Question

我必须将一个大文件加载到内存中，我想找到一个子字符串。哪种方法更快？

//应用程序初始化

string instring  = "which is faster find in string or list..."; // large string +- 150MB
List<string> inlist = new List<string>();
foreach (string word in instring) {
    inlist.Add(word);
}

//按钮单击

if (instring.Contains("find")) {
  ...
}

或

if (inlist.Contains("find")) {
  ...
}

我在我的案例中做了一些测量。字符串搜索是最快的。

Singel search:
Boyer-Moore search found - elapsed: 00:00:00.0025893
String search found - elapsed: 00:00:00.0026120
List search not found - elapsed: 00:00:00.0026394

Multi search:
Boyer-Moore search found - elapsed: 00:00:00.0027377
Boyer-Moore search found - elapsed: 00:00:00.0028308
Boyer-Moore search found - elapsed: 00:00:00.0029269
Boyer-Moore search found - elapsed: 00:00:00.0030234
Boyer-Moore search found - elapsed: 00:00:00.0031210

String search found - elapsed: 00:00:00.0032474
String search found - elapsed: 00:00:00.0032653
String search found - elapsed: 00:00:00.0032832
String search found - elapsed: 00:00:00.0033015
String search found - elapsed: 00:00:00.0033201


List search not found - elapsed: 00:00:00.0033629
List search not found - elapsed: 00:00:00.0033826
List search not found - elapsed: 00:00:00.0033961
List search not found - elapsed: 00:00:00.0034155
List search not found - elapsed: 00:00:00.0034345

Answer 1

你正在测试完全不同的东西。

例如，假设您确实在寻找“find”，并且您有一个文件：

If you're interested in finding the answer, make sure you know the question.

如果你把它分成一个字符串列表，每个单词一个，那么“find”就不会出现 - 因为它只是“发现”这个词的一部分。然而，使用string.Contains 将找到它，因为它是一个子字符串。

您应首先制定所需的行为，以最简单，最优雅的方式实施，然后衡量效果。如果这符合您所期望的表现，那么您就完成了。如果没有，您可以尝试改进它，在每个点测量并确保您仍然获得所需的行为。

Answer 2

通过缓冲区流式传输文件并按行分析它可能会更好。在这两种情况下，您都必须阅读整个文件，但是当您构建列表时，您必须在内存中包含完整的文件内容

来自microsoft msdn

的

c＃示例

using System;
using System.IO;

class Test 
{
    public static void Main() 
    {
        try 
        {
            // Create an instance of StreamReader to read from a file.
            // The using statement also closes the StreamReader.
            using (StreamReader sr = new StreamReader("TestFile.txt")) 
            {
                string line;
                string subString = "find this";
                // Read and display lines from the file until the end of 
                // the file is reached.
                while ((line = sr.ReadLine()) != null) 
                {
                    if ( line.Contains(substring) ) 
                    {
                         Console.WriteLine("Found string");
                         break;
                    }
                }
            }
        }
        catch (Exception e) 
        {
            // Let the user know what went wrong.
            Console.WriteLine("The file could not be read:");
            Console.WriteLine(e.Message);
        }
    }
}

哪个更快：在字符串或列表中查找？

2 个答案: