Question

我一直在寻找Contains中可用的Exists，Any和List<T>方法之间的效果基准。我只想出于好奇而发现这一点，因为我总是在这些中感到困惑。关于SO的许多问题描述了这些方法的定义，例如：

LINQ Ring: Any() vs Contains() for Huge Collections
Linq .Any VS .Exists - Whats the difference?
LINQ extension methods - Any() vs. Where() vs. Exists()

所以我决定自己做。我将其添加为答案。对结果有任何更多见解是最受欢迎的。我还对数组进行了基准测试以查看结果

Answer 1

根据文件：

List.Exists（对象方法）

确定List（T）是否包含与之匹配的元素由指定谓词定义的条件。

IEnumerable.Any（扩展方法）

确定序列的任何元素是否满足条件。

List.Contains（对象方法）

确定元素是否在List中。

<强>基准：

<强> CODE：

    static void Main(string[] args)
    {
        ContainsExistsAnyShort();

        ContainsExistsAny();
    }

    private static void ContainsExistsAny()
    {
        Console.WriteLine("***************************************");
        Console.WriteLine("********* ContainsExistsAny ***********");
        Console.WriteLine("***************************************");

        List<int> list = new List<int>(6000000);
        Random random = new Random();
        for (int i = 0; i < 6000000; i++)
        {
            list.Add(random.Next(6000000));
        }
        int[] arr = list.ToArray();

        find(list, arr);
    }

    private static void ContainsExistsAnyShort()
    {
        Console.WriteLine("***************************************");
        Console.WriteLine("***** ContainsExistsAnyShortRange *****");
        Console.WriteLine("***************************************");

        List<int> list = new List<int>(2000);
        Random random = new Random();
        for (int i = 0; i < 2000; i++)
        {
            list.Add(random.Next(6000000));
        }
        int[] arr = list.ToArray();

        find(list, arr);
    }

    private static void find(List<int> list, int[] arr)
    {
        Random random = new Random();
        int[] find = new int[10000];
        for (int i = 0; i < 10000; i++)
        {
            find[i] = random.Next(6000000);
        }

        Stopwatch watch = Stopwatch.StartNew();
        for (int rpt = 0; rpt < 10000; rpt++)
        {
            list.Contains(find[rpt]);
        }
        watch.Stop();
        Console.WriteLine("List/Contains: {0:N0}ms", watch.ElapsedMilliseconds);

        watch = Stopwatch.StartNew();
        for (int rpt = 0; rpt < 10000; rpt++)
        {
            list.Exists(a => a == find[rpt]);
        }
        watch.Stop();
        Console.WriteLine("List/Exists: {0:N0}ms", watch.ElapsedMilliseconds);

        watch = Stopwatch.StartNew();
        for (int rpt = 0; rpt < 10000; rpt++)
        {
            list.Any(a => a == find[rpt]);
        }
        watch.Stop();
        Console.WriteLine("List/Any: {0:N0}ms", watch.ElapsedMilliseconds);

        watch = Stopwatch.StartNew();
        for (int rpt = 0; rpt < 10000; rpt++)
        {
            arr.Contains(find[rpt]);
        }
        watch.Stop();
        Console.WriteLine("Array/Contains: {0:N0}ms", watch.ElapsedMilliseconds);

        Console.WriteLine("Arrays do not have Exists");

        watch = Stopwatch.StartNew();
        for (int rpt = 0; rpt < 10000; rpt++)
        {
            arr.Any(a => a == find[rpt]);
        }
        watch.Stop();
        Console.WriteLine("Array/Any: {0:N0}ms", watch.ElapsedMilliseconds);
    }

<强>结果

***************************************
***** ContainsExistsAnyShortRange *****
***************************************
List/Contains: 96ms
List/Exists: 146ms
List/Any: 381ms
Array/Contains: 34ms
Arrays do not have Exists
Array/Any: 410ms
***************************************
********* ContainsExistsAny ***********
***************************************
List/Contains: 257,996ms
List/Exists: 379,951ms
List/Any: 884,853ms
Array/Contains: 72,486ms
Arrays do not have Exists
Array/Any: 1,013,303ms

Answer 2

最快的方法是使用HashSet。 Contains的{{1}}为O（1）。

我带了你的代码并添加了HashSet的基准 HashSet<int>的性能成本几乎为零。

HashSet<int> set = new HashSet<int>(list);

结果

void Main()
{
    ContainsExistsAnyShort();

    ContainsExistsAny();
}

private static void ContainsExistsAny()
{
    Console.WriteLine("***************************************");
    Console.WriteLine("********* ContainsExistsAny ***********");
    Console.WriteLine("***************************************");

    List<int> list = new List<int>(6000000);
    Random random = new Random();
    for (int i = 0; i < 6000000; i++)
    {
        list.Add(random.Next(6000000));
    }
    int[] arr = list.ToArray();
    HashSet<int> set = new HashSet<int>(list);

    find(list, arr, set);

}

private static void ContainsExistsAnyShort()
{
    Console.WriteLine("***************************************");
    Console.WriteLine("***** ContainsExistsAnyShortRange *****");
    Console.WriteLine("***************************************");

    List<int> list = new List<int>(2000);
    Random random = new Random();
    for (int i = 0; i < 2000; i++)
    {
        list.Add(random.Next(6000000));
    }
    int[] arr = list.ToArray();
    HashSet<int> set = new HashSet<int>(list);

    find(list, arr, set);

}

private static void find(List<int> list, int[] arr, HashSet<int> set)
{
    Random random = new Random();
    int[] find = new int[10000];
    for (int i = 0; i < 10000; i++)
    {
        find[i] = random.Next(6000000);
    }

    Stopwatch watch = Stopwatch.StartNew();
    for (int rpt = 0; rpt < 10000; rpt++)
    {
        list.Contains(find[rpt]);
    }
    watch.Stop();
    Console.WriteLine("List/Contains: {0}ms", watch.ElapsedMilliseconds);

    watch = Stopwatch.StartNew();
    for (int rpt = 0; rpt < 10000; rpt++)
    {
        list.Exists(a => a == find[rpt]);
    }
    watch.Stop();
    Console.WriteLine("List/Exists: {0}ms", watch.ElapsedMilliseconds);

    watch = Stopwatch.StartNew();
    for (int rpt = 0; rpt < 10000; rpt++)
    {
        list.Any(a => a == find[rpt]);
    }
    watch.Stop();
    Console.WriteLine("List/Any: {0}ms", watch.ElapsedMilliseconds);

    watch = Stopwatch.StartNew();
    for (int rpt = 0; rpt < 10000; rpt++)
    {
        arr.Contains(find[rpt]);
    }
    watch.Stop();
    Console.WriteLine("Array/Contains: {0}ms", watch.ElapsedMilliseconds);

    Console.WriteLine("Arrays do not have Exists");

    watch = Stopwatch.StartNew();
    for (int rpt = 0; rpt < 10000; rpt++)
    {
        arr.Any(a => a == find[rpt]);
    }
    watch.Stop();
    Console.WriteLine("Array/Any: {0}ms", watch.ElapsedMilliseconds);

    watch = Stopwatch.StartNew();
    for (int rpt = 0; rpt < 10000; rpt++)
    {
        set.Contains(find[rpt]);
    }
    watch.Stop();
    Console.WriteLine("HashSet/Contains: {0}ms", watch.ElapsedMilliseconds);
}

Answer 3

值得一提的是，这种比较有点不公平，因为 Array 类并不拥有 Contains() 方法，它通过顺序 IEnumerable<T> 使用 Enumerator 的扩展方法，因此未针对 Array进行优化实例;另一方面， HashSet<T> 有自己的实现针对所有尺寸进行了全面优化。

为了公平地比较，您可以使用为 int Array.IndexOf() 实例实施的静态方法 Array ，即使它使用 { {1}} 循环效率稍高于 for 。

话虽如此， Enumerator 的表现类似于 HashSet<T>.Contains() 的小集合，我想说，最多5个元素，对大型集合更有效。

包含，存在和任何的性能基准测试

3 个答案: