I don’t see how the first version would compile, and the second version won’t do anything unless you use the result. It doesn’t remove anything from the existing collection – indeed, there may not even be an in-memory collection backing it. It just returns a sequence which, when iterated over, will return the appropriate values. … Read more
Assuming your objects are of the same type, you can use either Union or Concat. Note that, like the SQL UNION keyword, the Union operation will ensure that duplicates are eliminated, whereas Concat (like UNION ALL) will simply add the second list to the end of the first. IEnumerable<T> first = …; IEnumerable<T> second = … Read more
No, IEnumerable doesn’t have many extension methods on it: IEnumerable<T> does. They are two separate interfaces, although IEnumerable<T> extends IEnumerable. The normal LINQ ways of converting are to use the Cast<T>() and OfType<T>() extension methods which do extend the nongeneric interface: IEnumerable<TextBox> textBoxes = Controls.OfType<TextBox>(); IEnumerable<Control> controls = Controls.Cast<Control>(); The difference between the two is … Read more
Further to mquander’s answer and Dan Blanchard’s comment, here’s a LINQ-friendly extension method that performs a Fisher-Yates-Durstenfeld shuffle: // take n random items from yourCollection var randomItems = yourCollection.Shuffle().Take(n); // … public static class EnumerableExtensions { public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source) { return source.Shuffle(new Random()); } public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source, Random rng) … Read more
I would use !sequence.Any(), personally. If you really need to, you could always write your own extension method: public static bool IsEmpty<T>(this IEnumerable<T> source) { return !source.Any(); } Then you can write: if (sequence.IsEmpty())
It isn’t needed in C++, and here’s why: C# only supports dynamic polymorphism. So to create a reusable algorithm, you need an interface which all iterators will implement. That’s IEnumerator<T>, and IEnumerable<T> is a factory for returning an iterator. C++ templates, on the other hand, support duck typing. That means you don’t need to constrain … Read more
From LINQPad: C#: age_Centers.Select(c => c.Id).First(); age_Centers.Select(c => c.Id).FirstOrDefault(); age_Centers.Select(c => c.Id).Take(1).Dump(); SQL: SELECT TOP (1) [t0].[Id] FROM [age_Centers] AS [t0] GO SELECT TOP (1) [t0].[Id] FROM [age_Centers] AS [t0] GO SELECT TOP (1) [t0].[Id] FROM [age_Centers] AS [t0] *Note that Take(1) enumerates and returns an IQueryable.
Arrays do implement IEnumerable<T>, but it is done as part of the special knowledge the CLI has for arrays. This works as if it were an explicit implementation (but isn’t: it is done at runtime). Many tools will not show this implementation, this is described in the Remarks section of the Array class overview. You … Read more
var item = eLevelData.ElementAt(index); If your collection is typed as IEnumerable instead of IEnumerable<T> you’ll need to use the Cast extension method before you can call ElementAt e.g. var item = eLevelData.Cast<RMSRequestProcessor.RMSMedia>().ElementAt(index)
The problem is with your GetHashCode. You should alter it to return the hash code of AllianceName instead. int IEqualityComparer<Village>.GetHashCode(Village obj) { return obj.AllianceName.GetHashCode(); } The thing is, if Equals returns true, the objects should have the same hash code which is not the case for different Village objects with same AllianceName. Since Distinct works … Read more