布尔列表检查列表中的每个项目是否为假 [英] Bool list check if every item in list is false

问题描述

我有一个包含很多值的 List<bool>.检查列表中的每一项是否等于 false 的最有效方法是什么?

I have a List<bool> with lots of values. What is the most efficient way to check if every single item in the list equals false?

推荐答案

这里没有提到的一个明显更快的解决方案是使用 包含

A significantly faster solution, not mentioned here, is using Contains

if (!myList.Contains(true))
    // Great success - all values false! 

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我将 Contains 与 IEnumerable.Any 进行了比较，Contains 返回速度更快.在我的测试中，IEnumerable.All 的性能与 IEnumerable.Any 相同，可能在后台对这两个函数使用了类似的算法.我还检查了 IEnumerable.Exists，它的性能优于 IEnumerable.Any 和 IEnumerable.All，但仍然比 Contains 慢代码>.

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I have compared Contains against IEnumerable.Any and Contains returns faster. In my tests IEnumerable.All performed the same as IEnumerable.Any, perhaps a similar algorithm is used for both these functions under the hood. I also checked IEnumerable.Exists which performed better than IEnumerable.Any and IEnumerable.All, but was still slower than Contains.

在 10,000,000 个布尔条目列表中(我也尝试了 0 和 1 个条目，结果相似)，我得出了以下指标:

Of a list of 10,000,000 bool entries (I also tried 0 and 1 entries, with similar results), I came up with the following metrics:

经过任何 = 95ms

全部经过 = 88 毫秒

Elapsed via All = 88ms

经过 Exists = 27ms

Elapsed via Exists = 27ms

经过包含 = 17ms

Contains 比 Any 快约 5.59 倍！

用以下代码测试:

// setup initial vars
var myList = new List<bool>();
for (int x = 0; x < 10000000; x++)
    myList.Add(false);  

var containsAllFalse = false;
Stopwatch sw = new Stopwatch();

// start test
sw.Start();
containsAllFalse = !myList.Any(x => x);
sw.Stop();

// get result for Any
var timeAny = sw.ElapsedMilliseconds;

// reset variable state (just in case it affects anything)
containsAllFalse = false;   

// start test 2
sw.Restart();
containsAllFalse = myList.All(x => x == false);
sw.Stop();

// get result for All
var timeAll = sw.ElapsedMilliseconds;

// reset variable state (just in case it affects anything)
containsAllFalse = false;   

// start test 3
sw.Restart();
containsAllFalse = !myList.Exists(x => x == true);
sw.Stop();

// get result for All
var timeExists = sw.ElapsedMilliseconds;

// reset variable state (just in case it affects anything)
containsAllFalse = false;   

// start test 4
sw.Restart();   
containsAllFalse = !myList.Contains(true);          
sw.Stop();

// get result from Contains
var timeContains = sw.ElapsedMilliseconds;

// print results
var percentFaster = Math.Round((double)timeAny / timeContains, 2);
Console.WriteLine("Elapsed via Any = {0}ms", timeAny);
Console.WriteLine("Elapsed via All = {0}ms", timeAll);
Console.WriteLine("Elapsed via Exists = {0}ms", timeExists);
Console.WriteLine("Elapsed via Contains = {0}ms", timeContains);
Console.WriteLine("Contains is ~{0}x faster than Any!", percentFaster);

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请注意，这仅适用于类型只能具有两种状态的类型(即它不适用于 >2 状态的变量，例如 Nullable<bool>)em>

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Note this will only work with types where type can only have two states (i.e. it won't work variables of >2 states, such as Nullable<bool>)

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