确定是否IEnumerable< T>包含另一个IEnumerable< T>的任何对象. [英] Determine if an IEnumerable<T> contains any object of another IEnumerable<T>

问题描述

我有2个IEnumerable<int>

IEnumerable<int> x;
IEnumerable<int> y;

确定x中是否存在y中的int的最佳最佳方法是什么?
目前我正在使用:

What is the best best way to determine if any int in y is present in the x?
Currently I'm using:

return x.Intersect<int>(y).Count() > 0;

循环遍历并分别进行测试会更快吗?

Would it be significantly faster to loop through and test each individually?

foreach (int i in x)
{
    foreach (int j in y)
    {
        if (i == j) return true;
    }
}
return false;

列表相对较轻，如果考虑的话，x的整数不超过50，y的整数不超过4.

The lists are relatively light, with not more than 50 ints in x and 4 in y if that matters in the consideration.

推荐答案

使用

It would be fastest to use the Any method instead of the Count method:

return x.Intersect<int>(y).Any();

这假定 IEnumerable<int> 实现也不实现 ICollection<int> .在这种情况下，Count(在IEnumerable<T>实现ICollection<T>的情况下)是O(N)运算，而Any总是 是O(1)运算. (因为它仅检查单个元素).但是，Count的行为是一个实现细节，您不应依赖于此.

This assumes that the IEnumerable<int> implementation doesn't also implement ICollection<int>. In that case, Count (in the case where IEnumerable<T> implements ICollection<T>) is an O(N) operation while Any is always an O(1) operation. (as it only checks for a single element). However, the behavior of Count is an implementation detail, and you shouldn't rely on that.

我已经在博客文章中对此问题进行了更深入的介绍 详细介绍了何时使用Count()与Any().总结:

I've written about this more in-depth in a blog post that goes into detail about when to use Count() vs. Any(). In summary:

• DO 使用Enumerable.Any扩展方法来检查序列中元素的存在.
• 请勿在与零的比较中使用Enumerable.Count扩展方法，因为以下在语义上是等效的:
  • sequence.Count() == 0
  • !sequence.Any()
  • DO use Enumerable.Any extension method to check for the existence of elements in the sequence.
  • DO NOT use Enumerable.Count extension method in comparisons against zero, as the following are semantically equivalent:
    • sequence.Count() == 0
    • !sequence.Any()
    • sequence.Count != 0
    • sequence.Any()
    • sequence.Count != 0
    • sequence.Any()

    这篇关于确定是否IEnumerable< T>包含另一个IEnumerable< T>的任何对象.的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！