEnumerator1() accessor to private. This way, the compiler doesn't complaint about not implementing the interface member, and I simply throw a NotImplementedException within the method's body. However, I wonder whether it is a good practice, or if I shall proceed differently, as perhaps a method alias or something like so. What is the best approach while implementing an interface such as IEnumerable<T> that requires the implementation of two different methods with the same name? EDIT #1 Does VB.NET reacts differently from C# while implementing interfaces, since in VB.NET it is explicitly implemented, thus forcing the GetEnumerator1(). Here's the code: Public Function GetEnumerator() As System.Collections.Generic.IEnumerator(Of T) Implements System.Collections.Generic.IEnumerable(Of T).GetEnumerator // Code here... End Function Public Function GetEnumerator1() As System.Collections.Generic.IEnumerator Implements System.Collections.Generic.IEnumerable.GetEnumerator // Code here... End Function Both GetEnumerator() methods are explicitly implemented, and the compile will refuse them to have the same name. Why?

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  • What happens when ToArray() is called on IEnumerable ?

    - by Sir Psycho
    I'm having trouble understanding what happens when a ToArray() is called on an IEnumerable. I've always assumed that only the references are copied. I would expect the output here to be: true true But instead I get true false What is going on here? class One { public bool Foo { get; set; } } class Two { public bool Foo { get; set; } } void Main() { var collection1 = new[] { new One(), new One() }; IEnumerable<Two> stuff = Convert(collection1); var firstOne = stuff.First(); firstOne.Foo = true; Console.WriteLine (firstOne.Foo); var array = stuff.ToArray(); Console.WriteLine (array[0].Foo); } IEnumerable<Two> Convert(IEnumerable<One> col1) { return from c in col1 select new Two() { Foo = c.Foo }; }

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  • Efficiently Combine MatchCollections in .Net Regex

    - by Laramie
    In the simplified example, there are 2 Regular Expressions, one case sensitive, the other not. The idea would be to efficiently create an IEnumerable collection (see "combined" below) combining the results. string test = "abcABC"; string regex = "(?<grpa>a)|(?<grpb>b)|(?<grpc>c)]"; Regex regNoCase = new Regex(regex, RegexOptions.IgnoreCase); Regex regCase = new Regex(regex); MatchCollection matchNoCase = regNoCase.Matches(test); MatchCollection matchCase = regCase.Matches(test); //Combine matchNoCase and matchCase into an IEnumerable IEnumerable<Match> combined= null; foreach (Match match in combined) { //Use the Index and (successful) Groups properties //of the match in another operation } In practice, the MatchCollections might contain thousands of results and be run frequently using long dynamically created REGEXes, so I'd like to shy away from copying the results to arrays, etc. I am still learning LINQ and am fuzzy on how to go about combining these or what the performance hits to an already sluggish process will be.

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  • IEnumerable doesn't have Count

    - by Alexander
    I have the following method: public bool IsValid { get { return (GetRuleViolations().Count() == 0); } } public IEnumerable<RuleViolation> GetRuleViolations(){ //code here } Why is it that when I do .Count above it is underlined in red? I got the following error: Error 1 'System.Collections.Generic.IEnumerable' does not contain a definition for 'Count' and no extension method 'Count' accepting a first argument of type 'System.Collections.Generic.IEnumerable' could be found (are you missing a using directive or an assembly reference?) c:\users\a\documents\visual studio 2010\Projects\NerdDinner\NerdDinner\Models\Dinner.cs 15 47 NerdDinner

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  • LINQ and set difference

    - by Pierre
    I have two collections a and b. I would like to compute the set of items in either a or b, but not in both (a logical exclusive or). With LINQ, I can come up with this: IEnumerable<T> Delta<T>(IEnumerable<T> a, IEnumerable<T> b) { return a.Except (b).Union (b.Except (a)); } I wonder if there are other more efficient or more compact ways of producing the difference between the two collections.

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  • Foreach over a collection of IEnumerables

    - by sdr
    I have 3 IEnumerables that I want to iterate over. I want to do something like this: IEnumerable<Car> redCars = GetRedCars(); IEnumerable<Car> greenCars = GetGreenCars(); IEnumerable<Car> blueCars = GetBlueCars(); foreach(Car c in (redCars + greenCars + blueCars)) { c.DoSomething(); } ... The best way I can think of is: ... List<Car> allCars = new List(); allCars.AddRange(redCars); allCars.AddRange(greenCars); allCars.AddRange(blueCars); foreach(car in allCars) { ... } ... Is there a more concise way to do this? Seems like combinding IEnumberables should be trivial.

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  • check existense between two IEnumerable

    - by sunglim
    IEnumerable<String> existedThings = from mdinfo in mdInfoTotal select mdinfo.ItemNo; IEnumerable<String> thingsToSave = from item in lbXReadSuccess.Items.Cast<ListItem>() select item.Value; Here are two IEnumerable. I want to check whether a value in existedThings exist in thingsToSave. O.K. I can do that with 3 line code. bool hasItemNo; foreach(string itemNo in existedThings) hasItemNo= thingsToSave.Contains(itemNo); But, It looks dirty. I just want to know if there better solution.

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  • OData EndPoint/DataService Using IEnumerable<IQueryable>

    - by Elijah Glover
    I am using NHibernate with NHibernate.Linq, and have a bunch of dynamically loading modules each with their own POCO's and Mappings (ClassMap<POCO). I have created OData services before, but normally with a datacontext and IQueryable as Properties/Getters. What I want is to create the service by passing in IEnumerable, into the constructor IEnumerable<IQueryable>> queryableObjects; var dataService = new DataService(queryableObjects); Is this at all possible?

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  • Most efficient algorithm for merging sorted IEnumerable<T>

    - by franck
    Hello, I have several huge sorted enumerable sequences that I want to merge. Theses lists are manipulated as IEnumerable but are already sorted. Since input lists are sorted, it should be possible to merge them in one trip, without re-sorting anything. I would like to keep the defered execution behavior. I tried to write a naive algorithm which do that (see below). However, it looks pretty ugly and I'm sure it can be optimized. It may exist a more academical algorithm... IEnumerable<T> MergeOrderedLists<T, TOrder>(IEnumerable<IEnumerable<T>> orderedlists, Func<T, TOrder> orderBy) { var enumerators = orderedlists.ToDictionary(l => l.GetEnumerator(), l => default(T)); IEnumerator<T> tag = null; var firstRun = true; while (true) { var toRemove = new List<IEnumerator<T>>(); var toAdd = new List<KeyValuePair<IEnumerator<T>, T>>(); foreach (var pair in enumerators.Where(pair => firstRun || tag == pair.Key)) { if (pair.Key.MoveNext()) toAdd.Add(pair); else toRemove.Add(pair.Key); } foreach (var enumerator in toRemove) enumerators.Remove(enumerator); foreach (var pair in toAdd) enumerators[pair.Key] = pair.Key.Current; if (enumerators.Count == 0) yield break; var min = enumerators.OrderBy(t => orderBy(t.Value)).FirstOrDefault(); tag = min.Key; yield return min.Value; firstRun = false; } } The method can be used like that: // Person lists are already sorted by age MergeOrderedLists(orderedList, p => p.Age); assuming the following Person class exists somewhere: public class Person { public int Age { get; set; } } Duplicates should be conserved, we don't care about their order in the new sequence. Do you see any obvious optimization I could use?

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  • Trying to implement a method that can compare any two lists but it always returns false

    - by Tyler Pfaff
    Hello like the title says I'm trying to make a method that can compare any two lists for equality. I'm trying to compare them in a way that validates that every element of one list has the same value as every element of another list. My Equals method below always returns false, can anyone see why that is? Thank you! using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; public class IEnumerableComparer<T> : IEqualityComparer<IEnumerable<T>> { public bool Equals(IEnumerable<T> x, IEnumerable<T> y) { for(int i = 0; i<x.Count();i++){ if(!Object.Equals(x.ElementAt(i), y.ElementAt(i))){ return false; } } return true; } public int GetHashCode(IEnumerable<T> obj) { if (obj == null) return 0; return unchecked(obj.Select(e => e.GetHashCode()).Aggregate(0, (a, b) => a + b)); } } Here is my data I'm using to test this Equals method. static void Main(string[] args) { Car car1 = new Car(); car1.make = "Toyota"; car1.model = "xB"; Car car2 = new Car(); car2.make = "Toyota"; car2.model = "xB"; List<Car> l1 = new List<Car>(); List<Car> l2 = new List<Car>(); l1.Add(car1); l2.Add(car2); IEnumerableComparer<Car> seq = new IEnumerableComparer<Car>(); bool b = seq.Equals(l1, l2); Console.Write(b); //always says false Console.Read(); } } Car class class Car { public String make { get; set; } public String model { get; set; } }

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  • Retain IEnumerable<T> value during postback

    - by ScG
    I have an IEnumerable< T which is declared on the page like this: IEnumerable< Person person; When the page postsback, the person list is null. How can I retain the values of person list without declaring it as static? Sr. devs in my company say that you should not declare the list as static.

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  • Select the next N elements of an IEnumerable<T>

    - by sassafrass
    Say you've got some IEnumerable called S of length N. I would like to select all continuous subsequences of length n <= N from S. If S were, say, a string, this'd be pretty easy. There are (S.Length - n + 1) subsequences of length n. For example, "abcdefg" is length (7), so that means it has (5) substrings of length (3): "abc", "bcd", "cde", "def", "efg". But S could be any IEnumerable, so this route isn't open. How do I use extension methods to solve this?

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  • Why is there no Sum() extension for IEnumerable<uint>

    - by dss539
    It seems that Sum not defined for IEnumerable<uint> (and other unsigned integers, for that matter) var s = new int[] { 1, 2, 3 }; s.Sum(); //works fine var us = new uint[] { 1, 2, 3 }; us.Sum(); //missing method I would like to know: Have I done something fundamentally wrong/misunderstood the situation? What design decisions might cause the omission of IEnumerable<uint>.Sum()? MSDN: Enumerable.Sum

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  • Can someone please explain this lazy evaluation code?

    - by Tejs
    So, this question was just asked on SO: http://stackoverflow.com/questions/2740001/how-to-handle-an-infinite-ienumerable My sample code: public static void Main(string[] args) { foreach (var item in Numbers().Take(10)) Console.WriteLine(item); Console.ReadKey(); } public static IEnumerable<int> Numbers() { int x = 0; while (true) yield return x++; } Can someone please explain why this is lazy evaluated? I've looked up this code in Reflector, and I'm more confused than when I began. Reflector outputs: public static IEnumerable<int> Numbers() { return new <Numbers>d__0(-2); } For the numbers method, and looks to have generated a new type for that expression: [DebuggerHidden] public <Numbers>d__0(int <>1__state) { this.<>1__state = <>1__state; this.<>l__initialThreadId = Thread.CurrentThread.ManagedThreadId; } This makes no sense to me. I would have assumed it was an infinite loop until I put that code together and executed it myself.

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  • Pair-wise iteration in C# or sliding window enumerator

    - by f3lix
    If I have an IEnumerable like: string[] items = new string[] { "a", "b", "c", "d" }; I would like to loop thru all the pairs of consecutive items (sliding window of size 2). Which would be ("a","b"), ("b", "c"), ("c", "d") My solution was is this public static IEnumerable<Pair<T, T>> Pairs(IEnumerable<T> enumerable) { IEnumerator<T> e = enumerable.GetEnumerator(); e.MoveNext(); T current = e.Current; while ( e.MoveNext() ) { T next = e.Current; yield return new Pair<T, T>(current, next); current = next; } } // used like this : foreach (Pair<String,String> pair in IterTools<String>.Pairs(items)) { System.Out.PrintLine("{0}, {1}", pair.First, pair.Second) } When I wrote this code, I wondered if there are already functions in the .NET framework that do the same thing and do it not just for pairs but for any size tuples. IMHO there should be a nice way to do this kind of sliding window operations. I use C# 2.0 and I can imagine that with C# 3.0 (w/ LINQ) there are more (and nicer) ways to do this, but I'm primarily interested in C# 2.0 solutions. Though, I will also appreciate C# 3.0 solutions.

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  • Why Enumerable.Range is faster than a direct yield loop?

    - by Morgan Cheng
    Below code is checking performance of three different ways to do same solution. public static void Main(string[] args) { // for loop { Stopwatch sw = Stopwatch.StartNew(); int accumulator = 0; for (int i = 1; i <= 100000000; ++i) { accumulator += i; } sw.Stop(); Console.WriteLine("time = {0}; result = {1}", sw.ElapsedMilliseconds, accumulator); } //Enumerable.Range { Stopwatch sw = Stopwatch.StartNew(); var ret = Enumerable.Range(1, 100000000).Aggregate(0, (accumulator, n) => accumulator + n); sw.Stop(); Console.WriteLine("time = {0}; result = {1}", sw.ElapsedMilliseconds, ret); } //self-made IEnumerable<int> { Stopwatch sw = Stopwatch.StartNew(); var ret = GetIntRange(1, 100000000).Aggregate(0, (accumulator, n) => accumulator + n); sw.Stop(); Console.WriteLine("time = {0}; result = {1}", sw.ElapsedMilliseconds, ret); } } private static IEnumerable<int> GetIntRange(int start, int count) { int end = start + count; for (int i = start; i < end; ++i) { yield return i; } } } The result is like this: time = 306; result = 987459712 time = 1301; result = 987459712 time = 2860; result = 987459712 It is not surprising that "for loop" is faster than the other two solutions, because Enumerable.Aggregate takes more method invocations. However, it really surprises that "Enumerable.Range" is faster than the "self-made IEnumerable". I thought that Enumerable.Range will take more overhead than the simple GetIntRange method. What is the possible reason for this?

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  • Convert IEnumerable<dynamic> to JsonArray

    - by Burt
    I am selecting an IEnumerable<dynamic> from the database using Rob Conery's Massive framework. The structure comes back in a flat format Poco C#. I need to transform the data and output it to a Json array (format show at bottom). I thought I could do the transform using linq (my unsuccessful effort is shown below): using System.Collections.Generic; using System.Json; using System.Linq; using System.ServiceModel.Web; .... IEnumerable<dynamic> list = _repository.All("", "", 0).ToList(); JsonArray returnValue = from item in list select new JsonObject() { Name = item.Test, Data = new dyamic(){...}... }; Here is the Json I am trying to generate: [ { "id": "1", "title": "Data Title", "data": [ { "column1 name": "the value", "column2 name": "the value", "column3 name": "", "column4 name": "the value" } ] }, { "id": "2", "title": "Data Title", "data": [ { "column1 name": "the value", "column2 name": "the value", "column3 name": "the value", "column4 name": "the value" } ] } ]

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  • Is yield break equivalent to returning Enumerable<T>.Empty from a method returning IEnumerable<T>

    - by Mike Two
    These two methods appear to behave the same to me public IEnumerable<string> GetNothing() { return Enumerable.Empty<string>(); } public IEnumerable<string> GetLessThanNothing() { yield break; } I've profiled each in test scenarios and I don't see a meaningful difference in speed, but the yield break version is slightly faster. Are there any reasons to use one over the other? Is one easier to read than the other? Is there a behavior difference that would matter to a caller?

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