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Questions tagged [ienumerable]

IEnumerable, and its generic counterpart IEnumerable are .NET interfaces for iterating (or enumerating) through a collection of items.

The IEnumerable interface (in the System.Collections namespace) contains only a single member, the GetEnumerator() method, which returns an IEnumerator.

The generic counterpart to IEnumerable, IEnumerable<T> (added to the System.Collections.Generic namespace in the .NET framework 2.0) also contains only a single member, the GetEnumerator() method; this returns an IEnumerator<T>.

Interaction with the IEnumerable<T> interface is often done through extension methods, for example First(), Last() and Count().

It is possible to obtain a generic IEnumerable<T> from an IEnumerable by calling either of the extension methods Cast<T>(), or OfType<T>(), depending on the case.

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Array.Count() much slower than List.Count()

When using the extension method of IEnumerable Count(), an array is at least two times slower than a list. Function Count() List 2,299 int[] 6,903 From where did the…
Cyril Gandon
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LINQ Single() Exception for 0 or multiple items

I have some IEnumberable collection of items. I use .Single() to find a specific object in the collection. I choose to use Single() because there should only ever be one specific item. However, if one doesn't exist, then I need to create it and add…
Justin Self
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When should I use IEnumerator for looping in c#?

I was wondering if there are any times where it's advantageous to use an IEnumerator over a foreach loop for iterating through a collection? For example, is there any time where it would be better to use either of the following code samples over the…
lomaxx
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C# yield in nested method

If I step through the following code the call to ReturnOne() is skipped. static IEnumerable OneThroughFive() { ReturnOne(); yield return 2; yield return 3; yield return 4; yield return 5; } static IEnumerator…
David
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Using Seq functions on an IEnumerable

I'm trying to apply Seq functions on an IEnumerable. More specifically, it's System.Windows.Forms.HtmlElementCollection which implements ICollection and IEnumerable. Since an F# seq is an IEnumerable, I thought I could write let foo =…
John Reynolds
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Debugging an IEnumerable method

I have a method with returns an IEnumerable and I'm trying to debug the code inside that method. Each time I step through the code in Visual Studio during debug, it steps over the method in question. When I place a breakpoint inside the method it…
Jamie Dixon
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Is there an IEnumerable implementation that only iterates over it's source (e.g. LINQ) once?

Provided items is the result of a LINQ expression: var items = from item in ItemsSource.RetrieveItems() where ... Suppose generation of each item takes some non-negligeble time. Two modes of operation are possible: Using foreach would…
zzandy
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Is it possible to extend arrays in C#?

I'm used to add methods to external classes like IEnumerable. But can we extend Arrays in C#? I am planning to add a method to arrays that converts it to a IEnumerable even if it is multidimensional. Not related to How to extend arrays in C#
Jader Dias
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IEnumerable<> vs List<> as a parameter

In general I tend to use IEnumerable<> as the type when I pass in parameters. However according to BenchmarkDotNet: [Benchmark] public void EnumeratingCollectionsBad() { var list = new List(); for (int i = 0; i < 1000; i++) { …
Murdock
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IEnumerable vs T[]

I just realize that maybe I was mistaken all the time in exposing T[] to my views, instead of IEnumerable. Usually, for this kind of code: foreach (var item in items) {} item should be T[] or IEnumerable? Than, if I need to get the count of…
stacker
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Finding symmetric difference with LINQ

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 Delta(IEnumerable a, IEnumerable b) { return…
Pierre Arnaud
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Enumerating Collections that are not inherently IEnumerable?

When you want to recursively enumerate a hierarchical object, selecting some elements based on some criteria, there are numerous examples of techniques like "flattening" and then filtering using Linq : like those found here : link text But, when you…
BillW
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Code for adding to IEnumerable

I have an enumerator like this IEnumerable page; How can I add a page (eg: D:\newfile.txt) to it? I have tried Add, Append, Concat etc But nothing worked for me.
Sudha
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Caching IEnumerable

public IEnumerable ListModules() { foreach (XElement m in Source.Descendants("Module")) { yield return new ModuleData(m.Element("ModuleID").Value); } } Initially the above code is great since there is no need to…
djskinner
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How to group items by index? C# LINQ

Suppose I have var input = new int[] { 0, 1, 2, 3, 4, 5 }; How do I get them grouped into pairs? var output = new int[][] { new int[] { 0, 1 }, new int[] { 2, 3 }, new int[] { 4, 5 } }; Preferably using LINQ
Jader Dias
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