哪种方法性能更好:.Any() vs .Count() >0? [英] Which method performs better: .Any() vs .Count() > 0?

问题描述

在 System.Linq 命名空间中，我们现在可以扩展我们的 IEnumerable 的 拥有Any() 和 Count() 扩展方法.

in the System.Linq namespace, we can now extend our IEnumerable's to have the Any() and Count() extension methods.

最近有人告诉我，如果我想检查一个集合中是否包含 1 个或多个项目，我应该使用 .Any() 扩展方法而不是 .Count() >0 扩展方法，因为 .Count() 扩展方法必须遍历所有项目.

I was told recently that if i want to check that a collection contains 1 or more items inside it, I should use the .Any() extension method instead of the .Count() > 0 extension method because the .Count() extension method has to iterate through all the items.

其次，一些集合有一个 属性(不是扩展方法)，它是 Count 或 Length.使用它们而不是 .Any() 或 .Count() 会更好吗?

Secondly, some collections have a property (not an extension method) that is Count or Length. Would it be better to use those, instead of .Any() or .Count()?

是/否?

推荐答案

如果您从具有 .Length 或 .Count(例如 .Length>ICollection、IList、List 等) - 那么这将是最快的选择，因为它没有需要经过Any()所需的GetEnumerator()/MoveNext()/Dispose()序列检查非空 IEnumerable 序列.

If you are starting with something that has a .Length or .Count (such as ICollection<T>, IList<T>, List<T>, etc) - then this will be the fastest option, since it doesn't need to go through the GetEnumerator()/MoveNext()/Dispose() sequence required by Any() to check for a non-empty IEnumerable<T> sequence.

对于IEnumerable，Any()通常会更快，因为它只需要查看一次迭代.但是，请注意 Count() 的 LINQ-to-Objects 实现确实会检查 ICollection(使用 .Count 作为优化) - 因此，如果您的基础数据源直接是一个列表/集合，则不会有很大的不同.不要问我为什么不使用非通用的 ICollection...

For just IEnumerable<T>, then Any() will generally be quicker, as it only has to look at one iteration. However, note that the LINQ-to-Objects implementation of Count() does check for ICollection<T> (using .Count as an optimisation) - so if your underlying data-source is directly a list/collection, there won't be a huge difference. Don't ask me why it doesn't use the non-generic ICollection...

当然，如果您使用 LINQ 对其进行过滤等(Where 等)，您将拥有一个基于迭代器块的序列，因此这个 ICollection 优化没用.

Of course, if you have used LINQ to filter it etc (Where etc), you will have an iterator-block based sequence, and so this ICollection<T> optimisation is useless.

通常使用 IEnumerable :坚持使用 Any() ;-p

In general with IEnumerable<T> : stick with Any() ;-p

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